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The effects of spring feeding strategy on pasture productivity, sward quality, and animal performance within intensive pasture-based dairy systems

Open AccessPublished:December 23, 2022DOI:https://doi.org/10.3168/jds.2021-21272

      ABSTRACT

      The objective of this research was to evaluate how different feeding strategies based on various pasture availability (PA) treatments within intensive seasonal production systems affected pasture production and utilization, sward quality, and the milk production, body weight (BW), and body condition score (BCS) of dairy cows. The performance data were obtained from a 3-yr experiment conducted previously (2018–2020, inclusive). In total, records from 208 spring-calving dairy cows were available for analysis. The animals were randomly allocated to 1 of 3 PA grazing treatments in spring that varied in average pasture cover (measured as herbage mass available above 3.5 cm) that was established via different pasture management strategies in the previous autumn. Thus, the opening average pasture cover across all paddocks on February 1 was 1,100 kg of dry matter (DM)/ha for high pasture availability (HPA), 880 for medium pasture availability (MPA), and 650 for low pasture availability (LPA), respectively. The measurements were taken over an 8-wk period during the first grazing rotation in spring, commencing on February 16 (±2 d) and finishing when all paddocks were grazed once on April 12 (±5 d). Paddocks that were part of the HPA treatment showed the highest pregrazing herbage masses and pregrazing sward heights (1,645 kg of DM/ha and 8.2 cm, respectively) compared with MPA (1,412 kg of DM/ha and 7.5 cm, respectively) and LPA (1,170 kg of DM/ha and 6.9 cm, respectively). Owing to the differences in PA, daily herbage allowance was greatest for HPA (11.7 kg of DM/cow), intermediate for MPA (10.2 kg of DM/cow), and lowest for LPA (8.8 kg of DM/cow), with the remaining feed deficit composed of additional daily grass silage supplementation (0.8, 1.5, and 2.8 kg of DM/cow for HPA, MPA, and LPA, respectively), while the daily concentrate and daily total feed allowance were equal between treatments during spring (2.7 and 15.0 kg of DM/cow). Despite salient differences in fresh pasture used, complementing pasture intake with grass silage did not affect daily or cumulative milk, solids-corrected milk, fat, or protein yield or milk constituents. Similarly, BW and BCS were also unaffected by PA treatment. The results highlight the importance of high spring pasture utilization and grazing efficiency achievable with higher pregrazing herbage masses, which also allow larger animal intakes from grazed pasture as the cheapest feed source during spring. Moreover, targeting an adequate pasture supply at the commencement of calving increases the grazing days per hectare and lowers the requirement for supplementary feed on farm, particularly when facing increasing variability in climatic conditions.

      Key words

      INTRODUCTION

      Worldwide, grazing systems have increasingly received recognition for their ancillary benefits, not only on animal performance (
      • Dillon P.
      • Crosse S.
      • Stakelum G.
      • Flynn F.
      The effect of calving date and stocking rate on the performance of spring-calving dairy cows.
      ;
      • Claffey A.
      • Delaby L.
      • Boland T.
      • Egan M.
      Implications of adapting autumn grazing management on spring herbage production—The effect on late lactation milk production and the subsequent response in early lactation animal performance.
      ), health, and welfare (
      • Arnott G.
      • Ferris C.P.
      • O'Connell N.E.
      Welfare of dairy cows in continuously housed and pasture-based production systems.
      ;
      • Mee J.F.
      • Boyle L.A.
      Assessing whether dairy cow welfare is “better” in pasture-based than in confinement-based management systems.
      ), but also for their contribution to ecosystem services (
      • Rook A.J.
      • Tallowin J.R.
      Grazing and pasture management for biodiversity benefit.
      ;
      • Delaby L.
      • Finn J.A.
      • Grange G.
      • Horan B.
      Pasture-based dairy systems in temperate lowlands: Challenges and opportunities for the future.
      ), resulting in growing popularity among consumers (
      • Conner D.S.
      • Campbell-Arvai V.
      • Hamm M.W.
      Consumer preferences for pasture-raised animal products: Results from Michigan.
      ). Hence, maximizing days at pasture, and therefore the proportion of grazed grass in the cows' diet, is a crucial differentiation factor among consumers and also allows dairy farms to build more sustainable and resilient systems (
      • Horan B.
      • Roche J.R.
      Defining resilience in pasture-based dairy-farm systems in temperate regions.
      ). Extending the grazing season has been reported to improve animal performance and substantially reduce feed costs, particularly during periods of low pasture growth in spring when inclement weather conditions prevail (
      • Roche J.
      • Dillon P.
      • Crosse S.
      • Rath M.
      The effect of closing date of pasture in autumn and turnout date in spring on sward characteristics, dry matter yield and milk production of spring-calving dairy cows.
      ;
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.P.
      • Delaby L.
      • O'Mara F.
      Effect of spring grazing date and stocking rate on sward characteristics and dairy cow production during midlactation.
      ;
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ). Grazing management practices play a critical role in increasing pasture utilization in spring and autumn and thus dictate the grazing season length (
      • Carton O.
      • Brereton A.
      • O'Keeffe W.
      • Keane G.
      Effects of autumn closing date and grazing severity in a rotationally grazed sward during winter and spring: 1. Dry matter production.
      ;
      • O'Donovan M.
      • Delaby L.
      Sward characteristics, grass dry matter intake and milk production performance is affected by timing of spring grazing and subsequent stocking rate.
      ;
      • Evers S.H.
      • Delaby L.
      • Fleming C.
      • Pierce K.M.
      • Horan B.
      Effect of 3 autumn pasture management strategies applied to 2 farm system intensities on the productivity of spring-calving, pasture-based dairy systems.
      ). The significance of adequate pasture availability (PA) at the onset of a compact calving season in spring before sufficient pasture becomes available, when feed demand exceeds daily pasture growth, has been previously documented (
      • Roche J.
      • Dillon P.
      • Crosse S.
      • Rath M.
      The effect of closing date of pasture in autumn and turnout date in spring on sward characteristics, dry matter yield and milk production of spring-calving dairy cows.
      ;
      • Claffey A.
      • Delaby L.
      • Boland T.
      • Egan M.
      Implications of adapting autumn grazing management on spring herbage production—The effect on late lactation milk production and the subsequent response in early lactation animal performance.
      ).
      Recent intensification on pasture-based dairy farms, indicated by increased numbers of animals per hectare [stocking rate (SR);
      • Hanrahan L.
      • Geoghegan A.
      • O'Donovan M.
      • Griffith V.
      • Ruelle E.
      • Wallace M.
      • Shalloo L.
      PastureBase Ireland: A grassland decision support system and national database.
      ;
      • Ma W.
      • Renwick A.
      • Bicknell K.
      Higher intensity, higher profit? Empirical evidence from dairy farming in New Zealand.
      ;
      • Claffey A.
      • Delaby L.
      • Boland T.
      • Egan M.
      Implications of adapting autumn grazing management on spring herbage production—The effect on late lactation milk production and the subsequent response in early lactation animal performance.
      ;
      • Delaby L.
      • Finn J.A.
      • Grange G.
      • Horan B.
      Pasture-based dairy systems in temperate lowlands: Challenges and opportunities for the future.
      ], has led to an increase in herd demand and thus a shortening of the grazing season, with more animals spending fewer days at pasture (
      • Macdonald K.
      • Penno J.
      • Nicholas P.
      • Lile J.
      • Coulter M.
      • Lancaster J.
      Farm systems—Impact of stocking rate on dairy farm efficiency.
      ;
      • McCarthy B.
      • Delaby L.
      • Pierce K.
      • Brennan A.
      • Horan B.
      The effect of stocking rate and calving date on milk production of Holstein–Friesian dairy cows.
      ;
      • Clay N.
      • Garnett T.
      • Lorimer J.
      Dairy intensification: Drivers, impacts and alternatives.
      ). Consequently, the need to purchase and use additional imported supplements has increased, resulting in production costs becoming higher (
      • Hanrahan L.
      • Geoghegan A.
      • O'Donovan M.
      • Griffith V.
      • Ruelle E.
      • Wallace M.
      • Shalloo L.
      PastureBase Ireland: A grassland decision support system and national database.
      ;
      • Ma W.
      • Renwick A.
      • Bicknell K.
      Higher intensity, higher profit? Empirical evidence from dairy farming in New Zealand.
      ). Moreover, in Irish temperate grazing conditions, the autumn closing date, when a paddock is grazed for the last time before animals are housed for the winter, has a significant effect on spring PA (opening pasture cover, OPC) (
      • Culleton N.
      • Lemaire G.
      • Keane G.
      The effects of autumn management on grass growth in winter and spring.
      ;
      • O'Donovan M.
      • Delaby L.
      • Peyraud J.L.
      Effect of time of initial grazing date and subsequent stocking rate on pasture production and dairy cow performance.
      ;
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.
      • O'Mara F.
      • Delaby L.
      The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer.
      ). Previous studies reported an increase in spring pasture yields of 10 to 15 kg of DM/ha for each day that paddocks were closed earlier in autumn (
      • O'Donovan M.
      • Dillon P.
      • Rath M.
      • Stakelum G.
      A comparison of four methods of herbage mass estimation.
      ;
      • Lawrence D.
      • O'Donovan M.
      • Boland T.
      • Kennedy E.
      Effects of autumn and spring defoliation management on the dry-matter yield and herbage quality of perennial ryegrass swards throughout the year.
      ;
      • Claffey A.
      • Delaby L.
      • Boland T.
      • Egan M.
      Implications of adapting autumn grazing management on spring herbage production—The effect on late lactation milk production and the subsequent response in early lactation animal performance.
      ), which, in return, required additional silage supplementation and earlier housing of animals in late lactation (
      • Roche J.
      • Dillon P.
      • Crosse S.
      • Rath M.
      The effect of closing date of pasture in autumn and turnout date in spring on sward characteristics, dry matter yield and milk production of spring-calving dairy cows.
      ;
      • O'Donovan M.
      • Dillon P.
      • Rath M.
      • Stakelum G.
      A comparison of four methods of herbage mass estimation.
      ;
      • Claffey A.
      • Delaby L.
      • Boland T.
      • Egan M.
      Implications of adapting autumn grazing management on spring herbage production—The effect on late lactation milk production and the subsequent response in early lactation animal performance.
      ). However, few studies have paid sufficient attention to the effects of additional pasture accumulation throughout autumn as a management strategy to achieve optimum average pasture cover (APC) at housing without shortening the grazing season length in late lactation. In addition, the carry-over effects of these differently managed swards on pasture growth, utilization, sward quality, and animal performance in the subsequent spring require further evaluation. Many component studies have mostly focused on identifying the most appropriate SR (
      • Stakelum G.
      • Dillon P.
      The effect of grazing pressure on rotationally grazed pastures in spring/early summer on subsequent sward characteristics.
      ;
      • McCarthy B.
      • Pierce K.M.
      • Delaby L.
      • Brennan A.
      • Horan B.
      The effect of stocking rate and calving date on reproductive performance, body state, and metabolic and health parameters of Holstein-Friesian dairy cows.
      ), daily herbage allowance (DHA;
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.P.
      • Delaby L.
      • O'Mara F.
      Effects of grass pasture and concentrate-based feeding systems for spring-calving dairy cows in early spring on performance during lactation.
      ), or postgrazing sward height (PGSH;
      • Sayers H.
      • Mayne C.
      Effect of early turnout to grass in spring on dairy cow performance.
      ;
      • Ganche E.
      • Delaby L.
      • O'Donovan M.
      • Boland T.
      • Galvin N.
      • Kennedy E.
      Post-grazing sward height imposed during the first 10 weeks of lactation: Influence on early and total lactation dairy cow production, and spring and annual sward characteristics.
      ) in spring, without evaluating the between-year variation in PA that affects the management decisions at farm level. This issue will become even more important in the near future, as recent reports have highlighted how climate change will increase the frequency and severity of unfavorable weather patterns, thus increasing the variability of grazing system performance (
      • Ghahramani A.
      • Howden S.M.
      • del Prado A.
      • Thomas D.T.
      • Moore A.D.
      • Ji B.
      • Ates S.
      Climate change impact, adaptation, and mitigation in temperate grazing systems: A review.
      ;
      • IPCC
      Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
      ). Therefore, the objective of this study was to evaluate how different feeding strategies based on the variation in PA established in the previous autumn affected the performance of spring-calving grazing systems in early lactation within an extended grazing season over 3 consecutive years.

      MATERIALS AND METHODS

      The experiment was undertaken at the Animal and Grassland Research and Innovation Centre, Teagasc Moorepark, Ireland (50°7N; 8°16W), over a 3-yr period (2018, 2019, and 2020) as part of a larger systems experiment evaluating the biological and economic impact of alternative pasture management strategies on pasture and animal performance. All procedures involving cows during the experiment were approved by the Teagasc Animal Ethics Committee and were in accordance with the project authorization (AE19132/I196) received from the Health Products Regulatory Board, which is responsible for the implementation of European Union legislation (Directive 2010/63/EU) for the protection of animals used for scientific purposes in Ireland. The measurement period for the spring experiment lasted for 8 wk, starting on February 16 (±2 d) and concluding at the end of first grazing rotation on April 12 (±5 d).

      Experimental Design

      A grazing area of 48 ha was used to evaluate 3 PA treatments that were established each autumn before the subsequent spring. The treatments were analyzed beginning with the turnout of cows to pasture in early February. The establishment of the on-farm OPC for the 3 PA was a result of altered grazing management strategies during the previous autumn that consisted of achieving different target closing covers on December 1 as outlined by
      • Evers S.H.
      • Delaby L.
      • Fleming C.
      • Pierce K.M.
      • Horan B.
      Effect of 3 autumn pasture management strategies applied to 2 farm system intensities on the productivity of spring-calving, pasture-based dairy systems.
      . The treatments included low PA (LPA), medium PA (MPA), and high PA (HPA). The target closing cover for LPA was 400 kg of DM/ha on December 1 and was based on data from PastureBase Ireland (
      • Hanrahan L.
      • Geoghegan A.
      • O'Donovan M.
      • Griffith V.
      • Ruelle E.
      • Wallace M.
      • Shalloo L.
      PastureBase Ireland: A grassland decision support system and national database.
      ). These data indicated that approximately 70% of farms cease the grazing season with insufficient herbage, which hinders them from meeting the high feed demand at turnout in spring (

      Egan, M., M. O'Donovan, D. Hennessey, J. Maher, and M. O'Leary. 2017. Winning the spring grazing challenge! Irish Grassland Association National Dairy Conference, Kilkenny, Ireland.

      ;
      • Hanrahan L.
      • Geoghegan A.
      • O'Donovan M.
      • Griffith V.
      • Ruelle E.
      • Wallace M.
      • Shalloo L.
      PastureBase Ireland: A grassland decision support system and national database.
      ). Medium PA represented best practice recommendations (
      • Tuñon G.
      • Kennedy E.
      • Horan B.
      • Hennessy D.
      • Lopez-Villalobos N.
      • Kemp P.
      • Brennan A.
      • O'Donovan M.
      Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season.
      ) of a target closing pasture cover of 550 to 600 kg of DM/ha based on a SR of 2.5 cows/ha (
      • Teagasc
      Grazing Notebook.
      ). Finally, HPA represented an incremental increase in herbage accumulation from the national recommendation (800 kg of DM/ha). Although similar closing pasture covers were achieved for all PA each year during autumn, the OPC differed significantly between years (Table 1) because of fluctuating weather conditions and pasture growth rates (Figure 1, Figure 2). On February 1, the average OPC reported in this study were 650, 880, and 1,100 kg of DM/ha (measured >3.5 cm) for LPA, MPA, and HPA, respectively.
      Table 1Opening pasture cover (OPC) for pasture availability treatment for the experimental years
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      LPAMPAHPA
      Closing cover (kg of DM/ha)420650870
      No. of days since last grazed137143150
      OPC (kg of DM/ha)6508801,100
       Year 1550720980
       Year 27209901,160
       Year 36809401,100
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      Figure thumbnail gr1
      Figure 1Mean (a) soil temperature at 10-cm depth and (b) cumulative monthly rainfall during the study period (dark gray bars) and surrounding months (light gray bars) compared with the previous 10-yr average (black line) values (±standard error) measured on site.
      Figure thumbnail gr2
      Figure 2Mean (a) average daily growth rates per week and (b) percentage of area grazed for each year while adhering to guidelines from the spring rotation planner; year 1 = ▴; year 2 = ▪; year 3 = ♦, with the star marking the average annual target for finish of first grazing rotation on April 10. Date shown as day/month (± SE).
      Each year, a total of 144 spring-calving cows were randomly assigned prior to calving to 1 of the 3 grazing treatments. Groups were balanced by expected calving date, lactation number (3.2 ± 1.75), breed (Holstein-Friesian or Jersey × Holstein-Friesian crossbred), genetic merit (economic breeding index, €177 ± 36.4), BW (572 ± 70.8 kg), and BCS (3.1 ± 0.32). Where possible, animals remained within the same treatment group throughout the study. Ultimately, 208 individual animals were included in the study over the 3 years.

      Grazing and Animal Management

      The free-draining experimental site consisted of a total of 48 ha of permanent grassland that was divided into 34 paddocks per treatment, with paddocks balanced for soil fertility and type, location, sward species, and distance to the milking parlor. Over 80% of the swards on the farm were made up of perennial ryegrass (Lolium perenne L.) and some white clover (Trifolium repens L.), with a maximum proportion of 15%. On a weekly basis, the APC for each PA treatment was measured using visual estimation methods as described by
      • O'Donovan M.
      • Dillon P.
      • Rath M.
      • Stakelum G.
      A comparison of four methods of herbage mass estimation.
      so that grazing decisions for paddock and area allocations according to guidelines from the spring rotation planner (SRP) could be made. Overall, the SRP, as outlined by
      • Bryant A.
      • L'Huillier P.
      Better use of pastures.
      and
      • Macdonald K.A.
      • Roche J.R.
      Back to the future—Making pasture work for you this spring.
      , was used as a grazing management guide to ensure consistent daily (and weekly) area allocation between PA treatments between years. The SRP allowed an increasing daily grazing area allocation to each farmlet during the first grazing rotation so that by the time grass growth equaled pasture demand of the herd (in kg of DM/ha), the entire initial area was grazed and the second grazing rotation could begin on a 21-d grazing rotation thereafter (Figure 2b). Depending on weather conditions and grass growth rates, we allowed flexibility in the weekly area allocation from the SRP. When weekly growth rates were low, daily and weekly area allocations were reduced and the grazing rotation was slowed by introducing additional supplementary feed to ensure a consistent proportion of grazed grass in the animals' diet, where possible. During periods of high pasture growth rates, the proportion of grazed grass was increased and the end of the first grazing rotation was adjusted accordingly, providing that sufficient pasture was available on second-rotation paddocks. Thus, the daily area allocation from the SRP and the availability of pasture as a result of the different OPC in each PA dictated the DHA per cow.
      After a minimum of 3 d postcalving, cows were assigned to their PA treatment. Daily concentrate allowance was equal between PA (2.7 kg of DM postcalving) and was fed in the milking parlor during morning and evening milkings. Fresh pasture was generally offered after morning and evening milkings, mostly on a 12-h basis but depended on the feeding strategy as dictated by PA. On days with heavy rainfall, on-off grazing (
      • Kennedy E.
      • McEvoy M.
      • Murphy J.
      • O'Donovan M.
      Effect of restricted access time to pasture on dairy cow milk production, grazing behavior, and dry matter intake.
      ) was practiced to avoid poaching damage, and during severe weather conditions (heavy rain or snow) on some occasions during the spring, cows were housed and allocated an equal amount of silage. Where necessary, back fences were used to avoid damage to previously grazed soil. At the start of each week, the progress on the SRP and weekly growth rates were assessed so decisions could be made on how much silage was to be offered to each PA treatment individually in the shed. If grass silage supplementation was required to compensate for lower DHA as a result of lower OPC within a treatment, animals were either housed during the day, at night, or after 3 h of grazing after the evening milking until further decisions were made throughout the spring, depending on meeting the weekly grazing area targets from the SRP and weekly growth rates. The grass silage that was consumed was recorded. Once the first grazing rotation was finished, all treatments were managed similarly throughout the main grazing season (April 12 until July 15) following the recommended management practices (
      • Teagasc
      Grazing Notebook.
      ). The start of the second grazing rotation depended on projected daily growth rates from the model developed by
      • Ruelle E.
      • Delaby L.
      • Hennessy D.
      Predicting grass growth: The MoSt GG model.
      and pregrazing herbage mass (HM) on second-rotation paddocks to gradually transition the animals' diet, keeping the combined pasture and supplementary intake as constant as possible.

      Herbage Measurements and Chemical Analysis

      Before each grazing, a sample strip (approximately 1.2 × 10 m) of fresh pasture was harvested from each paddock with an Etesia mower (Etesia UK Ltd.). The weight of the harvested pasture was then subsequently recorded, and 2 subsamples respectively weighing 0.1 and 0.3 kg (fresh weight) were collected. One subsample was dried for 16 h at 90°C for DM determination (
      • Beecher M.
      • Hennessy D.
      • Boland T.
      • O'Donovan M.
      • Lewis E.
      Comparing drying protocols for perennial ryegrass samples in preparation for chemical analysis.
      ), while the other was processed for chemical analysis. Ten compressed sward height (CSH) measurements were recorded before (precutting CSH) and after (postcutting CSH) harvesting on each cut strip, using a folding grass plate meter with a steel plate (Jenquip Rising Plate Meters; diameter 355 mm and 3.2 kg/m2).
      Pregrazing HM was calculated as outlined by
      • O'Donovan M.
      • Dillon P.
      • Rath M.
      • Stakelum G.
      A comparison of four methods of herbage mass estimation.
      :
      Pregrazing HM (kg DM/ha) = fresh weight (kg) × area (length × 1.2 m) × 10,000 × DM%/100.


      Sward density was calculated, using the following formula (
      • Delaby L.
      • Peyraud J.-L.
      • Bouttier A.
      • Peccatte J.-R.
      Effet d'une réduction simultanée de la fertilisation azotée et du chargement sur les performances des vaches laitières et la valorisation du pâturage.
      ):
      Sward density (kg DM/cm/ha) = pregrazing HM (kg DM/ha)/(precutting CSH − postcutting CSH).


      Before and after each grazing, pregrazing sward height and PGSH were determined by taking 30 CSH measurements diagonally across the paddock. The average paddock pregrazing HM was corrected to 3.5 cm by the equation of
      • Delaby L.
      • Peyraud J.-L.
      • Bouttier A.
      • Peccatte J.-R.
      Effet d'une réduction simultanée de la fertilisation azotée et du chargement sur les performances des vaches laitières et la valorisation du pâturage.
      :
      Pregrazing HM (kg DM/ha) = (pregrazing sward height (cm) − 3.5 cm) × sward density (kg DM/cm/ha).


      Daily herbage allowance was determined as a result of the area allocated based on the SRP and was calculated based on the residency time within each paddock and above a cutting height of 3.5 cm, using the following formula:
      Daily herbage allowance (kg DM/cow/d) = area (ha/d) × pregrazing HM (kg DM/ha)/number of cows.


      Total herbage removed and individual daily herbage removed were calculated above the actual PGSH recorded after grazing with the following formulas:
      Total herbage removed (kg DM/ha) = (pregrazing sward height − PGSH) × sward density,


      Daily herbage removed (kg DM/cow/d) = area (ha/d) × total herbage removed (kg DM/ha)/number of cows.


      The efficiency of grazing was also determined using the method of
      • Delaby L.
      • Peyraud J.-L.
      • Bouttier A.
      • Peccatte J.-R.
      Effet d'une réduction simultanée de la fertilisation azotée et du chargement sur les performances des vaches laitières et la valorisation du pâturage.
      based on the following formula:
      Grazing efficiency (%) = total herbage removed/pregrazing HM.


      Total pasture production per hectare per year was calculated as the pregrazing HM, minus the postgrazing HM of the previous rotation as determined by the method described by
      • O'Donovan M.
      • Dillon P.
      • Rath M.
      • Stakelum G.
      A comparison of four methods of herbage mass estimation.
      . Daily pasture growth rates were then calculated by dividing the herbage accumulated by the interval between grazing. Grazing days per hectare were calculated as the total number of cows at pasture on the days when the paddock was being grazed. When cows were housed during the day or at night, this was counted as 0.5 grazing days. Daily growth rates between first grazing and previous closing date were calculated as the total growth (pregrazing HM − previous postgrazing HM) divided by the number of days between grazings.
      Samples for chemical analysis were taking during the first grazing rotation (in 2018, 2019, and 2020). The subsample taken from the sample strip (0.3 kg fresh weight) was frozen at −18°C, bowl-chopped, freeze-dried at −50°C for 120 h, and then milled through a 1-mm sieve. All samples were then analyzed by wet chemistry for ash, ADF, NDF (
      • Van Soest P.J.
      • Robertson J.B.
      • Lewis B.A.
      Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition.
      ), CP (Leco FP-428; Leco Australia Pty Ltd.), and OM digestibility as described by
      • Morgan D.J.
      • Stakelum G.
      • O'Dwyer J.
      Modified neutral detergent cellulose digestibility procedure for use with the ‘Fibertec’ system.
      and modified by
      • Garry B.
      • O'Donovan M.
      • Beecher M.
      • Delaby L.
      • Fleming C.
      • Baumont R.
      • Lewis E.
      Predicting in vivo digestibility of perennial ryegrass using the neutral detergent cellulase method: Updating the equation.
      . The energy content of the pasture, expressed as Unité Fourragère Lait, which is equivalent to the energy content of 1 kg of standard barley of around 1,760 kcal, was subsequently calculated as described by
      • INRA
      INRA Feeding System for Ruminants.
      . The concentrate offered was collected monthly and analyzed for DM, ash, CP, and NDF (Table 2). Silage samples were collected weekly during periods of housing, dried at 40°C for 72 h, and analyzed for DM, ash, ADF, NDF, CP, and in vitro DM digestibility (Table 2).
      Table 2Quality of concentrate and silage (SD) offered as supplementary feed during spring
      ItemConcentrateSilage
      DM digestibility0.69 (3.832)
      CP (g/kg of DM)174 (15.3)175 (20.0)
      ADF (g/kg of DM)326 (39.4)
      NDF (g/kg of DM)289 (65.3)507 (46.5)
      Ash (g/kg of DM)94 (8.4)91 (12.6)
      UFL
      UFL = Unité Fourragère Lait, equivalent to 1,760 kcal similar to that of 1 kg of standard barley (INRA, 2018).
      1.04 (0.007)0.84 (0.064)
      1 UFL = Unité Fourragère Lait, equivalent to 1,760 kcal similar to that of 1 kg of standard barley (
      • INRA
      INRA Feeding System for Ruminants.
      .

      Animal Measurements

      Milk Production.

      Cows were milked twice daily at 0700 and 1530 h. Individual cow milk yield (kg) was recorded at each milking (Dairymaster), and milk samples were collected from successive evening and morning milkings once a week to determine milk fat, protein, and lactose concentrations. The milk samples were then analyzed in the laboratory using a Milkoscan 203 (Foss Electric DK-3400), and weekly yields and solids-corrected milk (SCM;
      • Tyrrell H.F.
      • Reid J.T.
      Prediction of the energy value of cow's milk.
      ), fat, protein, lactose, and fat plus protein (milk solids; MS) yields were subsequently calculated. According to the calving date, only cows with a minimum lactation duration of 4 wk during the experiment were retained for analysis (n = 114, 115, and 108 in years 1, 2, and 3, respectively). Milk, fat, protein, lactose, and MS yields per hectare (from grazed pasture) were derived from the sum of the daily milk and MS yield from all cows within their respective treatment in each paddock during those specific days of grazing and dividing by the area of the paddock. Similarly, the number of grazing days per hectare was calculated by adding up the total number of cows in each treatment grazing in each paddock and dividing by the area of the paddock.

      BW and BCS.

      During the experiment, individual cow BW and BCS were recorded fortnightly upon exit from the milking parlor using an electronic scale with the Winweigh software package (Tru-Test Limited). The BCS was measured by one individual throughout the experiment on a scale of 1 to 5 (1 = emaciated, 5 = obese) in increments of 0.25 as outlined by
      • Edmonson A.
      • Lean I.
      • Weaver L.
      • Farver T.
      • Webster G.
      A body condition scoring chart for Holstein dairy cows.
      .

      Feeding Strategy.

      Daily herbage allowance was derived from the available pasture within the allocated daily area from the SRP. The concentrate allowance was similar between PA, recorded daily, and fed in equal proportions during morning and evening milkings. The required silage allocation was adjusted for each PA to fill the feed deficit as calculated from the DHA and concentrate allowance.

      Statistical Analyses

      All pasture and milk variables were analyzed using SAS version 9.4 (SAS Institute Inc., 2010). The grazing parameters, including pregrazing sward height, pregrazing HM, PGSH, postgrazing HM, herbage removed, grazing efficiency, total pasture used, daily feed allowances (pasture and grass silage), grazing days per hectare, and cumulative feed supplements, were analyzed using PROC MIXED in SAS. Paddock was the experimental unit and included as the random effect. Month nested within year was included as a repeated effect; a compound symmetry covariance structure among records provided the best fit to the data. Fixed effects tested for inclusion in the models were PA (LPA, MPA, and HPA), year (1–3), and month (February, March, April), and their interactions.
      Performance data (daily milk yield, milk constituent yield, milk composition, BW, and BCS) were analyzed including the fixed effects of PA treatment (LPA, MPA, and HPA), breed (Holstein-Friesian or Jersey × Holstein-Friesian crossbred), parity (1, 2, 3, 4, ≥5), experimental week (1–8), and year (1–3), and their interactions. Experimental week was introduced as a repeated measure, and cow was the experimental unit. A compound symmetry presented the best fit for the variables analyzed. A new variable was created as YearCow to account for multiple lactations for some individual cows and was treated as a random effect. Calving day of the year and the genetic merit were fitted as continuous covariates.

      RESULTS

      Meteorological Data

      Meteorological data were recorded daily at the experimental site for the duration of the experiment. Overall interannual mean soil temperature and precipitation levels were similar to the 10-yr average values during the 3-yr study period. However, extremely contrasting weather conditions prevailed during 2 consecutive springs in years 1 and 2, which significantly affected the results of the grazing experiment (Figure 1). Precipitation was below average during February in year 1, while total precipitation during March was 284% of mean values. Air temperatures dropped below 0°C on a total of 29 d during February and March in year 1. As a result, the mean soil temperature at 10-cm depth was 4.0°C and 5.4°C for February and March, respectively, which was 1.5°C (27%) and 1.6°C (23%) lower than the 10-year averages. The cooler temperatures in turn greatly inhibited pasture growth and availability for the majority of the first grazing rotation of that year. In addition, because of severe snow and rainfall in year 1, all cows were housed for a total of 7 d. In contrast, mean air and soil temperatures during spring in year 2 were above the 10-yr average, and animals were never housed for a full day despite wetter conditions than in previous years. Indeed, soil temperatures in February in year 2 were 7.3°C, which was 1.8°C (32%) warmer compared with the 10-yr average (5.5°C), with only 5 d between February and March on which air temperatures dropped below 0°C. Finally, although precipitation levels during February in year 3 were high in comparison with 10-yr average levels (+176%), overall precipitation during the study period and mean air and soil temperatures were similar to the 10-yr average and cows were housed for 2 d in total during the spring.

      Pasture Production, Grazing Characteristics, Daily Herbage and Supplement Allocation, and Pasture Quality During Spring

      Year had a significant effect (P < 0.001) on all spring pasture characteristics, resulting in the greatest growth rates (Figure 2) and pasture production during year 2 (1,810 kg of DM/ha pregrazing HM), in comparison with the lower (1,096 kg of DM/ha) and intermediate (1,600 kg of DM/ha) yields for years 1 and 3, respectively. Similarly, the OPC and therefore pregrazing HM available to animals within each PA treatment differed significantly between years (P < 0.001). The OPC (Table 1) and pregrazing HM (Table 3) were greatest in year 2 (+390 and +839 kg of DM/ha, respectively) and lowest in year 1 (580 and 968 kg of DM/ha, respectively). The lowest PGSH (P < 0.001) was achieved in year 2 (3.1 cm), whereas grazing efficiency was significantly lower (P < 0.001) in year 3 (−8%) compared with years 1 and 2 (108%). As a consequence, milder weather in year 2 led to the greatest (P < 0.001) HM removal and total pasture used compared with the other years. Conversely, the lowest number of days at pasture were achieved in year 1 (−36 d) compared with years 2 and 3 (115 d). Hence, both daily and cumulative concentrate and silage supplementation differed significantly (P < 0.001) between years in response to pasture growth variability, resulting in the greatest supplementary feed allocation in year 1 (Table 4). Year also had a significant yet minor effect (P < 0.001) on all pasture quality parameters (Table 5). Organic matter digestibility was highest in year 1 (80.0%), intermediate in year 3 (79.4%), and lowest in year 2 (78.8%), while sward CP content was greater in year 2 (+41 g/kg) than year 1 (216 g/kg).
      Table 3The effect of pasture availability (PA) treatment on spring pre- and postgrazing pasture characteristics
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      SEP-value
      LPAMPAHPAYearPAYear × PA
      Pregrazing swards
       Sward height (cm)6.9
      Similar superscript letters within a row indicate P > 0.05.
      7.5
      Similar superscript letters within a row indicate P > 0.05.
      8.2
      Similar superscript letters within a row indicate P > 0.05.
      0.18<0.001<0.0010.92
      Year 15.26.06.6
      Year 28.68.99.6
      Year 37.07.78.4
       Herbage mass
      Measured >3.5 cm.
      (kg of DM/ha)
      1,170
      Similar superscript letters within a row indicate P > 0.05.
      1,413
      Similar superscript letters within a row indicate P > 0.05.
      1,645
      Similar superscript letters within a row indicate P > 0.05.
      47.6<0.001<0.0010.517
      Year 16909701,242
      Year 21,6241,7332,061
      Year 31,1971,5341,631
      Postgrazing swards
       Sward height (cm)3.33.43.40.06<0.0010.6780.880
      Year 13.43.53.4
      Year 23.13.13.2
      Year 33.43.53.6
       Herbage mass
      Measured >3.5 cm.
      (kg of DM/ha)
      −53−39−9824.3<0.0010.1770.688
      Year 1−391−35
      Year 2−104−122−221
      Year 3−174−39
       Herbage removed (kg of DM/ha)1,261
      Similar superscript letters within a row indicate P > 0.05.
      1,496
      Similar superscript letters within a row indicate P > 0.05.
      1,767
      Similar superscript letters within a row indicate P > 0.05.
      44.5<0.001<0.0010.703
      Year 17359711,241
      Year 21,8411,9952,395
      Year 31,2071,5211,664
       Grazing efficiency (%)1051041070.020.0110.4830.513
      Year 1109103105
      Year 2106108115
      Year 3100100102
       Total pasture used (kg of DM/ha)2,794
      Similar superscript letters within a row indicate P > 0.05.
      3,319
      Similar superscript letters within a row indicate P > 0.05.
      4,099
      Similar superscript letters within a row indicate P > 0.05.
      115.8<0.001<0.0010.714
      Year 11,6182,1102,928
      Year 23,9444,2975,332
      Year 32,8203,5514,039
       Grazing days (no./ha)82
      Similar superscript letters within a row indicate P > 0.05.
      109
      Similar superscript letters within a row indicate P > 0.05.
      117
      Similar superscript letters within a row indicate P > 0.05.
      5.0<0.001<0.0010.333
      Year 1538795
      Year 2106117124
      Year 387124132
      a–c Similar superscript letters within a row indicate P > 0.05.
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      2 Measured >3.5 cm.
      Table 4The effect of pasture availability (PA) treatment on daily feed allowance and cumulative feed supplementation
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      SEP-value
      LPAMPAHPAYearPAYear × PA
      Daily feed allowance (kg of DM/cow)
       DHA
      DHA = daily herbage allowance, measured >3.5 cm.
      8.8
      Similar superscript letters within a row indicate P > 0.05.
      10.2
      Similar superscript letters within a row indicate P > 0.05.
      11.7
      Similar superscript letters within a row indicate P > 0.05.
      0.42<0.001<0.0010.006
      Year 15.67.810.5
      Year 211.611.812.0
      Year 39.011.012.5
      Concentrate2.72.72.70.12<0.0010.970.99
       Grass silage2.8
      Similar superscript letters within a row indicate P > 0.05.
      1.5
      Similar superscript letters within a row indicate P > 0.05.
      0.8
      Similar superscript letters within a row indicate P > 0.05.
      0.23<0.001<0.0010.004
      Year 14.32.61.5
      Year 20.80.70.5
      Year 33.41.20.5
       Total14.914.815.40.33<0.0010.3060.695
      Year 115.215.316.3
      Year 214.714.414.3
      Year 314.814.715.4
      Cumulative supplementary feed (kg of DM/cow)
       Concentrate1411581515.6<0.0010.1090.460
       Grass silage178
      Similar superscript letters within a row indicate P > 0.05.
      118
      Similar superscript letters within a row indicate P > 0.05.
      77
      Similar superscript letters within a row indicate P > 0.05.
      5.2<0.001<0.001<0.001
      Year 1316252179
      Year 2583616
      Year 31606637
      a–c Similar superscript letters within a row indicate P > 0.05.
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      2 DHA = daily herbage allowance, measured >3.5 cm.
      Table 5The effect of pasture availability (PA) treatment on sward nutritive value during spring
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      SEP-value
      LPAMPAHPAYearPAYear × PA
      OM digestibility (%)79.779.179.20.17<0.0010.0120.111
      CP (g/kg of DM)2402332373.4<0.0010.2560.850
      ADF (g/kg of DM)2162182152.7<0.0010.5730.771
      NDF (g/kg of DM)3863903953.6<0.0010.5450.546
      Ash (g/kg of DM)98103972.60.0430.2290.428
      UFL
      UFL = Unité Fourragère Lait, equivalent to 1,760 kcal similar to that of 1 kg of standard barley (INRA, 2018).
      1.011.011.010.0040.0020.5440.297
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      2 UFL = Unité Fourragère Lait, equivalent to 1,760 kcal similar to that of 1 kg of standard barley (
      • INRA
      INRA Feeding System for Ruminants.
      .
      Pasture availability had no significant effect (P = 0.75) on cumulative spring pasture production (1,502 kg of DM/ha) between January 1 and the end of the first grazing rotation. Moreover, despite significant differences in APC and thus pasture supply (Figure 3), PA did not have an effect on daily pasture growth between the final grazing in autumn and the first grazing in spring (2.6 kg of DM/ha per day). This outcome is based on an average grazing interval between autumn and spring of 150, 143, and 137 d for HPA, MPA, and LPA, respectively. Significant differences were found in pregrazing HM and sward height between PA (P < 0.001). Over the entire study period, HPA achieved the greatest mean pregrazing sward height (8.2 cm) and HM (1,645 kg of DM/ha) compared with MPA (7.5 cm and 1,412 kg of DM/ha, respectively) and LPA (6.9 cm and 1,170 kg of DM/ha, respectively; Table 3). Despite these consistently large differences in herbage supply, no significant differences were evident in sward density (340 kg of DM/cm), postgrazing sward height (3.4 cm), postgrazing HM (−64 kg of DM/ha), or grazing efficiency (105%) between PA in spring (P > 0.05; Table 3). Nonetheless, distinct differences (P < 0.001) in cumulative pasture utilization were apparent during spring; HPA used 780 and 1,305 kg of DM/ha of additional pasture in comparison with MPA (3,152 kg of DM/ha) and LPA (2,604 kg of DM/ha), respectively. Similarly, total grazing days per hectare in spring were greatest for HPA and MPA (+35 and +27 d) compared with LPA (82 d). No significant year × PA interactions (P > 0.05) were found in any pregrazing or postgrazing characteristics. The effect of PA on sward chemical composition during spring is outlined in Table 5. The PA treatment had no significant effect on CP, ADF, NDF, or ash contents of spring grazed swards. A slight, yet significant (P < 0.05) increase was observed in OM digestibility for LPA (+0.6%) compared with both MPA and HPA (79.2%).
      Figure thumbnail gr3
      Figure 3Effect of pasture availability treatment on (a) average weekly pasture cover (kg DM/ha available >3.5 cm) during the spring study period and (b) weekly average pregrazing herbage mass; low pasture availability = ▴; medium pasture availability = ▪; high pasture availability = ♦ (± SE).
      The feeding strategy between PA differed throughout the springs as demonstrated by the significant year × PA interactions for DHA and daily grass silage supplementation (Table 4) owing to the aforementioned variability in pasture supply between years. Although increasing PA by virtue of increased OPC in spring significantly affected supplementary feed requirements within the herd diet in years 1 and 3, this effect was not evident in year 2. All treatments were allocated an equally high DHA (11.8 kg of DM) and required similar daily silage supplementation (0.7 kg of DM) owing to the exceptional pasture growth rates and abundance of pasture supply experienced during winter and spring in year 2. The DHA for HPA was consistently high across all years (11.7 kg of DM), but as a consequence of the additional PA in years 1 and 3, HPA achieved a greater DHA (10.5 and 12.5 kg of DM; P < 0.001) compared with both MPA (7.8 and 11.0 kg of DM/cow in years 1 and 3, respectively) and LPA (5.6 and 9.0 kg of DM/cow in years 1 and 3, respectively). Accordingly, and because daily concentrate supplementation was held constant, daily silage supplementation was reduced in years 1 and 3 (P < 0.001) where DHA was greater for MPA and HPA so that total daily feed allowance was not affected by PA (15.0 kg of DM; P > 0.05).
      On average over the 3-yr study period, cumulative silage supplementation in spring was reduced (P < 0.001) from 178 kg of DM/cow for LPA to 118 (−34%) and 77 kg of DM/cow (−56%) for MPA and HPA, respectively. Although the effect of PA on silage supplementation requirements was evident in each year of the study, the greatest reduction in absolute spring silage requirements for MPA and HPA were greatest in year 1 (−64 and −137 kg of DM/cow, respectively) and year 2 (−94 and −123 kg of DM/cow, respectively) when below average pasture growth increased pasture supply deficits to LPA. To partially compensate for LPA in year 1, the first grazing rotation was extended by 12.5 and 8 d during year 1 compared with years 2 and 3, respectively, to maintain pasture supply and protect regrowth in advance of commencing rotation 2. Despite large interannual variations in pasture growth and availability, no significant year × PA interaction was evident for any sward quality parameters measured.

      Milk Production Performance, DMI, BW, and BCS During Spring

      Year had a significant effect on all milk production parameters analyzed (Table 6). In line with the lower concentrate supplementation, mean daily milk and SCM yield were reduced by 1.6 and 1.1 kg during year 2 in comparison with years 1 and 3 (22.7 and 24.1 kg for milk yield and SCM, respectively). Nonetheless, the greatest milk fat content (+1.3 g/kg; P < 0.001) was evident in year 2 compared with the other years (50.1 g/kg). Milk protein content was similar in years 2 and 3 (34.6 g/kg) but lowest in year 1 (34.0 g/kg). At the same time, the combination of increased milk composition and reduced yield during spring in year 2 resulted in lower mean daily fat, protein, and MS yields compared with years 1 and 3.
      Table 6The effect of pasture availability treatment (PA) on daily milk production, BW, and BCS during spring
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      SEP-value
      LPAMPAHPAYearPAYear × PA
      Daily milk production
       Milk yield (kg/cow)22.322.022.20.25<0.0010.7350.846
      Year 122.522.522.4
      Year 221.421.021.0
      Year 323.022.623.2
       Fat yield (g/cow)109.3110.6112.21.41<0.0010.3510.214
      Year 1110.0113.2110.6
      Year 2105.1108.6108.6
      Year 3112.6110.1117.1
       Protein yield (g/cow)75.575.676.10.85<0.0010.8700.170
      Year 173.676.374.6
      Year 274.473.573.2
      Year 378.677.280.4
       Lactose yield (g/cow)104.0104.2105.01.26<0.0010.8280.148
      Year 1103.2108.7106.1
      Year 2100.998.7101.7
      Year 3107.9105.1107.1
       SCM
      SCM = solids-corrected milk.
      yield (kg/cow)
      23.523.824.00.26<0.0010.4840.452
      Year 123.424.323.8
      Year 222.923.323.3
      Year 324.324.024.8
       Milk solids yield (kg/cow)1.851.861.880.021<0.0010.4570.18
      Year 11.831.871.85
      Year 21.801.821.82
      Year 31.911.901.98
       BW (kg)4924894946.9<0.0010.6730.0109
      Year 1480477472
      Year 2496495501
      Year 3501495509
       BCS
      BCS, measured 1 to 5 (Edmonson et al., 1989).
      2.902.902.900.0140.0010.9760.747
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      2 SCM = solids-corrected milk.
      3 BCS, measured 1 to 5 (
      • Edmonson A.
      • Lean I.
      • Weaver L.
      • Farver T.
      • Webster G.
      A body condition scoring chart for Holstein dairy cows.
      .
      During the 8-wk experimental period, PA had no significant impact (P > 0.05) on cumulative or mean daily milk, fat, protein, lactose, SCM, or MS yields (23.6 kg, 118.3 g, 80.8 g, 111.6 g, 25.4 kg, and 1.99 kg, respectively; Figure 4). Similarly, PA also had no significant impact on milk composition (Table 7). Fat, protein, and lactose composition were 50.4, 34.4, and 46.5 g/kg, respectively, across the 3 springs. However, no significant year × PA interactions were found for milk fat, protein or lactose content. A significant interaction occurred between year × PA for BW (P < 0.05).
      Figure thumbnail gr4
      Figure 4Effect of pasture availability treatment on (a) mean daily milk fat plus protein (milk solids) yield and (b) mean daily solids-corrected milk (SCM) yield; low pasture availability = ▴; medium pasture availability = ▪; high pasture availability = ♦ (± SE).
      Table 7The effect of pasture availability (PA) treatment on daily milk composition during spring
      ItemTreatment
      LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.
      SEP-value
      LPAMPAHPAYearPAYear × PA
      Milk composition (g/kg)
       Fat49.750.850.80.4580.0290.1390.288
      Year 149.750.850.3
      Year 249.952.151.3
      Year 349.449.450.7
       Protein34.234.634.50.191<0.0010.3260.152
      Year 133.534.134.2
      Year 234.835.134.5
      Year 334.234.534.8
       Lactose46.246.746.60.112<0.0010.2570.078
      Year 145.747.046.5
      Year 246.246.947.3
      Year 346.846.346.1
      1 LPA = low pasture availability; MPA = medium pasture availability; HPA = high pasture availability.

      DISCUSSION

      Improving the efficiency of grazing production systems is considered a primary opportunity for the dairy industry (
      • EU
      LIFE helps farming and forestry adapt to climate change. Adaptation in Agriculture.
      ). At the same time, however, the recent intensification of dairy systems is associated with reduced reliance on grazing and increased confinement in many European countries (
      • Delaby L.
      • Finn J.A.
      • Grange G.
      • Horan B.
      Pasture-based dairy systems in temperate lowlands: Challenges and opportunities for the future.
      ). Among the main peculiarities of pasture-based production systems, the high dependence on the natural forces of climate is of grave importance, while the negative impacts of climate change on agricultural productivity (
      • Ortiz-Bobea A.
      • Ault T.R.
      • Carrillo C.M.
      • Chambers R.G.
      • Lobell D.B.
      Anthropogenic climate change has slowed global agricultural productivity growth.
      ) are likely to be accentuated within grazing systems (
      • Ghahramani A.
      • Howden S.M.
      • del Prado A.
      • Thomas D.T.
      • Moore A.D.
      • Ji B.
      • Ates S.
      Climate change impact, adaptation, and mitigation in temperate grazing systems: A review.
      ). For Ireland, regional climate models predict an increase in mean annual temperatures by 1 to 1.6°C by 2050 with an increased frequency of summer dry conditions and wetter winters (
      • Nolan P.
      • Flanagan J.
      High-Resolution Climate Projections for Ireland—A Multi-Model Ensemble Approach.
      ). On that basis, sustainable grazing systems must be adapted to this increased level of fluctuating climatic conditions and unpredictable pasture growth and quality. This adaptation is particularly relevant in spring when energy intake is comparably low and animals are under considerable nutritional stress and require high levels of attention postcalving. This study demonstrates that adapting the feeding strategy by increasing PA for the beginning of the grazing season will maximize grazing days per hectare and minimize the requirements for costly feed supplements, while also maintaining high pasture utilization and grazing efficiency to a high standard of animal performance. Simultaneously, periods of feed shortages as a result of extreme weather conditions can be overcome with the introduction of additional grass silage without affecting animal performance.
      The overall level and differentials in spring PA reported herein are similar to previous studies (
      • McEvoy M.
      • Kennedy E.
      • Murphy J.
      • Boland T.
      • Delaby L.
      • O'Donovan M.
      The effect of herbage allowance and concentrate supplementation on milk production performance and dry matter intake of spring-calving dairy cows in early lactation.
      ;
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ) and within the normal range for early spring pasture reported previously (
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.P.
      • Delaby L.
      • O'Mara F.
      Effect of spring grazing date and stocking rate on sward characteristics and dairy cow production during midlactation.
      ).
      • Holmes C.W.
      • Hoogendoorn C.J.
      • Ryan M.P.
      • Chu A.C.P.
      Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 1. Milk production in early spring: Effects of different regrowth intervals during the preceding winter period.
      reported greater milk yield and constituents when cows were grazing significantly lower pregrazing HM (−2,200 kg of DM/ha difference) during spring at a similar DHA. However, a greater daily milk yield was associated with a greater total feed intake owing to increased pregrazing HM and thus DHA in previous studies that showed differences in pregrazing HM similar to the values reported in the current study (
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.
      • O'Mara F.
      • Delaby L.
      The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer.
      ;
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ). In accordance with the present study,
      • Roche J.
      • Dillon P.
      • Crosse S.
      • Rath M.
      The effect of closing date of pasture in autumn and turnout date in spring on sward characteristics, dry matter yield and milk production of spring-calving dairy cows.
      found no effect on milk yield at similar total DMI, despite significant differences in DHA and a 50% reduction in total grass silage supplementation between treatments in early lactation. In addition, although the reduction in mean silage supplementation requirements during spring in MPA and HPA swards was modest (−60 and −101 kg of DM/cow), it nonetheless represents an important saving in feed costs (equivalent to €15 and €25 per cow per year, respectively), while the total cost savings in terms of ancillary costs are anticipated to be 60% greater based on previous findings (
      • Ramsbottom G.
      • Horan B.
      • Berry D.P.
      • Roche J.
      Factors associated with the financial performance of spring-calving, pasture-based dairy farms.
      ).
      Notwithstanding the major differences in pregrazing HM during the study, no significant impacts on pasture regrowth were observed.
      • Chapman D.
      • Tharmaraj J.
      • Agnusdei M.
      • Hill J.
      Regrowth dynamics and grazing decision rules: Further analysis for dairy production systems based on perennial ryegrass (Lolium perenne L.) pastures.
      previously observed that when pastures are consistently grazed to 4 cm, ryegrass plants will adapt to maximize leaf area in the subgrazing horizon so that sufficient leaf area remains after grazing to quickly restore rates of photosynthesis. All swards in this study were consistently grazed to 3.1 to 3.6 cm during spring. Furthermore, numerous previous studies reported a reduction in sward quality in high pregrazing HM swards with a prolonged winter rest interval (
      • Wales W.J.
      • Doyle P.T.
      • Stockdale C.R.
      • Dellow D.W.
      Effects of variations in herbage mass, allowance, and level of supplement on nutrient intake and milk production of dairy cows in spring and summer.
      ;
      • Hennessy D.
      • O'Donovan M.
      • French P.
      • Laidlaw A.S.
      Factors influencing tissue turnover during winter in perennial ryegrass-dominated swards.
      ;
      • Lawrence D.
      • O'Donovan M.
      • Boland T.
      • Kennedy E.
      Effects of autumn and spring defoliation management on the dry-matter yield and herbage quality of perennial ryegrass swards throughout the year.
      ) and increased leaf senescence (
      • Hennessy D.
      • O'Donovan M.
      • French P.
      • Laidlaw A.S.
      Factors influencing tissue turnover during winter in perennial ryegrass-dominated swards.
      ;
      • Looney C.
      • Hennessy D.
      • Wingler A.
      • Claffey A.
      • Egan M.
      An examination of the effect of autumn closing date on over-winter herbage production and spring yield.
      ), which was exacerbated by elevated PGSH and lower pasture utilization during spring (
      • Holmes C.W.
      • Hoogendoorn C.J.
      • Ryan M.P.
      • Chu A.C.P.
      Some effects of herbage composition, as influenced by previous grazing management, on milk production by cows grazing on ryegrass/white clover pastures. 1. Milk production in early spring: Effects of different regrowth intervals during the preceding winter period.
      ;
      • McEvoy M.
      • Kennedy E.
      • Murphy J.
      • Boland T.
      • Delaby L.
      • O'Donovan M.
      The effect of herbage allowance and concentrate supplementation on milk production performance and dry matter intake of spring-calving dairy cows in early lactation.
      ). In contrast, PA treatment had no effect on PGSH (3.4 cm) or grazing efficiency (105%) during spring within the current study. In addition, our results indicate that sward quality during spring is relatively insensitive to differences in pregrazing HM, similar to results observed by
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      .
      • Chapman D.
      • Tharmaraj J.
      • Agnusdei M.
      • Hill J.
      Regrowth dynamics and grazing decision rules: Further analysis for dairy production systems based on perennial ryegrass (Lolium perenne L.) pastures.
      also previously observed that the number of high-quality live leaves sustained per tiller varies seasonally and can be as high as 3.6 to 3.8 leaves per tiller during late spring, further corroborating our results. Although both
      • Jacobs J.L.
      • Rigby S.E.
      • McKenzie F.R.
      • Ward G.N.
      • Kearney G.
      Effect of lock up and harvest dates on dairy pasture dry matter yield and quality for silage in south-western Victoria.
      and
      • Looney C.
      • Hennessy D.
      • Wingler A.
      • Claffey A.
      • Egan M.
      An examination of the effect of autumn closing date on over-winter herbage production and spring yield.
      associated an increasing HM with declines in DM digestibility and CP and an increase in NDF due to differences in proportions of leaf, stem, and senescent materials in the sward, these effects were mitigated by increased DHA in the study of
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      , who observed increased spring milk production within consistently higher pregrazing HM swards and thus DHA. In contrast, HPA in the current study did not achieve a significantly greater DHA across all years compared with MPA and LPA.
      Beyond the mean impacts of PA treatments observed during our study period, the extreme variability in spring weather conditions between years had pernicious effects on pasture productivity and sward quality and therefore represents an important contribution from the study. Despite similar closing pasture covers within treatment as part of the study design during the previous autumn (
      • Evers S.H.
      • Delaby L.
      • Fleming C.
      • Pierce K.M.
      • Horan B.
      Effect of 3 autumn pasture management strategies applied to 2 farm system intensities on the productivity of spring-calving, pasture-based dairy systems.
      ), the OPC differed significantly (by up to 250 kg of DM/ha) within PA treatments between years. In year 1, below average soil temperatures in early spring led to negligible pasture growth rates (Figure 2a). In such circumstances, reducing area allocation per day, introducing additional supplementary feed, and extending the first grazing rotation have been recommended to maintain animal performance despite pasture deficits (
      • Bryant A.
      • L'Huillier P.
      Better use of pastures.
      ;
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ). In this study, the end of the first grazing rotation during year 1 was extended by 12.5 and 8 d compared with years 2 and 3, respectively. Consequently, cows spent fewer days at pasture in year 1 (79 d) compared with both year 2 (+37 d) and year 3 (+22 d) and therefore, greater cumulative levels of silage (+691%) and concentrate (+216%) supplementation were required within all PA treatments during such conditions. Similar impacts of delayed spring pasture growth have been reported within both controlled experiments (
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ) and commercial data sets (
      • Hanrahan L.
      • Geoghegan A.
      • O'Donovan M.
      • Griffith V.
      • Ruelle E.
      • Wallace M.
      • Shalloo L.
      PastureBase Ireland: A grassland decision support system and national database.
      ). These results highlight the significant impacts of inclement weather conditions on feed requirements and costs within intensive temperate grazing systems.
      The absence of significant year × PA treatment interactions on pasture productivity within the study across a range of climatic conditions emphasizes the relevance of an adequate feeding strategy in which increasing PA and thereby increasing the proportion of grazed pasture in spring is a robust strategy to maintain a high reliance on pasture utilization and reduce supplementary feed requirements. In contrast to LPA and MPA, whereby DHA differed significantly between years, HPA maintained a consistently high DHA across all years (11.7 kg of DM/ha). Nonetheless, it is noteworthy that no reduction in milk output was observed between years because additional levels of grass silage and concentrate supplementation attenuated the effects of variable conditions on animal performance (
      • Ferris C.P.
      • Gordon F.J.
      • Patterson D.C.
      • Kilpatrick D.J.
      • Mayne C.S.
      • McCoy M.A.
      The response of dairy cows of high genetic merit to increasing proportion of concentrate in the diet with a high and medium feed value silage.
      ;
      • Kennedy E.
      • O'Donovan M.
      • Murphy J.P.
      • Delaby L.
      • O'Mara F.
      Effects of grass pasture and concentrate-based feeding systems for spring-calving dairy cows in early spring on performance during lactation.
      ), which might present an opportunity when severe weather conditions are present for the majority of the spring. Overall, these results further corroborate the importance of adequate feed budgeting, regular measurements, and flexible management strategies to meet prevailing climatic and pasture growth conditions within pasture-based dairy systems, in particular during spring (
      • O'Donovan M.
      • Delaby L.
      • Peyraud J.L.
      Effect of time of initial grazing date and subsequent stocking rate on pasture production and dairy cow performance.
      ;
      • Claffey A.
      • Delaby L.
      • Galvin N.
      • Boland T.M.
      • Egan M.
      The effect of spring grass availability and grazing rotation length on the production and quality of herbage and milk in early spring.
      ).

      CONCLUSIONS

      Efficient pasture-based dairy systems are characterized by high milk output per unit of land, and striking the correct balance between herbage quantity and quality is critical. The findings of this study accentuate that increasing PA in spring plays a critical role in an effective feeding strategy to continuously maximize the total pasture used and to maintain high levels of animal performance on a predominantly pasture-based diet in early lactation. In fact, the high rate of pasture utilization and grazing efficiency and the significant reduction in supplementary feed suggest that farm profitability can be enhanced via precise autumn and spring grazing management practices. Moreover, the results highlight that increasing PA in spring will provide a feed buffer to consistently ensure high grazing days per hectare within intensive grazing systems in the future, irrespective of increasing climatic variability.

      ACKNOWLEDGMENTS

      The authors acknowledge the financial support of the Dairy Research Levy and the Teagasc Walsh Scholarship scheme. The project is a collaborative initiative supported by both Teagasc (Ireland) and INRA (France). The authors have not stated any conflicts of interest.

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