sorghum-Effects of season, variety type, and trait on dry matter yield, nutrient composition, and predicted intake and milk yield of whole-plant sorghum forage

Sorghum forage is an important alternative to high-quality forage in regions where climatic and soil conditions are less desirable for corn production for silage and producing comparable nutritive value is challenging. The objective of this experiment was to assess the effects of season (spring vs. summer), sorghum variety type (forage sorghum vs. sorghum-sudangrass), and trait [brown midrib (BMR) vs. non-BMR] on dry matter (DM) yield, nutrient composition, and predicted intake and milk yield of whole-plant sorghum forage grown in Florida from 2008 to 2019. Whole-plant sorghum forage was harvested at a targeted 32% of DM, and each year, spring (April) and summer (July) trials were established. A total of 300 forage sorghum and 137 sorghum-sudangrass hybrids were tested for a total of 437 hybrids, of which 199 hybrids contained the BMR trait and 238 were non-BMR. An interaction between season and sorghum variety type was observed for DM yield. Dry matter yield was greater for the spring season than the summer season, with sorghum-sudangrass outperforming forage sorghum only during the spring season. In addition, BMR hybrids had a lower DM yield than non-BMR hybrids, regardless of season and variety type. An interaction between season and trait was observed for predicted neutral detergent fiber digestibility after 30 h of incubation in rumen fluid (NDFD 30h ). Predicted NDFD 30h was greater for BMR sorghum in comparison to non-BMR sorghum, but BMR sorghum had slightly greater predicted NDFD 30h when grown in the spring than summer, whereas no seasonal differences were found for predicted NDFD 30h across non-BMR sorghum. An interaction between season, variety type, and trait was observed for predicted dry matter intake at 45 (DMI 45 ), 55 (DMI 55 ), and 65 (DMI


INTRODUCTION
Sorghum [Sorghum bicolor (L.) Moench] is an important forage source for dairy cows in the southern United States, and other areas worldwide with a similar climate, because certain climatic and soil conditions are less desirable for corn (Zea mays L.) silage production.Feeding sorghum silage is popular due to greater water use efficiency, more flexibility for later planting, and higher tolerance to drought conditions, when compared with feeding corn silage (Marsalis et al., 2009).Moreover, current high corn prices and low silage inventories require dairy farmers to plant other high-quality forages.Whole-plant sorghum is a great alternative because it has a lower cost of production and a greater tolerance to disease and pathogens (Frederiksen and Rosenow, 1979).Even though the chemical composition of corn and sorghum is driven by the effects of environment and management practices (e.g., fertilization), sorghum nutritive value is typically lower than corn nutritive value when grown under similar conditions; therefore, producers often seek strategies to improve sorghum-Effects of season, variety type, and trait on dry matter yield, nutrient composition, and predicted intake and milk yield of whole-plant sorghum forage M. R. Pupo, 1 M. O. Wallau, 2 and L. F. Ferraretto 1 * forage quality and lactation performance by dairy cows (Sánchez-Duarte et al., 2019).
Several sorghum variety types with high-yield potential are available to forage growers and dairy farmers, with the most common being forage sorghum and sorghum-sudangrass [Sorghum bicolor (L.) Moench × Sorghum sudanense (Piper) Stapf].These variety types differ in plant structure, leaf-to-stem proportion (Balasko and Nelson, 2003), and hence, nutritional value, as the greater amounts of mesophyll cells found in leaves are more digestible than nonchlorenchymatous parenchyma cells, predominant in the lignified stem (Adesogan et al., 2019).Forage sorghum plants characteristically have wider flat leaves and a greater proportion of grain than sorghum-sudangrass.Sorghum-sudangrass has much narrower leaves and more profuse tillers (Buxton and O'Kiely, 2003), which makes this more suitable for multiple cut systems for production of hay, haylage, and green-chop forage or grazing production systems, even though some farmers practice a single harvest of sorghum-sudangrass for silage production.
Although forage sorghum and sorghum-sudangrass are widespread, NDF digestibility of sorghum plants is still a lingering concern.Breeding improvements within these sorghum variety types have been focused on cell wall composition by reducing lignin concentration, therefore improving whole-plant sorghum forage nutritive value (Cherney et al., 1991).Lignin is the primary indigestible component of NDF and restricts enzyme access to the digestible NDF fractions, such as cellulose and hemicellulose (Humphreys and Chapple, 2002).The brown midrib (BMR) trait has been selected due to its reduced lignin concentration and corresponding meaningful benefits in digestibility compared with conventional sorghum (Marsalis et al., 2009;Sánchez-Duarte et al., 2019).In general, the literature highlights greater intake and lactation performance for BMR in comparison to conventional sorghum silage (Sánchez-Duarte et al., 2019).The combination of variety type and trait selection can reduce the NDF digestibility of sorghum forage, thereby increasing rumen fill, limiting DMI, and impairing milk yield (Oba and Allen, 1999;Adesogan et al., 2019) of high-producing dairy cows; however, even sorghum forage of lower nutritive value is an important alternative to dairy production systems as a suitable forage source for diets with lower energy requirements such as dairy replacements or dry cow diets.
In addition to the improvements obtained through genetic selection and management practices, environmental factors have a substantial influence on forage nutritive value.In tropical and subtropical climates, for example, forage grown during the summer season is often of lower nutritive value because of environmental stress (Sheehy et al., 2005).Recently, Allen et al. (2019) developed an equation to estimate DMI based on forage quality and ensure diets are formulated accounting for their filling effects.Because NDF concentration of forages changes widely depending on species, maturity, and growing environment (Adesogan et al., 2019), understanding these effects on sorghum forage allows a more precise assessment of DMI when balancing diets.Nevertheless, the interaction of season effects on sorghum forage of different variety types and traits is not clearly understood, limiting the ability of producers to make more profitable and efficient decisions.Thus, this experiment aimed to assess the effects of season (spring vs. summer), sorghum variety type (forage sorghum vs. sorghum-sudangrass), and trait (BMR vs. non-BMR) on DM yield, nutrient composition, and predicted intake and milk yield of whole-plant sorghum forage grown in Florida from 2008 to 2019.We hypothesized that BMR sorghum would have greater NDF digestibility, outperforming conventional sorghum in nutritive value and predicted animal performance at the expense of lower DM yield.Moreover, we hypothesized that the greater proportion of grains in forage sorghum would increase the nutritive value of the sorghum forage and increase predicted milk yield.

Location and Experimental Design
Twenty-four field trials were established between 2008 and 2019 at the University of Florida Plant Science Research and Education Unit (Citra; 29°24′33.7″N, 82°10′15.7″W).No animals were used in this study, and ethical approval for the use of animals was thus deemed unnecessary.Each year, spring (April) and summer (July) trials were established.A total of 300 forage sorghum and 137 sorghum-sudangrass hybrids were tested for a total of 437 hybrids, of which 199 hybrids contained the BMR trait and 238 were non-BMR.Seeds were obtained from multiple seed companies voluntarily participating in each trial (Advanta Seeds, Amarillo, TX; Agra Tech Inc., Pittsburg, CA; Ceres Inc., Thousand Oaks, CA; Croplan Genetics, West Shoreview, MN; Dyna-Gro Seed, Richmond, CA; Gayland Ward Seed, Hereford, TX; Meherrin Ag & Chemical, Severn, NC; Walter Moss Seed Company, Jacksboro, TX; Mojo Seed, Hereford, TX; S&W Seed Company, Longmont, CO; and Sorghum Partners, Longmont, CO).
The soil type was Arredondo-Gainesville (sand and loamy sand) association consisting of well-drained soils; the soil was rapidly permeable and formed in thick beds of sandy marine deposits.The summer trials conducted Sorghum was seeded in quadruplicate plots in 4 rows of 6 m each, spaced at 76 cm centers by a 4-row planter (John Deere MaxEmerge Plus 170, John Deere).Fertilizer applications followed University of Florida Institute of Food and Agricultural Sciences guidelines targeting approximately 225 kg•ha −1 N, 140 kg•ha −1 K, 65 kg•ha −1 P split in a starter application, followed by 2 split side-dressed applications at approximately boot stage (V5) and soft dough stage (V7) and overhead through irrigation at flag leaf.Pesticide application included Pendimethalin Penoxaline (Prowl, Basf), and Metolachlor (Dual, Syngenta) at planting for weed control, followed by an application of 1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine (Atrazine, Syngenta) at 10 cm; Tebuconazole (TebuStar, Albaugh LLC) and Pyraclostrobin (Headline, BASF) and Pyraclostrobin + Metconazole (Headline Amp, BASF) at head emergence for fungal disease control when necessary.Insecticide application consisted of Chlorantraniliprole (Coragen, FMC), Cyhalothrin (Besiege, Syngenta), Lambdacyhalothrin (Warrior, Syngenta), and Flubendiamide (Belt, Bayer Crop Science) divided into multiple applications, following the guidelines established by the University of Florida Institute of Food and Agricultural Sciences.All rates followed label guidelines.
Weather data were obtained from the University of Florida Institute of Food and Agricultural Sciences Extension, Florida Automated Weather Network.The averages for precipitation, humidity, and calculated temperature-humidity index are in Table 1.

Harvesting and Nutrient Analysis
Plants were monitored weekly for DM concentration and harvested at a targeted 32% of DM.At harvest, plants from the 2 middle rows of each plot were handcut to a 25-cm stubble, in a 3-m continuous section, and immediately processed with a single-row silage chopper (model #707, SN: 245797; CNH Industrial America LLC) set with a theoretical cut length of 17 mm and without a kernel processor.The weight of these harvested plots was recorded to estimate DM yield and a subsample collected to measure DM concentration.
Samples were dried in a forced-air oven set at 60°C for 48 h (Heratherm OMS100, SN: 51028873; Thermo Scientific), weighed to determine DM concentration, and then ground to pass through a 4-mm sieve in a Wiley mill (Thomas Scientific) for ease of sample shipment.These dried, ground samples were sent to a commercial laboratory (Dairyland Laboratories Inc., Arcadia, WI) and then ground to pass through a 1-mm sieve in a cyclone mill (Udy Corporation) and analyzed by near-infrared spectroscopy (Foss model 5000; Foss-NIR System).Prediction equations were used to calculate concentrations of CP, starch, sugar, NDF, and predicted NDF digestibility after 30 h of incubation in rumen fluid (predicted NDFD 30h ).Calibrations were developed based on their routine wet chemistry assays.Briefly, CP concentration (method 990.03) was deter- mined by multiplying N concentration by a conversion factor of 6.25 (AOAC International, 1997).Starch concentration was determined according to Vidal et al. (2009).Sugar concentration was determined by adapting the procedure from Derias (1961).Neutral detergent fiber (aNDF) concentration (method 2002.04) was determined using an amylase-treated method corrected for residual ash (AOAC International, 2016).The NDFD 30h was determined using the adapted method of Goering and Van Soest (1970).Residue was analyzed by the same NDF method described previously.Summative equations were used to predict TDN (Weiss, 1998).The digestible NDF harvested (NDFD yield) was calculated as follows: NDFD yield = DM yield × NDF% × NDF digestibility%.

Intake and Milk Yield Simulation
Intake simulations were performed using the equation by Allen et al. (2019).Forage neutral detergent fiber digestibility (FNDFD) is positively related to DMI and milk yield (Oba and Allen, 1999); however, because ration filling effects on intake are exacerbated as milk yield increases (Allen et al., 2019), we conducted simulations to assess the greater limitation of DMI as milk yield increases.We performed predictions of the potential effect of sorghum hybrids on DMI of lactating cows with a milk yield of 35 (DMI 35 ), 45 (DMI 45 ), 55 (DMI 55 ), or 65 (DMI 65 ) kg/d.Briefly, the equation includes linear and quadratic effects of ADF, NDF, forage neutral detergent fiber (FNDF), ADF/NDF ratio, and FNDFD, as well as their linear and quadratic interactions, and milk yield and its interaction with ration factors.Experimental diets consisted of sorghum forage (34.0% of DM), alfalfa haylage (16.0% of DM), and concentrate (50.0% of DM).Alfalfa haylage was composed of 37.9% NDF, 45.4% NDFD, and 32.8% ADF.Concentrate was composed of 18.6% NDF and 13.4% ADF.Diets were formulated to have the same forage-to-concentrate ratio, regardless of the chemical composition of the hybrids.Diet was chosen based on a recent study from our laboratory, which analyzed all the required parameters for the other ingredients.Predicted milk yield per unit of forage yield (kg of milk/ Mg of forage) was estimated based on the equations of Milk2006 (Shaver et al., 2006).

Statistical Analysis
Data were analyzed as a completely randomized design in a 2 × 2 × 2 factorial arrangement of treatments to evaluate the effect of season (spring vs. summer), variety type (forage sorghum vs. sorghum-sudangrass), and trait (BMR vs. non-BMR) using linear mixed-model procedures (PROC GLIMMIX, SAS 9.4; SAS Institute Inc.).Model included the fixed effects of season, sorghum variety type, trait, and their 2-and 3-way interactions.Sorghum hybrids within year was a random effect (Assefa et al., 2016).Mean separation among treatments and interactions involving seasons, sorghum variety types, and traits were obtained using the LSMEANS statement and, after an overall significant F-test, were compared using the sequentially rejective Bonferroni t-test option.Statistical significance was declared at P ≤ 0.05.Main effects were presented and discussed only if no interaction effects were significant (P > 0.05).Two-way interactions are presented and discussed only in the absence of a significant (P < 0.05) 3-way interaction.

RESULTS AND DISCUSSION
Plant environment has a major effect on forage nutritive value.Environmental stress can be caused by several factors, including high temperatures, water deficit, lack of nutrients, and incidence of pests, which are commonly observed during summer season.Precipitation, temperature, and relative humidity varied across the years of the study, but the most consistent differences were due to the growing season.For example, the summer season had, on average, temperatures 3.6°C greater than spring season, with 3.5 mm less precipitation, and 5.4% more humidity, resulting in a temperaturehumidity index 6.3 units higher.Year-to-year and seasonal-temperature variations, as shown in Table 1, influence forage growth rate and yield, alter forage nutritive value, and affect performance of dairy cows.
Probability values of main and interaction effects of all response variables are reported in Table 2. Dry matter was not statistically analyzed because it was considered harvesting criteria.Average DM concentration was 30.9 versus 28.9% (SD = 0.55) for spring and summer, 30.0 versus 29.7% (SD = 0.56) for forage sorghum and sorghum-sudangrass, and 29.7 versus 30.1% (SD = 0.54) for BMR and non-BMR trait, respectively.

Forage Yield and Nutritive Value
An interaction between season and sorghum variety type was observed for DM yield.Dry matter yield was greater for spring than summer season (17.1 vs. 11.6 Mg/ha on average, respectively), with sorghum-sudangrass outperforming forage sorghum during spring season (18.0 vs. 16.2Mg/ha, respectively); however, no significant differences were recorded for summer, regardless of sorghum variety type (11.6 Mg/ha, on average).Dry matter yields were similar to previous studies harvested between July and August, with a pro-  (Venuto and Kindiger, 2008) and 15.8 Mg/ha for forage sorghum (Lyons et al., 2019).Likewise, an interaction between season and sorghum variety type was observed for NDFD yield (Table 3; P = 0.001) and was greatest (1.7 Mg/ha) for spring sorghum-sudangrass, intermediate for spring forage sorghum (1.5 Mg/ha), and lowest for both sorghum variety types grown during the summer season (1.1 Mg/ha, on average).Greater DM yield for spring sorghum-sudangrass partially explains greater NDFD yield.Increased yields are usually achieved when forages are cultivated at temperatures within their optimal range (Fick et al., 1988).When grown at warmer temperatures, forages tend to produce less (Prasad et al., 2015).
Crude protein was affected by season (Table 3; P ≤ 0.01), and CP concentration was greater for summer compared with spring season (8.0 vs. 7.0% of DM, respectively).Season effects on CP concentration are likely related to environmental stress stimulating cell division and elongation rates.High temperatures boost leaf appearance and increase its growth rates (Bos et al., 2000), at the expense of reduced leaf width and thickness.This switch in growth patterns increases the number of leaves, but leaves are narrower in comparison to leaves of plants grown under optimal environmental conditions.Additionally, environmental stress decreases stem diameter and plant height (Prasad et al., 2008).Thus, greater CP concentration for summer planting might be a dilution effect because of the change in the leaf-to-stem ratio.Likewise, McCuistion et al. (2010) observed reduced CP concentration with increasing DM yield, which was also detected in the current study for sorghum planted during spring season.A main effect of trait was observed for CP, where BMR was greater than non-BMR (7.9 vs. 7.1% of DM, respectively).McCollum et al. (2005) reported that BMR hybrids had about 0.6% units greater CP concentration than non-BMR hybrids because BMR plants have greater proportion of leaves, the main source of CP in sorghum.No sorghum variety type differences were detected (P > 0.05) for CP (7.5% of DM, on average).The NASEM (2021) model was used to assess the potential benefits of greater CP concentration on diet formulation.Briefly, the same intake simulation diet was used for this exercise across all 4 production levels (35, 45, 55, and 65 kg/d).A comparison between the highest and lowest treatment means for CP concentration (8.47 vs. 6.68% of DM, respectively) was performed while keeping concentrations of other nutrients constant.Model outputs are in Appendix Table A1.Briefly, MP-allowable milk was greater for the highest sorghum CP concentration, when compared with the lowest sorghum CP concentration, and the magnitude of this response increased with greater milk production (1.63, 1.77, 1.92, and 2.07 kg/d difference for 35, 45, 55, and 65 kg/d, respectively).Greater CP concentrations could help offset yield drags of BMR hybrids and summer planting.
For starch concentration, a main effect of season was observed (Table 3; P ≤ 0.01), where it was greater for spring than summer (14.5 vs. 10.6% of DM, respectively).Li et al. (2013) reported similar patterns for starch concentration under high temperatures, due to early termination of starch accumulation in developing grains.Environmental stress (e.g., heat and drought) may affect the starch biosynthesis by changing its enzyme activities, decreasing grain-filling period, and providing less substrate for the development of sorghum grains (Jiang et al., 2003).Starch concentration was also affected by sorghum variety type (Table 3; P ≤ 0.001) and was greater for forage sorghum than sorghum-sudangrass (15.8 vs. 9.3% of DM, respectively).Presumably, forage sorghum has a greater capacity to produce grain, whereas sorghum-sudangrass produces fewer seeds.Greater starch concentration in forages reduces the inclusion of cereal grains in dairy diets or increases dietary starch concentration.Reducing the cereal grain amounts fed to dairy cows is vital in eras of high-grain prices, whereas dietary starch concentration is positively related to milk yield (Ferraretto et al., 2013).A similar exercise to CP concentrations was conducted for assessment of the potential benefits of starch concentration on diet formulation using the highest and lowest starch concentration treatment means (18.9 vs. 6.9% of DM, respectively) reported in the current study.Briefly, NE L -allowable milk increased along with starch concentration and the magnitude of this response increased for high-producing cows (Appendix Table A1).No trait effects were detected (P > 0.05) for starch concentration (12.6% of DM, on average).
No effects of sorghum variety type or trait were detected (P > 0.05; Table 3) for sugar concentration (4.3 and 4.4% of DM, on average, respectively).Sugar concentration was affected by season (P ≤ 0.01), which was greater for spring than summer (5.5 vs. 3.1% of DM, respectively).Environmental stress, such as heat and drought, leads to a greater cell wall development as a metabolic sink response.This metabolic sink is characterized by the conversion of sugars to structural components (Deinum and Dirven, 1975), explaining the reduction of sugar concentration during the summer planting observed in this study.This premise is corroborated by NDF concentrations.An interaction between season and sorghum variety type was observed for NDF concentration (Table 3; P ≤ 0.01).Concentration of NDF was greatest for sorghum-sudangrass regardless of season (59.4% of DM, on average), whereas NDF concentration was greater for forage sorghum grown in the summer (54.9% of DM) than spring (52.2% of DM).
Likewise, an interaction between season and sorghum variety type was observed (Table 3; P ≤ 0.01) for TDN concentration, where forage sorghum was greatest regardless of season (60.0% of DM, on average), and summer sorghum-sudangrass had a greater (56.8% of DM) concentration than spring sorghum-sudangrass (54.9% of DM).Forage sorghum most likely produces a crop containing a larger proportion of grain by weight, whereas sorghum-sudangrass produces fewer seeds, lowering the overall starch concentration (Getachew et al., 2016).Alternatively, producers could enhance sorghum-sudangrass nutritive value by increasing the number of harvests, which is an important choice espe- cially for the summer season.Previous studies reported that managing crops targeting solely for maximum yield production lowers the nutritional value of the forage (Rooney and Aydin, 1999).Further research is warranted to elucidate season and hybrid effects when sorghum-sudangrass is harvested multiple times instead of a single cut.Moreover, an interaction between season and trait was observed for TDN concentration (Table 3, P = 0.03), where spring non-BMR sorghum was lowest (55.9% of DM) in comparison to other treatments, which did not differ (58.6% of DM, on average).Still, the TDN range in the current study resembles previous sorghum trials, ranging from 56.3 to 71.3% of DM (Miller and Stroup, 2003).
An interaction between season and trait was detected (Table 3, P = 0.01) for predicted NDFD 30h and was greater for BMR (49.8% NDF, on average) in comparison to non-BMR sorghum (44.5% NDF, on average), but BMR sorghum had slightly greater predicted NDFD 30h when grown in the spring (50.5% NDF) than summer (49.0%NDF), whereas no seasonal differences were found for predicted NDFD 30h across non-BMR sorghum (44.5% NDF, on average).Genetic advances have been used to improve forage fiber digestibility by reducing lignification in sorghum plants.Brown midrib sorghum-mutant hybrids commonly have reduced lignin concentration, and the biochemical structure of lignin is modified because of reduced p-coumaric acid and smaller p-coumaric acid: ferulic acid ratio, which is known to have a negative relationship with cell wall digestion (Cherney et al., 1991).Grant et al. (1995) observed 23% greater apparent total-tract NDF digestibility for BMR than conventional sorghum silage (49.2 vs. 40.1% NDF, respectively).Likewise, Sánchez-Duarte et al. (2019) reported greater total-tract NDF digestibility for BMR sorghum than conventional sorghum (61.7 vs. 56.4% NDF, respectively).Environmental stress during summer planting may have altered cell wall synthesis within BMR sorghum plants.High temperatures during the summer season can decrease leaf elongation duration and stem diameter, although the stem is more lignified under temperature stress (Adesogan et al., 2019).Grabber (2005) reported that each percentageunit increase in lignin concentration in cereal plants was associated with a 2 percentage-units decrease in cell wall digestibility.These changes, when combined with increased lignification, explain the slightly lower NDF digestibility for BMR grown during summer than spring.

Predicted Dry Matter Intake and Milk Yield
No season or trait effects were detected (Table 3; P > 0.05) for predicted DMI 35 (24.4 kg/d, on average); however, predicted DMI 35 was affected by sorghum variety type (Table 3; P = 0.001), where it was greater for forage sorghum than sorghum-sudangrass (24.5 vs. 24.2kg/d, respectively).An interaction between season × variety type × trait was observed for predicted DMI 45 , DMI 55 , and DMI 65 ( Predicted DMI differences between BMR and non-BMR hybrids were primarily driven by NDFD 30h .Oba and Allen (1999) reported a 0.17 kg/d greater DMI for each percentage-unit greater in situ or in vitro FNDFD.Moreover, a meta-analysis of feeding trials highlighted a 0.83 kg/d greater DMI for BMR sorghum silage compared with conventional sorghum silage (Sánchez-Duarte et al., 2019).Feeding less-digestible forages increases ruminal digesta retention time and restricts consumption due to rumen fill limitation (Allen, 2014;Mertens, 1994).These ration filling effects on intake become more pronounced as milk yield increases (Allen et al., 2019), as corroborated by our simulation results.
An interaction between season and sorghum variety type was observed for milk yield per Mg of forage (Table 3; P = 0.01), where it was greatest for spring forage sorghum (1,473 kg/Mg), intermediate for summer forage sorghum (1,379 kg/Mg), and lowest for sorghum-sudangrass, regardless of season (1,238 kg/ Mg, on average).The lower NDF concentration, but greater NDFD 30h , starch, and TDN concentrations of forage sorghum, increased its predicted milk yield per unit of forage in comparison to sorghum-sudangrass.Greater fiber concentrations in dairy diets are inversely related to energy density.In this current study, the energy provided by forage sorghum was greater than sorghum-sudangrass because reduced starch concentration and NDF digestibility lower the energy supplied by sorghum plants to dairy cows.Greater energy density observed for forage sorghum due to starch concentration increases dietary starch concentration, which is associated with greater milk production (Ferraretto et al., 2013;Appendix Table A1).Furthermore, each percentage-unit increase in FNDFD measured in vitro or in situ is associated with 0.25 kg/d greater FCM.A meta-analysis by Sánchez-Duarte et al. ( 2019) reported a 1.64 kg/d greater milk yield when cows were fed a BMR sorghum-based diet than when cows were fed conventional sorghum.
Data from this study suggest greater potential for intake and milk yield could partially offset yield drags of BMR sorghum hybrids.Yet, top-and poor-performing hybrids can exist in each of these categories evaluated, and evaluating individual hybrids is advised.In addition, hybrid selection should consider not only sorghum variety type and trait, but also adaptation to regional conditions, tolerance to pests and diseases, and tolerance to abiotic stress to allow these hybrids to express their maximum potential.A beneficial strategy might be producing a combination of highly digestible BMR forages for high-producing cows, while also producing bulky, lower nutritive value forage for dairy replacements, dry, and low producing cows.This would likely balance the needs for greater yields and nutritive value of dairy herds.

CONCLUSIONS
Under the conditions of this experiment, the BMR forage sorghum planted during the spring season had better nutritive value per unit of forage than other treatments, whereas fewer benefits of the trait were observed for the summer planting.Spring planting had greater total production of biomass, NDF digestibility, and starch concentration, increasing the estimates of milk yield per megagram of forage.In general, forage sorghum was of greater nutritional value than sorghumsudangrass.Producers should target summer sorghumsudangrass as a choice for dairy replacements or dry cows because of its lower forage nutritive value.In addition, forage growers planting sorghum-sudangrass should consider BMR mutant hybrids as an alternative to achieve nutritive value and milk response comparable to those found for forage sorghum.The expression of BMR, and its positive effect on nutritive value, can be capitalized on more during spring rather than summer planting.Producers may use the outcomes of this retrospective study to identify and select the assertive sorghum variety types and trait combinations needed to overcome oscillations of yield and forage nutritive value between growing seasons.Sorghum variety type and trait selection are crucial to minimize discrepancies in forage nutritive value of sorghum forage between seasons and increase intake of high-producing dairy cows.

Table 1 .
Pupo et al.: SORGHUM FORAGE NUTRITIVE VALUE Average precipitation, humidity, and temperature-humidity index (THI) during the spring and summer season for 24 sorghum trials in Florida from 2008 to 2019 1Crop establishment of spring planting (April to July) and summer planting (July to November). 2 Data were obtained from the University of Florida Institute of Food and Agricultural Sciences Extension, Florida Automated Weather Network. 3 Temperature-humidity index was calculated by THI = (1.8 × temperature + 32) − (0.55 − 0.55 × relative humidity/100) × [(1.8 × temperature + 32) − 58] according to Segnalini et al. (2011).
Pupo et al.: SORGHUM FORAGE NUTRITIVE VALUE ductivity of up to 17.1 Mg/ha for sorghum-sudangrass

Table 2 .
Pupo et al.: SORGHUM FORAGE NUTRITIVE VALUE Statistical analysis (P-values) of the interaction effects for season, sorghum variety type, and trait on the nutrient composition and harvested-yield responses in whole-plant sorghum Allen et al. (2019)lograms per day, FNDF was forage NDF (% of NDF), FNDFD was forage NDF digestibility (% of FNDF), and MY was milk yield (kg/d), according toAllen et al. (2019).

Table 3 .
Pupo et al.: SORGHUM FORAGE NUTRITIVE VALUE Effects of season, sorghum variety type, and trait (BMR = brown midrib) on the nutrient composition and harvested-yield responses in whole-plant sorghum Item 1 2Greatest standard error of the mean.