Performance, structural growth, and digestibility by Holstein calves fed different amounts of milk through step-up/step-down or conventional methods

Early life milk intake can influence the survival and future productivity of replacement heifers. The present study determined the effects of different amounts of milk through step-up/step-down or conventional feeding methods on the performance of dairy calves. Thirty-nine Holstein calves (18 male and 21 female) were used in a completely randomized design. Calves were randomly allocated to 1 of 3 treatments: (1) conventional milk feeding (CONV; 4.5 L/d of milk from d 1 to 50 and 2 L/d of milk at d 51 and 52 of the study; total milk intake = 229 L); (2) low milk intake with step-up/ step-down method (L-SUSD, 4 L/d of milk from d 1 to 10, 6 L/d from d 11 to 20, 8 L/d from d 21 to 30, 6 L/d from d 31 to 40, 4 L/d from d 41 to 50, and 2 L/d milk at d 51 and 52 of the study, total milk intake = 284 L); (3) high milk intake with step-up/step-down method (H-SUSD, 6 L/d of milk from d 1 to 10, 8 L/d from d 11 to 20, 10 L/d from d 21 to 30, 8 L/d from d 31 to 40, 6 L/d from d 41 to 50, 4 L/d milk at d 51, and 2 L/d milk at d 52 of the study, total milk intake = 386 L). All calves were weaned at d 52 and followed until d 70. Performance data (every week), skeletal growth (d 52 and 70), and ruminal fermentation parameters and di-gestibility (d 35, 55, and 70) were analyzed as repeated measurements with PROC MIXED of SAS version 9.3 (SAS Institute Inc.


INTRODUCTION
Early life nutrition is an important factor that can influence the survival and future productivity of replacement heifers (Soberon et al., 2012).Calves receive the majority of their nutrition from milk during the pre-ruminant phase (Drackley, 2008), and calves are generally raised on either conventional (CONV) or enhanced milk feeding programs (Drackley, 2008;Khan et al., 2011).In the CONV method, calves are fed a restricted amount of milk (8-10% of birth BW, approximately 3-6 L/d) during the preweaning period in an effort to encourage solid feed intake (Drackley, 2008).Enhanced milk feeding programs provide calves with more nutrition in early life than conventional milk feeding methods (Drackley, 2008;Khan et al., 2011).
Several enhanced milk feeding programs including intensified nutrition (Stamey et al., 2012), ad libitum or free-access milk feeding (Jasper and Weary, 2002;De Paula Vieira et al., 2008), step-down milk feeding (Khan et al., 2007a,b) and step-up/step-down methods (Terré et al., 2006(Terré et al., , 2007;;Omidi-Mirzaei et al., 2015;Mirzaei et al., 2018) have been evaluated.In comparisons among different methods of enhanced milk feeding, the stepup/step-down method (SUSD) milk feeding procedure was found to improve the performance of dairy calves compared with step-down and CONV procedures (Omidi-Mirzaei et al., 2015).The SUSD procedure is a method for providing greater amounts of milk to calves early in life while also encouraging starter intake and promoting early rumen development and performance.In this method, milk feeding is gradually increased to reach a peak in the middle of the milk feeding period before it is gradually decreased to the original level toward the end of the period.
Although some studies have reported greater preweaning weight gain, greater structural growth, and improved feed efficiency (Omidi- Mirzaei et al., 2015), others have shown that feeding high amounts of milk through SUSD to young calves decreased starter feed intake, growth, and reticulorumen development (Terré et al., 2006(Terré et al., , 2007)).The effects of enhanced milk feeding on the general health of calves has been examined in several experiments.Several studies have reported that enhanced milk feeding conditions do not affect the morbidity or mortality risks, the number of morbid days, or health scores for preweaning calves (Khan et al., 2007a,b;Omidi-Mirzaei et al., 2015).In contrast, Quigley et al. (2006) and Diaz et al. (2001) found that calves consuming greater amounts of milk had more fluid fecal consistency, experienced more morbid days, and required more veterinary treatment than calves fed on a restricted milk replacer feeding level.Huber et al. (1984) and Quigley et al. (2006) reported higher rectal temperature in calves fed enhanced milk feeding than calves fed the CONV method.Moreover, enhanced milk feeding has also been associated with lower apparent nutrient digestibility around weaning (35 d of study), compared with CONV restricted milk feeding methods (Terré et al., 2007).
The discrepancies observed among studies may be due to differences in the amounts, methods, and quality of the liquid feed (milk or milk replacer) fed, weaning age, or different management conditions (milk feeding frequency) among the studies.For instance, calves that are raised on SUSD programs and are weaned too early can experience a growth check at weaning and may lose some of the growth advantages of feeding more milk during the preweaning stage (Terré et al., 2006(Terré et al., , 2007)).By contrast, the amount of milk fed in the preweaning period through SUSD differed from 180 to 424 L in previous studies (180 L, Terré et al., 2007;244 L, Terré et al., 2006;424 L, Omidi-Mirzaei et al., 2015;311-417 L, Mirzaei et al., 2018).Mirzaei et al. (2018) indicated that different amounts of milk feeding through SUSD method and different age of weaning could affect dairy calves' performance.Moreover, calves were fed milk twice daily (Jasper and Weary, 2002;Terré et al., 2006Terré et al., , 2007;;Khan et al., 2007a,b;Stamey et al., 2012;Omidi-Mirzaei et al., 2015;Mirzaei et al., 2018) in most of the previous experiments on enhanced milk feeding programs.Providing large amounts of milk twice daily has been linked to reduced insulin sensitivity, which may have consequences for future metabolic responses (Bach et al., 2013a).
Our hypothesis was that the difference in the amount of milk consumption of preweaning calves fed 3 times daily through the SUSD method may affect performance, digestibility, and health traits compared with the CONV method.The objectives of this study were to compare the effects of 2 amounts of milk under SUSD milk feeding with conventional milk feeding on structural growth, digestibility, and health scores in Holstein calves that were fed milk 3 times daily and weaned at 55 d of age.

MATERIALS AND METHODS
The present experiment was carried out at Mohandesie Agriculture and Animal Husbandry, Isfahan, Iran.Animal procedures were performed in accordance with protocol no.19293, approved by the Iranian Council of Animal Care (1995).

Animals, Management, and Diets
Thirty-nine 3-d-old Holstein dairy calves (42 ± 1.5 kg BW) were used in the current study (13 calves per treatment: 6 males and 7 females).The calves were separated from their dams immediately after birth, weighed, and moved to individual pens (1.2 × 2.5 m) bedded with sawdust, which was renewed every 24 h.The gate in front of each pen had 2 openings for access to milk and feed buckets mounted on the outside.
The calves were fed 4 L of colostrum (i.e., 1.5 L fed within 2 h of life and 2.5 L fed 8 h after the first feeding).On d 2 of life, transition milk (4.5 L) was fed in 2 equal meals.The calves were blocked by date of birth and within block randomly assigned to 1 of 3 treatments, using initial BW and sex as secondary blocking factors on d 3 of age.The animals were distributed randomly to 1 of 3 milk feeding protocols (Figure 1 .There were no refusals of milk.Whole milk samples were obtained weekly and analyzed for fat, CP, lactose, and total solids using an infrared spectrophotometer (Foss Milkoscan, Foss Electric).The calves received whole milk (temperature adjusted to 39 ± 0.5°C using a water bath) containing 3.74 ± 0.13% fat, 3.19 ± 0.01% CP, 5.37 ± 0.15% lactose, and 12.54 ± 0.52% total solids in steel buckets 3 times daily at 0700, 1600, and 2200 h.
The calves were weaned at d 52 of the study and fed the experimental diets until d 70.From d 3 to 70 of the study, all calves had free access to fresh water and ad libitum starter feed intake by offering an amount that resulted in the residue of 5 to 10% of offered feed after 24 h.The starter feed was formulated according to the Cornell Net Carbohydrate and Protein System, version 5.1.The ingredients and nutrient composition of the starter are given in Table 1.

Sampling and Laboratory Analyses
Starter feed intake and total DMI (TDMI, milk plus starter feed) were determined daily and averaged weekly.Individual BW was recorded every week.Feed efficiency (FE = kg of BW gain/kg of total DMI) and  Contained per kg of supplement: 1,500,000 IU of vitamin A, 380,000 IU of vitamin D, 13,000 IU of vitamin E, 12,000 mg of Mn, 2,000 mg of Fe, 4,000 mg of Cu, 18,000 mg of Zn, 250 mg of I, and 125 mg of Se.
ADG were also calculated weekly.Feed samples were collected every week throughout the study and stored at −20°C until chemical analysis.Subsamples of feeds were mixed thoroughly and analyzed (AOAC International, 2002) for DM (method 925.40),CP (method 2001.11),ether extract (method 920.39), ash (method 942.05), and NDF (using heat-resistant α-amylase and sodium sulfite) according to Van Soest et al. (1991) with the Ankom Fiber Analyzer system (Ankom Technology).
The health of calves was monitored by using the procedure described by Khan et al. (2007b).Fecal scores were recorded daily at 0800 h using the following scales: 1 = normal; 2 = soft to loose; 3 = loose to watery; 4 = watery, mucous, slightly bloody; 5 = watery, mucous, and bloody.A scour day was considered if the scour score was ≥3.
Body measurements were made according to Khan et al. (2007b) at the start of the experiment (d 3), at weaning (d 52), and at the end of the study (d 70).Measurements included body length (distance between the points of shoulder and rump), withers height (distance from base of the front feet to the withers), heart girth (circumference of the chest), body barrel (circumference of the belly before feeding), hip height (distance from base of the rear feet to hook bones), and hip width (distance between the points of hook bones).
On d 35, 55, and 70 of the study, rumen fluid samples were collected with a stomach tube 3 h after the morning feeding.The first 10 mL were discarded because of possible saliva contamination, and rumen pH was measured immediately using a hand-held pH meter (HI 8318, Hanna Instruments).The sample was squeezed through 4 layers of cheesecloth, and a 10-mL aliquot was frozen at −20°C until analysis.After thawing at room temperature, the ruminal fluid filtrates were centrifuged at 3,000 × g at 4°C for 20 min and analyzed for NH 3 by the colorimetric phenol-hypochlorite method (Broderick and Kang, 1980).
Fecal grab samples were collected for 3 d at d 35, 55, and 70 of study for evaluating nutrient digestibility.Fecal samples were collected directly from the rectum of each calf at 1000 and 1600 h.The samples were frozen (−20°C) until analysis.These samples were dried in a forced-air oven at 60°C for 72 h, ground to pass through a 1-mm screen, and analyzed for OM and CP as described for feeds.Apparent total-tract digestibility of nutrients was determined using acid-insoluble ash as an internal marker (Van Keulen and Young, 1977).

Statistical Analyses
Statistical analyses were performed using PROC MIXED in SAS (version 9.3;SAS Institute Inc., 2002), with the individual calf as experimental unit.Data for starter feed intake, TDMI, and rectal temperature recorded daily were first averaged over every week; then starter feed intake, TDMI, ADG, FE, BW, rectal temperature, digestibility, ruminal fermentation parameters, and skeletal growth data were analyzed as repeated measures, with period (week or sampling times) as the repeated variable using the following model: where Y ijk = the dependent variable, μ = the overall mean, T i = the fixed effect of treatment, P j = the fixed effect of period, (T × P) ij = the interaction between treatment and period, C k = the random effect of calf, β (X i − X) is the covariate variable (initial BW and structural growth variables), and ε ijk the error term.The abnormal fecal score days were analyzed using the model Y ik = μ + T i + C k + ε ik , with all terms as previously described but omitting the period term (j).Before analyses, all data were screened for normality using the UNIVARIATE procedure of SAS.The autoregressive (order 1) covariance structure was the best fit for these data as determined by the lowest Akaike's information criterion.Fecal score was analyzed by PROC GLIM-MIX and fitted to the Poisson distribution using a log-link function.Least squares means were computed and compared using the Tukey test, and significant differences and tendencies were stated at P ≤ 0.05 and 0.05 < P ≤ 0.10, respectively.

RESULTS
Starter feed intake, TDMI, ADG, BW, and FE results are presented in Table 2.As provided, calves consumed 229, 284, and 386 L milk through the CONV, L-SUSD, and H-SUSD treatments, respectively.We observed a treatment × time interaction for TDMI (P < 0.001; Figure 2) as follows: TDMI differed among all treatments where H-SUSD > L-SUSD > CONV during d 11 to 38 of study, and H-SUSD was different from other treatments during d 3 to 10 and d 39 to 70 of study.Starter feed intake (785 vs. 594 g/d, P = 0.048) and ADG (678 vs. 552 g/d, P = 0.003) were higher in calves receiving milk through the H-SUSD treatment than in those on the CONV treatment, and L-SUSD treatment was intermediate for those traits.Feed efficiency (0.43 vs. 0.50, P = 0.009) was lower in calves receiving milk through the H-SUSD procedure than other treatments.The H-SUSD calves tended to have greater BW (62.1 vs. 58.6 kg, P = 0.072) than calves fed CONV or L-SUSD treatments.Regardless of treatments, ADG, starter feed intake, and BW increased as calves aged (P < 0.001), whereas FE increased from d 1 to 52 of study and decreased from d 52 to 70 of study.No interactions were identified between treatment and time (P > 0.10) for ADG, starter feed intake, FE, or BW.
The results for structural growth are presented in Table 3.The treatments had no effect on structural growth parameters, except for hip width, which tended to be greater in H-SUSD calves than CONV calves (P = 0.079).As expected, skeletal growth parameters increased as calves aged (P < 0.001).However, no interactions were observed for treatment × time (P > 0.10) with respect to skeletal growth measurements.
The treatments had no effect on the fecal score, scouring days, and rectal temperature in calves (P > 0.10).Moreover, the time effect and the treatment × time interaction (P > 0.10) were not significant for fecal score, scouring days, or rectal temperature (Table 4).
As shown in Table 5, the treatments did not affect digestibility or rumen parameters; however, the time effect was significant for rumen pH, which decreased during d 35 to 55 of the study (P = 0.009).No interactions were identified between treatment and time (P > 0.10) for digestibility and rumen parameters.

DISCUSSION
This study examined effect of different amounts of milk through step-up/step-down and conventional methods on the performance of Holstein dairy calves fed milk 3 times daily.Our hypothesis was that the difference in the amount of milk consumption of preweaning calves through SUSD method compared with the CONV method may affect performance, digestibility, and health traits.
Increasing milk intake in the H-SUSD treatment increased the TDMI compared with L-SUSD and CONV methods during d 3 through 10 and d 39 through 70 of the study.Greater milk consumption in SUSD milkfed calves can increase digestive capacity (De Passillé et al., 1992), and the growth factors and hormones in milk could enhance the growth and maturation of the gastrointestinal tract of calves (Blum and Baumrucker, 2002).Greater milk and starter consumption by the H-SUSD calves compared with those fed CONV led to higher ADG and BW.
In agreement with our results, Omidi- Mirzaei et al. (2015) reported that starter feed intake, TDMI, and ADG were greater in SUSD calves than those in the CONV and step-down treatments during the preweaning period.However, Khan et al. (2007a,b) reported that consumption of starter feed was greater during the pre-step period and lesser during the post-step and postweaning (d 51-90) periods in calves provided milk using the CONV method compared with stepdown calves.Moreover, Terré et al. (2006Terré et al. ( , 2007) ) noted that starter feed intake was greater for CONV than for SUSD calves during preweaning and postweaning until 45 d of the study but similar afterward, although no differences in TDMI were detected during the preweaning period (Terré et al., 2007).Calves fed SUSD were heavier than CONV calves at the end of the study (Terré et al., 2006).
In line with our results, Khan et al. (2007a,b) reported that ADG, BW, and TDMI were greater in calves on the step-down method than in those on the CONV method.However, and in contrast with our results, they reported calves on the step-down method had greater feed efficiency than calves on the CONV method (Khan et al., 2007a,b).The discrepancies observed among the different studies could be attributed to differences in the weaning methods, amounts of milk fed before weaning, milk feeding frequency, or weaning age.For example, Terré et al. (2006Terré et al. ( , 2007) ) reported lesser starter feed intake for their step-up/step-down calves than conventionally fed calves during the pre-and postwean- Means within a row with different superscripts are significantly different (P < 0.05). 1 CONV = conventional milk feeding; L-SUSD = low plane of milk intake with step-up/step-down method; H-SUSD = high plane of milk intake with step-up/step-down method.
2 Tr = treatment effect; T = time effect; Tr × T = the interaction between treatment and time.
ing periods.In those experiments (Terré et al., 2006(Terré et al., , 2007)), calves had access to starter feed only for 35 and 38 d during the preweaning period; however, similar to our results, when calves were weaned at 56 d of age and had access to starter feed throughout the preweaning period, the starter feed intake did not decrease with greater milk consumption through the SUSD method in comparison with CONV calves (Omidi- Mirzaei et al., 2015).This observation shows that calves fed a high level of milk through the SUSD method need time to adapt to solid feed; in other words, calves with a high milk intake should be weaned at the age of >50 d to maintain their starter feed consumption and ADG in the weaning period.Terré et al. (2006) noted that the SUSD treatment may have delayed rumen function in calves weaned at 38 d of study because of lower starter feed intake.However, Khan et al. (2007b) reported that calves fed greater milk through step-down method and weaned at d 49 had greater rumen papillae concentration and greater weight of the forestomach, which was  attributed to their higher solid feed intake and earlier initiation of ruminal fermentation compared with conventionally fed calves.These results indicated that calves weaned at around 50 d of age have enough time to develop their rumen and adapt to use starter feed as the only source of energy.In agreement with this finding, Hu et al. (2020) in a meta-analysis study, showed that calves fed higher amounts of milk replacer had starter feed intake after weaning similar to calves fed lower milk replacer when they weaned at d 56 of age.
In addition, Bach et al. (2013b) reported that feeding large amounts of milk replacer resulted in similar starter feed intake from d 53 of age onward.
The greater starter feed intake during d 30 to 52 of study than d 1 to 30 of study in all treatments is probably a result of reduced milk supply and the associated decrease in nutrient availability.Another reason for the increased consumption of starter feed may be a hyperphagic response caused by the reduced supply of milk and nutrients (Khan et al., 2007b).Starter feed intake in H-SUSD calves was greater than in calves fed CONV.It might be that the greater BW and increased digestive tract capacity (Khan et al., 2007b) resulting from the increased milk intake of H-SUSD calves, resulted in greater demand for nutrients and increased consumption of solid feed (Khan et al., 2007a).Similarly, Khan et al. (2007a,b) indicated that a decrease in milk consumption increased starter feed intake by Holstein calves.
Greater starter feed intake by SUSD methods probably contributed to ruminal development earlier than in calves fed CONV (Khan et al., 2007b).The greater TDMI and possible related ruminal activity increased the ADG in calves fed H-SUSD compared with calves fed CONV.The ADG and BW in calves fed L-SUSD were numerically greater than CONV calves but were not significant, and this suggests that the difference in milk intake in these methods (L-SUSD vs. CONV) was not great enough to affect the calves' performance.Moreover, it indicated that the total amount of milk consumption had a greater effect on calves' performance than the milk feeding method.In confirmation of our results, Daneshvar et al. (2015Daneshvar et al. ( , 2017) ) and Khani et al. (2017) showed that when the total amount of milk consumed was similar, the milk feeding procedures (step-down, CONV, SUSD) had a negligible effect on calves' performance.The improved ADG and BW in H-SUSD calves relative to CONV calves could be due to the greater starter feed intake in these animals.More consumption of starter feed probably induced earlier rumen development and establishment of ruminal fermentation (Khan et al., 2007b).
Overall, the H-SUSD calves had lower FE than the CONV and L-SUSD animals.This might be because H-SUSD calves had higher total DMI than CONV and L-SUSD animals.In contrast with our observations, Omidi- Mirzaei et al. (2015) reported greater values of FE for their SUSD calves compared with calves fed con-   ventionally during the pre-and postweaning periods.However, Khan et al. (2007b) reported no difference in FE between calves fed CONV or step-down methods.
In agreement with our results, Mirzaei et al. (2018) reported that calves fed L-SUSD had greater FE than calves fed H-SUSD (0.63 vs. 0.57).In the current experiment, calves fed lower milk (CONV and L-SUSD) used nutrients more efficiently than calves fed a greater amount of milk (H-SUSD).
Results of the effects of the amount of milk consumption and milk feeding method on body measurements of dairy calves are disparate.In agreement with our results, no differences were observed in body measurements between H-SUSD or L-SUSD calves (Mirzaei et al., 2018).Moreover, Terré et al. (2006) observed no difference in withers height between calves fed SUSD or CONV.In contrast, Omidi- Mirzaei et al. (2015) reported that the SUSD procedure increased body length, withers height, heart girth, hip height, and hip width compared with the step-down and CONV calves.Khan et al. (2007b) reported greater withers height at 2 mo of age in calves fed with a step-down program compared with the CONV method.
Young calves are particularly susceptible to diarrhea during the milk feeding period (Quigley et al., 2006;Daneshvar et al., 2017); however, calves fed through the SUSD method safely consumed greater amounts of milk without any noticeable increase in calf fecal score or scouring days compared with the CONV method.Occurrence of diarrhea, rectal temperature, and scouring days were not affected by milk feeding method in the present experiment.Similar results were documented previously by Omidi- Mirzaei et al. (2015) and Khan et al. (2007a,b), employing different milk feeding methods.These results indicate that if milk is provided in small and frequent meals, calves can consume and digest greater amounts of milk than that given under a conventional feeding system.
Rumen pH was similar between treatments but decreased from d 35 to 55 of the study.The lower rumen pH could be attributed to greater rumen development in calves (Khan et al., 2007b).One possibility for lower pH values may be reflected by increased high-starch starter feed intake from d 35 to 55 of the study.Terré et al. (2007) reported greater apparent DM, OM, NDF, and CP digestibilities in CONV compared with SUSD calves at 1 wk after weaning.Moreover, Daneshvar et al. (2015) noted that apparent DM and OM digestibilities tended to be lower in step-down fed calves than CONV calves.In Terré et al. (2007), the SUSD calves fed lesser starter feed intake had greater rumen pH, which indicated that SUSD calves had a less developed rumen than CONV animals.However, in the current experiment, calves fed H-SUSD had greater starter feed intake and lower rumen pH at weaning, which indicates a more developed rumen than CONV calves.These results indicated that when calves have enough time (>50 d) until weaning, higher milk feeding did not reduce nutrient digestibility.Hill et al. (2010) reported that when calves had lesser starter feed intake before weaning due to greater milk feeding, nutrient digestibility could be decreased postweaning.

CONCLUSIONS
Our results showed that calves fed a high amount of milk through the SUSD method 3 times daily and weaned at the age of 52 d could maintain their starter feed consumption and ADG in the weaning period.The ADG and BW in calves fed L-SUSD were not significantly higher than CONV calves, which suggests that the difference in milk intake was not great enough to affect performance.Moreover, our results indicated that total amount of milk consumption had a greater effect on calves' performance than milk feeding method.
Calves fed through the SUSD method safely consumed greater amounts of milk, with no noticeable increase in fecal score or scouring days, compared with the CONV method.Moreover, higher milk feeding did not decrease digestibility of DM and OM in SUSD calves.
): (1) conventional milk feeding (CONV; 4.5 L/d of milk from d 1 to 50 and 2 L/d milk at d 51 and 52 of the study; total milk intake = 229 L); (2) low milk intake with step-up/step-down method (L-SUSD, 4 L/d of milk from d 1 to 10, 6 L/d from d 11 to 20, 8 L/d from d 21 to 30, 6 L/d from d 31 to 40, 4 L/d from d 41 to 50, and 2 L/d milk at d 51 and 52 of the study; total milk intake = 284 L); and (3) high milk intake with Valehi et al.: MILK FEEDING METHODS AND CALF PERFORMANCE step-up/step-down method (H-SUSD, 6 L/d of milk from d 1 to 10, 8 L/d from d 11 to 20, 10 L/d from d 21 to 30, 8 L/d from d 31 to 40, 6 L/d from d 41 to 50, 4 L/d milk at d 51, and 2 L/d milk at d 52 of the study; total milk intake = 386 L) Figure 1.Schematic representing the amounts of milk consumed (kg/d) by calves fed milk by different procedures and weaned at 52 d of the study: conventional (4.5 L/d of milk at d 1-50; 2 L/d of milk at d 51 and 52 of the study; total milk intake = 229 L); low plane of milk intake with step-up/step-down method (L-SUSD: 4 L/d of milk, d 1-10; 6 L/d, d 11-20; 8 L/d, d 21-30; 6 L/d, d 31-40; 4 L/d, d 41-50; and 2 L/d, d 51 and 52; total milk intake = 284 L); high plane of milk intake with step-up/step-down method (H-SUSD: 6 L/d of milk, d 1-10; 8 L/d, d 11-20; 10 L/d, d 21-30; 8 L/d, d 31-40; 6 L/d, d 41-50; 4 L/d, d 51; and 2 L/d, d 52 of the study; total milk intake = 386 L).

Figure 2 .
Figure 2. Mean total DMI (g/d) in calves (13 per treatment) fed different amounts of milk with different procedures.Error bars represent SEM at each time point.Values are shown separately for Holstein calves fed conventional (CONV, •), low plane of milk intake with step-up/ step-down method (L-SUSD, ○), and high plane of milk intake with step-up/step-down method (H-SUSD, ▼).During the study, P-values for the effects of treatments, time, and interaction between treatments and time were <0.001, <0.001, and <0.001, respectively, and SEM was 63.6.

2
Tr = treatment effect; T = time effect; Tr × T = the interaction between treatment and time.3Days with score ≥3.

Table 1 .
Ingredients and chemical composition of starter feed 2 Valehi et al.: MILK FEEDING METHODS AND CALF PERFORMANCE

Table 2 .
Valehi et al.: MILK FEEDING METHODS AND CALF PERFORMANCE Average DMI of starter feed, total DMI, ADG, BW, and feed efficiency in Holstein calves (n = 13 per treatment) fed milk through different methods

Table 3 .
Structural growth (cm) in Holstein calves (n = 13 per treatment) fed milk through different methods

Table 4 .
Valehi et al.: MILK FEEDING METHODS AND CALF PERFORMANCE Fecal scores, number of abnormal fecal score days, and rectal temperature in Holstein calves (n = 13 per treatment) fed milk through different methods

Table 5 .
Nutrient digestibility, rumen pH, and rumen ammonia in Holstein calves (n = 13 per treatment) fed milk through different methods 1CONV = conventional milk feeding; L-SUSD = low plane of milk intake with step-up/step-down method; H-SUSD = high plane of milk intake with step-up/step-down method.