Determination of energy and protein requirements of preweaned dairy calves: A multistudy approach

The first studies concerning nutrient requirements for preweaned dairy calves were from the 1920s and 1930s; however, few studies were published in the following decades. We aimed to determine energy and protein requirements of preweaning Holstein and Holstein × Gyr dairy calves in a multistudy meta-regression. We used a database composed of individual measurements of 166 preweaned male calves (138 submitted to treatments and 28 used as the reference group) from 4 studies that used the methodology of comparative slaughter. Animals with less than 15/16 of Holstein genetic composition were considered crossbred Holstein × Gyr, whereas other animals were considered Holstein. Net energy requirements for maintenance (NE_M) were determined by the regression between heat production and metabolizable energy intake (MEI). The metabolizable energy requirements for maintenance were calculated by the iterative method, and the efficiency of use of metabolizable energy for maintenance was obtained by NE_M divided by the metabolizable energy requirements for maintenance. Net energy requirements for gain (NE_G) were estimated using a regression of the retained energy (RE) as a function of empty body weight (EBW) and empty body gain (EBG). The efficiency of use of metabolizable energy for gain was estimated by the regression of RE as a function of MEI, but with partitioning the MEI into MEI from liquid feed and MEI from starter feed. Additionally, the effect of a liquid feed (milk or milk replacer) was tested on the slope of the regression. The metabolizable protein requirements for maintenance (MP_M) were estimated using the intercept of the regression between the metabolizable protein intake (MPI) and average daily gain. The MP_M was determined as the ratio between the intercept and the metabolic body weight. Net protein requirements for gain (NP_G) were estimated by the regression between retained protein, EBG, and RE. The efficiency of use of metabolizable protein for gain was estimated by the regression of the retained protein as a function of MPI, but with partitioning the MPI into MPI from liquid feed and MPI from starter feed. Additionally, the effect of a liquid feed (milk or milk replacer) was tested on the regression slope. Breed did not influence any of the nutrient requirements' estimates. The NE_M was estimated as 70.2 kcal/metabolic body weight per day. The efficiency of use of metabolizable energy for maintenance observed was 66%. The NE_G was estimated by the equation NE_G = 0.0901 × EBW^0.75 × EBG^0.9539. The efficiency of use of metabolizable energy for gain was estimated as 57.6, 49.3, and 41.2% for milk, milk replacer, and starter feed, respectively. The MP_M was estimated as 4.22 g/EBW^0.75 per day, and the NP_G was determined by the equation: NP_G = 30.06 × EBG + 70.98 × RE. The efficiency of use of metabolizable protein for gain was estimated as 71.9, 59.2, and 44.4% for milk, milk replacer, and starter feed, respectively. We concluded that no differences were observed in energy and protein requirements between Holstein and Holstein × Gyr crossbred cows. The efficiencies of use of metabolizable energy and protein are greater for milk when compared with milk replacer and starter feed. Therefore, we propose that the equations generated herein should be used to estimate energy and protein requirements of preweaned Holstein and Holstein × Gyr crossbred dairy calves raised under tropical conditions.

Energy and protein requirements of Holstein × Gyr crossbred heifers

Nutrient requirements in cattle are dependent on physiological stage, breed and environmental conditions. In Holstein × Gyr crossbred dairy heifers, the lack of data remains a limiting factor for estimating energy and protein requirements. Thus, we aimed to estimate the energy and protein requirements of Holstein × Gyr crossbred heifers raised under tropical conditions. Twenty-two crossbred (½ Holstein × ½ Gyr) heifers with an average initial BW of 102.2 ± 3.4 kg and 3 to 4 months of age were used. To estimate requirements, the comparative slaughter technique was used: four animals were assigned to the reference group, slaughtered at the beginning of the experiment to estimate the initial empty BW (EBW) and composition of the animals that remained in the experiment. The remaining animals were randomized into three treatments based on targeted rates of BW gain: high (1.0 kg/day), low (0.5 kg/day) and close to maintenance (0.1 kg/day). At the end of the experiment, all animals were slaughtered to determine EBW, empty body gain (EBG) and body energy and protein contents. The linear regression parameters were estimated using PROC MIXED of SAS (version 9.4). Estimates of the parameters of non-linear regressions were adjusted through PROC NLIN of SAS using the Gauss-Newton method for parameter fit. The net requirements of energy for maintenance (NEm) and metabolizable energy for maintenance (MEm) were 0.303 and 0.469 MJ/EBW0.75 per day, respectively. The efficiency of use of MEm was 64.5%. The estimated equation to predict the net energy requirement for gain (NEg) was: NEg (MJ/day) = 0.299 × EBW0.75 × EBG0.601. The efficiency of use of ME for gain (kg) was 30.7%. The requirement of metabolizable protein for maintenance was 3.52 g/EBW0.75 per day. The equation to predict net protein requirement for gain (NPg) was: NPg (g/day) = 243.65 × EBW-0.091 × EBG. The efficiency of use of metabolizable protein for gain (k) was 50.8%. We observed noteworthy differences when comparing to ME and protein requirements of Holstein × Gyr crossbred heifers with other systems. In addition, we also observed differences in estimates for NEm, NEg, NPg, kg and k. Therefore, we propose that the equations generated in the present study should be used to estimate energy and protein requirements for Holstein × Gyr crossbred dairy heifers raised in tropical conditions in the post-weaning phase up to 185 kg of BW.

Energy and protein requirements of crossbred Holstein × Gyr calves fed milk with milk replacer containing increasing dry-matter concentrations

Context There is a lack of studies concerning the nutrient requirements of dairy calves, mainly, evaluating different genetic groups. Aims The objective was to quantify energy and protein requirements of dairy calves up to 60 days, testing the influence of genetic composition (Holstein or crossbred Holstein × Gyr) on these requirements. Methods The study involved 42 bull calves (3 days of age), including animals with less than 15/16 Holstein composition (considered crossbred) and animals with more than 15/16 Holstein pedigree (considered purebred). Six calves were slaughtered at the start of the experiment to estimate the initial body composition of the animals. Of the remaining animals, four formed the maintenance group (fed 3 L/day of raw milk), and the other 32 were distributed into four treatments, which consisted of 6 L/day of raw milk, with increasing DM contents of 13.5%, 16.1%, 18.2% and 20.4% respectively. The DM contents were corrected for adding milk replacer to the raw milk. All animals had free access to starter feed and water. Digestibility trials were conducted at 28 and 56 days of life, with total faeces collection being performed for 5 days and urine collection for a period of 24 h. At 60 days of life, the animals were slaughtered to determine their body composition. Key results Net energy requirements for maintenance and metabolisable energy requirements for maintenance were 57.6 and 86.8 kcal/(empty bodyweight, EBW)0.75.day respectively. The efficiency of utilisation of metabolisable energy for maintenance was 66%. Net energy requirements for gain (NEg, Mcal/day) can be estimated by the following equation: , where EBG is empty body gain (kg/day) and EBW is in kilograms. The efficiency of utilisation of metabolisable energy for gain was 27%. The metabolisable-protein requirement for maintenance was 3.22 g/EBW0.75.day. Net protein requirement for gain (NPg, g/day) can be estimated by the following equation:, where RE is retained energy (Mcal/day). The efficiency of utilisation of metabolisable protein for gain was 59.1%. Conclusions Genetic group does not affect energy or protein requirements of pre-weaned calves. The estimates presented here can be used to calculate nutrient requirements of pre-weaned calves aged up to 60 days. Implications Inclusion of milk replacer in the liquid feed had a negative impact on diet quality.