Carter Rachel E, Emenheiser Joseph C, Zinn Steven A, Govoni Kristen E, Felix Tara L, Reed Sarah A
Department of Animal Science, University of Connecticut, Storrs, CT 06269, USA.
Department of Extension, University of Connecticut, Storrs, CT 06269, USA.
Transl Anim Sci. 2025 Jan 20;9:txaf005. doi: 10.1093/tas/txaf005. eCollection 2025.
The production of crossbred beef × dairy (B × D) calves is increasing; however, evaluation of pre-weaning feeding strategies for B × D calves is limited. We hypothesized that both male and female B × D calves fed added fat and protein through milk replacer would have increased muscle growth, muscle fiber cross-sectional area, average daily gain, BW, and morphometric measurements. We also hypothesized that calves fed the additional fat and protein milk replacer would have upregulation of regulatory genes involved in muscle hypertrophy. SimAngus × Holstein calves ( = 42) were assigned to one of two milk replacers: 30.0% crude protein (CP), 32% crude fat (CF) milk replacer (HPHF, = 11 males, 11 females), or 22% CP, 20% CF milk replacer (CON, = 10 males, 10 females) from 0 to 8 wk of age. B × D calves were weighed at birth and weekly thereafter. At week 2 and 8, longissimus muscle biopsies were collected for muscle fiber cross-sectional area (CSA) or gene expression analysis. Ultrasounds were performed at 4 and 8 wk of age to quantify ribeye area (REA), and backfat and rump fat thickness. Morphometric measurements, BW, CSA, and ultrasound data were analyzed with PROC MIXED with animal as the subject and fixed effects of milk replacer, age, sex, and their interactions. Gene expression data were analyzed in R Studio. Calves that consumed the HPHF milk replacer were heavier than calves consuming the CON milk replacer (HPHF: 70.7 ± 0.39 kg; CON: 68.5 ± 0.41 kg; < 0.01). At 8 wk of age, HPHF calves tended to have 14% larger muscle fiber CSA than CON calves ( = 0.06). No differences due to diet were observed for REA or fat thickness (≥ 0.38). Expression of MyoD tended to be 34% greater in CON females than HPHF females at 2 wk (= 0.06), but at 8 wk, HPHF females tended to express 39% more MyoD than CON females (= 0.09). Myogenin expression was 3% greater in CON calves than HPHF calves at 2 wk (= 0.02), and CON females tended to express 52% more IGF-1 than HPHF females (= 0.07). Feeding a milk replacer with a protein and fat content similar to beef cow milk improves B × D calf growth compared with a conventional milk replacer with less protein and fat. Improvements in early growth may improve B × D carcass quality and quantity, with the potential to increase return to the producer.
杂交肉牛×奶牛（B×D）犊牛的产量正在增加；然而，针对B×D犊牛断奶前饲养策略的评估却很有限。我们假设，通过代乳粉添加脂肪和蛋白质喂养的雄性和雌性B×D犊牛，其肌肉生长、肌纤维横截面积、平均日增重、体重以及形态测量值都会增加。我们还假设，喂养添加了脂肪和蛋白质代乳粉的犊牛，参与肌肉肥大的调控基因会出现上调。将SimAngus×荷斯坦犊牛（n = 42）分配到两种代乳粉之一：粗蛋白（CP）含量30.0%、粗脂肪（CF）含量32%的代乳粉（HPHF，n = 11头雄性，11头雌性），或CP含量22%、CF含量20%的代乳粉（CON，n = 10头雄性，10头雌性），从0至8周龄进行喂养。B×D犊牛在出生时称重，此后每周称重一次。在第2周和第8周，采集背最长肌活检样本用于肌纤维横截面积（CSA）或基因表达分析。在4周龄和8周龄时进行超声检查，以量化眼肌面积（REA）、背膘和臀膘厚度。形态测量值、体重、CSA和超声数据采用PROC MIXED程序进行分析，以动物为研究对象，代乳粉、年龄、性别及其交互作用作为固定效应。基因表达数据在R Studio中进行分析。食用HPHF代乳粉的犊牛比食用CON代乳粉的犊牛更重（HPHF：70.7±0.39千克；CON：68.5±0.41千克；P < 0.01）。在8周龄时，HPHF犊牛的肌纤维CSA比CON犊牛大14%（P = 0.06）。在REA或脂肪厚度方面未观察到饮食差异（P≥0.38）。在2周龄时CON组雌性MyoD表达量比HPHF组雌性高34%（P = 0.06），但在8周龄时，HPHF组雌性MyoD表达量比CON组雌性高39%（P = 0.09）。在2周龄时CON组犊牛Myogenin表达量比HPHF组犊牛高3%（P = 0.02），CON组雌性IGF - 1表达量比HPHF组雌性高52%（P = 0.07）。与蛋白质和脂肪含量较低的传统代乳粉相比，喂养蛋白质和脂肪含量与肉牛牛奶相似的代乳粉可改善B×D犊牛的生长。早期生长的改善可能会提高B×D胴体的质量和数量，有可能增加生产者的回报。
