Robinson Research Institute, School of Medicine, University of Adelaide, Adelaide, SA, 5005, Australia.
Robinson Research Institute, School of Medicine, University of Adelaide, Adelaide, SA, 5005, Australia; Queensland Sperm Morphology Laboratory, Goondiwindi, Queensland, 4390, Australia.
Theriogenology. 2020 Aug;152:69-82. doi: 10.1016/j.theriogenology.2020.04.030. Epub 2020 Apr 24.
The practice of feeding replacement-breeding bulls on high energy diets after weaning to meet liveweight (LW) and carcass expectations between 18 and 24 months of age negatively affects reproductive potential. This experiment reports upon the effects of an alternative management strategy aimed at improving calfhood nutrition in rangeland-reared bulls to enhance LW and live carcass characteristics at 2 years. Following artificial insemination (AI cohort; n = 26), or natural mating, subsequent to the addition of bulls at 39 d post-AI (NM cohort; n = 36), primiparous Santa Gertrudis heifers grazing rangeland pastures with bull calf progeny were allocated at parturition to receive either nil supplement (control; CON) or provided with unrestricted access to a pelleted vegetable protein meal-based supplement containing 35% CP (SUPP) until weaning at 199 ± (SD) 26 d. The mean estimated pellet consumption by SUPP heifers during lactation was 2.6 ± (SEM) 0.5 kg DM daily. Grazing diet quality measurements indicated nutritional restriction of CON heifers until at least 115 d of lactation. This was confirmed by lower blood urea nitrogen concentrations at 88 d (P < 0.001) and greater mean NEFA (P < 0.001) concentrations. Rainfall during mid-lactation subsequently improved grazing diet quality; thus the CON heifers experienced moderate nutritional restriction across lactation, but sufficient to reduce milk yield by 1.6 kg/d (P < 0.001) and maternal LW at weaning by 18.4 kg (P < 0.001). Bulls reared by SUPP heifers were 17.5 kg heavier at weaning (P = 0.001) and had elevated IGF-I and leptin concentrations between 4 and 4.5 months of age (P < 0.05). Effects on metabolic hormones during calfhood were cohort specific, with greater concentrations of IGF-I confined to AISUPP bulls and NMSUPP bulls demonstrating greater concentrations of leptin. Bulls were amalgamated at weaning and grazed common pastures without supplementation until the experiment concluded at 675 d. Pre-weaning plane of nutrition did not affect the LW, carcass fat depth, IGF-I or leptin concentrations of bulls after weaning. Mean eye muscle area (EMA) was greater in SUPP compared to CON bulls (68.5 ± 0.9 cmvs 65.2 ± 0.9 cm; P < 0.05) and AISUPP bulls tended to have greater EMA (P = 0.06) than AICON bulls from 495 d of age. Thus when primiparous heifers experience moderate nutritional restriction during lactation, supplementation may have persistent effects upon increasing carcass muscle characteristics of bull progeny.
在断奶后，为了满足 18 至 24 月龄时的活重（LW）和胴体预期，用高能日粮饲养替代繁殖公牛会对繁殖潜力产生负面影响。本实验报告了一种替代管理策略的效果，该策略旨在改善牧场饲养公牛的犊牛期营养，以提高 2 岁时的 LW 和活胴体特性。在人工授精（AI 组；n=26）或自然交配后，公牛在 AI 后 39 天添加（NM 组；n=36），随后配种的初次产 Santa Gertrudis 小母牛在牧场放牧，其后代有公牛小牛，在分娩时被分配接受无补充（对照；CON）或自由采食含有 35%CP 的颗粒状植物蛋白日粮补充剂（SUPP），直到 199±（SD）26d 断奶。SUPP 小母牛在哺乳期的平均估计颗粒料消耗量为每天 2.6±（SEM）0.5kgDM。放牧日粮质量测量表明，CON 小母牛至少在哺乳期 115d 内存在营养限制。这一点从 88d 时血液尿素氮浓度较低（P<0.001）和更高的平均 NEFA（P<0.001）浓度得到证实。随后，中期哺乳期的降雨改善了放牧日粮的质量；因此，CON 小母牛在整个哺乳期经历了适度的营养限制，但足以减少 1.6kg/d 的产奶量（P<0.001）和断奶时的母体 LW（P<0.001）。由 SUPP 小母牛饲养的公牛断奶时重 17.5kg（P=0.001），并且在 4 至 4.5 个月时 IGF-I 和瘦素浓度升高（P<0.05）。犊牛期的代谢激素的影响是特定于群体的，IGF-I 浓度较高仅限于 AISUPP 公牛，而 NMSUPP 公牛则表现出较高的瘦素浓度。公牛在断奶时混合在一起，在没有补充的情况下共同放牧，直到 675d 实验结束。断奶前的营养水平并不影响断奶后公牛的 LW、胴体脂肪深度、IGF-I 或瘦素浓度。与 CON 公牛相比，SUPP 公牛的眼肌面积（EMA）更大（68.5±0.9cm 对 65.2±0.9cm；P<0.05），并且 AISUPP 公牛的 EMA 从 495d 开始有增大趋势（P=0.06），而 AICON 公牛则没有。因此，当初次产小母牛在哺乳期经历适度的营养限制时，补充剂可能会对公牛后代的胴体肌肉特性产生持续影响。
