This 2-yr study evaluated the growth and puberty attainment of Bos indicus-influenced beef heifers offered 2 different postweaning concentrate supplementation amounts and delivery frequencies. On day 0 of each year, 64 Brangus crossbred heifers were stratified by initial body weight (BW) and age (mean = 244 ± 22 kg; 314 ± 17 d) and assigned into 1 of 16 bahiagrass pastures (4 heifers/pasture/yr). Treatments were randomly assigned to pastures in a 2 × 2 factorial design (4 pastures/treatment/yr) and consisted of concentrate dry matter (DM) supplementation at 1.25% or 1.75% of BW which were offered either daily (7×) or 3 times weekly (3×) for 168 d. On day 56 of each year, heifers were assigned to an estrus synchronization protocol consisting of intravaginal controlled internal drug release (CIDR) insertion on day 56, CIDR removal on day 70, i.m. injection of 25 mg of prostaglandin F_2α (PGF_2α) on day 86, and i.m. injection of 100 µg of gonadotropin-releasing hormone and timed-AI at 66 h after PGF_2α injection (day 89). Heifers were exposed to Angus bulls from day 89 to 168 (1 bull/pasture). Pregnancy diagnosis was assessed on day 213 of each year. Supplementation amount × frequency effects were not detected (P ≥ 0.12) for any variable, except for plasma concentrations of glucose (P = 0.10) and urea nitrogen (PUN; P = 0.01). Herbage mass, herbage allowance, and nutritive value did not differ (P ≥ 0.12) among treatments. Increasing supplementation DM amount from 1.25% to 1.75% of BW increased (P ≤ 0.05) plasma concentrations of insulin-like growth factor 1 (IGF-1), overall average daily gain (ADG), final BW, percentage of pubertal heifers on day 89, pregnancy and calving percentages, and percentage of heifers calving within the first 21 d of the calving season. However, reducing the supplementation frequency from daily to 3× weekly, regardless of supplementation amount, did not impact overall pregnancy and calving percentages (P ≥ 0.42), but caused (P ≤ 0.05) fluctuations in plasma concentrations of insulin and IGF-1 and decreased (P ≤ 0.03) overall ADG, final BW, puberty attainment on days 56, 89, and 168, and percentage of heifers calving during the first 21 d of the calving season. Hence, increasing the supplement DM amount did not prevent the negative effects of reducing the frequency of supplementation (3× vs. 7× weekly) on growth and reproduction of replacement Bos indicus-influenced beef heifers.

中文翻译：

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补充频率和添加量可调节受Bos indicus影响的牛肉小母牛的断奶后生长和生殖性能。

这项为期2年的研究评估了Bos indicus的生长和青春期受影响的小母牛提供了2种不同的断奶后浓缩物补充量和输送频率。在每年的第0天，按初始体重（BW）和年龄（平均= 244±22 kg； 314±17 d）对64个Brangus杂交小母牛进行分层，并分配给16个百吉草牧场中的1个（4个小母牛/牧草/年） ）。处理以2×2因子设计随机分配给牧场（4种牧场/处理/年），并以每日体重（7×）或3次提供的BW的1.25％或1.75％的浓缩干物质（DM）组成。每周（3x）次，持续168天。在每年的第56天，将小母牛分配到发情同步方案，该方案包括在第56天插入阴道内控制内药物释放（CIDR），在第70天去除CIDR，注射25 mg前列腺素_F2α（_PGF2α）在第86天，并在注射_PGF2α（第89天）的66小时内注射100μg促性腺激素释放激素和定时AI 。从第89天到168天，小母牛都暴露于安格斯公牛（1头公牛/牧草）。每年第213天评估妊娠诊断。补充量×频率效应未检出（P ≥0.12）对于任何变量，除了葡萄糖的血浆浓度（P = 0.10），尿素氮（PUN; P = 0.01）。牧草质量，牧草补贴，和营养价值没有差异（P处理间≥0.12）。增重DM量从体重的1.25％增加到1.75％（P≤0.05）血浆胰岛素样生长因子1（IGF-1）的浓度，总平均日增重（ADG），最终体重，第89天的青春期小母牛的百分比，怀孕和产犊的百分比以及在第一次内产犊的母牛的百分比产犊季节的21天。然而，减少所述补充频率从每天3×每周，无论补充量的，并不影响总体怀孕和产犊百分数（P ≥0.42），但引起的（P ≤0.05）在胰岛素和IGF-1和血浆浓度的波动减少（P≤0.03）总体日增重，最终体重，在第56、89和168天达到青春期，以及在产犊季节的前21天产犊的小母牛的百分比。因此，增加补充DM的量并不能防止减少补充频率（每周3次，每周7次）对替代Bos indicus影响的牛肉小母牛生长和繁殖的负面影响。