VetEnt Research, 49 Benson Road, Te Awamutu, New Zealand 3800.
VetEnt Research, 49 Benson Road, Te Awamutu, New Zealand 3800.
J Dairy Sci. 2022 Jul;105(7):6271-6289. doi: 10.3168/jds.2021-21460. Epub 2022 May 28.
Calf and dam separation is an area of growing public interest, and timely separation is also a practical challenge for pastoral farmers to achieve for all calves. Very few studies have investigated the success of leaving calves with their dams in pastoral conditions, so this observational study assessed serum total protein (STP) in calves born at pasture and left to suckle from their dams for up to 24 h. It also investigated failure of transfer of passive immunity (FPT) once calves had been provided colostrum from the farmer and some factors that may contribute to the risk of FPT. Over 2 years, 8 farms (4 in the North Island, 4 in South Island of New Zealand) were involved in an observational study where cows and calves were observed for 24 h a day for 2 wk per farm. Observers recorded the time from birth to first suckling, number of suckling events, time of calf removal from the dam, and ambient temperature. Calves were blood sampled on arrival at housing, before receiving colostrum from the farmer (d 1), and again 2 d later (d 3) to test for STP concentration. On d 1, 689 calves had blood samples collected, at a median of 11.5 (interquartile range 5.6 to 19.2) hours postbirth. Of these, 283 calves [41.1%; 95% confidence interval (CI) 37.4 to 44.9%] had STP >52 g/L (proportion by farm ranged from 10 to 78%). On d 3, 680 blood samples were collected, of which 16.0% (95% CI 13.5 to 19.0) had FPT (STP ≤52 g/L) with proportion by farm ranging from 2.5 to 31.6%. The FPT risk at d 3 in calves that did not suckle before housing was 2.91 (95% CI 2.04 to 4.13) times the risk in calves that suckled. For every hour longer postbirth that it took for a calf to have its first suckling event, odds of FPT at d 3 increased by 1.21 (95% CI 1.08 to 1.36) times, and compared with calves that only suckled once, calves that suckled 2, 3-5, or >5 times had 0.42 (95% CI 0.15 to 0.99), 0.35 (95% CI 0.15 to 0.76), and 0.10 (95% CI 0.005 to 0.47) times the odds of FPT, respectively. For every 1-percentage-point increase in the Brix % of the colostrum, the odds of FPT decreased by 33% (95% CI 24- to 42). Calves that suckled in the paddock and were fed colostrum with ≥22% Brix had the highest STP, and lowest odds of FPT, of any suckling/Brix % combination. There was a trend for STP to be greater in calves that suckled in the paddock and fed <22% Brix compared with calves that did not suckle in the paddock and fed ≥22% Brix. However, the calves in the former group also tended to have a greater risk of FPT at d 3, and a greater STP variability. There were very large between-farm variabilities for rates of suckling, colostrum feeding, and FPT risk that urgently require further investigation for calves born at pasture.
犊牛和母牛分离是一个日益受到关注的领域，及时分离对于牧民来说也是一个实际的挑战，他们需要让所有的犊牛都能成功地与母牛分离。很少有研究调查在放牧条件下让犊牛与母牛一起生活的成功率，因此这项观察性研究评估了在牧场出生并让其在 24 小时内吸吮母乳的犊牛的血清总蛋白 (STP)。它还调查了犊牛从农民那里获得初乳后被动免疫转移失败 (FPT) 的情况，以及可能导致 FPT 风险的一些因素。在 2 年的时间里，新西兰北岛和南岛的 8 个农场（每个岛 4 个）参与了一项观察性研究，每天 24 小时观察母牛和犊牛，每个农场观察 2 周。观察者记录了犊牛从出生到第一次哺乳的时间、哺乳次数、犊牛从母牛身边带走的时间和环境温度。犊牛到达畜舍时进行血液采样，在接受农民提供的初乳前（d1）和 2 天后（d3）再次进行采样，以检测 STP 浓度。在 d1，采集了 689 头犊牛的血液样本，中位数为 11.5 小时（四分位距 5.6 至 19.2 小时）。其中，283 头（41.1%；95%置信区间 37.4%至 44.9%）的 STP 浓度大于 52g/L（农场间的比例范围为 10%至 78%）。在 d3，采集了 680 份血液样本，其中 16.0%（95%置信区间 13.5%至 19.0%）有 FPT（STP≤52g/L），农场间的比例范围为 2.5%至 31.6%。在畜舍中未哺乳的犊牛在 d3 的 FPT 风险是哺乳犊牛的 2.91 倍（95%置信区间 2.04 至 4.13）。犊牛第一次哺乳事件发生的时间每增加 1 小时，d3 的 FPT 风险就会增加 1.21 倍（95%置信区间 1.08 至 1.36），与只哺乳一次的犊牛相比，只哺乳一次、2 次、3-5 次或>5 次的犊牛的 FPT 风险分别为 0.42（95%置信区间 0.15 至 0.99）、0.35（95%置信区间 0.15 至 0.76）和 0.10（95%置信区间 0.005 至 0.47）。每增加 1 个百分点的初乳 Brix%，FPT 的可能性就会降低 33%（95%置信区间 24%至 42%）。在牧场上哺乳且接受≥22%Brix 初乳的犊牛的 STP 最高，FPT 的可能性最低，任何哺乳/Brix%组合中都没有。与不在牧场上哺乳且接受≥22%Brix 初乳的犊牛相比，在牧场上哺乳且接受<22%Brix 初乳的犊牛的 STP 有增加的趋势，但在牧场上哺乳且接受<22%Brix 初乳的犊牛发生 FPT 的风险更大。然而，前者组的犊牛在 d3 时的 FPT 风险和 STP 变异性也更大。犊牛的哺乳率、初乳喂养率和 FPT 风险的农场间差异非常大，迫切需要对在牧场出生的犊牛进行进一步调查。
