University José do Rosário Vellano - UNIFENAS, Alfenas, MG, 37130-000, Brazil.
University José do Rosário Vellano - UNIFENAS, Alfenas, MG, 37130-000, Brazil.
Theriogenology. 2020 Apr 1;146:26-30. doi: 10.1016/j.theriogenology.2020.01.064. Epub 2020 Jan 29.
The study aimed to verify whether a hormone protocol started at Day 13 (D13) after Timed Artificial Insemination (TAI) influences the conception rate. Nelore cows (primiparous and multiparous) from two commercial beef farms (n = 1,431) were first TAI (D0). Timed AI was performed in lots (TAI Lots) ranging from 187 to 346 cows. On D13, regarding the TAI lot, cows were assigned for either receiving (Resynch group, n = 1,002) or not (Control group, a subset of approximately 30%, n = 429) another hormone protocol for resynchronization. The same hormone protocol was used for the first TAI and for the resynchronization, except for 1 mg instead of 2 mg of estradiol benzoate (EB) at the begging of the protocol. Eight days later (D21), the Resynch group was checked for corpus luteum blood flow by color Doppler ultrasonography, and in those detected as non-pregnant, the protocol was completed and a 2nd TAI was performed at D23. Pregnancy diagnosis was later (D30) performed by B-mode ultrasonography in the control group and confirmed in the presumptive pregnant cows from the 1st TAI of the Resynch group. The remaining cows were checked for pregnancy 30 days after the 2nd TAI (experimental Day 53). The statistical model to explain conception rate considered the effects of Group (Control or Resynch), Farm, Parity (primiparous or multiparous), Sire, Technician (who perform AI), TAI Lot and pertinent interactions (GroupParity, GroupFarm and Group*TAI Lot). The statistical analyses of the model were performed using the Proc Glimmix (SAS virtual University Edition). The conception rate for the 1st TAI was similar (P > 0.4) between Control (50.3%, 216/429) and Resynch group (52.6%, 527/1002). The positive predictive diagnostic on D21 showed high relation with PD30 (90.7%, 527/581). In Resynch group, non-pregnant cows (n = 421, 1002 minus 581) were re-inseminated. The conception rate of the 2nd TAI (42.8%, 180/421) was affected (P < 0.002) by side effects of the Farm (48.5 vs. 33.1%) and Parity (51.2 vs. 40.3%, for multiparous vs. primiparous, p < 0.001). Nevertheless, after the 2 TAIs of the Resynch group, the cumulative conception rate was 70.5% (707/1002). In conclusion, the early resynchronization of cows with a low (1 mg) EB dose and progesterone device at D13 after TAI can be used as a strategy to reduce conception interval in beef cattle, and thus to increase the number of pregnant cows from artificial insemination after the breeding season.
本研究旨在验证定时人工授精（TAI）后第 13 天（D13）开始的激素方案是否会影响受孕率。来自两个商业肉牛场的荷斯坦奶牛（初产和经产）（n=1431）首先进行 TAI（D0）。定时 AI 按批次（TAI 批次）进行，范围从 187 头至 346 头。在 D13，根据 TAI 批次，将奶牛分为接受（Resynch 组，n=1002）或不接受（Control 组，约 30%的子集，n=429）另一个激素方案进行同步发情。第一次 TAI 和同步发情时使用相同的激素方案，只是方案开始时雌二醇苯甲酸酯（EB）的剂量从 2 毫克减少至 1 毫克。8 天后（D21），通过彩色多普勒超声检查 Resynch 组的黄体血流，在未怀孕的牛中，完成方案并在 D23 进行第二次 TAI。稍后（D30），在 Control 组通过 B 型超声进行妊娠诊断，并在 Resynch 组第一次 TAI 的假定怀孕牛中确认。其余奶牛在第二次 TAI 后 30 天（实验第 53 天）检查妊娠情况。解释受孕率的统计模型考虑了组（Control 或 Resynch）、农场、胎次（初产或经产）、父本、技术员（进行 AI 的人员）、TAI 批次和相关交互作用（组胎次、组农场和组*TAI 批次）的影响。使用 Proc Glimmix（SAS 虚拟大学版）对模型进行统计分析。Control 组（50.3%，216/429）和 Resynch 组（52.6%，527/1002）的第一次 TAI 受孕率相似（P＞0.4）。D21 的阳性预测诊断与 PD30 高度相关（90.7%，527/581）。在 Resynch 组中，未怀孕的奶牛（n=421，1002 减去 581）被重新授精。第二次 TAI（42.8%，180/421）的受孕率受到农场（48.5 与 33.1%）和胎次（51.2 与 40.3%，经产与初产，p＜0.001）的副作用的影响。然而，在 Resynch 组进行了两次 TAI 后，累积受孕率为 70.5%（707/1002）。综上所述，TAI 后第 13 天（D13）使用低剂量（1 毫克）EB 和孕酮装置进行奶牛早期同步发情，可以作为一种策略，缩短肉牛的受孕间隔，从而增加配种季后人工授精的怀孕奶牛数量。
