Fixed-time artificial insemination with estradiol and progesterone for Bos indicus cows II: strategies and factors affecting fertility.

In Experiments 1, 2, and 3, we evaluated the effects of temporary weaning (TW), equine chorionic gonadotropin (eCG), and follicle-stimulating hormone (FSH) treatments on results of a fixed-time artificial insemination (TAI) protocol in postpartum Bos indicus cows. In Experiment 1, treatment with 400 IU eCG or with TW for 48 h consistently improved pregnancy rates (PRs) at TAI, but, in Experiment 2, FSH treatment was less effective than eCG or TW. In Experiment 3, the inclusion of eCG treatment in cows subjected to TW did not improve PRs. We concluded that TW or 400 IU eCG should be included in the TAI protocol in postpartum Bos indicus cows to enhance fertility. In Experiment 4, we used records from heifers and cows treated with the proposed protocol during the 2006-2007 (n=27,195) and 2007-2008 (n=36,838) breeding seasons from multiple locations in Brazil to evaluate factors potentially affecting PRs. Overall PR at TAI was 49.6% (31,786 of 64,033). Pregnancy rate differed (P<0.01) among farm within location (results ranging between 26.8% and 68.0%; P<0.01), cow group within farm, by breed (Bos indicus, 48.3% [26,123 of 54,145]; Bos taurus, 61.7% [3652 of 5922]; and crossbred Bos indicus x Bos taurus, 50.7% [2011 of 3966]), category (nulliparous, 39.6% [2095 of 5290]; suckled primiparous, 45.2% [3924 of 8677]; suckled multiparous, 51.8% [24,245 of 46,767]; and nonsuckled multiparous, 46.1% [1522 of 3299]), body condition score at TAI (< or =2.5, 43.0% [3409 of 7923]; 3.0, 49.6% [18,958 of 38,229]; and > or =3.5, 52.7% [9419 of 17,881]). Days postpartum at beginning of protocol did not affect PR (30 to 60 d, 47.6% [4228 of 8881]; 61 to 90 d, 51.7% [16,325 to 31,572]; and 91 to 150 d, 50.8% [7616 to 14,991]; P>0.1). Pregnancy rate was also consistently affected (P<0.01) by sire (results ranging from 7.2% to 77.3%) and artificial insemination technician (results ranging from 15.1% to 81.8%).