Strategies to improve pregnancy per insemination using sex-sorted semen in dairy heifers detected in estrus

The objective was to improve pregnancy per artificial insemination (P/AI, 35-42 d after AI) in virgin Jersey heifers bred by AI of sex-sorted semen after being detected in estrus Giving 100 g of GnRH at first detection of estrus, with AI 12 h later, did not affect P/AI in Experiment I [GnRH = 472% (100/212) vs No GnRH = 51 7% (104/201), P = 0 38] or Experiment II [GnRH = 53 1% (137/258) vs No GnRH = 486% (122/251), P = 0 43] In these two experiments estrus detection was done with tail-head chalk or a HeatWatch (R) system respectively In Experiment III, a single insemination dose (2 1 X 10(6) sperm) 12 h after estrus detection (n = 193), a double dose at 12 h (n = 193), or a double dose involving insemination 12 and 24 h after estrus detection (n = 190) did not affect P/AI (87/193 = 45 1% 85/193 = 440%, and 94/190 = 495%, respectively, P = 0 51) However, P/AI was Influenced by the number of AI service (First, 115/208 = 55 3%3, Second, 94/204 = 46 1%(a), and Third, 57/165 = 34 8%(b), P = 0 004) In Experiment IV the P/AI of heifers inseminated from 12 to 16 h after the onset of estrus (40/106 = 377%) was less (P = 0 03) than those inseminated from 16 1 to 20 h (85/164 = 51 8%), and 20 1 to 24 h (1301234 = 55 6%) However the P/AI for heifers inseminated from 24 1 to 30 h (61/134 = 45 5%) did not differ from that of any other interval In conclusion, in Jersey heifers inseminated with sex-sorted semen, P/AI was not significantly affected by giving GnRH at detection of estrus or a double insemination dose but it was higher with AI 16 1 to 24 h vs 12 to 16 h after the onset of estrus (C) 2010 Elsevier Inc All rights reserved