60 Reproductive Performance After Timed Artificial Insemination Followed by Timed Embryo Transfer of In Vitro-Produced Embryos in Beef Cattle

Abstract

The combined use of timed AI (TAI) and embryo transfer (TET) has the potential to increase reproductive efficiency in beef cattle. This study evaluated reproductive performance in beef cattle after TAI followed by TET of in vitro-produced embryos at the onset of the breeding season. A total of 476 multiparous non-suckling Bos taurus females (body condition scores of 2.9 ± 0.4 on 1 to 5 scale) were oestrous synchronized with 2 mg of oestradiol benzoate (IM) and a 1.9-g intravaginal progesterone release device (Day –11), which was removed on Day –2, followed by 0.48 mg of sodium cloprostenol, 400 IU of eCG, and 0.5 mg of oestradiol cypionate (IM). In experiment I [no heat detection (HD), or no HD, n = 387], TAI was carried out 48 h later (Day 0), whereas in experiment II (after HD, n = 89), AI was performed 12 h after the onset of oestrus up to 48 h after intravaginal insert removal, when remaining females were inseminated (Day 0). Day-7 blastocysts produced by IVF from abattoir-derived oocytes were individually transferred (TET) 7 days after TAI (Day 7) to 186/387 and 44/89 females in experiments I and II, respectively, ipsilateral to the corpus luteum. Then, fertile mature Bos taurus bulls were introduced on Day 12 into the herds (1:25) up to Day 90. Determinations of pregnancy outcome after TAI, TAI+TET or natural mating, twinning rates, and pregnancy losses were done by ultrasonography and rectal palpation on Days 30, 60, and 125. Data were analysed by the Chi-squared test (P < 0.05). Pregnancy rates (Day 30) were lower after TAI (104/201, 51.7%) than after TAI+TET (126/186, 67.7%) with no HD (experiment I), but similar between TAI (32/45, 71.1%) and TAI+TET (30/44, 68.2%) after HD (experiment II). Twinning rates were lower in TAI groups with no HD (6/104, 5.8%) and after HD (2/32, 6.2%) than in TAI+TET groups with either no HD (42/126, 33.3%) or with HD (14/30, 46.7%). Overall pregnancy was similar between groups after the end of the breeding season: 90.0% (181/201) and 90.3% (168/186) for TAI and TAI+TET with no HD, and 84.4% (38/45) and 84.1% (37/44) for TAI and TAI+TET after HD. Pregnancy losses were higher after TAI+TET with no HD (27/126, 21.4%) than TAI+TET after HD (3/30, 10.0%), and TAI with (2/32, 6.3%) or without (9/104, 8.7%) HD. The TAI+TET with no HD resulted in fewer fetuses per served (0.69) and pregnant (1.30) female than TAI+TET after HD (0.89 and 1.44), whereas TAI with no HD had fewer fetuses than TAI after HD per served (0.50 v. 0.69) but not per pregnant female (1.05 v. 1.03), with both being lower than the TAI+TET groups. In summary, TET after TAI with no HD increased pregnancy and twinning rates. Also, heat detection increased pregnancy rates after TAI and twinning rates after TAI+TET. The TAI+TET combination may be advisable for reproductive schemes with no HD, whereas no benefit of TAI+TET was seen over TAI regarding pregnancy rate if TAI is coupled with HD, but HD may increase prolificacy after TAI+TET. The economics of the use of TAI+TET is under evaluation, by assessing calving, weaning, and postnatal weight gain rates between groups.