Effect of Time of Artificial Insemination on Pregnancy Rates, Calving Rates, Pregnancy Loss, and Gender Ratio After Synchronization of Ovulation in Lactating Dairy Cows

Abstract

In order to assess the optimal time of artificial insemination (AI) in relation to ovulation, lactating dairy cows (n = 732) from herds with rolling herd averages of 9980 to 11,800 kg from three milkings per day were randomly assigned to five groups by stage of lactation and parity. Ovulation was synchronized by administration of GnRH followed 7 d later with PGF2 alpha followed 2 d later with a second treatment with GnRH. Cows were inseminated at 0, 8, 16, 24, or 32 h after the second injection of GnRH (ovulation occurs between 24 and 32 h after GnRH). Pregnancy diagnoses were performed by ultrasound at 25 to 35 d post-AI. Pregnancy rates per AI were similar for the groups inseminated at 0, 8, 16, and 24 h and lower for the group inseminated at 32 h. A significant quadratic effect of treatment suggests that the middle time periods (8, 16, and 24 h) may produce the greatest pregnancy rate per AI. However, the group inseminated at 0 h had lowest pregnancy loss, and the group inseminated at 32 h tended to have the greatest pregnancy loss compared with that of the other groups. The calving rate was similar between the groups inseminated at 0, 8, 16, and 24 h and lower in the group inseminated at 32 h. The time of AI also appeared to affect gender of calf: cows bred at 0 and 32 h having a higher percentage of female offspring. In conclusion, there appears to be substantial flexibility in the time of AI after the second injection of GnRH, and lower reproductive rates were observed only when AI was after the time of ovulation.

Breeding Services and the Factors Influencing Their Use on Smallholder Dairy Farms in Central Uganda

“…The observed higher proportion of males in AI could be related to timing. Pursley et al [15] showed that in oestrus-synchronized cattle cows that inseminated early (0 hrs) and late (32 hrs) had higher proportions of producing female calves, but with less conception rates than those bred in between these times. In principle, technicians chose to carry out AI at times that ensured maximum conception rates rather than targeting proportions of male or female calves.…”

The Incidence of Repeat Breeding in Dairy Cows under Tropical Condition

“…Therefore, it is important to identify causes of repeat breeding to deal with this problem. The incidence of repeat breeding will be increased by inadequate estrous detection (Heuwieser et al, 1997;Pursley et al, 1998) resulting in errors in timing of insemination in relation to the onset of standing estrus, or insemination of cows not in estrus (Yusuf et al, 2010a). The other potential factors were also suggested, such as quality of semen and insemination technique (Hallap et al, 2006;Morrel, 2006), uterine and/or cervical/vaginal infections (Moss et al, 2002), endocrine disorders (Gustafsson, 1998;Bage et al, 2002;Lopez-Gatius et al, 2004), ovulation failures (Kimura et al, 1987;Silvia, 1994), obstructed oviducts, defective ova, anatomical defects of reproductive tract (Silvia, 1994), and early embryonic death (Gustafsson, 1998;Bage et al, 2002).…”

Fixed-time artificial insemination in beef cattle

“…Since this paper, many studies have evaluated the fertility of lactating dairy cows following the Ovsynch protocol, and pregnancy rates per AI have varied from 27% to 39% [11-13,15,18,19]. These pregnancy rates have been similar to [11,12] or only slightly lower [18,20] than the pregnancy rates with AI after oestrus detection or after oestrus detection following synchronisation of oestrus with PGF 2α in the control cows.…”