Effects of presynchronization and length of proestrus on fertility of grazing dairy cows subjected to a 5-day timed artificial insemination protocol

Abstract

2016-10-17T18:53:41

Behavioral and hormonal pattern of repeat breeder cows around estrus

“…There are several compelling findings that associate lower conception rates in cows with reduced proestrus duration: Dadarwal et al (2013) found that cows with proestrus of 12 and 36 h had conception rates of 11 and 46% respectively. Ribeiro et al (2012) found a similar trend of lower conceptions rates in cows with shorter proestrous period. Although not consistent among various studies, smaller follicles and low E 2 contents in cows with short proestrus have, in themselves, been the probable reasons for reproduction failure.…”

Synchronisation of ovulation for management of reproduction in dairy cows

“…A second and larger study in three high-producing herds demonstrated that the double Ovsynch increased P/AI from 38.2% to 46.3% compared with the Presynch-Ovsynch (Herlihy et al, 2012). Finally, a large study involving three seasonally pasture-based milk production herds resulted in similar fertility responses when cows were subjected to the double Ovsynch compared with the Presynch-Ovsynch (Ribeiro et al, 2012b). Therefore, if the choice is to subject all cows to timed AI, or if herds have a high prevalence of anovular cows, the programme of choice should be the double Ovsynch protocol for the first postpartum insemination.…”

“…Ovulation to the first injection of GnRH improves synchronisation of the oestrus cycle and reduces the period of follicular dominance, both associated with greater P/AI (Vasconcelos et al, 1999; Bleach et al, 2004;Santos et al, 2010a). Complete CL demise following treatment with PGF 2α and the timing of the final GnRH are also critical to expose cows to an adequate period of proestrus (Ribeiro et al, 2012b), which controls priming of the uterus for the establishment of pregnancy and the final stages of follicle maturation. Finally, fertility is modulated by the interval between induction of ovulation with the second GnRH and AI (Pursley et al, 1997), as it determines the window during which oocyte and sperm cells are viable for fertilisation (Saacke, 2008).…”

“…Allowing 56 h of proestrus helps in additional growth of the ovulatory follicle and increased exposure to oestradiol (Peters and Pursley, 2003), which is thought to be needed to avoid short oestrus cycles after induced ovulation. On the other hand, for cows subjected to the 5-day timed AI programme, which results in smaller ovulatory follicles and reduced concentrations of oestradiol in the plasma around the time of AI compared with the Ovsynch protocol (Santos et al, 2010a), the length of proestrus should be extended to 72 h (Bisinotto et al, 2010b;Ribeiro et al, 2012b). Therefore, a careful balance involving follicle/oocyte maturation and timing between sperm and oocyte availability must be considered so that optimal fertility can be achieved.…”

“…The benefits of presynchronisation compared with using an intravaginal insert during the protocol was attributed to an increased proportion of cows with a CL on the 1 st day of the timed AI programme and increased ovulatory response to the initial GnRH treatment. In all studies reported by Ribeiro et al (2011Ribeiro et al ( , 2012aRibeiro et al ( and 2012b, the 5-day timed AI protocol was utilised in an attempt to reduce the period of follicle dominance and the diameter of the pre-ovulatory follicle.A summary of fertility responses of grazing cows subjected to timed AI protocols based on GnRH and PGF 2α , with or without supplemental progesterone, from recently published studies is presented in Table 1. P/AI varied with experiment, and it was less when cows had not been presynchronised or when the study focused on the subpopulations of cows with high prevalence of anovulation (McDougall, 2010b).…”