Increased fertility in lactating dairy cows resynchronized with Double-Ovsynch compared with Ovsynch initiated 32 d after timed artificial insemination

Abstract

The objective was to determine if using a Double-Ovsynch protocol [DO; Pre-Resynch: GnRH-7 d-PGF(2α)-3 d-GnRH, 7 d later Breeding-Resynch: GnRH-7 d-PGF(2α)-56 h-GnRH-16 h-timed artificial insemination (TAI)] to resynchronize ovulation after a previous TAI would increase synchrony and pregnancies per AI (P/AI) compared with an Ovsynch protocol initiated 32 d after TAI (D32; GnRH-7 d-PGF(2α)-56 h-GnRH-16 h-TAI). Lactating Holstein cows at various days in milk and prior AI services were blocked by parity and randomly assigned to resynchronization treatments. All DO cows received the first GnRH injection of Pre-Resynch 22 d after TAI, and cows (n=981) diagnosed not pregnant using transrectal ultrasonography 29 d after TAI continued the protocol. Pregnancy status for all D32 cows was evaluated 29 d after TAI so fertility and pregnancy loss could be compared with that of DO cows. All D32 cows received the first GnRH injection of Ovsynch 32 d after TAI, and cows (n=956) diagnosed not pregnant using transrectal palpation 39 d after TAI continued the protocol. In a subgroup of cows from each treatment, ultrasonography (n=751) and serum progesterone (P4) concentrations (n=743) were used to determine the presence of a functional corpus luteum (CL) and ovulation to the first GnRH injection of D32 and Breeding-Resynch of DO (GnRH1), luteal regression after PGF before TAI, and ovulation to the GnRH injection before TAI (GnRH2). Overall, P/AI 29 d after TAI was not affected by parity and was greater for DO compared with D32 cows (39 vs. 30%). Pregnancy loss from 29 to 74 d after TAI was not affected by parity or treatment. The percentage of cows with a functional CL (P4 ≥1.0 ng/mL) at GnRH1 was greater for DO than D32 cows (81 vs. 58%), with most DO cows having medium P4 (60%; 1.0 to 3.49 ng/ml), whereas most D32 cows had either low (42%; <1.0 ng/mL) or high (36%; ≥3.5 ng/mL) P4 at GnRH1. Ovulation to GnRH1 was similar between treatments but was affected by serum P4 at GnRH. Cows with low P4 (<1.0 ng/mL) had the greatest ovulatory response (59%), followed by cows with medium (≥1.0 to 3.49 ng/mL; 38%) and then high (≥3.50 ng/mL; 16%) P4 at GnRH1. A greater percentage of DO cows were synchronized compared with D32 cows (72 vs. 51%) primarily due to a greater percentage of D32 than DO cows without a functional CL at the PGF injection before TAI (35 vs. 17%) or without complete CL regression before GnRH2 (17 vs. 7%). We conclude that DO increased fertility of lactating dairy cows during a resynchronization program primarily by increasing synchronization of cows during the Ovsynch protocol before TAI.

Physiological and practical effects of progesterone on reproduction in dairy cattle

“…A particularly surprising result from this study was that all of the effect of hCG on fertility was due to a dramatic increase in primiparous cows (39.5%; 215/544 Control primiparous; 49.7%; 266/535 hCG-treated primiparous) with no change due to hCG treatment in multiparous cows (36.0%; 351/975 Control multiparous; 35.7%; 330/925 hCG-treated multiparous). Numerous other studies have reported that first parity cows generally have higher fertility than older cows particularly when cows are bred after protocols that provide excellent synchrony of ovulation for fixed time AI Souza et al, 2008;Giordano et al, 2012b). However, our experiment does not provide a clear explanation for the differences between parities in the fertility effects of hCG.…”

“…Similar to the first study, cows ovulating a follicle of the second follicular wave (high P4 concentrations) had greater P/AI that cows ovulating the first follicular wave (low P4) (41.7% v. 30.4%) (Bisinotto et al, 2010a). Other studies have also reported that low P4 at the beginning of the Ovsynch protocol results in decreased P/AI compared with cows with high P4 concentrations Denicol et al, 2012;Giordano et al, 2012aGiordano et al, , 2012bGiordano et al, and 2013a. In addition, a recent study (Bisinotto et al, 2013) compared cows with a CL at the initiation of a synchronized ovulation program to cows either without a CL, that were untreated, or cows without a CL that were treated with two intravaginal P4 implants (two CIDRs).…”

“…This has been clearly shown in numerous studies using timed AI programs (Souza et al, 2007;Brusveen et al, 2008;Bisinotto et al, 2010b;Giordano et al, 2012b and. In addition, studies on cows that receive AI after detection of estrus, have generally reported that minor elevations in P4 near AI are also detrimental to fertility (De Silva et al, 1981;Waldmann et al, 2001;Ghanem et al, 2006), although some studies did not obtain this result (Erb et al, 1976;Plym Forshell et al, 1991).…”

“…In summary, circulating P4 near AI, >0.1 ng/ml in a study using estradiol to induce ovulation (Pereira et al, 2013) or > 0.3 to 0.5 ng/ml in studies using GnRH to induce ovulation (Souza et al, 2007;Brusveen et al, 2009;Santos et al, 2010;Martins et al, 2011b;Ribeiro et al, 2012;Giordano et al, 2012b), is detrimental to fertility in dairy cattle, but the underlying physiological mechanisms that reduce fertility are not well understood. An additional PGF2α treatment in cows receiving Ovsynch and more precise detection of estrus may help to minimize the percentage of cows with elevated circulating P4 near AI.…”

“…Elevated P4 in vitro, also increased total α-inhibin production by the cumulus-oocyte complex, which may reduce embryo development after cleavage (Silva et al, 1999). Further, the reduced endometrial thickness that accompanies slight elevations in P4 (Souza et al, 2011) may indicate other major effects of P4 on the blood flow and functionality of the uterus and these changes could underlie the reduced embryo development.In summary, circulating P4 near AI, >0.1 ng/ml in a study using estradiol to induce ovulation (Pereira et al, 2013) or > 0.3 to 0.5 ng/ml in studies using GnRH to induce ovulation (Souza et al, 2007;Brusveen et al, 2009;Santos et al, 2010;Martins et al, 2011b;Ribeiro et al, 2012;Giordano et al, 2012b), is detrimental to fertility in dairy cattle, but the underlying physiological mechanisms that reduce fertility are not well understood. An additional PGF2α treatment in cows receiving Ovsynch and more precise detection of estrus may help to minimize the percentage of cows with elevated circulating P4 near AI.…”