Pregnancy Rates Per Artificial Insemination for Cows and Heifers Inseminated at a Synchronized Ovulation or Synchronized Estrus

Abstract

Two synchronization protocols were tested for lactating dairy cows and heifers. Nulliparous dairy heifers (13 to 23 mo; n = 155) and primiparous and multiparous dairy cows (60 to 289 d postpartum; n = 310) were assigned randomly to two treatments. Controls received 25 mg of PGF2 alpha and were artificially inseminated according to the a.m.-p.m. rule following detected estrus. All controls that were not detected in estrus were injected with 25 mg of PGF2 alpha at 14-d intervals until artificial insemination (AI) at a detected estrus or until timed AI at 72 to 80 h after a third sequential injection of PGF2 alpha. Treated cows and heifers received a protocol that used GnRH and PGF2 alpha to synchronize ovulation (Ovsynch). Cows and heifers that were treated with Ovsynch were injected i.m. with 100 micrograms of GnRH at a random stage of the estrous cycle. Seven days later, cows and heifers in this group received 25 mg of PGF2 alpha followed by a second injection of 100 micrograms of GnRH 30 to 36 h later. Subsequently, the treated cows and heifers received AI 16 to 20 h after the second injection of GnRH. Pregnancy rates per AI were similar (38.9% vs. 37.8%) for control cows and cows treated with the Ovsynch protocol, respectively. However, pregnancy rate per AI was greater for control heifers (74.4%) than for heifers treated with Ovsynch (35.1%). Evaluation of serum progesterone concentrations at each hormonal injection indicated that the first injection of GnRH synchronized luteal function of lactating dairy cows but not of heifers. In summary, one fixed-time AI at a synchronized ovulation provided similar pregnancy rates per AI as did AI following the a.m-p.m. rule after estrus had been induced by PGF2 alpha in lactating cows, but the fixed-time AI was not effective for heifers because of the lack of synchronization.

Comparison of an oestrus synchronisation protocol with oestradiol benzoate and PGF2α and insemination at detected oestrus to a timed insemination protocol (Ovsynch) on reproductive performance of lactating dairy cows

“…However, the reproductive management advantage of the OVS program is that the insemination rate is higher. That reduces the mean days to first AI and days open and accelerated the rate of accumulated pregnancies [6,8,31]. In the current study, pregnancy rates either to the first or overall up to the fourth AI for primiparous and multiparous cows were similar.…”

“…Therefore, development of treatment programs that can effectively induce oestrus and ovulation in cows can have a major effect on herd reproductive performance. The Ovsynch program was developed allowing cows to be inseminated without the need for oestrus detection and improving reproductive performance during the early postparum period (around 50 d) with no labour investment for detecting oestrous [6][7][8][9]. Such a protocol consists of an injection of GnRH agonist given at random stages of the oestrous cycle followed, 7 d later by an injection of PGF 2α .…”

Synchronization of ovulation in crossbred dairy heifers using gonadotrophin-releasing hormone agonist, prostaglandin F2<FONT FACE=Symbol>a</FONT> and human chorionic gonadotrophin or estradiol benzoate

“…If a second injection of GnRH agonist is administered 36 to 48 h following PGF2a administration the ovulation is synchronized (3)(4)(5) and timed AI 16 to 24 h after the second dose of GnRH results in pregnancy rates similar to those observed in cows bred during normal estrus (4-7). Pursley et al (3) reported that pregnancy rates after timed AI were similar to those for cows bred 12 h after estrus detection (37.8 vs 38.9%). On the other hand, Roy and Twagiramungu (8), waiting only 6 days between the first GnRH injection and PGF2a administration, observed a high pregnancy rate (62.2%) in fixed-time AI beef heifers.…”

“…The administration of a second dose of GnRH 24 to 48 h after PGF2a causes a more precise synchronization of ovulation in both Bos taurus (7,32) and Bos indicus cows (33) and permits timed artificial insemination (3,5,32,34,35). Pursley et al (7) reported that all Holstein cows and 75% of the heifers ovulated within a period of 24 to 32 h after the second GnRH administration.…”

“…GnRH analog administration followed 7 days (d) later by prostaglandin F2a (PGF2a) is a synchronization system whereby the animals show a better homogeneity of follicular development at the time of induced luteolysis (2). If a second injection of GnRH agonist is administered 36 to 48 h following PGF2a administration the ovulation is synchronized (3)(4)(5) and timed AI 16 to 24 h after the second dose of GnRH results in pregnancy rates similar to those observed in cows bred during normal estrus (4-7). Pursley et al (3) reported that pregnancy rates after timed AI were similar to those for cows bred 12 h after estrus detection (37.8 vs 38.9%).…”