Timing of Ovulation and Conception Rate in Primiparous and Multiparous Cows after Synchronization of Ovulation with GnRH and PGF_2α

Abstract

Conception rates after Ovsynch have been higher in primiparous than in multiparous cows. The objective of this study was to investigate whether this difference might be due to differences in ovulation rate or follicular size. The experiment was conducted with 136 Holstein Frisian cows from a commercial herd in Brandenburg, Germany. All cows were synchronized using Buserelin (GnRH analogue) at day -10, Tiaprost (PGF2alpha analogue) at day -3 and again GnRH at day -1. Timed artificial insemination (TAI) was carried out 16-20 h after the second dose of GnRH on day 0. Milk samples for analysis of milk progesterone were obtained on days -17, -10, -3 and at TAI. Progesterone concentrations were used to determine the stage of oestrus cycle at the start of the synchronization protocol and to investigate the presence of functional luteal tissue before treatment with PGF2alpha and TAI. All animals were examined by ultrasound at the second treatment with GnRH, at AI, 8 and 24 h after AI. Overall synchronization rate (proportion of cows with an ovulation within 40 h after GnRH) was 86.8% in primiparous and 88.2% in multiparous cows, respectively. Ovulation occurred earlier in primparous than in multiparous cows (p < 0.05) and ovulatory follicles were smaller. Conception rates were numerically higher in primiparous cows but the difference was not significant. Cows that displayed signs of oestrus on day -1 and received an additional AI on this day were more likely to conceive than cows that only received TAI 16 to 20 h after GnRH2. It is concluded that ovulation occurs earlier in primiparous than in multiparous cows after Ovsynch. However, a significant relationship between these differences and the probability of conception could not be established.

Timing of Ovulation and Fertility of Heifers After Synchronization of Oestrus with GnRH and Prostaglandin F2α

“…2003). The occurrence of oestrus early after PGF 2 α was more frequent in primiparous than in older cows (Tenhagen et al. 2003).…”

“…The synchronization rate of the GPG protocol, defined as percentage of animals ovulating within 40 h after the second dose of GnRH was lower than in lactating dairy cows (Vasconcelos et al. 1999; Tenhagen et al. 2003) but higher than that reported for heifers by Pursley et al.…”

“…While some studies found higher fertility in small follicles (Vasconcelos et al. 1999) others could not demonstrate any relation (Tenhagen et al. 2003) or claimed that ovulation of small follicles may interfere with formation of a sufficiently active CL because of premature ovulation (Peters and Pursley 2003).…”

The effect of ovulatory follicle size at the time of insemination onpregnancy rate in lactating dairy cows

“…Relationship between the follicle size and P/AI at 31 days: a) estimated conception rate and b) real P/AI at 31 days. are known to produce more milk than primiparous cows, and increasing milk production, feed intake, and steroid metabolism could have potential effects on the increasing follicle size in multiparous cows (8,30). Heat stress during the warm season is accepted as a major cause of low fertility in dairy cows.…”

“…Smaller follicles were also found to be related to high embryo survival (25). However, other studies showed that follicle size does not affect pregnancy in cows (8,(16)(17)(18). Thus, the objectives of this study were to detect to relationship between follicle size and P/AI and to determine the factors that affect follicle size at the time of AI in lactating dairy cows.…”