Effect of genetic merit, milk yield, body condition and lactation number on in vitro oocyte development in dairy cows.

摘要

The effects of milk yield, body condition score (BCS) and lactation number on the number of oocytes recovered and blastocysts formed were studied following in vitro maturation, fertilization and culture of cattle oocytes collected from 48 high and 46 medium genetic merit dairy cows in their first and third lactation. The cows were slaughtered between 125 and 229 days postpartum. Ovaries were recovered, and 2- to 10-mm follicles were aspirated. Cleavage rate and number of blastocysts were determinedat 44 h and 7 days after insemination respectively. Oocytes from high genetic merit cows formed fewer blastocysts and had lower cleavage and blastocyst formation rates than those from medium genetic merit cows (0.36±0.19, 70.4 and 6.8% vs. 0.85±0.22, 77.4 and 11.4%, respectively). The effect of milk production was tested by grouping cows in their third lactation into high and low groups. There was no difference in number of oocytes recovered and subsequent development into blastocysts between the cowsin the high milk production group (4559-5114 kg, n = 20) and cows in the low yield (3162-3972 kg, n = 20) group (6.9±1.34 vs. 8.9±1.32, respectively). The effect of BCS was tested by grouping cows in their first or third lactation into high and low groups. Cleavage and blastocyst formation rates were greater for oocytes from cows with a high BCS (3.3-4.0, n = 20) than a low BCS (1.5-2.5, n = 20) (75.7 vs. 61.9% and 9.9 vs. 3.0%, respectively). Cows in the first lactation yielded fewer oocytes (5.7±1.24)than cows in the third lactation (7.8±0.79). It is concluded that the quality of oocytes probably contributes to reduced fertility, often evident in high genetic merit dairy cows.