Pregnancy rates in dairy cows following the administration of a GnRH analogue at the time of artificial insemination or at mid-cycle post insemination.
Lactating Holstein dairy cows (n=1,533) were allocated to one of three treatment groups, with Group I (n=514) receiving 10 microg of a GnRH analogue (buserelin) at artificial insemination (AI) and Group II (n=503) receiving 10 microg of the same analogue at both the time of AI and at 12 days post AI. Herdmates in Group III (n=516) were inseminated on the same day and served as contemporary AI controls. The trial was conducted on five large dairy farms during the spring and summer months in Saudi Arabia. Pregnancy rates were determined by palpation per rectum between 33 and 50 days following AI. The first service pregnancy rate for the control cows (42.4%) was lower (P<0.05) than that for cows treated with the GnRH analogue at AI (48.8%) or for the combined treatment at AI and at Day 12 post AI (51.5%). No additive effect on the pregnancy rate was noted from the combined analog treatment. The overall increase in pregnancy rate from the analogue treatment at AI resulted from an 11% increase in pregnancy rate in first parity cows over that of contemporary controls (P<0.05) and a 14.7% increase in pregnancy for cows mated at 40 to 59 days post partum and treated with the analogue at AI over that of the corresponding controls (P<0.05). The pregnancy rates from repeat AI (interval<or=30 days) were similar across treatments (45.7% for Group I, 42.9% for Group II and 47.8% for Group III). In this study, the GnRH analogue may have enhanced the ovulation rate and possibly luteal function in cows with reduced hypothalamic GnRH release under environmental stress.
Ryan
D P
DP
Department of Animal Science, LSU Agricultural Center, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Kopel
E
E
Boland
M P
MP
Godke
R A
RA