The effect of prostaglandin F(2α) administration at the time of insemination on the pregnancy rate of dairy cows.

This paper addresses the question whether the pregnancy rate of dairy cows and heifers may be affected by administering prostaglandin F(2α) at the time of artificial insemination. A field trial involving 1031 dairy cows and heifers distributed to a large number of small dairy farms in an area of extensive farming in central Germany provided evidence that intramuscular administration of 25mg Dinoprost (Dinolytic(®)) at the time of insemination has no effect on pregnancy rate (61% of the cows and heifers were pregnant in both prostaglandin F(2α)-treated and saline control groups). On the other hand, deposition of 0.5mL of a 0.5mg/mL Dinoprost solution in the uterine lumen immediately after artificial insemination gave rise to a pregnancy rate of 66% as compared with 59% in saline controls. The increase in pregnancy rate of 229 prostaglandin F(2α)-treated animals (66% pregnant) over that of 226 saline controls (59% pregnant) amounted to 12%. This improvement was not statistically significant (P=0.12). Factors exerting a significant effect on pregnancy rate were parity (74% pregnancies in heifers versus 57% in cows, P<0.01 and 65% pregnancies in first parity-cows versus 55% in older cows, P<0.01) and season (57% during the barn season versus 64% during the pasture season, P<0.05), whereas length of service period, level of milk production and serum or milk progesterone level at the time of insemination did not. A follow-up trial involving more animals will have to be conducted aimed at confirming the promising results obtained by intrauterine PGF(2α) administration.