The effect of prostaglandin F2α 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 F2α 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 25 mg Dinoprost (Dinolytic®) at the time of insemination has no effect on pregnancy rate (61% of the cows and heifers were pregnant in both prostaglandin F2α-treated and saline control groups). On the other hand, deposition of 0.5 mL of a 0.5 mg/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 F2α-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 PGF2α administration.