Estrous cycle synchronization in dairy heifers with the prostaglandin analog alfaprostol (II).
Over a two year period, 276 dairy heifers (German Black Pied x Holstein Friesian) received one or two injections i.m. of 1.5 mg/100 kg body weight of the PGF analog alfaprostol. Only animals not showing heat after the first injection were treated twice, with the same dose, 11 days apart. Before treatment, 71% of the heifers were cycling regularly, 12% were cycling irregularly and 17% were not observed in heat prior to treatment. Animals in heat were inseminated once or twice, 18 to 24 h apart. In response to the first injection, 60.5% of all treated animals came into heat; 38% showed heat after the 2nd treatment. Three of the six non-responding animals were later diagnosed as freemartins. Heat was well synchronized. Twenty seven percent, 60% and 9% of all first inseminations occurred on days two, three and four after treatment (s), respectively; 65% of all heifers conceived from the first insemination. Pregnancy rates after one or two inseminations were 66.0% and 63.8%, respectively. At the second a.i., 45% of all animals had already ovulated. Pregnancy rates from first a.i. after one or two treatments with alfaprostol were 60.1% and 72.2%, respectively. Years had no influence on any of the parameters observed. Stage of cycle in which the first treatment occurred had a strong influence on the occurrence of heat and on conceptions as well. Of the animals treated between days 6 and 18% of their cycles, 92.6% responded with heat to the first treatment and 79% conceived. When animals were treated for the first time between days 19 and 5 of their cycles, only 28.8% came into heat and only 23.8% conceived. After the 2nd treatment, 71.2% of the latter group came into heat and 73.1% conceived.