Effect of alfaprostol on postpartum reproductive efficiency in brahman cows and heifers

Brahman cows (n=54) and heifers (n=18) were randomly allotted by calving date, sex of calf and age to one of four treatment groups. Group 1 received no treatment (control), Group 2 received 5 mg alfaprostol (AP) i.m. on Day 21 postpartum, Group 3 received 5 mg AP i.m. on Day 32 postpartum and Group 4 received 5 mg AP i.m. on both Days 21 and 32 postpartum. Blood samples were collected via tail vessel puncture at 30 min-intervals for 8 h from half the animals in each group on Days 21 and 32 postpartum, with AP injection administered 2 h after sampling had begun. All cows were bled at weekly intervals. Samples were processed to yield serum and stored at -20 degrees C until assayed for luteinizing hormone (LH) or progesterone (P4). All cattle were maintained with epididymectomized marker bulls and were artificially inseminated (A.I.) at first estrus. Serum P4 was below 1 ng/ml prior to AP treatment in all animals and did not differ (P>0.10) between treatments. Alfaprostol treatment affected mean postpartum interval (from parturition to return to standing estrus and subsequent corpus luteum formation with serum progesterone concentrations>1 ng/ml; P<0.08). The control group (84.8+/-7.9 d) did not differ from Group 2 (86.3+/-11.1 d) or Group 3 (66.7+/-5.5 d) but did differ (P<0.09) from Group 4 (65.1+/-6.4 d). Cattle injected on Day 32 had a shorter (P<0.01) postpartum interval than those not receiving treatment on that day (65.9+/-4.2 vs 85.7+/-6.8 d). Pregnancy rate was affected (P<0.05) by AP treatment. The control group (72.2%) did not differ (P>0.10) from any group but, Group 2 (50.0%) was lower (P<0.04) than Group 3 (83.3%) and (P<0.02) Group 4 (88.9%). Cattle treated on Day 32 (Groups 3 and 4) had a higher (P<0.02) pregnancy rate (86.1%) than those not treated on Day 32 (Groups 1 and 2; 61.1%). Serum LH was affected by day (P<0.0003) and treatment by day (P<0.07) but not by time (P>0.10). Treatment Group 3 (P<0.08) and Group 4 (P<0.0003) mean LH concentrations differed between Days 21 and 32 postpartum. Cattle receiving AP treatment on Day 32 postpartum had a higher (P<0.04) cumulative frequency of return to estrus by 100 days postpartum than nontreated cattle.