COMPARISON OF THE EFFECT OF 2 ANALOGS OF PROSTAGLANDIN-F2-ALPHA ON ESTRUS SYNCHRONIZATION IN BEEF-CATTLE

The objective of this study was to compare the efficiency of cloproste nol and fenprostalene in synchronizing estrus. Before treatment, estru s was detected during 4.5 d for multiparous cows in exp. 1 (n = 105) a nd 7.5 d for primiparous and nulliparous females in exp. 2 (n = 86). F emales that were not in estrus (exp. 1: n = 74 and exp. 2: n = 58) rec eived at random, either 500 mug of cloprostenol (i.m.) or 1 mg of fenp rostalene (s.c.). Cattle synchronized with cloprostenol or fenprostale ne that presented estrus within 5 d showed similar fertility rates (ex p. 1: 86.1% vs. 88.0% and exp. 2: 89.3% vs. 72.2% for cloprostenol and fenprostalene, respectively) and PGF2alpha-estrus intervals (exp. 1: 68 h vs. 73 h and exp. 2: 57 h vs. 57 h). However, the incidence of sy nchronization (exp. 1: 97.3% vs. 67.6%, P < 0.001; and exp. 2: 93.3% v s. 64.3%, P < 0.01) and pregnancy rates (exp. 1: 83.8% vs. 59.5%, P < 0.05; and exp. 2: 83.3 % vs. 46.4 %, P < 0.01) were statistically high er for cloprostenol than for fenprostalene. In exp. 2, primiparous cow s and heifers obtained similar reproductive performances. The fertilit y rate of cattle treated with cloprostenol in exp. 2 was higher than t hat of untreated cattle (89.3% vs. 50.0%, P < 0.001, n = 56). In exp. 1, the variance of interval to estrus was similar for both analogues, but in exp. 2, it was less variable after the administration of clopro stenol (P < 0.05). Intervals between cloprostenol injection and estrus (0-10 and 0-15 d) were shorter (P < 0.05) and less variable (P < 0.00 1) than fenprostalene-estrus intervals. These results indicate that cl oprostenol has a better potential for estrus synchronization than fenp rostalene.