ChileanJAR

A study was conducted to determine fertility levels when prostaglandin F₂& (PGF₂&) is used in estrous synchronization followed by artificial insemination (Al) at prefixed time, as well as to determine the effect of some environmental conditions over fertility. The study was carried out at Hidango Subexperimental Station, VI Region, Chile. Rectal palpation was performed to determine all the cycling females; the cows with 50 to 70 days after calving and heifers over 280 kg of body weight were selected. Two doses of PGF₂& with 11 days interval were applied; after this, 4 treatments were stablished. T1: 25 heifers, with two Al performed at 55 and 72 hours post second dose of PGF₂&; T2: 25 heifers, with a single Al at 63 hours after the last PGF₂& administration, and adose of buserelin intramuscular (1 M) at the moment of Al; T3: 25 cows, artificially inseminated 72 and 96 hours after the last PGF₂& dose; and T4: 25 cows, with a single Al, 72 hours post PGF₂&, plus adose of buserelin 1M at Al. For the statistical analysis, the t test and chi square test were carried out separately for the heifers and the cows groups. The pregnancy levels obtained for T1, T2, T3 and T4 were 28,32,44 and 37.5%, respectively. No significant differences were observed between the heifers'groups and the cows groups (P > 0.05). In all the treatments the pregnant females showed greater body weight than the nonpregnant ones, but this difference was significant (P < 0.05) only in T2. The pregnancy rates for the females which presented estrous after the second PGF₂& administration were 48 and 47% for heifers and cows, respectively, and for those females which didn't present estrous, were 0 and 23% respectively. Significant improvements in fertility could be achieved by controlling management factors such as estrous detection and assuring a good overa