Factors influencing estrus and conception in dairy heifers after prostaglandin F 2-alpha

Abstract

The influence of interval between insemination (AI) and estrus on subsequent fertility of PGF 2α-treated (two injections of 25 mg, 11 days apart) heifers was assessed in two experiments. In Experiment I, 240 heifers were allotted to Control (AI 8 to 16 hr after estrus detection), PGF 2α-E (AI 8 to 16 hr after estrus within five days of second PGF 2α) or PGF 2α-T (AI 80 hr after second PGF 2α). In Experiment II, 130 heifers were assigned to control (AI as before) or PGF 2α (AI 72 or 80 hr after second PGF 2α) with half the PGF 2α heifers receiving 100 μg GnRH 72 hr after first PGF 2α. Heifers of both experiments that were bred at a predetermined time were arrayed by interval from AI to estrus. Conception rates of heifers detected in estrus from 32 hr before AI to 24 hr after AI did not differ (x 2=3.35, df=5, P>0.5). The percentage of GnRH-treated heifers in estrus within five days (81.8%) was not (P>0.75) greater than those not receiving GnRH (77.3%) but they had higher (P<0.05) serum progesterone (P 4) concentration at second PGF 2α (3.17 vs 2.41 ng/ml). When P 4 values were arrayed for both groups at 1 ng intervals, the percentage of heifers exhibiting estrus increased with increasing P 4 level (P<0.05).