Prostaglandin F2 for Lactating Dairy Cows with a Palpable Corpus Luteum but Unobserved Estrus

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Abstract
Two experiments were done in 17 daily herds to study the effectiveness of prostaglandin F2.alpha. (treatment) in inducing luteolysis and reducing intervals to conception of 308 cycling lactating dairy cows. Cows with unobserved estrus before 1st insemination (Experiment 1) and non-pregnant cows with unobserved estrus after insemination (Experiment 2) were eligible for treatment. Cows in Experiment 1 were assigned alternately either to an untreated control group of 85 or to a group of 138 that received 25 mg prostaglandin F2.alpha. after detection of a corpus luteum by ovarian palpation. Cows were inseminated either at estrusor at 72 and 96 h posttreatment in the absence of detected estrus. Intervals from treatment to estrus, to 1st service, and to conception were longer for controls than for treated cows. Conception at 1st service was similar for controls (39%) and for treated (43%) cows. Procedures were similar for Experiment 2. Intervals from treatment to estrus and treatment to 1st service were longer for control cows, and treatment to conception tended to be longer for 39 controls than for 46 treated cows. Conception at 1st service was similar for controls (52%) and treated (44%) cows. Prostaglandin F2.alpha. was 91% effective for inducing luteolysis based on progesterone concentrations in blood serum. Successful treatment depended on accurate diagnosis of a functional corpus luteum. Days from treatment to conception were reduced for cows with unobserved estrus if treated cows were inseminated at estrus or by appointment in the absence of detected estrus.