Abstract

Summary. Post-pubertal Holstein heifers with palpable corpora lutea were injected i.m. with 25 mg PGF-2α to bring all animals to the follicular phase of the oestrous cycle. After 3 oronasal treatments with secretions from oestrous cows or water, heifers were observed for oestrus and inseminated about 12 h after the onset of oestrus. In Exp. I, heifers were treated with water or a mixture of urine and cervical mucus from oestrous cows at 6, 30 and 56 h after the PGF-2α injection. The percentage of heifers in oestrus within 72 h after PGF-2α was 86% for urine + cervical mucus-treated heifers and 60% for water-treated heifers (P > 0·05). Days to oestrus and conception rate after A.I. did not differ between the treatments. The degree of synchrony of oestrus after PGF-2α was significantly greater (P < 0·05) in the animals receiving urine + mucus treatment. In Exp. II, urine and cervical mucus from oestrous cows were separately tested in comparison to water. Test substances were applied at the time of PGF-2α injection, and 6 and 30 h later. The percentage of heifers in oestrus within 72 h after PGF-2α (100%) was highest (P < 0·05) in the cervical mucus-treated heifers but the conception rate (24%) was the lowest. The days to oestrus did not differ amongst groups but the degree of synchrony of oestrus after PGF-2α was greatest (P < 0·05) in animals treated with cervical mucus. These data indicate that a priming pheromone in the cervical mucus of oestrous cows can affect the ovarian function of herdmates and thereby improve synchrony of oestrus after PGF-2α injection.

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