Annotations file for RDA184Page: 1Author/editor: is short title acceptable?Reproductive and Endocrine Changes in Dairy Cows Given GnRH at Different Intervals Postpartum

Contents The reproductive organs of 91 cows in the university herd were palpated at least twice per week from 12 to 53 days postpartum (PP). Based upon uterine and cervical involution and tone, ovarian condition and fluid discharge at 12 to 18 days PP they were classified as normal or abnormal. Within each group they were randomly assigned to receive either saline or 100 μg of GnRH at 12 to 18 days or 100 μg of GnRH at 22 to 28 days PP. Milk samples were taken for progesterone determinations three times per week until the first breeding or up to 90 days PP. A subset of 23 cows completed a frequent blood sampling programme at 0 h (just prior to treatment), 1, 2, 4, 8 and 12 h later and every 12 h for 15 days following treatment. Values for milk and serum progesterone in samples taken during the same time period were highly correlated, r = 0.90, and were consistent with ovarian changes detected by palpation. Cows classified as normal initially continued to be normal, and GnRH had little effect. In the abnormal groups of cows at 28 days PP, 41% of the saline group and 77% of those treated with GnRH at 12 to 18 days PP had fully involuted uteri. Early treatment of abnormal cows with GnRH improved the reproductive efficiency, resulting in 95 days open compared with 129 days for saline‐treated abnormals. In conclusion, treatment with GnRH was effective in hastening the return to normal of cows classified initially as abnormal, and appears to be cost effective in maintaining an optimal calving interval.