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Reproductive Performance of Holstein Cows Administered GnRH Analog Hoe 766 (Buserelin) 26 to 34 Days Postpartum^1,2,

Cornell University, Ithaca, NY 14853

Abstract

During the fourth week postpartum, 443 healthy Holstein cows milked thrice daily were randomly divided among four groups to receive 0, 2, 8 and 32 µg of the GnRH analog HOE 766. Intervals from calving to first estrus and to first breeding, from breeding to conception and conception rates at first breeding were calculated to measure treatment response, and progesterone was measured in the fat-free portion of milk samples collected twice weekly during the first 4 wk following treatment. Uterine involution at the time of treatment was estimated by palpation per rectum. Twenty percent of the cows examined were classified as having delayed uterine involution (abnormal). By analyzing milk progesterone patterns it was determined that 38% of the animals were in the luteal phase of an estrous cycle when treated. Cows without luteal tissue (<1 ng of progesterone/ml milk) given 8 or 32 µg of HOE 766 increased in progesterone to >1 ng/ml within 7 d in 77 and 72% of the cows compared with 40 and 57% for cows receiving 0 and 2 µg (P<.05). This increase in progesterone was followed by a normal estrous cycle within 4 wk in a higher proportion of cows treated with the two higher doses of GnRH analog (87 and 86%) compared with 67 and 70% of those receiving 0 or 2 µg of the analog (P<.005). There were no treatment differences (P>.05) for other traits analyzed, but cows with a normal progesterone cycle were observed in estrus and were bred sooner (P<.01) than those with irregular progesterone patterns. It was concluded that the GnRH analog hastened the onset of normal ovarian cycles in cows milked thrice daily.

¹ This research was partially supported by Hoechst-Roussel Pharmaceuticals, Inc.

² Appreciation is expressed to Dr. John Paul of American Hoechst Corp., Animal Health Division, for the supply of HOE 766, to John Gilliland and the management of Charles McArthur Dairies for the cattle, to Dr. T. J. Reimers for the progesterone assay, to Dr. Haim Sturman, Todd Burdick, Jeff Vosburg, Wendy Kimmel and Ted Rounsaville for help with various aspects of the study and to Harriette Stracar and Tina Babbi for manuscript preparation.

³ Present address: Departamento de Reproducción Animal, Facultad de Veterinaria, Montevideo, Uruguay.

⁴ Dept. of Anim. Sci.

⁵ Send reprint requests to this author.

⁶ American Hoechst Corp., Somerville, NJ.