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Luteinizing Hormone Concentrations in Serum of Postpartum Beef Cows Injected with Microencapsulated Luteinizing Hormone-Releasing Hormone Analog¹

Washington State University, Pullman 99164-6332

Abstract

Twenty-five cows were divided equally into five groups to determine whether [D-Trp⁶]-luteinizing hormone releasing hormone (LHRH-A) microencapsulated in poly (DL-lactide co-glycolide) would increase basal serum concentrations of LH during the postpartum period. On d 5 postpartum, cows were injected i.m. with 2 ml of vehicle alone (Group 1) or vehicle containing microcapsules calculated to release .4, 1.6, 6.4 or 25.6 µg LHRH-A per day for approximately 30 d (Groups 2, 3, 4 and 5, respectively). Cows were bled every 15 min for 4 h immediately before and after injection and every 15 min for 4 h at weekly intervals for the next 4 wk to evaluate serum profiles of LH. Estrus was determined by twice daily observations and confirmed by serum progesterone. More cows in Groups 2, 3, 4 and 5 exhibited pulsatile patterns of LH after LHRH-A injection than in Group 1 (P < .06). More pulses of LH were observed after LHRH-A injection in Groups 4 and 5 than in Group 1 (P < .01). Mean concentrations of LH within treatment groups did not change during the initial injection, except in Group 5. All cows in Group 5 had a surge of LH immediately after injection. The induced surge of LH in two cows in Group 5 cows resulted in progesterone profiles similar to those during a normal luteal phase. Days to first postpartum estrus were not different among the five treatment groups. Microencapsulated LHRH-A given at a dose estimated to release 25 µg LHRH-A/d was effective in elevating LH concentrations following injection. However, effectiveness of this hormonal treatment in shortening postpartum anestrus was not substantiated.

¹ Scientific Paper No. 7978, College of Agric. and Home Econ. Res. Center, Washington State Univ., Pullman. Project No. 0137. This research was supported in part by USDA Animal Health Grant No. 83-CRSR-2-2185.

² Dept. of Anim. Sci., Washington State Univ.

³ Present address: Dept. of Aquaculture, National Taiwan College of Marine Sci. and Technol., Keelung, Taiwan.

⁴ Endocrine, Polypeptide and Cancer Inst., Veterans Admin. Medical Center, Tulane Univ. School of Medicine, New Orleans, LA 70146.

⁵ Reprint requests: Dr. J. J. Reeves, Dept. of Anim. Sci., Washington State Univ., Pullman, WA 99164-6332.