Luteinizing hormone concentrations in serum of postpartum beef cows injected with microencapsulated luteinizing hormone-releasing hormone analog.
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 micrograms 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 less than .06). More pulses of LH were observed after LHRH-A injection in Groups 4 and 5 than in Group 1 (P less than .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 micrograms LHRH-A/d was effective in elevating LH concentrations following injection. However, effectiveness of this hormonal treatment in shortening postpartum anestrus was not substantiated.
Roberts
A J
AJ
Washington State University, Pullman 99164-6332.
Chang
C F
CF
Schally
A V
AV
Reeves
J J
JJ
D000780:Anestrus / Q000187:drug effects*; D000818:Animals; D002214:Capsules; D002417:Cattle / Q000097:blood*; D004971:Estrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology*; D007273:Injections, Intramuscular / Q000662:veterinary; D007986:Luteinizing Hormone / Q000097:blood*; D049590:Postpartum Period / Q000187:drug effects*; D011247:Pregnancy; D011673:Pulsatile Flow; D011897:Random Allocation
D002214:Capsules; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone