Animal Science Department

 

Date of this Version

4-1-1994

Comments

Published in BIOLOGY OF REPRODUCTION 51, 1248-1254 (1994). Copyright © Society for Study of Reproduction. Used by permission.

Abstract

We tested the hypothesis that endogenous pulses of LH have a role in development and maintenance of CL during the estrous cycle of the bovine female. Twenty heifers were synchronized to estrus by treating two times with prostaglandin F 11 days apart (Day 0 = behavioral estrus). Heifers were then randomly assigned to one of four treatments (n = 5/group). Heifers were treated with an antagonist to LHRH (LHRH-Ant; N-Ac-D-Nal[2]1,4C1-D-Phe2 ,D-Pa[3] 3,D-Cit 6,D-Ala10-LHRH; 10 μg/kg body weight) or vehicle (5% mannitol) once every 24 h: 1) LHRH-Ant Days 2-7, 2) LHRH-Ant Days 7-12, 3) LHRH-Ant Days 12-17, 4) no LHRH-Ant (control). Blood samples were collected from the jugular vein twice daily on Days 0-24, and area under the profile of progesterone in circulation during the luteal phase of the estrous cycle was characterized from the start of each treatment period until the demise of CL or Day 24, whichever came first. Luteolysis was considered to have occurred when three consecutive samples contained less than 1 ng progesterone/ml plasma. Areas under the profile of progesterone in circulation during the luteal phase of the estrous cycle were compared to those of heifers from the control group for the same period. LHRH-Ant treatment diminished LH pulses in all treatment groups compared to control (p < 0.05). Treatment with LHRH-Ant on Days 2-7 diminished function of CL (3.72 ± 0.93 vs. 7.36 ± 1.02 units, respectively; p < 0.05). Heifers treated with LHRH-Ant on Days 7-12 also had reduced function of CL (3.02 ± 0.33 vs. 6.75 ± 0.99 units, respectively; p < 0.01). However, treatment with LHRH-Ant on Days 12-17 did not influence function of CL (3.97 ± 1.02 vs. 4.27 ± 0.80 units, respectively; p > 0.10). The data support our hypothesis that endogenous pulses of LH have a role in development and maintenance of CL during the estrous cycle of bovine females.

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