Luteinizing Hormone Response to Pulsatile Luteinizing Hormone-Releasing Hormone in Prepubertal Heifers

Abstract

The effects of 12 hourly 5-μg injections of luteinizing hormone-releasing hormone on luteinizing hormone release, were examined in 18 prepubertal Holstein heifers at 4, 7, or 10 mo of age. During a 6-h pretreatment period, mean serum luteinizing hormone concentrations and mean number of endogenous luteinizing hormone episodes per hour were not influenced by age. The 12-h treatment regimen induced a pulsatile release of luteinizing hormone in all heifers. The magnitude, pattern, and total amount of luteinizing hormone released were not influenced by age. However, in the 4 and 10-mo-old age groups, magnitude of luteinizing hormone response to the 3rd hourly injection of luteinizing hormone-releasing hormone was greater than the response to the second injection. Magnitudes of luteinizing hormone responses decreased with time after the 4th hourly injection through the 12th injection and patterns of decline appeared similar among the three age groups.The pituitary of the prepubertal dairy heifer is able to respond to an hourly pulsatile administration of luteinizing hormone-releasing hormone and this treatment regimen appears to produce a self-priming effect on luteinizing hormone release.