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Relationships among Growth Hormone and Prolactin Secretory Parameter Estimates in Holstein Bulls and Their Predicted Differences for Lactational Traits

U.S. Department of Agriculture³, Clay Center, NE 68933

Abstract

Selection of dairy sires is based on the production records of their female ancestors, half-sibs and daughters. No trait expressed by the sire is used. Concentrations of growth hormone (GH) and prolactin (PRL), hormones produced in both males and females that are fundamental in lactation, may be correlated with production. A study was conducted to determine whether measures of these hormones in the sire would be useful predictors of lactational ability of daughters. Blood samples were collected at 15-min intervals for 8 h from 26 Holstein bulls (5.5 yr of age) that had one progeny summary available. Plasma concentrations of GH and PRL were quantified and the mean and baseline concentrations and the frequency and mean amplitude of the secretory peaks were determined for each bull. Concentrations among these values and bulls' predicted differences (PD) were determined. Significant negative correlations were detected for frequency of GH peaks and PD for yield of milk, fat and protein; correlations were positive for PRL baseline concentrations and PD for fat and protein (P < .10), and correlations were negative for frequency of PRL peaks and PD for milk, fat and protein (P < .10). Addition of estimates of bull hormone secretory parameters to breeding values based on performance of relatives considerably improved the accuracy (R²) for predicting progeny performance from sire information. Certain characteristics of the patterns of GH and PRL secretion may be heritable and aid in identification of superior dairy animals.

¹ The author wishes to thank Tom Howard and the barn personnel at ABS who were so helpful during collection of the blood samples; the blood sampling crews, S. Reece, R. Jaeger, K. Sorenson, M. Robinson, R. Studnicka and J. Dague; D. Taubenheim, whose assistance was invaluable in preparation for and in sample collection and assay of samples; Frank Dickinson and Leigh Walton at the Animal Improvement Program Laboratory for the performance data; D. George and J. Watts for typing the manuscript. The gifts of the purified preparations of GH and PRL and the anti-oGH-serum by the National Institutes of Health and the anti-oPRL-serum by D. J. Bolt are acknowledged and appreciated.

² ARS, Roman L. Hruska U.S. Meat Anim. Res. Center, P. O. Box 166, Clay Center, NE, 68933.

³ Mention of trade names or companies does not constitute an implied warranty or endorsement by the USDA or the author.