Somatotropin and prolactin profile characteristics in proven AI dairy sires

Blood samples were collected at 20-min intervals for 8 h from 16 Holstein sires, each of which had U.S. Department of Agriculture (USDA) and Northeast AI Sire Comparison (NEAISC) progeny test evaluation data available. Plasma somatotropin (ST) and prolactin (PRL) concentrations were measured, and resulting endocrine profiles were analyzed by PULSAR, a microcomputer-based hormone peak-detection program. The number of ST peaks during the sampling period was negatively related to USDA Predicted Transmitting Ability (PTA) for fat yield, milk, and fat product value (PTA+), and for milk, fat, and protein product value (PRO+), and ST peak length was negatively related to PTA for protein percentage (PTA %P). Interpeak interval for ST was positively related to NEAISC percentage of Protein Deviation (%P). Prolactin peak length was correlated positively with both USDA PTA %P and NEAISC %P, and peak frequency was correlated positively with NEAISC %P. Interpeak interval for PRL was related positively to NEAISC Milk and Fat Deviations. Area under PRL profile was negatively related (P less than .05) to USDA PTA+ and PRO+, and NEAISC Fat Deviation and Dollars. The results indicated that endocrine traits in mature dairy sires are correlated with genetic merit for economically important production traits and suggested that such profile characteristics may be useful in selecting young sires for progeny testing programs.