GROWTH HORMONE RESPONSE AS AN INDICATOR OF GENETIC MERIT IN DAIRY SIRES

GENETIC PROGRESS FOR ECONOMICALLY IMPORTANT PRODUCTION TRAITS IN DAIRY CATTLE IS DEPENDENT ON THE ACCURATE SELECTION OF GENETICALLY SUPERIOR INDIVIDUALS TO SERVE AS PARENTS OF THE SUBSEQUENT GENERATION. PROGENY TESTING PROGRAMS HAVE BEEN ESTABLISHED BY THE ARTIFICIAL INSEMINATION INDUSTRY TO IDENTIFY SUPERIOR SIRES, AND HAVE PROVEN TO BE VERY EFFECTIVE SINCE THEIR INCEPTION, BUT ARE QUITE COSTLY. DISCOVERING A PHYSIOLOGICAL MARKER ASSOCIATED WITH GENETIC MERIT WOULD REDUCE COSTS BY IMPROVING ACCURACY OF YOUNG BULL SELECTION METHODS. THEEREFORE, THE OBJECTIVE OF THE PHASE I PROPOSAL IS TO DETERMINE WHETHER GROWTH HORMONE (GH) RESPONSE TO EXOGENOUS GROWTH ORMONE-RELEASING FACTOR (GRF) IS RELATED TO GENETIC MERIT FOR PRODUCTION TRAITS IN DAIRY SIRES. BLOOD SAMPLES WILL BE COLLECTED AT DEFINED INTERVALS FOR TWO HOURS BEFORE AND TWO HOURS AFTER GRF ADMINISTRATION. RESPONSE VARIABLES WILL INCLUDE MAXIMUM GH, AVERAGE GH AND AREA UNDER GH RESPONSE CURVE. FORTY-EIGHT SIRES WILL RECEIVE A DOSAGE OF GRF AS DETERMINED THROUGH DOSAGE TRAILS. GROWTH HORMONE RESPONSE WILL BE CORREELATED WITH KNOWN USDA PREDICTED TRANSMITTING ABILITIES FOR YIELD TRAITS. ADDITIONALLY, SEMEN QUALITY CHARACTERISTICS WILL BE MONITORED BEFORE AND AFTER GRF ADMINISTRATION TO INSURE THAT GRF SO ADMINISTERED DOES NOT HAVE A NEGATIVE EFFECT ON SEMEN PRODUCTION.