ENDOCRINE AND THERMAL RESPONSES TO GNRH TREATMENT AND PREDICTION OF SPERM OUTPUT AND VIABILITY IN HOLSTEIN-FRIESIAN BREEDING BULLS

A study was conducted to determine changes in serum LH and testosteron e concentrations and in scrotal surface temperature (SST; measured wit h infrared thermography) following GnRH treatment and to predict the n umber of spermatozoa collected and the proportion that were viable. Ho lstein-Friesian breeding bulls (n=22, average age, 24.3 mo; range, 15 to 41 mo) were examined twice 30 d apart. Concurrently, semen was coll ected twice weekly with an artificial vagina. Treatment with GnRH (100 mu g, im) increased (P<0.0001) serum LH and testosterone concentratio ns and increased (P<0.0001) SST (range 0.6 to l.l degrees C; P<0.05) a t the top and bottom of the scrotum. In regression models to predict t he total number of spermatozoa, significant independent variables incl uded ultrasonic echotexture of the testes (negative slope), scrotal wi dth (positive slope) and SST at the bottom of the scrotum 45 min after GnRH treatment (positive slope). In regression models to predict the percentage of live spermatozoa, ultrasonic echotexture was a significa nt independent variable (negative slope). Measurement of testicular ul trasonic echotexture and SST after GnRH treatment augmented measuremen t of testicular size for predicting the number and percentage of live spermatozoa. (C) 1998 by Elsevier Science Inc.