MORPHOLOGIC, ENDOCRINE AND THERMOGRAPHIC MEASUREMENTS OF TESTICLES INCOMPARISON WITH SEMEN CHARACTERISTICS IN MATURE HOLSTEIN-FRIESIAN BREEDING BULLS

Twenty Holstein-Friesian breeding bulls (62-79 months of age) were exa mined 3 times, at 30-day intervals. Scrotal thermograms for assessment of scrotal surface temperature (SST) and blood samples for plasma tes tosterone concentrations were taken just before and then 45 and 90 min , respectively, after treatment with GnRH (50 mu g, Gonavet, i.m. per bull). Following GnRH treatment, there generally were significant incr eases in mean values of both top SST (range, -0.1 to 1.4 degrees C) an d bottom SST (range, 0.3 to 1.8 degrees C). Scrotal circumference was highly repeatable but SST and video-measurements of scrotal dimensions were less repeatable, because apparently they were affected by ambien t temperature. Plasma testosterone concentrations before GnRH treatmen t were more repeatable than those after GnRH treatment. Correlations b etween examinations of 0.67 to 0.81 and -0.14 to 0.47, respectively, b ut the converse was true for SST measurements. Semen was collected wit h an artificial vagina 3 times per week for 12 weeks starting 2 weeks before the first examination. The total number of spermatozoa per ejac ulate was highly repeatable and the percentage of motile and live sper matozoa were relatively consistent. Separate regressions for each vari able and for each examination were conducted for these 3 semen charact eristics as dependent variables. For the number of spermatozoa per eja culate and for the percentage of motile spermatozoa, significant indep endent variables were plasma testosterone concentrations and differenc e between top and bottom SST, respectively. The slopes of these equati ons were nearly all negative and the R-2 was from 0.15 to 0.42. For pr ediction of the percentage of live spermatozoa, both SST gradient and plasma testosterone concentrations were significant independent variab les. For these regressions, the slopes were negative and the regressio n coefficients were generally lower than for the other 2 dependent var iables (range, 0.16 to 0.25). Treatment with GnRH and assessment of SS T and plasma testosterone concentrations have some correlation with th e semen production in the mature bull. (C) 1998 Elsevier Science B.V. All rights reserved.