Effects of GnRH treatment on scrotal surface temperatures in bulls.

Two experiments were conducted to characterize scrotal surface temperature (SST) in bulls treated with gonadotropin releasing hormone (GnRH). In Experiment 1, Angus bulls (n = 10, 18 mo, 597 kg) were given GnRH (400 ng/kg) or saline, IV. Bottom SST increased approximately 1.7 degrees C (P < 0.005) over time (0 to 90 min) at an ambient temperature of 5 degrees C. However, there was no significant effect of GnRH treatment and temperature increases were attributed to stress. When the experiment was repeated at an ambient temperature of 25 degrees C, SST was elevated prior to treatment, with no subsequent significant increase. Experiment 2 was conducted with Charolais bulls (n = 6, 12-14 mo, 517 kg) with an emphasis on minimizing stress. Bottom SST increased approximately 2 degrees C (P < 0.05) between 0 and 45 min after GnRH treatment, supporting the hypothesis that GnRH treatment increases SST in bulls. In conclusion, it was apparent that stress, high ambient temperatures, and GnRH treatment can all increase SST in bulls.

Morphologic, endocrine and thermographic measurements of testicles in comparison with semen characteristics in mature Holstein-Friesian breeding bulls.

Twenty Holstein-Friesian breeding bulls (62-79 months of age) were examined 3 times, at 30-day intervals. Scrotal thermograms for assessment of scrotal surface temperature (SST) and blood samples for plasma testosterone concentrations were taken just before and then 45 and 90 min, respectively, after treatment with GnRH (50 micrograms, Gonavet, i.m. per bull). Following GnRH treatment, there generally were significant increases in mean values of both top SST (range, -0.1 to 1.4 degrees C) and 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 ambient temperature. Plasma testosterone concentrations before GnRH treatment were more repeatable than those after GnRH treatment. Correlations between examinations of 0.67 to 0.81 and -0.14 to 0.47, respectively, but the converse was true for SST measurements. Semen was collected with an artificial vagina 3 times per week for 12 weeks starting 2 weeks before the first examination. The total number of spermatozoa per ejaculate was highly repeatable and the percentage of motile and live spermatozoa were relatively consistent. Separate regressions for each variable and for each examination were conducted for these 3 semen characteristics as dependent variables. For the number of spermatozoa per ejaculate and for the percentage of motile spermatozoa, significant independent variables were plasma testosterone concentrations and difference between top and bottom SST, respectively. The slopes of these equations were nearly all negative and the R2 was from 0.15 to 0.42. For prediction of the percentage of live spermatozoa, both SST gradient and plasma testosterone concentrations were significant independent variables. For these regressions, the slopes were negative and the regression coefficients were generally lower than for the other 2 dependent variables (range, 0.16 to 0.25). Treatment with GnRH and assessment of SST and plasma testosterone concentrations have some correlation with the semen production in the mature bull.

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 testosterone concentrations and in scrotal surface temperature (SST; measured with infrared thermography) following GnRH treatment and to predict the number of spermatozoa collected and the proportion that were viable. Holstein-Friesian breeding bulls (n = 22, average age, 24.3 m.o.; range, 15 to 41 m.o.) were examined twice 30 d apart. Concurrently, semen was collected twice weekly with an artificial vagina. Treatment with GnRH (100 micrograms, i.m.) increased (P < 0.0001) serum LH and testosterone concentrations and increased (P < 0.0001) SST (range 0.6 to 1.1 degrees C; P < 0.05) at the top and bottom of the scrotum. In regression models to predict the total number of spermatozoa, significant independent variables included ultrasonic echotexture of the testes (negative slope), scrotal width (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 significant independent variable (negative slope). Measurement of testicular ultrasonic echotexture and SST after GnRH treatment augmented measurement of testicular size for predicting the number and percentage of live spermatozoa.

Synthesis of transferrin and transferrin mRNA in bovine Sertoli cells in culture and in vivo: sequence of partial cDNA clone for bovine transferrin.

Techniques were developed for generating enriched cultures of bovine Sertoli cells and indifferent supporting cells (immature Sertoli cells). The [35S]methionine and [35S]sulfate-labeled proteins secreted by cultured cells were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and fluorography. The electrophoretic pattern of the major Sertoli cell-secreted proteins was distinct from that of the major proteins secreted by cultured peritubular cells (the predominant contaminating cell type). Five major polypeptides ranging in molecular mass from 22 kDa to 77 kDa were resolved by 2D-PAGE in reducing conditions and were assigned numbers for reference purposes. Polypeptides 1 and 2 appeared to be analogous to two rat Sertoli cell-secreted proteins, sulfated glycoprotein-1 and sulfated glycoprotein-2, because of similar molecular mass, isoelectric point, subunit composition, sulfation, and sialation characteristics. Transferrin was detected in conditioned medium by immunoprecipitation using an antibody to bovine serum transferrin. Cultured Sertoli cells isolated from prepubertal bulls secreted higher levels of transferrin than did cells isolated from infant bulls. An 850 bp cDNA corresponding to the 3' portion of bovine transferrin mRNA was cloned and sequenced. Transferrin message was shown to be present in testicular tissue isolated from infant and prepubertal bulls and it increased as bulls matured. Levels of testicular transferrin mRNA were subsequently shown to correlate with daily sperm production in yearling beef bulls.