Abstract :
The reproductive performance of young adult rams (age 13 or 14 months) of the Dorset, Finnish Landrace (Finn), Suffolk
and Scottish Blackface (Blackface) breeds was evaluated over 14 months, beginning in June (latitude 50◦N). Blood FSH, LH
and testosterone signals were examined in relation to testicular function as rams passed through their second sexual cycle.
Consistent with estrual activity of ewes at this latitude, the testes were relatively large and testosterone concentrations higher
for longer durations in the Dorset and Finn rams. Increases in FSH concentration in the summer were soon followed by
increases in testicular size in all four breeds, but only in the Finns and Suffolks did changes in FSH and scrotal circumference
continue to parallel each other throughout the year. Basal (interpulse) LH was associated with LH pulse frequency (r ≥ 0.64,
P < 0.01) in the four breeds and was, on average, five-fold higher (∼1 ng/ml) when the testes were developed than regressed.
Whereas the relationship between changes in testosterone and LH pulse frequency throughout the testicular cycle was highly
significant in each breed (r ≥ 0.63, P < 0.01), such a relationship with basal LH was observed only in the Blackface rams
(r = 0.74). Regression of the testes was aligned with decreases in testosterone, but not with numbers of sperm voided in
urine. Other than in the Finns, changes in sperm output resembled those in testosterone 60 days earlier, especially in the
Suffolks and Blackface (r ≥ 0.73, P < 0.01). Results indicate that FSH secretion per se can play a central role in regulating
the magnitude of the testicular cycle in both seasonal and relatively nonseasonal breeds, while participation of basal LH in
regulating testosterone secretion and of testosterone in regulating sperm output (spermatogonial proliferation) may be more
important in the seasonal breeds. Normal breed differences were noted in adult body weight, testicular size (e.g. smaller in
the Blackface) and sexual behavior (e.g. more intense for the Finn). Scottish Blackface rams, a rare breed in Canada, adapted
well to the severe prairie climate.
© 2004 Elsevier B.V. All rights reserved
Keywords :
breeds , Gonadotrophic hormones , Testicular function , Seasonality , Adult ram
