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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 |
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