Studies on the adaptability of three breeds of sheep to a tropical environment modified by altitude V. The annual fluctuation in breeding ability of rams maintained on Rhodesian highveld

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Abstract
Semen characteristics and libido were observed for 34 months in German Merino, Persian Blackhead and indigenous ‘Native’ rams maintained on Rhodesian highveld. Birth rate from controlled service was determined during 23 of these months.1. Breeding ability, as judged by semen production and libido, was continuous in all rams. A fluctuation in birth rate from controlled service was due more likely to seasonal variation in female fertility than in seminal fertilizing capacity.2. Monthly changes occurred in all seminal characteristics but only those in sperm concentration were consistent between years. In all breeds spermatogenic activity was high in spring and mid-summer, low in late summer and autumn.