Seasonal patterns of LH, testosterone and semen quality in the Northern pintail duck (Anas acuta)

This study characterized seasonal changes in circulating LH and testosteron e and in semen production and quality in the Northern pintail duck. Plasma LH and testosterone were measured in blood samples collected weekly through out the year from eight males exposed to natural fluctuations in day length and temperature. Semen quality was evaluated weekly in these same males fr om April-June, the months when spermatozoa were produced. Semen quality (ba sed on sperm concentration and normal morphology) peaked 0-2 weeks after sp erm production onset and decreased sharply before sperm production cessatio n in late June. Nadir LH concentrations were measured in July and August wi th peak LH observed in May and November. There were clear seasonal patterns in circulating testosterone with July-September values being less (P<0.05) than October-December which, in turn, were less (P<0.05) than January-Marc h. Maximal circulating testosterone (P<0.05) occurred during April-June, co incident with semen production. Weekly circulating LH during the breeding s eason was directly related to testosterone concentrations (P<0.01), but was not correlated to any specific semen or sperm trait (P>0.05). Testosterone concentrations throughout the breeding season were correlated (P<0.05) to total numbers of spermatozoa produced (volume x cell concentration) and per cent normal sperm morphology. In summary, the Northern pintail experiences seasonal hormone fluctuations, with maximum circulating testosterone coinci ding with peak ejaculate quality reflected by the production of high number s of morphologically normal spermatozoa.