Íslenskar landbúnaðarrannsóknir - 01.09.1981, Qupperneq 57

Íslenskar landbúnaðarrannsóknir - 01.09.1981, Qupperneq 57
ÍSL. LANDBÚN. j. agr. res. icel. 1981 13, 1-2: 55-60 Seasonal variation in testis size of Icelandic rams Ólafur R. Dýrmundsson The Agricultural Soáety of lceland Btendahöllin, P.O.Box 7080 Reykjavík, Iceland Pétur Sigtryggsson and Stefán Sch. Torsteinsson The Agricultural Resarch Institute Keldnaholt, Reykjavík, Iceland ABSTRACT The paper reports on the first evidence of a relationship between seasonality and testis size of adult Icelandic rams. In situ measurements of testes diameter were found to be highly correlated with testes weight whereas variation in testes diameter was largely independent of the age and the body weight of these adult rams. Therefore, measuring the diameter of the testes gave a fairly accurate estimate of their size. Testes diameter measurements taken in autumn, winter, spring and summer, respectively, over a period of24 months, showed a similar pattern of seasonal variation in both years. Thus the highest values were recorded in autumn, followed by winter and summer values with the smallest diameter in spring. The autumn and spring values differed by 15% on the average. The seasonal variation in testis size is discussed with particular reference to daylight relationships reported in the scientific literature. INTRODUCTION Recent studies have shown that seasonal oestrous activity in Icelandic ewes is ex- tended from late November into May (Ólafur R. Dýrmundsson, 1978 a & 1979). However, sporadic breeding may occur during summer and autumn but appears to be relatively rare and of little practical importance (Ólafur R. Dýrm- undsson, 1979; Ólafur R. Dýrmunds- son and Stefán Aðalsteinsson, 1980). Ólafur R. Dýrmundsson (1978b) rep- orted on the sexual development of Ice- landic rams but information has been lacking on the effect of season on repr- oductive performance of males of this breed. Further studies have now been conducted and this report presents evi- dence of a relationship between seasona- lity and testis size of Icelandic rams.
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