Íslenskar landbúnaðarrannsóknir - 01.09.1981, Blaðsíða 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.