Sheep - AgRIS

concentration decreased, more than 90% of the sperms were found dead and the number of
abnormal spermatozoa also increased. In the month of June, the wave motion was completely
absent, during the months from July to September, there was complete cessation of
spermatogenic activity. The semen was devoid of spermatozoa, ejaculates were watery and
resembled those obtained from vasectomised rams. The restoration of normal spermatogenesis
started from the end of October. There was remarkable improvement in November. The
average initial motility was 3.2; the percentage of abnormal spermatozoa came down to 10.6%
and the semen quality was excellent in December and January as in indigenous rams. The
semen picture was normal andthe abnormal sperm count was only 3 to 4%. These variations in
semen quality are attributed to the variations in ambient temperature. It is evident that there is
periodic rhythm for spermatogenesis. This pattern is influenced mainly by high temperature
leading to deteriorating changes in semen quality which usually start from the mid summer.
The semen quality gradually improves by mid-autumn. It is not clearly known to what extent
the factors such as shade availbale, winds, amount of wool on rams, availability of greens, feed,
short term heat waves present in some summers and absent in others and frequency of service
and /or collections, influence the semen production.
Decline in semen quality should invariably be accompanied by a gross reduction in the
initial motility, sperm count and increase in the proportion of abnormal spermatozoa. It is on
the basis of such changes in semen picture of rams in areas away from the equator that a gross
decline in semen quality has been reported by Comstock et al. (1945), Bogart and Mayer (1946)
and Cupps et al., (1960). Despande (1970) reported that in Bannur x Somali rams, the best
semen samples were obtained during spring and winter.
Sarkar et al (1971) investigated the seasonal changes in semen characteristics of Magra
rams. Semen samples were collected from each experimental animal on every third day using
transistrised elextro-ejaculateors. The average volume of semen was found to be 0.71 ml in
winter. this value was significant higher than the values obtained in spring. Average values for
motility, mass activity and sperm concentration was 70.27%, 3.66 and 1.783 million/ml.
respectively but no significant differences were observed.
Sahni and Roy (1972) reported that summer had an adverse effect on the production of
corrideale semen but the season had no effect on the semen production of half-bred rams under
kopical conditions.
Sahni and Roy (1972) observed that the incidence of abnormal spermatozoa is negligible in
the native and crossbreds during different seasons. A very high percentage of abnormal
spermatozoa was observed in Corriedale and Romney Marsh breeds during summer season.
Studies show that shifting indigenous rams even from far distant areas to other tracts which
fall within the broad range oftropic and subtropics do not impair the reproductive effficiency of
Mandya rams which were brought to North India from South, an approximate distance of about
1500 km, did not alter their reproductive fficiency. The variations in temperature or duration of
daylight had no effect on the production of quality semen throughout the year (Sahni and Roy,
1969).
iii) Day light
Ortavant (1958) studied interaction between temperature and photoperidism on
spermatozoal production. His P-32 tracer studies in spermatogenesis show that the rate of
division of primary spermatocytes and time of subsequent maturation are relatively unaffected
by the photoperidic environment but the number of spermatids which survive the complete
maturation process are affected. The failure rate was observed to be high under conditions of
increasing daily illumination. He observed that the effect of high temperature in the spring and
early summer months superimposed on this basis photoperidodic effect is to destory a high
proportion of the relatively few spermatozoa which have survived the maturation process.
Deshpande (1970) observed that during spring and winter, the day length varied between 11.02
and 12.56 hours, whereas, the actual day light hours varied from 7.7 to 9.8 hours and the semen
quality was best during this season.
405