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Seasonal Variations in the Occurrence of Conceptions in Karakul Sheep

United States Department of Agriculture¹

Abstract

An experiment was conducted at Beltsville, Maryland, to determine the extent of the breeding season in Karakul and grade Karakul sheep and the possibilities of obtaining more than one lamb crop per year. The females of all ages were kept with rams at all times for nearly four years (July 1, 1942 to March 31, 1946).

Conceptions among non-nursing (lambs pelted) and otherwise dry ewes occurred chiefly during August to November, with a peak of sexual activity in September and October. A small portion (10.3 percent) of the ewes exposed to breeding in July conceived, and similar proportions conceived among those exposed during December, January, and February. Few ewes conceived in March, only one in May, and none during April and June.

Only 13 ewes conceived while nursing lambs and these conceptions occurred during September, October, and November, during and just after the peak of sexual activity in non-nursing ewes.

Some conceptions occurred among ewe lambs between the ages of 7 and 12 months and all of these took place during September to January, inclusive.

A study of intervals from lambing to conception showed that most ewes whose lambs were born in the spring, and pelted, did not conceive again until the following fall. The same was true of ewes that nursed lambs, for they conceived about 2 to 3 months after weaning or 7 to 8 months after lambing, on the average. The average interval between lambing and conception was much shorter among ewes that conceived during January, February, and March, indicating a tendency for ewes that lambed in the fall and early winter (and whose lambs were pelted) to conceive again before the anestrous period that characterized the flock during April, May, and June.

The rates of conception per ewe per year, calculated from days from lambing to conception plus duration of pregnancy, in relation to days per year, were 1.2 for ewes that did not rear lambs, and 1.03 for ewes that nursed lambs.

Age of ewe at first conception varied from 7 to 33 months and averaged 14. Most ewes that conceived under one year of age did so during October to January, while those that conceived for the first time at later ages were more apt to do so during August to October.

The data indicate that, under conditions at Beltsville, Maryland, the possibilities of obtaining an extra lamb crop per year from Karakul and grade Karakul ewes are very limited.

¹ Bureau of Animal Industry, Washington 25, D. C, and Beltsville, Md.