Detection of early pregnancy in sheep by the rosette inhibition test

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Abstract
The rosette inhibition test, an established test for determining the immunosuppressive potential of antilymphocyte serum, was applied to sheep serum after mating. The rosette inhibition titer was much higher (12-26) in 7 sheep which were fertilized and remained pregnant for up to 21 days than in 5 sterile ewes mated with intact rams (8-10). The difference was apparent by 24 h after mating. One ewe had high titers for 6 days after mating but these then dropped and she returned to estrus. Early embryonic loss was suspected. Another ewe which returned to estrus had consistently low titers. The rosette inhibition test can be used to detect fertilization, early embryonic death and continued pregnancy in sheep.