Close contact with spontaneously cycling Saint Croix ewes triggers cyclic activity in seasonally anestrous Suffolk ewes

Abstract

In domestic goats, oestrous activity may be induced by close contact with cyclic females. As tropical breeds of sheep show light seasonality or are even unaffected by season, the purpose of this study was to examine the hypothesis that cyclic activity may be induced in anestrous Suffolk ewes by close contact with spontaneously cycling Saint Croix ewes. The experiment was conducted with 17 anestrous Suffolk ewes that were assigned to one of two groups. Although Suffolk ewes in the Control group (n = 9) remained isolated, those of the treated group (n = 8) were joined (Day 0) and maintained in close contact with 20 Saint Croix ewes for 38 days. Serum progesterone concentration was measured in all ewes in blood samples collected on Days –8, –2, 8, 13, 18, 23, 28, 33 and 38. Before Day 0, 17/20 Saint Croix ewes were cycling, but no Suffolk ewe had luteal levels of progesterone. By Day 13, more treated than Control Suffolk ewes had progesterone luteal concentrations (8/8 vs 1/9; P = 0.0004). It was concluded that spontaneously cycling Saint Croix ewes induce cyclic activity in anestrous Suffolk ewes.