The influence of the introduction of rams on the incidence of oestrus in Merino ewes.

Abstract

Two series of observations were carried out on the effect of the presence of the ram on the incidence of oestrus in ewes. In each series a group of Merino ewes was run continuously with vasectomized rams (the continuous group) and another group (the changing group), the ewes of which had been held separate from rams, was joined with the rams for a period of one month only, fresh ewes having been introduced each month. Each series of observations occupied a period of 12-15 months. In all except the spring months most of the ewes of both the continuous group and the changing group exhibited oestrus. During the spring months of one year, 1942, most of the ewes of the changing group exhibited oestrus but many of those in the continuous group failed to do so. During the spring months of the other year, 1943, most of the ewes of the changing group failed to exhibit oestrus as well as most of those of the continuous group, but whereas the proportion which exhibited oestrus did not fall below 30 per cent. in the changing group, it fell as low as 5 per cent. in the continuous group. The differences between the continuous group and the changing group in the proportion of ewes which exhibited oestrus during September and October 1942, and October 1943, are significant at the 1 per cent. level of probability, and that during August 1942 is significant at the 5 per cent. level. These significant differences in the behaviour of the ewes must be attributed to the difference in their previous association with rams.

Importance of non-olfactory ram stimuli in mediating ram-induced ovulation in the ewe

“…1 subsequently ovulated within 4 days of contact with novel rams questions the proposal that ewes need to be preconditioned by a period of pre-isolation before they will respond to the ram effect (Underwood et al, 1944;Riches & Watson, 1954 (Purvis et al, 1971 The results of the present study therefore demonstrate that the ram effect is mediated by a combination of stimuli from the ram, the most important of which may be visual and tactile cues. Olfactory cues, in the Merino breed at least, may not be as important in mediating this phenomenon as was previously thought from work using other breeds of sheep.…”

New understanding of an old phenomenon: uncontrolled factors and misconceptions that cast a shadow over studies of the ‘male effect’ on reproduction in small ruminants

“…Importantly, this series of neuroendocrine events did not occur in ewes reexposed to familiar rams after only 15 min of separation ( Figure 2). Together, these observations indicate that females that are continuously with males do not completely lose their ability to respond to all male stimuli, as suggested in the original reports (1,15,16). Instead, the ewes appear to become habituated to specific males and only males that are sufficiently novel can induce a neuroendocrine response typical of the male effect.…”

Factors Affecting the Secretion of Luteinizing Hormone in the Ewe

“…For some obscure reason, this effect has become known as 'teasing'. The continuous presence of rams throughout the year does not maintain cyclic activityindeed, if they are to ovulate during anoestrus the ewes need to be preconditioned by a period of complete isolation from the rams (Underwood et al, 1944;Riches & Watson, 1954;Radford &Watson, 1957). The ability of rams to interrupt seasonal anoestrus has now been observed in various other breeds in Israel, North America, South Africa, France and New Zealand (Eyal, 1958;Smith et al, 1958;Hunter & Lishman, 1967;Prud'hon & Denoy, 1969;Edgar & Bilkey, 1963;Martin & Scaramuzzi, I 983).…”