A study of relationships of breed, time of mating, level of nutrition, live weight, body condition, and face cover to embryo survival in ewes

Abstract

Embryo survival was studied in flocks of 500 Saxon Merino and 500 Border Leicester x Merino ewes introduced to rams in either summer or autumn. The ewes were fed 200, 100 or 25 % of a maintenance diet from day 2 to day 16 after mating. Embryo survival was greatest in ewes fed the maintenance diet. There was no suggestion that live weight, face cover or condition score were important factors affecting embryo survival. Embryo survival in the twin ovulating cross-breds was higher than in the twin ovulating Merinos, but there was no significant difference in embryo survival in ewes with single ovulations. Embryo survival in ewes with twin ovulations was significantly higher at the autumn mating than in summer. INTRODUCTIONRecently Edey (1969) reviewed prenatal mortality in sheep and concluded that more work is required to define the nature and magnitude of the effects on embryo survival of high and low planes of nutrition, and of body condition. Edey considered that in such experiments it is essential that the possible confounding effects of pre-mating nutrition and different ovulation rates be excluded or at least considered. The experiment reported in this paper attempts to follow this advice. In addition, there is designed within the experiment an examination of two further possibly confounding factors, breed of ewe and time of mating.

Reproductive performance in ewes fed varying levels of cut lucerne pasture around conception

“…The conclusion that feeding ad libitum levels of lucerne in early pregnancy may have increased embryo mortality is consistent with previous studies where ewes were fed at twice maintenance (Cumming et al, 1975;Parr et al, 1987), although a high rate of feeding has not increased embryo mortality in other studies (Lightfoot et al, 1976). Pregnancy rates were not reduced in the current study, in contrast to that of Parr et al (1987).…”

“…Feeding at twice maintenance levels has been shown to cause embryo mortality in both naturally cycling (Cumming et al, 1975) and oestrous synchronised (Parr et al, 1987) ewes, compared with ewes fed at maintenance levels. The clearance rate of progesterone through the liver is higher when feed intake is increased, which leads to reduced circulating concentrations of progesterone (Parr et al, 1993) that may be associated with lower pregnancy rates (Parr et al, 1987).…”

Overfeeding during early pregnancy reduces peripheral progesterone concentration and pregnancy rate in sheep

“…Over-feeding has previously been linked with embryonic mortality (El-Sheikh et al, 1955;Foote et al, 1959;Cumming et al, 1975;Brien et al, 1977Brien et al, , 1981, but the mechanism(s) causing this loss has not been understood. In studies using exogenous progestagen therapy (Pearce et al, 1984;Peterson et al, 1984;Smith et al, 1985) no mention was made of nutritional conditions in early pregnancy.…”

Review of sheep body condition score in relation to production characteristics

“…Although some studies have found no effect of BCS on embryo mortality, for example in Merino and Merino cross ewes across a range of BCS (Cumming et al 1975), and when comparing Scottish Blackface ewes with BCS of 1.5-1.75 with those of 2.75-3.0 (Rhind et al 1984a), most other studies report that embryo mortality does vary with BCS. For example, Scottish Blackface ewes with low BCS (1.5) had higher embryo mortality in the early stages of pregnancy than ewes with higher BCS (3.0), but that BCS had no effect after day 26 of pregnancy (Gunn et al 1972).…”