Effects of facial eczema on ewe reproduction and postnatal lamb survival in romney sheep

Abstract

Mating and lambing data from the Romney facial eczema (FE) selection flocks at Ruakura were collated in order to study the effects of FE susceptibility on subsequent reproduction. The data analysed were ewe fertility (numbers of ewes lambing, as a % of those joined), litter size at birth, and postnatal lamb survival. Two of the flocks, selected for resistance (R) or susceptibility (S) to FE, were established from similar foundation stock in 1975. Two other flocks were established in 1982, with foundation stock different from the R and S flocks, one of them (P) being bred for resistance, alongside a contemporary control (C) flock. The data comprised 3520 matings and 2847 lambings of ewes in 1982–90. The FE challenge was administered by intubation to young males and (in some years) to young females, using the fungal toxin, sporidesmin. Susceptibility to a given FE challenge was measured as an increase in concentration of the serum enzyme, gamma-glutamyltransferase (GGT). The logetransformed GGT values were added as covariates in analyses of performance for the 2 years when females were dosed with sporidesmin. Pastures were sprayed with fungicide in autumn to minimise natural FE challenge at mating time. Ewe fertility was greater by 10.6% in the R than S flock (P < 0.01), but did not differ significantly between the P and C flocks. Thus the S flock had probably declined in fertility, rather than the R flock increasing in fertility. About 40% of the difference between R and S flocks was explained by differences in sub-fertile ram effects. For the 1987-born females, there was a significant decrease in fertility in 1989 and 1990 with elevated GGT (10.2% per unit increase in logeGGT); for 1988-born females, the regression was in the same direction (4.0% per unit increase) but not significant. Over all 9 years there was a lower litter size (P < 0.05) in the S than the R flock by 0.07 lambs per ewe (or 5%), but not between the P and C flocks. Neither pair of flocks differed significantly in lamb survival, nor did litter size or lamb survival show a significant relationship with GGT following dosing as a ewe lamb. Overall, FE in sheep produced more severe effects on fertility than on litter size or lamb survival. © 1991 Taylor & Francis Group, LLC.