A note on the effect of post-mating stocking rate on reproductive performance of Greyface ewes

Abstract

Continuously grazed rye grassl clover swards with surface heights of 8 to 10 cm at 5 weeks before a synchronized mating and 7·5 cm at mating were grazed by 151 Greyface ewes stocked at 12 per ha until mating. The effects of two stocking rates (eight and 16 ewes per ha) for 6 weeks over the mating and post-mating period were then studied on live weight, body condition and reproductive peformance. Sward height fell more rapidly post mating when stocked at 16 ewes per ha than at eight ewes per ha, but remained above 3·5 cm until 4 weeks after first mating under both rates. Ewes stocked at 16 per ha became significantly lighter and leaner than ewes stocked at eight per ha. There was no significant effect of post-mating stocking rate on reproductive performance in terms of conception rate and lambing rate to first mating or lambing rate to all matings. Reproductive performance of Greyface ewes is therefore unlikely to be adversely affected by post-mating stocking rate on swards of 7 to 8 cm which do not fall below 3·5 to 4·0 cm until 3 to 4 weeks after mating.

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 3. The effect of choice of genotype, level of nitrogen fertilizer and lamb:ewe ratio

“…Although there were no differences between treatments in the body condition of the ewes at mating, there was a substantial and significant difference in the potential lambing rate of the two breeds. Within a breed there is a positive response in the reproductive performance of sheep to an increase in body condition (Gunn et al, 1990;1991a;b;1992), but the two breeds were in a similar body condition and differences in potential reproductive performance can be assumed to be derived principally from breed differences.…”

“…The experimental procedures adopted in the two previous experiments offer an objective way of comparing breeds of sheep in which nutrition is provided predominantly from grazed pasture. In the conclusion of the second experiment reported , it was suggested that the breed of sheep used, the Brecknock Cheviot, was performing at, or close to, its potential, whereas in the first experiment , using a Greyface ewe of higher potential reproductive performance (Gunn et al, 1990;1991a), a substantially higher level of lamb output per ewe was achieved at similar sward heights but in different locations and different environments.…”