A study of the effects of post-mating progesterone supplementation on the reproductive performance in the ewe : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in animal science at Massey University

Abstract

The aim of this study was to investigate the effects of post-mating progesterone supplementation, in the form of CIDRs, on the reproductive performance in recently mated ewes. The effect of two nutrition treatments were also examined by feeding two different pasture allwances to these ewes during a two week period immediately folliwing a synchronized mating. Two hundred and thirty four Border Leicester X Romney first cross ewes, compresed of 130 mixed-age ewes (3-8 years) and 104 two-tooth (maiden) ewes were flushed on increasing pasture allowance prior to joining. These ewes were naturally mated at a synchronized oestrus following a 13 day CIDR treatment period. During the three days following CIDR withdrawal, 88.0% of the ewes were mated. The mixed-age ewes came into oestrus significantly earlier that the two-tooth ewes (P < 0.001). There was a significant linear relationship between liveweight and onset of oestrus (P < 0.05), with the heavier two-tooth ewes coming on oestrus earlier than the lighter two-tooth ewes. This was not apparent in the mixed-age ewes. On Day 2 following mating, ewes were randoaly divided into either the high or low pasture allowance levels. Pasture allowance levels were monitored using an Ellinbank Pasture Meter (EPM). Levels of feed intake were estimated for a random sample of 20 ewes both before and after mating through the use of intraruminal chromium releasing devices (CRDs). Sward heights (representing quantity), botanical composition and in vitro digestibilities (representing quality) were recorded for both the flushing and the post-mating period. This information led to the estimation of voluntary herbage intakes during the flushing period (Period I) of 1.2 M, while the intake levels of the ewes following the mating (Period II) were calculated to be approximately 1.6 M and 1.0 M for the high and low pasture allowance levels, respectively.