Influence of Lupin Feeding before and after Joining on Plasma Progesterone and Fertility in Merino Ewes

Merino ewes (n = 300) grazing on sparse annual pasture and supplemented with hay were given a CIDR (controlled internal drug release) device to synchronise oestrus. Ewes in Groups 1 and 2 received 750 g/head of lupin grain each day for 9 days prior to the expected oestrus and ewes in Group 3 received a hay-only supplement. After joining ewes in Group 1 continued to receive the lupin supplement while ewes in Groups 2 and 3 received a hay-only supplement. Ewes were examined by endoscope on days 6 and 7 after mating to determine the number of corpora lutea (CL) and half of the ewes in each group were given a CIDR device on day 10. All ewes were blood sampled for plasma progesterone on day 12. CIDRs were removed on day 14 and returns to oestrus were detected. Ewes were ultrasonically scanned on days 65-66 when pregnancy was confirmed and foetal numbers were determined. Ewes fed lupins prior to joining had a significantly higher ovulation rate than those fed hay only (1.58 v. 1.46 ovulations per ewe ovulating, P < 0.05). Within ovulation class (1 or 2 + CL), mean peripheral plasma progesterone concentrations in ewes fed lupins after mating were significantly (P < 0.05) reduced compared with those fed hay only. Progesterone concentrations were similarly reduced in ewes given a CIDR and fed lupins after mating compared with those given a CIDR and fed hay only (P < 0.05). Pregnancy rate and the number of foetuses per ewe pregnant were not significantly different between Groups 1, 2 and 3. Treatment with CIDRs significantly (P < 0.05) increased the pregnancy rate of ewes in Group 3, but not in Group 1 or 2.