Effect of previous undernutrition on the ovulation rate of Merino ewes supplemented with lupin grain

Abstract

The effect of undernutrition on the ovulation rate of Merino ewes supplemented with lupins was examined in two experiments using a 2 x 2 factorial (low vs high nutritional plane x none vs supplemented) design. In both experiments, ewes were assigned at random to two equal-sized groups and differentially grazed for 8 weeks (low and high). In Experiment 1, flocks were recombined and managed as one group for 18 weeks and then divided into their original nutritional treatments 17 days prior to ovulation. Each of these groups was divided at random into equal-sized subgroups and one subgroup fed lupins for 10 days prior to ovulation. Restricting nutrition 6 months prior to ovulation resulted in a difference in mean liveweight between the low and high groups of 9.3 kg at the end of the 8-week period (P < 0.001). Ovulation rates per ewe were 1.06 +/- 0.07 (low, no supplement), 1.63 +/- 0.09 (low, lupin-supplemented), 1.28 +/- 0.09 (high, no supplement) and 1.57 +/- 0.08 (high, lupin-supplemented). The increase of 0.22 ovulations per ewe for the low vs high plane of nutrition without supplement was significant (P < 0.05). There was a significant interaction (P < 0.05) between previous nutrition imposed 6 months prior to ovulation and lupin supplementation, indicating that the ovulatory response to lupins was greater at the low compared with the high plane of nutrition (0.57 vs 0.29 extra ovulations per 100 ewes). In Experiment 2, the previous nutritional treatments were imposed for 8 weeks immediately before ovulation. Restricting feed intake in the low group resulted in a difference in mean liveweights between the two groups of 6.2 kg (P < 0.001) 6 weeks after the start of the nutritional treatments. Ovulation rates were 1.22 +/- 0.06 (low, no lupin supplement), 1.38 +/- 0.09 (low, lupin-supplemented), 1.67 +/- 0.08 (high, no lupin supplement) and 1.64 +/- 0.09 (high, lupin-supplemented). The effect of previous nutrition on ovulation rate was significant (P < 0.001) with 0.35 extra ovulations per ewe fed the high plane. Ewes in the low group responded to lupin supplementation with 0.16 extra ovulations per ewe (P = 0.06), whereas ewes previously fed on a high plane did not respond to the lupin treatment.