Plane of nutrition of Corriedale ewe lambs from foetal life to the onset of breeding affects weight at service and reproductive outcome

Abstract

The objective of this study was to identify periods in the life (foetal and postnatal) of Corriedale ewe lambs where different nutrition levels can affect bodyweight at breeding and pregnancy rate in their first year of life. The effect of three different phases of nutrition on the growth and pregnancy rate (n = 133) of Corriedale ewe lambs of 7 months of age were evaluated. Phase 1 included the last phase of gestation of their mothers (30 last days of gestation, Day –30; partum = Day 0) until marking (Day 24). Phase 2 was between marking and weaning (Day 114) and phase 3 between weaning to the onset of breeding (Day 207). For phase 1, 350 adult ewes had access to improved pastures (phase 1, H) or native pastures (phase 1, L). After lambing, all ewes and their lambs were offered native pastures. After marking only ewes bearing females lambs were kept. In phase 2, 67 lambs born to H and 66 lambs born to L ewes were sorted in two new treatments: access to native pastures supplemented with ~1% of their bodyweight with soybean meal (phase 2, H) or access to native pastures alone (phase 2, L). In phase 3, each of the lambs of the four treatments applied during phase 2 were sorted in two new treatments: access to improved pastures (phase 3, H) or native pastures supplemented with 0.7% of liveweight with soybean meal (phase 3, L). Breeding period lasted 41 days and pregnancy diagnosis was performed 86 days after the onset of breeding. The pregnancy rate varied from 0% to 47%. Phase 3 of nutrition was the only phase that affected pregnancy rate (28% vs. 10% for female lambs offered H and L plane of nutrition respectively; P = 0.005). A discriminative analysis demonstrated that the liveweight at breeding was the only variable that affected the success of pregnancy in ewe lambs (P = 0.0025). Moreover, the ewe lambs that were heavier at the onset of breeding (more than 35 kg or in average 38 kg) were the most successful to get pregnant (35% of pregnancy for lambs over 35 kg and 13% for lambs under 35 kg, P = 0.0044). In conclusion, under the conditions of this experiment, the most important parameters to explain successful pregnancy of ewe lambs were the growth rate after weaning, and the liveweight at the onset of breeding.