Influence of maternal liveweight on reproductive performance and wool production of heterozygous Booroola Merino × Coopworth (FecBFec+) and Merino × Coopworth ewes

Abstract

Abstract The concurrent and long-term effects of feeding high (H) and low (L) levels of nutrition from weaning to 4 years of age were measured in 188 high fecundity heterozygous Booroola Merino × Coopworth (BC) ewes (FecB Fec+) and 58 low fecundity New Zealand Merino × Coopworth (MC) ewes. Following the cessation of differential feeding, all groups were grazed on a common plane of nutrition for 2 years. There were no significant nutrition by genotype interactions for liveweight, lamb performance, or ewe lambing performance. During common feeding, carryover effects of restricted feeding were apparent only for liveweight and barrenness. The mature liveweight of H ewes was 60–70 kg throughout differential feeding, which was 12–15 kg heavier than L ewes. L ewes showed 58% compensatory growth but were still 5.1 kg lighter than H ewes (P < 0.05) at the end of the experiment. Ovulation rates of L ewes were 0.07–0.51 lower than their H contemporaries during differential feeding and this was significant (P < 0.05 or (P < 0.01) at four out of eight observations. Lamb birth weights in the L group were lower by 0.18–0.37 kg during differential feeding (P < 0.001 for 2-year-old ewes and P < 0,05 for 3–and 4–year-old ewes) and lamb weaning weights lower by 1.1–5.0 kg (P < 0.001 for 3–and 4–year–old ewes). Effects of nutrition on lamb mortality were variable and mostly non-significant. Plane of nutrition did not significantly affect the number of lambs born per ewe lambing (LB/EL) but it was associated with a 5–11 kg difference (P < 0.05 for 2 and 4 years of age and P < 0.01 for 3 years of age) in the total weight of lamb weaned per ewe lambing (TWW/EL). Barrenness was higher (P < 0.05) in H ewes in 1 year of differential feeding and 1 year of common feeding, so that the total weight of lamb weaned per ewe mated (TWW/EM) was not different between the two planes of nutrition. BC ewes were 8 kg lighter than MC ewes by the end of the study P < 0.001). They produced 1.261–.76 more ova (P < 0.001 for 1.5–to 5.5–year–old ewes), and gave birth to and weaned 0.86–1.15 (P < 0.001 for ewes aged 2–6 years) and 0.27–0.80 (P < 0.01 for 2–and 3–year–old ewes, P < 0.001 for 4–year-old ewes, and P < 0.05 for 5–year–old ewes) more lambs per ewe lambing respectively during the experiment. The total weight of lamb born per ewe lambing (TWB/EL) was 0.59–1.43 kg heavier for BC ewes throughout the study (P < 0.05 for 4–, 5–, and 6–year–old ewes). The TWW/EL and TWW/ EM were 3.7–6.5 kg and 0.9–7.1 kg heavier respectively during differential feeding only (TWW/ EL, P < 0.05 and P < 0.01 for 3 and 4 years of age respectively; TWW/EM, P < 0.05 for 4 years of age). Barrenness was not related to genotype.There was a significant nutrition × genotype interaction for greasy fleece weight (GFW) during differential feeding (P < 0.05 for 2–, 3–, and 4–year-old ewes). High BC ewes produced a heavier weight of greasy wool than H MC ewes but the GFW of L BC and L MC ewes were comparable. H ewes had heavier clean fleece weights (P < 0.001) and coarser fibre diameters (P < 0.001) during differential feeding but there was no carryover effect on wool characteristics in the period of common feeding. BC ewes produced coarser wool throughout the study (P <0.001 for 2–, 3–, and 4–year-old ewes, P < 0.05 for 5–year–old ewes, and P < 0.01 for 6–year–old ewes).