Lifetime Reproductive and Lamb Crop Yields of Fat-tailed Naeemi and Imported Border Leicester Merino Ewes in Intensive System of Production

Abstract

Local fat-tailed and imported thin-tailed sheep breeds are used for lamb production in hot arid zones. These animals are exposed to an extended summer (seven months) and shorter autumn, winter and spring seasons. The present study examined relative reproductive and lamb crop yields of low and high prolific Naeemi (N) and Border Leicester Merino (BLM) ewes under the intensive management system respectively. Mating systems used were N×N pure breeding and BLM×N rams in three-way crossing. The BLM ewes gave birth to 1.48 lambs per ewe per year as compared to 0.78 lambs per ewe per year for N. The weight of lambs born per ewe was 35% higher and weight weaned 45% higher for BLM ewes compared to N ewes.The lamb mortality was 10% with no significant differences between breeds. The parity significantly (P≤0.05) affected all reproductive traits in both the BLM and the N ewes, except the litter size in N, which was unaffected by parity. The N showed maximum reproduction at second parity (1.08 lambs/ewes) and BLM at third parity (1.63 lambs per ewe). While the lambs from BLM ewes’ first parity showed the highest mortality (21%), lambs from fifth parity showed the lowest mortality (4.5%). The weight of lambs born and weaned was significantly higher (P≤0.05) in autumn-mated than summer-mated BLM ewes. For BLM ewes, mortality was significantly higher (P≤0.05) in summer-born lambs than the lambs born in autumn, winter or spring. This study has demonstrated a moderate lifetime productivity of local N ewes and marked superiority of BLM to N for ewe reproduction and lamb crop yields under the intensive management system.