| Sumario: | Mortality was studied in relation to birth weight (BWT) and postpartum age in 3083 Horro lambs born over 15 years at Bako Research Center, IAR. Pre-weaning mortality rose with declining BWT (log y = 2.20- 0.35X; r = 0.9981), but the influence after weaning was less pronounced and linear (y = 23.78-1.93X; r = 0.5271). Overall, 1066 (34.6%) of the lambs died; 19.1% of lambs born died before weaning and 19.1 % of lambs weaned died before one year of age. Significantly more lambs died in the first week of life (231/2953 = 7.8%) than in any subsequent 7-day period (0.2-1.9%, P<0.001). But, although significant (P<0.01), a transient rise in mortality after weaning was small in magnitude (mean: 1.6 VS. 1.1% lambs died per week). Major gains in meat output could be achieved from Horro sheep by reducing lamb mortality; firstly by improved late-pregnancy health and nutrition of ewes, and thus BWT, and secondly by attention to ewe and lamb management during the first week after lambing.
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