Phenotypic and seasonal factors influence birth weight, growth rate and lamb mortality in D'man sheep maintained under intensive management in Tunisian oases

Growth and mortality rates of D'man lambs from an accelerated lambing management at the breeding Station of Chenchou of Gabes (Tunisia) are reported using records collected between 2004 and 2009. Lambs born in spring were consistently the heaviest at birth, at 30 and 70 days of age with the greatest average daily gains compared to those born in winter, autumn and summer. Birth weights were affected by litter size, ewe age and lambs from older ewes (2-10 years) grew faster than lambs born to young ewe (1 year). The overall mortality from birth to 70 days of age was 13.4%. Of all the total losses, 41% of the lambs died within 10 days of birth, 29% died between 10 and 30 days of age and 30% between 30 and 70 days. Mortality rate was significantly higher in winter (23.5%) than in spring (12.3%), autumn (10.2%) and summer (9.5%). Lambs in the low-weight category died more frequently (52.2%) than lambs from medium-weight (24.4%) to high-weight (1.8%) categories. Season, birth type and dam age are an important source of growth variation. The significant risk factors identified for mortality were season (winter), birth type (multiple) and weight class (<= 1.5 kg). (C) 2011 Elsevier B.V. All rights reserved.