Effect of intake level during milk-feeding period and protein content in the post-weaning diet on performance and body composition in growing lambs

Abstract

AbstractThe effect of intake level during the milk-feeding period and dietary protein content during the post-weaning period on performance, weight of components of the digestive tract and carcass and non-carcass chemical composition was investigated in 28 Churra lambs. A 2 × 2 factorial design was used with two intake levels during the milk-feeding period (Lmilk: 0·9 and Hmilk: 1·5 MJ gross energy per kg M0·75daily) and two concentrate supplements (Lprotein:barley grain and Hprotein: barley grain plus 200 g/kg fish meal) during the post-weaningperiod. After selecting an initial slaughter group of four 2-day-old lambs, 12 lambs were assigned randomly to each of two intake levels during a 4-week milk-feeding period and given food individually. Four lambs from each intake level were slaughtered at weaning (30 days old) and the remaining 16 were weaned between 30 and 49 days old (weaning period). Eight lambs from each nutritional regimen during the milk-feeding period were further divided into two equal groups and given food individuallyad libitumwith hay and the post-weaning concentrate, according to the experimental design until thefinal slaughter weight (20 kg) (post-weaning period). Lmitk lambs showed a capacity to grow as well as the Hmilkduring the weaning and post-weaning period and there were no differences (P> 0·05) in dry-matter intake and food conversion ratio among treatments. Before weaning, the weight of the reticulo-rumen was not affected by the intake level during the milk-feeding period. The most affected component of the gastrointestinal tract was the small intestine as proportion of the digestive tract which was lower in Lmilklambs (P< 0·05). At 20 kg live weight, the relative size of the reticulo-rumen was greater (P< 0·01) and the abomasum (P< 0·05) and large intestine (P< 0·01) were smaller in lambs which were given the Hprotein concentrate after weaning. The organic matter apparent digestibility (OMD,P< 0·05) and crude protein apparent digestibility (CPD,P< 0·05) of the post-weaning diets was greater in Lmilklambs and the Hproteinpost-weaning diet was associated with a greater dry-matter apparent digestibility, OMD and CPD when lambs were close to final slaughter weight. At 20 kg live weight, the proportion of protein in the carcass of Lmilklambs was greater (P< 0·05) than in Hmilklambs. The greater growth of the reticulo-rumen of the Lmilklambs might have increased solid food intake after the milk-feeding period, led to greater CPD of post-weaning diets and had consequences in terms of carcass composition.