Body chemical composition and utilization of dietary energy by male Saanen kids fed either milk to satiation or solid complete feeds with two proportions of straw

Abstract

Of 41 male kids, 14 were killed immediately after birth (3·3 kg BW); the remainder were either fed on goat milk to satiation or weaned at 10 kg BW. After achieving 15·7 kg BW, weaned kids were fed on complete diets including either 20 or 40% straw. Milk-fed kids were slaughtered at 16·8 or 26·7 kg BW, weaned kids at 15·7 or 29–30 kg BW, respectively (at least four kids per treatment). Empty BW as a proportion of final live BW was 0·91±0·02 in milk-fed kids compared to 0·85±0·04 and 0·76±0·04 in kids given complete feeds including 20 or 40% straw, respectively. Empty BW of kids in the heaviest groups were c. 24 kg for milk-fed or weaned kids. Energy and crude protein contents per kg empty BW increased from 4·5 MJ and 158 g in newborn kids to 12·2 MJ and 163 g in milk-fed kids or 10·4 MJ and 194 g in weaned kids, respectively. No influence of the feeding system was found on mineral contents of empty BW. Ca, P and K remained constant at 12·6, 7·7 and 1·9 g/kg, Mg increased from 0·32 to 0·46 g/kg and Na decreased from 2·0 to 1·3 g/kg. Differences in composition of live BW gain are mainly caused by differences in gut-fill. Efficiency of utilization of ME for growth was c. 0·75 in milk-fed kids even at high BW, but only 0·31 in weaned kids. Proportions retained of dietary N, Ca, P, Mg, Na and K were highest in milk-fed kids between birth and 16·8 kg BW: 0·57, 0·88, 0·78, 0·40, 0·37 and 0·10, respectively. They were lowest in kids fed on complete feed including 40% straw from 15·7 to 30·3 kg BW: 0·25, 0·26, 0·32, 0·04, 0·11 and 0·04, respectively. Weaning seems to be of greater influence on composition of BW gain and efficiency of utilization than the increase in empty BW.