Effects of live weight, maturity and genotype of sheep fed a hay-based diet, on intake, digestion and live weight gain

The effects of initial live weight (LW; 18 and 30 kg), maturity (40 and 65% mature LW) and genotype on dry matter intake (DMI), LW gain (LWG), organic matter digestibility (OMD), rumen outflow rate of solid phase and urinary allantoin-N excretion were examined in 14 and 21 female lambs from the local breed Churra da Terra Quente (CH) and Ile-de-France (IF), respectively. LW at 40 and 65% maturity was 18 and 30 kg and 30 and 49 kg for CH and IF lambs, respectively. Lambs were individually fed coarsely ground meadow hay (4 cm) ad libitum supplemented with a protein concentrate over a period of 12 weeks. DMI (g kg(-1) LW0.75) and rumen outflow rate were higher and OMD lower (P < 0.01) in CH than in IF lambs. irrespective of LW or degree of maturity. Daily allantoin-N excretion (mg kg(-1) LU) was higher in CH than in IF lambs (P < 0.10) at the same degree of maturity. LWG was unaffected by LW or maturity and was higher in IF than in CH lambs (P < 0.001; 92.3 vs. 47.1 g day(-1)). Regression analysis of LWG on digestible organic matter intake suggests that energy requirements for maintenance of CH lambs are higher than for IF lambs. It is suggested that differences between breeds in digestive ability and outflow rate should be confirmed at the same level of intake. Experiments should also be designed to measure energy retention and more closely estimate energy requirements for maintenance of the two breeds