Energy and protein value of lupin seed as a production ration or as a supplement for sheep fed chaffed wheaten hay

Abstract

Lupin seed was evaluated as a supplement to cereal hay and as the sole component of a production ration, by measuring energy, nitrogen (N), and carbon balances in 4-6 adult wether sheep. Seven diets of different combinations of lupin seed and chaffed wheaten hay were fed in sequence to 4 sheep. The hay was offered as a restricted ration of 800 g/day with and without 100 g lupin seed/day, and ad libitum with and without 2 levels of lupin seed (100, 400 g/day). In addition, lupin seed alone was offered at near maintenance and ad libitum to 6 sheep. The dry matter (DM) content of the wheaten hay contained 7.7 g N/kg DM and 572 g cell wall organic matter (CWOM), and its gross energy (GE) value was 18.1 MJ/kg DM. The GE was 49% digestible, and its metabolisable energy (ME) value was estimated at 6.4 MJ/kg DM at ad libitum intake levels. Corresponding values for the lupin seed fed alone were 49 g N, 199 g CWOM, 20.1 MJ GE, 86% digestible energy, and 15.7 MJ ME/kg. Ad libitum intakes of wheaten hay were below that required to sustain energy maintenance, but total DM intake was increased substantially with 100 g/day of lupin seed supplement. At higher levels of supplementation some substitution did occur, although the response was variable. Methane production was reduced by increasing the level of lupin seed in the ration, but ME and heat (both expressed in relation to DE) and energy balance (expressed in relation to ME) could each be effectively described by single rectilinear relationships, suggesting that the energy value of lupin seed was similar if used as a production ration or as a supplement. Energy values of lupin seed fed alone compared favourably with published values for other leguminous seeds and some cereal grains. Net availability of ME for gain was estimated to be 61%. Urinary N loss, in terms of apparently digested N or available energy, was very high when lupin seed was fed alone, indicating that protein retention was low compared with legume forages of similar N and cereal grain (e.g. oats). Therefore, although leguminous seeds have rely high levels of protein and obvious potential as energy and N supplements, it may not be valid to presume they are ipso facto important sources of amino acids for ruminants. High energy availability and a low potential for protein deposition would imply a significant diversion of energy into fat with such diets.