Energy values of whole lucerne (Medicago sativa) and of its stem and leaf fractions in immature and fully grown sheep

Abstract

Chopped lucerne hay (Medicago sativa) and a stem fraction derived from it were fed to two adult and two immature wethers ad libitum and at a level near maintenance. Energy, nitrogen, and carbon balances were measured during feeding and fasting. The hay contained 17% crude protein and 46% cell wall constituents (dry matter basis) and the stem, which was 53% of the total, contained 10% crude protein and 64% cell wall. Voluntary dry matter consumption rates of the hay (per kg 3/4) were 103 and 145 g/day by the adults and immatures, respectively; the corresponding values for the stem were 73 and 100 g/day. Maximum daily energy balances were 290-3 16 kJ/kg3/4 for the hay and approximately maintenance for the stem. With both ad libitum and restricted feeding, energy digestibility was higher for the hay (56- 63%) than for the stem fraction (45-51%). The metabolizable fraction of digestible energy was 78% at the low and 82% at the high level of feeding and tended to be greater with the stem than with the hay. At the lower feed intake, metabolizable energy was about 10 and 8 MJ/kg organic matter for whole lucerne and stem respectively. Net availability of metabolizable energy was 64 and 49% for maintenance and gain on the hay, compared with 53 and 34% on the stem. As estimated by difference, the energy values of leaf were: digestible energy, 76%; metabolizable energy, 77% of digestible energy or 12.4 MJ/kg organic matter; net availability of metabolizable energy, 78% for maintenance and 60% for gain. All these figures are for the adult sheep; the immature animals gave values that were lower to various degrees. Consideration of the present results together with published data for other samples of lucerne suggests that the use of equations based on study of grasses to predict the energy values of lucerne is likely to introduce significant bias. Equations for this limited set of data on lucerne are given, gross energy being related to crude protein content, metabolizable energy to crude fibre and net availability of metabolizable energy to metabolizable energy content.