The effects of concentrate energy source on energy utilisation by lactating dairy cows offered a range of grass silages

Abstract

Replacement of high starch with high digestible fibre ingredients in the concentrate has resulted in inconsistent effects on silage intake and milk yield and composition of lactating dairy cattle. These differences in animal performance may reflect effects of concentrate energy source on energy utilisation. The present study was undertaken to examine the effect of concentrate energy source on energy utilisation in lactating dairy cows offered a diverse range of grass silages.Three silages were harvested from perennial ryegrass swards after 39 day regrowth intervals. Silages A and C were produced from primary regrowths and Silage B from a secondary regrowth. Silages A, B and C were ensiled after 24, 0 and 0 h wilting intervals, treated with an inoculant, untreated or an inoculant respectively. Concentrates containing starch concentrations of 50, 209 and 385 g/kg DM, were prepared using barley, wheat, maize gluten, sugar beet pulp and citrus pulp as energy sources. The concentrates were formulated to contain similar concentrations of crude protein, effective rumen degradable protein, digestible undegradable protein, metabolisable energy and fermentable metabolisable energy and were offered at 10 kg/head/d in four equal feeds accounting for 0.57 of DM intake. The diets (3 silages x 3 concentrates) were offered to 18 lactating dairy cows, in a completely randomised experiment, for a minimum period of 28 days prior to the main recording period. Prior to entering open circuit respiration chambers, described by Gordon et al. (1995), cows were housed in individual stalls during a 6 day diet digestibility and nitrogen utilisation study.