A COMPARISON OF UNTREATED AND FORMALDEHYDE-TREATED BARLEY DISTILLERS SOLUBLES AND RAPESEED MEAL AS PROTEIN SUPPLEMENTS IN DAIRY-COWS GIVEN GRASS-SILAGE AD-LIBITUM

Twenty Friesian cows in four pens were arranged in a 4 x 4 Latin squar e experiment with 4 wk experimental periods to evaluate the effects on feed intake, milk yield and milk composition of treating barley dried distiller's solubles (DDS) with a formaldehyde reagent, and to compar e DDS with rapeseed meal as a protein supplement in dairy cows given a grass silage-based diet. The control diet (C) consisted of grass sila ge ad libitum fed with 8.5 kg/d of concentrate based on barley, oats a nd barley fibre (250, 250 and 500 g/kg dry matter (DM)). In three othe r diets 1.5 kg/d of the basal concentrate was replaced with rapeseed m eal (RSM) treated for reduced ruminal degradability, 1.5 kg of untreat ed DDS (UDDS) or 1.5 kg of DDS treated with formaldehyde reagent at th e level of 15 l/t (TDDS). On average, protein supplementation increase d silage and total DM intake by approximately 0.5 kg/d (P > 0.05). Mil k yield (P < 0.1), protein content (P < 0.05) and protein yield (P < 0 .01) were likewise increased. Untreated DDS had no effect on milk yiel d or milk composition as compared with diet C. Treatment of DDS with f ormaldehyde reagent tended to increase milk and protein yield as compa red with UDDS, and resulted in a milk yield similar to that obtained w ith the RSM supplement. Compared with RSM, the mean milk protein yield was lower (P < 0.01) when the diet was supplemented with DDS. Live we ight gain was higher (P < 0.05) in cows receiving RSM diet than in cow s receiving DDS diets. Calculation of energy balance showed that incre ased milk energy output in cows fed diets containing protein supplemen ts was mediated mainly through increased energy intake.