EFFECT OF DEHYDRATED LUCERNE IN MAIZE SIL AGE DIETS FOR DAIRY-COWS

The effects on milk production of the quantity and physical form of ad ded high quality (0. 75 UFL, 190 g CP/kg DM) dehydrated lucerne in a m aize silage-based diet were assessed. Sixteen high-producing Holstein cows were used in a 4 x 4 latin square design to evaluate 4 diets. The control diet (C) consisted of 80% maize silage, 8% energetic concentr ate, 10% protected soybean meal, 2% urea and mineral mix (table II). T he experimental diets contained either 2.5 or 5. 0 kg dehydrated lucer ne in a chopped form (mean particle size = 8.25 mm) (diets 2.5L and 5. 0L) or 5.0 kg of pelleted dehydrated lucerne (mean particle size = 0.6 8 mm) (diet 5.OB). The proportion of soybean meal was reduced when luc erne was given in order to obtain iso-nitrogenous diets. The 4 diets c overed 105% of the protein requirements and starch content was quite s imilar between the diets (270 g/kg DM). The experiment was carried out in mid-lactation (60 d post partum). The cows were fed individually a nd ad libitum (at least 10% refusals) and the ingredients were totally mixed. Milk production was unaffected by dehydrated lucerne (30.4, 31 .0, 30.3 and 30.7 kg/d for C, 2.5L, 5.0L and 5.OB, respectively, table III). Added dehydrated lucerne decreased milk fat content by 1.5 g/kg milk (P < 0.05) whatever the quantity and the physical form of lucern e. Milk fatty-acid composition was not affected by treatments although long-chain fatty-acids concentrations (18 carbon) were slightly incre ased (P < 0.05) when chopped lucerne was given (28.5 versus 25.7% of t otal fatty acids, P < 0.05). Milk protein content was not significantl y affected by the 2.5L treatment but was lowered when 5. 0 kg dehydrat ed lucerne was offered (-0.6 g/kg milk, P < 0.05). DM intake was incre ased when cows were fed the 2.5L diet (21.6 versus 20.9 kg/d for the c ontrol, P < 0.01) but was not modified in the 5.0L diet (table V). Thi s result might be explained by a favourable effect of lucerne on diet appetibility without adverse effect on rumen fill when the lower quant ity was offered. The DM intake was high in the 5.OB diet (21.9 kg/d) a nd this observed value was in good agreement with the value predicted by the French Fill Unit System when pelleted lucerne was assumed to be a concentrate. The blood glucose level was improved and the betahydro xybutyrate level was lowered when cows consumed the chopped lucerne (t able VII). In contrast, ground lucerne led to lower glucose and higher betahydroxybutyrate levels (P < 0.05) than the control treatment. It was concluded that mixing 2.5 kg dehydrated lucerne into a maize silag e-based diet causes a decrease in milk-fat content without adverse eff ect on milk protein and that the higher DM intake compensates for the lower energetic value of lucerne compared with maize silage. Nonethele ss, the energetic value remains a limiting factor to adding more lucer ne as a substitute of maize silage and soybean meal. The results showe d some evidence to prove a specific effect of lucerne physical form on milk-fat depression and on animal performance.