SUPPLY OF NUTRIENTS AND PRODUCTIVE RESPONSES IN DAIRY-COWS GIVEN DIETS BASED ON RESTRICTIVELY FERMENTED SILAGE

The objective of this paper is to review research which has evaluated the feeding of dairy cows with diets containing large proportions of g rass silage. In Finland, milk production systems evolved are based on the use of restrictively fermented silages. Higher potential yields, s maller production risks than with cereal grains, short grazing period and high digestibility of grasses grown in northern latitudes have fac ilitated this development. Factors affecting nutrient supply from thes e diets are discussed. Digestibility is determined mainly by the stage of maturity at harvesting and it is not markedly affected by the leve l of energy and protein supplementation. Intake of grass silage is inf luenced both by digestibility and fermentation characteristics. Effici ency of microbial synthesis is high in animals given diets based on re strictively fermented silage but rumen fermentation pattern is charact erised by low molar proportions of propionate. Production responses to additional concentrate are relatively small, especially when the amou nt of concentrate exceeds 10 kg day(-1). High substitution of silage d ry matter (DM), negative associative effects on digestion and partitio ning of energy towards body tissues account for small production respo nses. Protein supplementation has consistently increased milk protein yield but responses do not appear to be related to the level of milk p roduction, silage crude protein content, amount of concentrate or stag e of lactation. The new protein evaluation system provides an accurate prediction of protein yield with the typical Finnish dairy cow diets. The high slopes (ca. 0.5) between protein supply and milk protein yie ld within experiments suggest that protein supply is suboptimal and pr otein supplements are used with a high efficiency.