Milk production from silage: comparison of grass, legume and maize silages and their mixtures

Abstract

The high rates of rumen fermentation, physical breakdown and passage rates from the rumen of legume silages lead to higher intakes than for grass silages of comparable digestibility. Although total tract digestibilities for legume silages and maize silages are often lower than for grass silages, milk yields are usually higher. A further benefit of legumes and maize is the reduced rate of decline in digestibility. Legume silages often lead to a reduction in milk fat concentration and increased levels of polyunsaturated fatty acids, 18:2 n-6 and 18:3 n-3. This latter effect is related to reduced rumen biohydrogenation as a consequence of increased rumen passage rates or the effects of polyphenol oxidase. There is quite a wide range of maturities (300 – 350 g kg-1 DM) that leads to maximum dry matter intakes and milk production from maize silage; milk production is reduced with immature or over–mature maize crops. Forage chop length exerts a number of effects, both in the silo and in the rumen, but effects on rumen function, feed intake and milk production have been inconsistent. The high protein content and high N degradability of most legume silages is associated with a low efficiency of converting dietary N into milk N, with a concomitant increase in urine N. Reducing N intake by inclusion of maize silage in mixtures with legume silages leads to a marked reduction in urine N without loss of production potential. It is predicted, on the basis of their chemical composition and rumen kinetics, that legume silages and maize silages would reduce methane production relative to grass silage, though in vivo measurements are lacking. Extensive fermentation in the silo reduces the amount of fermentable substrate, and reduced methane production in comparison with grass silage where fermentation had been restricted by high levels of acid additive.