Factors governing the nutritional value of silage maize

Abstract

The morphological composition of the maize plant evolves up to the glazed grain stage (35 % dry matter (DM) in the whole plant), when the grain reaches its physiological maturity, making up 40 to 50 % of the DM. The chemical composition changes little after flowering except for starch content, which rises at the expense of water soluble carbohydrates. The digestibility of the organic matter (dMO) and the ingestibility of a particular maize measured in sheep hardly changed after the milky stage. These averaged respectively 71.5 + 2.2 % and 52.5 + 7.2 g DM/kg P^0.75 for the 20 maize plants we studied between 1964 and 1971. The dMO averaged 72.6 %and ranged from 67 to 78 % for the 15 normal hybrids studied by the "digestibility club" in 1987 and 1988. Apart from the bm maizes, the variations in digestiblity observed among varieties grown the same year in any particular location were slight and of the same order of magnitude as those observed for the same variety grown in different locations and in different years. Owing to its high DM, its non-limiting soluble carbohydrate content, and above all its low buffering capacity, maize keeps very well as silage if finely chopped. The dOM of silage was the same as that of the fresh cut plant. Its ingestibility in sheep was also closely similar, provided the silage was properly supplemented, particularly for nitrogen. However, dry matter intake by cattle increased with DM content up to approximately 35 %. The DM content of maize silage is thus the essential factor governing net energy intake in cattle. In fattening cattle, though it has been shown that live weight gain increases with DM content in silage maize, feeding efficiency and so probably energy value remains constant. This seems to be true also for dairy cattle. For the same DM content, intake and performance of fattening and dairy cattle, and the feeding efficiency and therefore the energy value varied in the same way as the digestibility of the silage. Animal performance was scarcely affected by devices such as mesh screens or rollers that reduce the amounts of whole grains in faeces. However, the effective energy value of the silage maize based feed, calculated from performance, depended on the nature and the amount of energy supplement intake.