Maize silage has become the major forage component in the ration of dairy cows over the last few decades. Khan, Yu, Ali, Cone and Hendriks published a review with information on the mean content and variability in chemical composition, fatty acid (FA) profile and ensiling quality of maize silages, and discussed the major factors causing these variations.
The effect of the broad range in chemical composition of maize silages on the total tract digestibility of dietary nutrients, milk production and milk composition of dairy cows was quantified and discussed in this review, as well as the optimum inclusion level of maize silage in the ration of dairy cows for milk production and composition. It was shown that the nutritive value of maize silages is highly variable and that most of this variation is caused by large differences in maturity at harvest. Maize silages ensiled at a very early stage (DM<250 g/kg) were particularly low in starch content and in starch/NDF ratio, resulting in a lower DM intake, milk yield and milk protein content.
The DM intake, milk yield and milk protein content increased with advancing maturity, reaching an optimum level for maize silages ensiled at DM contents of 300–350 g/kg, and then declined slightly at further maturity beyond 350 g/kg. The increase in milk and protein yields with the maturity of the maize silages were positively related to the increase in the starch/NDF ratio of the maize silages. On average, the inclusion of maize silage in grass silage-based diets improved the forage DM intake by 2 kg/day, milk yield by 1.9 kg/day and milk protein content by 1.2 g/kg.
Further comparisons showed that, in terms of milk and milk constituent yields, the optimum grass/maize silage ratio depends on the quality of both the grass and maize silages. Replacement of grass silage with maize silage in the ration, as well as an increasing maturity of the maize silages, altered the milk FA profile of the dairy cows, notably, the concentration of the cis-unsaturated fatty acid C18:3n-3 and the n-3/n-6 ratio decreased in the milk fat.Despite variation in the nutritive value, maize silage is rich in metabolizable energy and supports a higher DM intake and milk yield. Harvesting maize silages at a DM content between 300 and 350 g/kg and feeding in combination with grass silage results in a higher milk yield of dairy cows. The review has been published in the Journal of the Science of Food and Agriculture, 95 (2015) 238-252 and can be found via this link.