Silage and dairy cow production

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Abstract
Jersey cross-bred cows were fed unwilted pasture silage supplemented with either pasture or maize silage contributing 50% of the DM offered, or with a mixed protein concentrate constituting 8.5 or 17% of the ration DM. Pasture or protein concentrates increased the concentration and digestibility of N in the ration, increasing digestible N intake by 25 to 40%. Maize silage reduced ration N concentration and digestibility, lowering digestible N intake by 40%. Regression analysis indicated that diet type had a significant effect on milk yield and composition. Cows offered silage rations supplemented with pasture or protein concentrates produced more milk with higher concentrations of fat and protein than cows fed exclusively on silage at similar intakes of DE. When maize silage was the supplement, there was no effect on milk yield or composition. Differences in molar proportions of rumen VFA between diets were small, indicating that type of rumen fermentation is not important in limiting milk yield and composition of cows fed silage. Lack of a response in milk yield and composition to the maize silage supplement indicates that if microbial protein synthesis was limiting, it was not due to a lack of readily fermentable carbohydrate. It is suggested that milk protein synthesis is limited by the amount of protein entering the duodenum, a consequence of the low true protein content of high moisture silage.