Milk production from grass and byproducts : for improved sustainability of dairy production

Ruminants can produce meat and milk from fibrous feed and byproducts not suitable for human consumption. However, high-yielding dairy cows are generally fed high proportions of cereal grain and pulses, which can be consumed directly by humans. This thesis investigated the effect of diets high in forage and byproducts, of low human interest, on milk production, feed efficiency, metabolic status, and fertility. Enteric methane emissions when feeding glycerol or starch were also investigated. In a series of feeding studies, high quality grass-clover silage was included in dairy cow diets and the effects on feed intake and milk production were determined. Feeding byproduct-based concentrate to dairy cows compared with concentrate based on cereal grain and soybean meal, had no effect on feed intake and milk yield. However, feeding human-inedible byproducts increased net food production substantially. In a study comparing methane emissions from dairy cows fed glycerol or wheat starch, the results indicated that glycerol in the feed was available to rumen microbes to a larger extent than initially assumed and therefore did not have the potential to decrease enteric methane emissions. Dairy cows in early lactation fed low or high levels of byproduct-based concentrate showed no difference in total feed intake, milk yield, energy balance or indicators of metabolic status, although cows fed a low-concentrate diet decreased more in body weight than cows fed a high concentrate diet. When the study included only multiparous cows and extended over a whole lactation, cows offered a low-concentrate diet were found to have lower feed intake, but with no differences in milk yield, energy balance, feed efficiency or blood plasma metabolites between low- and high-concentrate diets. Thus, high producing dairy cows can perform well on high-forage and byproductbased diets virtually free of ingredients suitable for human consumption, without compromising milk production, feed efficiency or energy balance, thereby contributing to sustainable food production.