The effects of increasing the proportion of molasses in the diet of milking dairy cows on milk production and composition

Abstract

The objective of this experiment was to measure the effects on milk production and composition of including different levels of molasses, which is a good source of rumen-fermentable energy, in the diet. The experiment was a balanced Latin square design with four treatments and four periods, each of 4 weeks duration. There were five squares using a total of 20 Holstein/Friesian cows. At the start of the experiment cows were on average 32 days in milk (range 18–47 days), had an average body weight of 591 kg (range 516–716 kg) and an average milk yield of 27.5 kg/day (range 21.9–32.5 kg/day). The treatments consisted of 5 kg/day of a concentrate supplement plus one of the following molasses/grass–silage mixtures (g/kg) fed to appetite: (1) 0 molasses/1000 grass–silage, (2) 50 molasses/950 grass–silage (139 g/kg molasses on a DM basis), (3) 100 molasses/900 grass–silage (254 g/kg molasses on a DM basis), and (4) 150 molasses/850 grass–silage (351 g/kg molasses on a DM basis). Milk yield was measured daily, milk composition on three successive morning and evening milkings weekly and blood samples were taken once before an evening milking in the final week of each period. Protein composition was measured on a composite of one successive evening and morning milk sample in the final week of each period from twelve cows (3 squares). Intake was measured daily. Milk and constituent yields, milk composition and intake data from the final 2 weeks of each period were used to compare the treatments. There was a significant linear increase in milk yield ( p < 0.001), protein yield ( p < 0.001), protein concentration ( p < 0.01), casein concentration ( p < 0.05) and total dry matter intake ( p < 0.001) with increasing level of molasses inclusion. Plasma β-hydroxy butyrate levels were significantly higher ( p < 0.05) in diets containing molasses. It is concluded that including rumen-fermentable energy in the form of molasses in a grass–silage-based diet for dairy cows significantly increased milk production and improved composition.