Effect of toasting field beans and of grass-clover: Maize silage ratio on milk production, milk composition and sensory quality of milk

The effect of toasting field beans and of grass-clover: maize silage ratio on milk production, milk composition and the sensory quality of the milk was investigated in a 2 ⁎ 2 factorial experiment. Toasting of field beans resulted in lower milk contents of both fat (44.2 versus 46.1 g/kg, P = 0.02) and protein (33.5 versus 34.2 g/kg, P = 0.008), whereas milk production, urea and somatic cell contents were unaffected compared with the untreated field beans. Increasing the proportion of maize silage (from 9 to 21% of DM) in the ration decreased the content of urea in milk (P = 0.002), whereas milk production and milk content of fat and protein were unaffected. Milk from cows fed the high proportion of maize silage had a lower (P = 0.04) long-chain fatty acid content (≥ C18). Furthermore, milk from cows fed the high proportion of maize silage had a lower (13–26%) content of luteine (P = 0.03), 13-cis-β-carotene (P = 0.04) and β-carotene (P = 0.05). Toasting of field beans compared with untreated field beans did not affect the milk content of carotenoids and had only small effects on fatty acid composition. Regarding the sensory quality, the four treatments resulted in milk being characterized by a distinctly fatty mouthfeel and creamy flavour and a pronounced sugar-sweet taste and creamy odour. The higher proportions of maize in the feed resulted, in general, in milk characterized by a significantly more intense maize odour (P < 0.05). The effect of field bean toasting in combination with a high proportion of maize in the feed resulted in milk characterized by a significant and distinctly sour feed odour (P < 0.05). In conclusion, toasting field beans did not improve milk production, and toasted field beans in combination with a high proportion of maize in the feed resulted in milk with negative sensory characteristics. Increasing the proportion of maize silage at the expense of grass-clover silage did not affect milk production, but decreased the milk content of long-chain fatty acids, as well as the content of carotenes.