A crossover study was performed using 24 dairy cows to investigate whether pure ethanol in concentrations that could be found in well-fermented silages influenced milk composition or flavor. Cows were fed a standard ration of well-fermented grass silage for ad libitum intake and high moisture barley and a protein concentrate in restricted amounts. A daily dose of ethanol (600 g) was divided into three meals/d and fed with grass silage. When cows received ethanol, milk yields decreased slightly, but milk fat and protein concentrations increased so that energy-corrected milk yield increased by 0.9 kg/d. Milk concentrations of lactose and urea decreased, concentrations of ethanol and acetone increased, concentrations of free fatty acids increased slightly, and alpha-tocopherol concentrations were unaffected. The proportion of palmitic acid in milk fat increased, and the proportion of unsaturated acids decreased. Organoleptic milk quality was reduced because of an increase in milk tainted by feed flavors. The off-flavor could not be attributed solely to the ethanol transmitted to the milk. Precautions should be taken to avoid extensive production of ethanol during fermentation of grass silage and other feeds that are to be fed to dairy cows.

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Feeding lactating cows at a reduced level for a 6-d-period caused blood serum and milk free fatty acids (FFA) to rise. Milk lipolysis developed more slowly and lasted longer than elevation of the level of FFA in blood. In a second experiment protected rape seed oil was given to underfed animals and inhibited the development of rancidity in the milk. Since unsaturated fat reduced lipoprotein lipase activity in the underfed cow, this supplement appears to reduce the effect of underfeeding if it is accepted that a normal response to underfeeding is to improve the efficiency of fat metabolism through increased lipoprotein lipase activity.The occurrence of rancid flavour in milk is not uncommon and it is generally accepted that this defect is increased by physical handling. Free fatty acids (FFA) resulting from milk lipolysis, in particular butyric acid, are largely responsible for this rancid flavour. Differences exist between animals and within the period of lactation, in the degree of rancidity.These and other factors have been reviewed by Deeth & Fitz-Gerald (1976) and the effect of variation in the plane of nutrition has also been investigated (Stobbs, Deeth & Fitz-Gerald, 1973). A liberal supply of fresh grass in the diet seems to improve the condition (Jellema, 1975). The addition of palmitic acid to the feed increased rancidity in milk, while the opposite effect was observed with protected safflower oil (Astrup et al. 1979(Astrup et al. , 1980. In this paper the results from 2 experiments on underfeeding cows are reported. The first of these was concerned with the shortterm effect of underfeeding and the second involved feeding protected rape seed oil to underfed animals. METHODS Expt 1The daily net energy level of the feed was lowered by 6-24 % for 5-6 d in 5 trials with 52 lactating cows. This lowering of feed energy started at about 25 d post partum in trials 1, 2 and 4, at about 35 d post partum in trial 5, and later in trial 3. The feed reduction generally came about by reducing, proportionally, feed units from roughage and concentrates. Daily energy balances were calculated from intakes minus requirements for maintenance and milk production, based on Norwegian standards. Balances were negative even during the period preceding the feed reduction. The negative balances relative to requirements are expressed as percent underfeeding in Table 1.The cows were fed twice daily and milked at 07.00 and 16.00 each day. Milk samples were taken from each milking for 3 d and refrigerated. Blood samples were drawn

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