Brewer's yeast

Brewer's yeast is seldom used fresh as it spoils quickly and may cause watery flesh in pigs. An excellent source of protein of high biological value and digestibility, brewer's yeast is a very valuable component of poultry and pig rations, in which it is used, however, mostly for vitamins of the B complex and for unidentified but important growth factors in poultry production. When irradiated with ultraviolet light, it also provides vitamin D. If the yeast contains hop constituents, the bitter taste makes the feed unpalatable if included in large amounts. The bitter taste can be removed by mixing the slurry with a solution of sodium hydroxide and sodium phosphate at pH 10 and 45 -50 C, after which the mixture is concentrated, washed and dried. 

Brewer's yeast is usually included at levels of 2-5% in rations for pigs and poultry, but if the price of dried brewer's yeast is low, it can replace up to 80% of the animal protein in pig and poultry diets provided that additional calcium is added. Calves can be given up to 200 g per day of dried brewer's yeast, and in some cases it seems to increase the fat content of milk from cows. 

The yeast is usually roller-dried, which requires such expensive machinery that the process is economical only in large breweries. The yeast can, however, be mixed with the brewer's grain and dried as a mixture in a steam-tube drier. This method increases the value of the spent grain. 

Fresh yeast can be fed to cattle and pigs, who quickly get used to eating it. When large quantities are fed to swine, a mineral mixture with a high calcium and a low phosphorus content must be chosen, and vitamin B12 has to be added as well. Dairy cows may be fed 15 litres of fresh yeast daily, which will provide sufficient protein for 30 litres of milk but enough energy for only 10 litres of milk; therefore, fresh yeast should be fed together with an energy-rich low protein feed such as maize silage or root vegetables. Swine should be fed a litre of cooked or boiled yeast daily at the start of fattening, rising to 2 litres daily at the end. Fresh yeast should not be fed to suckling sows because of the danger of diarrhoea in piglets.