Laying hens were fed for a 48-wk period with a basal diet supplemented with a selected strain of Lactobacillus acidophilus at levels up to four million viable cells per gram of feed. Levels of egg production and feed conversion were significantly higher (8 and 14.8%, respectively) than in the control flock, and cholesterol values in yolks were decreased by 18.8%. It is suggested that the latter effect was a reflection of lower serum cholesterol concentrations in treated birds; a maximum reduction of over 55% followed incorporation of the culture into the feed. The level of viable cells in the feed was confirmed as being critical to register the above effects.

1. The influence of Lactobacillus acidophilus alone or in combination with zinc bacitracin on the performance of laying hens was monitored over a period of 4 months. 2. Lactobacillus acidophilus improved egg production, food conversion and reduced the cholesterol concentration in the eggs, but zinc bacitracin had no effect when administered alone. 3. In combination, bacitracin had an adverse effect on the otherwise beneficial activity of the culture.