Evaluation of methanol-grown bacteria and hydrocarbon-grown yeast as sources of protein for poultry: trials with laying birds.

1. Two 90-d trials were carried out with laying hens at peak production, for the evaluation of two single-cell protein (SCP) sources in practical-type layer diets of relatively low protein content. The SCP tested were: Pruteen, produced from methanol-utilising bacteria, and a Lavera-type yeast which utilises the normal paraffins of heavy gas oil. 2. In one trial the inclusion of 50 g yeast/kg diet had little effect on performance. Pruteen at the same concentration decreased production rate and egg size due to a significant reduction in food consumption (5%), but did not affect food utilisation. 3. In another trial diets containing 60 and 100 g Pruteen/kg had similar, non-significant depressive effects on production rate (about 8%), without affecting food intake, egg size or body weight. 4. The relatively low arginine concentration in Pruteen necessitated increasing the dietary protein content in order to meet the calculated requirements. 5. A 17-carbon fatty acid was introduced at low concentration into the diet by the inclusion of 100 g Pruteen/kg; only traces of it could be detected in the yolk lipids of eggs laid by hens fed on this diet.