Variations of metabolism and feed efficiency in laying R.I.R.-hens in relation to prenatal environmental temperatures.

Starting from an hypothesis concerning the long-term effects of exogenous treatment during the ontogeny of mammals and birds, we incubated Rhode Island Red (RIR) eggs at different prenatal temperatures (table 1) to study the feed efficiency, development, reproduction and energy metabolism of the hens. The maintenance requirement varied (up to 30 p. 100) as well as the feed conversion (up to 28 p. 100), but lower maintenance requirements did not always result in a significantly higher net energy gain nor in a higher feed efficiency above maintenance. Laying RIR hens from eggs incubated at 37.8 degrees C vs those from eggs incubated at 36.8 and 35.8 degrees C (days 1-10) showed a significantly (P less than or equal to 0.05) lower fasting heat production, resulting in lower maintenance requirement and higher energy balance mainly composed of fat energy. This was paralleled by a lower feed conversion rate during growth and reproduction. In fasting conditions, these animals showed a lower oxidative metabolism of fats and proteins.