The efficiency of utilisation of metabolisable energy (ME) for maintenance (k(m)) from diets containing maize and broken rice (BR) at 500 g/kg was studied in old White Leghorn (WL) and Rhode Island Red (RIR) laying hens using the respiration calorimetry technique. The maize-based diet contained 180.8 g crude protein (CP)/kg and 16.4 MJ gross energy (GE)/kg while the BR-based diet contained 173.2 g CP/kg and 16.3 MJ GE/kg. Diets were fed for 10 d, while an energy and nitrogen metabolism study was conducted during 3 d on an ad libitum-fed diet followed by another 3 d on two-thirds of the ad libitum-fed quantity. 2. ME values for the maize- and BR-based diets for WL hens were 73.3% and 77.6% of the GE, whereas for the RIR hens these were 77.7% and 80.0%, respectively. 3. Fasting heat productions, determined at the end of 24 h fast for WL and RIR hens were 473.2 and 366.1 kJ/kg W0.75/d, respectively. During fasting WL and RIR hens utilised body energy reserves with efficiencies of 84.9% and 73.7%, respectively. 4. The k(m) of maize- and BR-based diets for the WL hens were 81.6% and 79.6%, whereas for the RIR hens these were 74.2% and 76.0%, respectively. 5. ME for maintenance of WL and RIR hens were 589 and 499.6 kJ/kg W0.75/d, respectively. 6. It is concluded that although WL and RIR hens differ significantly in energy metabolism, their efficiency of utilisation of energy from maize- and BR-based diets are similar.
