Dietary effects on energy metabolism of laying hens as determined by indirect calorimetry.

Abstract

Indirect calorimetry was employed to evaluate adequacy of various diets for laying hens. Effects of supplemental fats (animal fat, corn oil, olive oil and menhaden oil) and their combinations were evaluated; phosphorus deficiency was used to evaluate effects of mineral inadequacy; and methionine deficiency was used to determine effects of dietary amino acid balance and protein quality. Addition of animal fat and vegetable oil to laying hen diets at a level of 7% significantly (P $<$.05) increased both maintenance metabolizable energy (ME) requirement and fasting heat production (FHP). With the exception of menhaden oil, all fat supplements significantly (P $<$.05) improved energy intake, energy retention (balance) and net energetic efficiency (NEE) of dietary ME conversion to net energy in eggs and body tissues. An olive oil-animal fat (1:1) combination produced the highest NEE (96%) and ME intakes. Comparison of egg yolk fatty acids with those in corn oil, animal fat, olive oil and olive oil-animal fat combination yielded correlation coefficients of.096,.890,.824 and.954, respectively, suggesting that fatty acids in the olive oil-animal fat combination most closely resemble those in egg fat. Diets formulated to contain 16% protein and.18% available phosphorus supported an egg production rate of 70.6% which was increased to 76.7% with supplementation to.35% available phosphorus. Feed intake and conversion were improved with phosphorus supplementation at the low protein level, but not at 19% protein. Heat production was higher for the low phosphorus-fed birds a each protein level. Daily maintenance ME requirement and FHP were increased with the high protein diets. The 16% dietary protein level was adequate to support both egg production and egg weight if sufficient available phosphorus was present in the diet. However, the 19% dietary protein level was detrimental to performance. Total sulfur amino acid (TSAA) intake and egg mass were increased with supplemental DL-methionine. Low TSAA levels resulted in higher heat production, and maintenance ME requirements with concomitantly lower NEE. A TSAA requirement of 514.7 mg/bird/day was estimated to support an egg mass of 47 g/bird/day. Indirect calorimetry estimated the TSAA requirements as 591.5 to 629.9 mg/bird/day for maximum energetic efficiency and energy balance, respectively.