Digestible, metabolizable and net energy values of 13 feedstuffs for growing pigs: effect of energy system

Abstract

Digestible (DE), metabolizable (ME) and net (NE) energy values and digestible nutrient contents of 17 complex diets were measured in 45 kg growing boars. Values for DE and ME were estimated from collection of faeces, urine and measurement of methane production, while NE was obtained from energy balances carried out in respiration chambers. Diets were prepared from 13 ingredients (wheat, barley, maize, tapioca, sweet potatoes, soyabean meal, rapeseed meal, sunflower meal, peas, maize distillers grains, maize gluten feed, cane molasses and animal fat), the inclusion levels of all ingredients being independent. The DE, ME, NE and digestible nutrients contents of ingredients were then calculated by regression of nutritive values of diets on levels of inclusions of ingredients. Digestibility of energy of diets was negatively affected by their neutral detergent fibre (NDF) content (−1.1% per 1% NDF). Digestibility of fat increased curvilinearly with dietary fat content. Energy evaluation systems (DE versus ME versus NE) affected the hierarchy between the tested ingredients: when the energy content of wheat was considered as 100, the energy values of soyabean meal, tapioca and animal fat were 101, 98 and 184 on a DE basis, 97, 99 and 187 on a ME basis and 66, 106 and 241 on a NE basis. The correspondence between measured NE of ingredients and NE values which can be calculated from available NE systems varied according to the system. The study indicates that the tabular DE content or nutrient digestibility coefficients of fibre or fat rich ingredients are overestimated when they are included in complex diets. The results emphasize the necessity for estimating energy values of pig feeds, and especially ingredients, on a NE basis. In addition, more attention should be paid to digestive interactions occurring with changes in feeding level or digestive capacity of the pigs, especially with complex diets.