The energy content of barley fed to growing pigs: characterizing the nature of its variability and developing prediction equations for its estimation.

Currently, the pork industry attempts to formulate energy levels in swine diets to within a tolerance of 1.5%. This is difficult to achieve in practice when the energy content of primary ingredients fluctuates by up to 15%. This experiment was carried out to define the sources of variation in the energy content of barley and to develop a practical method to accurately estimate the DE and ME content of individual barley samples. Four samples of each of five covered barley varieties (AC Lacombe, B-1602, Bedford, Harrington, and Manley) were collected to obtain a range of quality within each variety. Five measurements were collected on each barley sample using 60 crossbred barrows in an apparent total tract digestibility study. The barrows, average BW of 35.3 kg, were housed in individual metabolism crates to facilitate separate collection of urine and feces. Five-day collection periods followed 5-d diet acclimation periods. Levels of total beta-glucan, ADF, CP, and starch (90% DM) in the 20 barley samples ranged from 2.7 to 4.5%, 4.5 to 9.2%, 10.8 to 15.1%, and 42.3 to 53.4%, respectively. The mean DE and ME content of the 20 samples were 2,934 and 2,857 kcal/kg (90% DM), respectively, and varied among samples by 15.2% (447 kcal). The complex structural cell wall carbohydrates seemed to have the greatest influence on the energy content of individual barley samples. The ADF fraction alone accounted for 85% of the total variation in energy content of the 20 samples. Converted into a prediction equation, DE = 3,526 - 92.8 x ADF (90% DM), the ADF content was used to estimate the DE content of barley with 85% accuracy. This experiment confirms the large variation in the energy content of barley, describes the factors that influence this variation, and presents equations based on chemical and(or) physical measurements that may be used to predict the DE and ME content of individual barley samples.