The nutritive value of hulled and hulless barley for growing pigs. 1. Determination of energy and protein digestibility with the in vivo and in vitro method

An experiment was conducted to determine the digestibility of energy and crude protein (CP) in hulled and hulless barley with the in vivo and in vitro method. Six barrows were fed six diets according to a 6 × 6 Latin square design. The six diets included 950 g kg^-1 of four barleys and two mixtures. Diet A: hulled barley, c.v. Harrington I. Diet B: hulled barley, c.v. Harrington II. The origin of c.v. Harrington in diet B was different from that in diet A, and therefore referred to as c.v. Harrington II. Diet C: hulless barley, c.v. CDC Buck. Diet D: hulless barley, c.v. CDC Richard. Diet E: mixture of c.v. Harrington I and c.v. CDC Buck (50:50, wt/wt). Diet F: mixture of c.v. Harrington II and c.v. CDC Richard (50:50, wt/wt). The mixtures were created in order to establish linear regression equations between in vivo and in vitro methods. Chromic oxide was used as the digestibility marker. The barrows were fed twice daily, at 08.00 and 20.00 h. Each experimental period consisted of an 8-d adaptation period followed by a 2-d collection period of faeces. The initial and final average body weights of the barrows were 40 and 90 kg, respectively. The in vivo energy digestibilities were higher (P < 0.05) in the hulless (81.4 to 84.7%) than in the hulled barleys (76.9 to 77.6%). The digestible energy contents in the hulless barleys ranged from 14.01 to 14.60 MJ kg^-1 while the contents in the hulled barleys ranged from 13.05 to 13.16 MJ kg^-1 (as-fed). The average digestible CP contents in the hulled and hulless barleys were nearly similar and were 88.0 and 89.7 g kg^-1 (as-fed), respectively. The in vivo energy and CP digestibilities in the barleys and their mixtures can be accurately predicted by in vitro values, as these were very high correlations between these methods for energy (r² = 0.93) and CP (r² = 0.87).