The effect of feeding low-phytate hulless barley-soyabean meal diets differing in protein content to growing pigs on phosphorus and nitrogen excretion

Abstract

An experiment was conducted with growing pigs to determine the excretion of P and N in 4 barley-based diets formulated to contain 18 or 15% CP by using a normal hulless barley (HB) or a low-phytate hulless barley (LPHB). The HB contained 0.27% total P and 0.14% phytate P; the LPHB contained 0.24% total P and 0.03% phytate P. The diets were supplemented with lysine, methionine, threonine, and tryptophan to meet their apparent ileal digestible supplies according to the National Research Council (NRC). All diets were supplemented with inorganic P to meet the NRC recommendation for available P (0.23%). Eight barrows, average body weight 20.4 kg, were assigned to the 4 dietary treatments according to a repeated 4 × 4 Latin square design. The diets were fed at a rate of 2.5 the ME requirement for maintenance. The barrows were fed twice daily, at 8 a.m. and 4 p.m., equal amounts each meal. Water was added to the feed at a ratio of 2.5 to 1. Each experimental period consisted of a 7-d adaptation period followed by a 5-d collection of faeces and urine. The substitution of HB with LPHB decreased (P<0.001) the total P excretion by 33.5 and 35% for the 18 and 15% CP diets, respectively. Reducing the CP content from 18 to 15% decreased (P<0.001) the N excretion by 26% for both the HB and LPHB diets. With the reduction in CP content, there was a decrease (P<0.001) in the amount of N retained. The N:P ratio in excreta of pigs fed the LPHB diets was higher (P<0.001) than of pigs fed the HB diets. The digestibility of N was higher (P<0.001 ) in pigs fed the LPHB compared to the HB diets. The data indicate that P and N excretions can be greatly reduced by substitution of HB by LPHB, and by the reduction of the CP content, respectively in diets for growing pigs.