Response of 40-70 kg barrows and gilts to increasing ideal protein concentrations in the diet

In Belgium, crossing a hybrid dam with a Piétrain sire leads to a rather lean and meaty fattening pig type. A digestibility trial and a performance trial were carried out to determine protein needs of this pig type. Six experimental diets with increasing protein content were formulated with 0.65-1.25% apparent ileal digestible lysine. The feeds were formulated to the ideal protein composition, with lysine as the reference amino acid. Standardised and apparent digestible amino acid values of the extreme diets were measured in a digestibility trial with four gilts cannulated at the end of the ileum, with an average initial and final BW of 39.1 kg and 55.3 kg, respectively, using a protein-free feed to estimate the basal endogenous N-losses. A performance trial at 13-18 weeks of age (40-70 kg BW) was performed with barrows and gilts separately at six protein levels, balanced in lysine, threonine, methionine and tryptophan. The experiment consisted of 11 pens (of 5 animals) per treatment and per sex. Average daily gain (ADG) and feed conversion ratio (FCR) reached maximal performance within the experimental lysine range for both sexes. Based on the ADG-data for barrows and on the ADG- and FCR-data for gilts, a protein level for optimal performance corresponded with a standardised ileal digestible lysine concentration of 0.89% for barrows and of 1.07-1.09% for gilts.