Effect of dietary protein level (as substitution of maize with soybean meal) on growth rate and feed efficiency of the Cinta Senese pig in the growing-fattening period

This study aimed to provide first indications on the protein requirement of Cinta Senese pigs. The effect of various dietary protein contents on in vita performance was tested. Sixty Cinta Senese pigs were equally distributed in four dietary groups, balanced for sex (barrow and gilt) and live weight. At the start of the trial, pigs were approximately 130 d old and weighed an average 46.6 kg. Groups were fed four diets with different protein content (approximately 8, 10, 13 and 16%, named 8% P, 10% P, 13% P, 16% P, respectively), obtained by using different maize/soybean meal ratios. Diets were administered to pigs during the entire growing-fattening period in a controlled dose of 90 g/kg W0.75, until a maximum of 2.5 kg/d pro capite. Feed distributed per pen was recorded daily and individual weight and ultrasonic backfat thickness were periodically recorded. The trial lasted approximately 250 d and finished when animals reached the target slaughter weight of 145 kg. The 8% P diet determined a lower growth rate than the other diets; after 250 d, pigs receiving this diet were 20 kg lighter than those receiving the other diets. The 10% P diet determined body weights always lower than the 13% P and 16% P diets, but the difference decreased in the middle of the trial period. The pigs fed 13% P and 16% P diets showed the same growth rate. Moreover, through the whole growth period, the 8% P diet produced higher fat thickness than the other three diets, which showed similar results. The 8% P diet determined the highest FCIs. The 16% P diet showed the best feed conversion until approximately 70 kg of l.w., but after this weight it became progressively less efficient than the 10% P and 13% P diets. Consequently, the cumulative intake of that diet was the lowest only for the first 60 kg of gain. The 10% P diet gave the best FCI starting from 80 kg of l.w. In consideration of the cost of protein feed and the need to reduce N pollution, the 10% P diet could be the optimal compromise for growth-fattening in the Cinta Senese pig, certainly over 70 kg of l.w.