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© 2014 Ministerio de Agricultura Pesca y Alimentacion. All Rights Reserved. A meta-analysis was made of data from a total of 211 growing-finishing Iberian (IB) pigs from four separate and independent sets of trials. Within each set of trials, a factorial arrangement of treatments was used, involving several concentrations of ideal protein in the diets and two or three levels of feed intake. Pigs were slaughtered at several stages of growth from 10 to 150 kg body weight (BW). The partition of dietary protein in the body of the pigs, the empty-body gain (EBG), the chemical composition of EBG, growth of primal cuts in the cold eviscerated carcass (without head, feet, and tail), and mass of dissected tissues in trimmed shoulder and ham were determined. Linear regression equations allowed estimating N requirements for maintenance as 175 mg/(kg BW0.75 · kg dry-matter intake) · d–1 and an average value for the net efficiency of utilization of the dietary protein apparently absorbed of 0.386. In pigs offered adequate protein to energy diets, EBG was predicted as a function of average BW and feeding level (p < 0.001). Multiple regression equations were constructed, which derived nutrient (g kg–1) or energy (MJ kg–1) composition of EBG as a function of empty-body weight (EBW), dietary protein to energy ratio, and level of feeding (p < 0.001). These predictive equations, not applicable to pigs of lean and conventional genotypes, can contribute to the design of optimal feeding strategies to improve the efficiency of IB pig production systems and to achieve high quality standards in end products for the market.

Little information is available concerning mineral metabolism in suckling piglets. The utilization of milk minerals and the mineral composition of Iberian (IB) suckling piglets were studied in two consecutive experiments at different ambient temperatures (trial 1, 27 ± 2°C; trial 2, 22 ± 2°C). Milk composition and the piglets' performance were determined weekly over a 34 days lactation period and, at the end, body mineral contents were analyzed and mineral retention and bioavailability were calculated. The ash content in IB sows' milk and in suckling IB piglets was found to be higher than that reported for lean genotypes. During lactation, mean ash content per unit of body weight gain in IB piglets (40.6 g kg-1) was 42% higher than that observed for lean breeds, and weaned IB piglets contained 60% more Ca (11-12.7 g kg-1 empty body weight) and P (7-7.5 g kg-1 empty body weight), compared with conventional pigs. Minerals from milk were retained by the IB piglet with an overall efficiency of 78.3%, 66.3% and 48.7% for Ca, P and Mg, respectively. Significant differences between trials were observed in the mineral fraction composition of the milk, which were reflected in piglet body composition at weaning, presumably due to differences in ambient temperature. Present findings underline genotype differences in mineral composition of sow's milk and suckling piglets and may provide a useful starting point for formulating milk-replacer diets for IB piglets.