R. Barea

Effects of dietary protein content and feeding level on carcass characteristics and organ weights of Iberian pigs growing between 50 and 100 kg live weight

The effects of dietary protein content and level of feeding on carcass characteristics and organ weights were studied in castrated male Iberian pigs growing from 50 to 100 kg live weight (LW). Animals were offered four diets providing 145, 120, 95 and 70 g ideal crude protein (CP) per kg dry matter (DM) and 13·94, 14·29, 14·56 and 14·83 MJ metabolizable energy (ME) per kg DM, respectively. Three levels of feeding were assayed: 0·60, 0·80 and 0·95 of ad libitum intake. The pigs were slaughtered at 100 kg LW. Daily gain in carcass (carcass gain, g/day) and protein deposition (PD, g/day) in this component attained 76·2% and 78·8% of whole-body average daily gain and PD, respectively. Carcass gain improved with each decrease in dietary CP from 145 up to 120 g/kg DM and then levelled off. A small but significant effect of dietary CP on carcass composition was observed, due to an enhanced fat deposition in pigs fed the lowest protein content diet. Mean values of protein, fat, ash and water contents in the carcass were 101·8, 522·7, 27·6 and 353·7 g/kg respectively. PD in the eviscerated carcass was not affected significantly by dietary protein level but tended to reach a maximum value with the diet that provided 95 g CP per kg DM: 55·7 g/day at the highest feeding level assayed. Carcass energy retention (MJ/day) increased significantly ( P P P P

Response analysis of the Iberian pig growing from birth to 150 kg body weight to changes in protein and energy supply1

A total of 251 growing-finishing Iberian (IB) pigs, 32 of which were suckling piglets, were used in 5 separate sets of trials. The comparative slaughter procedure was used to determine nutrient and energy retention at several stages of growth from birth to 150 kg BW. A factorial arrangement was used within each set of trials, involving several concentrations of ideal protein in the diets as 1 factor and 2 or 3 levels of feed intake as the other. The main objective of these studies was to derive the optimal protein-to-energy ratio in the diet to allow for the expression of maximum protein deposition rates. The effect of feed restriction on growth performance, protein deposition, and fat deposition was also assessed. According to allometric equations, empty BW (EBW) was related to whole body components or total chemical constituents of empty body mass (P < 0.001). For pigs receiving solid feed, highly statistically significant multiple regression equations were constructed, which derived nutrient (g/kg) or energy (MJ/kg) composition as a function of EBW, dietary protein-to-energy ratio, and level of feeding (P < 0.001). In pigs offered adequate protein-to-energy diets, ADG at each stage of production was predicted as a function of the average BW and feeding level (P < 0.001). It was observed that the estimates of ME required for maintenance and net efficiency of utilization of ME for growth change were within rather narrow ranges throughout the growth stages studied. Preferred values (413 kJ/kg BW(0.75) × d(-1) and 0.593 for ME(m) and k(g), respectively) were obtained by regressing total energy retention (kJ/kg BW(0.75) × d(-1)) against ME intake (kJ/kg BW(0.75) × d(-1)). A multiple-regression approach revealed that in the IB pig, ME costs for protein deposition and fat deposition reach 60 and 62 kJ/g, which is considerably greater than in conventional or lean pig genotypes. In the IB pig, the maximum daily rate of protein deposition (PD(max), g) seemed to follow a linear-plateau shape with a breaking point at 32.5 kg BW, beyond which PD(max) remained at an average rate of 75 g × d(-1). The marginal efficiency of body protein deposition was estimated at each growth stage. In pigs fed on optimal or suboptimal protein-to-energy diets, the relationship between PD and ME intake declined, following a curvilinear pattern with increasing BW; thus, implying relative increases in lipid gain as BW increased.

Effects of pig genotype (Iberian v. Landrace × Large White) on nutrient digestibility, relative organ weight and small intestine structure at two stages of growth.

Although the effects of pig genotype on total-tract apparent digestibility (TTAD) have been widely reported in the literature, there is controversial information on the digestive capacity of indigenous breeds compared with lean-type pigs. The strategy of this study was to test the effects of pig genotype and crude protein (CP) supply on performance, digestive utilization of nutrients, relative organ weight and morphometric analysis of the small intestine. Thirty-eight Iberian (IB) and Landrace × Large White (LD) pigs were used. Three pigs per genotype were slaughtered at approximately 15 kg BW. The remaining pigs were fed one of two diets differing in CP content (13% or 17% as fed) using a pair-fed procedure. Feeding level was restricted at 0.8 × ad libitum of IB pigs. Nutrient digestibility and nitrogen (N) balance trials were performed at 30 and 80 kg BW. Four pigs per dietary treatment and genotype were slaughtered at approximately 50 and 115 kg BW. The gastrointestinal tract and the rest of the visceral organs were weighed and samples of the small intestine were taken to carry out histological and histometrical studies. Daily gain and gain-to-feed ratio were higher in LD than in IB pigs during the fattening and growing-fattening periods (P < 0.01). N TTAD was significantly higher for LD pigs at 30 kg BW (P < 0.05), whereas at 80 kg BW we observed greater values for digestibility of organic matter and energy in IB pigs (averaging 1.5%, P < 0.01). Both N retention (NR) and efficiency of NR were increased in LD pigs at 30 and 80 kg BW (30% as mean value). The proportional weight of the small intestine was greater in LD than in IB pigs at 50 and 115 kg BW. Histometry showed that IB presented a lower muscle layer thickness than LD pigs in ileum, irrespective of the BW (P < 0.05). In contrast, LD pigs showed approximately 10% higher ileal villi length and villi-to-crypt ratio than IB pigs at 115 kg BW. CP supply affected to a larger extent the small intestinal micro-anatomical structure of LD pigs at 50 kg BW. In conclusion, our results suggests that although the higher growth rate, NR and efficiency of NR observed in LD pigs might be associated with presumably more efficient structural aspects of the small intestine, the main differences between the two genotypes should be attributed to a larger extent to protein and energy utilization in tissues with consequences for the overall efficiency of energy use.

Evolution of the fatty acid profile of subcutaneous back-fat adipose tissue in growing Iberian and Landrace × Large White pigs.

The lipid content and fatty acid (FA) profile in pig tissues are strongly influenced by genotype and nutrient supply, with implications in meat quality. The de novo lipid synthesis and pattern of FA unsaturation could be an important cause of variation in the overall efficiency of energy utilization among breeds. To test the effects of pig genotype and CP supply on the evolution of back-fat tissue FA profile throughout the growing and finishing stages, 32 Iberian (IB) and Landrace × Large White (LR × LW) barrows were offered one of two diets differing in CP content (13% or 17% as fed). A pair-fed procedure (0.8 × ad libitum intake of IB pigs) was used. Subcutaneous fat samples were taken at the dorso-lumbar region at ∼38, 50, 65, 90 and 115 kg BW. Higher proportions of total monounsaturated FA (MUFA; P < 0.01) and lower proportions of total saturated FA (SFA; P < 0.01 to 0.05) were found in the outer back-fat layer of pigs both at 50 and 115 kg BW. Pig genotype affected the FA composition of both subcutaneous back-fat layers. The proportions of C18:0 and SFA in fat tissue were higher in IB than in LR × LW pigs from 38 to 65 kg BW, especially in the outer layer. In addition, MUFA contents were higher in IB pigs at 115 kg BW in both layers (+5% on average; P < 0.01). Increased proportions of C18:2 n-6 and polyunsaturated FA (PUFA) were found in LR × LW pigs, irrespective of the stage of growth and back-fat layer (P⩽0.02). At 50 kg BW, pigs receiving the high-protein diet presented the highest C18:2 n-6, C18:3 n-3, C20:5 n-3 and PUFA contents. A significant genotype × CP content interaction was observed for C18:3 n-3 because of the increased concentration of this FA in LR × LW pigs when offered the 17% CP diet (P < 0.05). Higher C16:0 and SFA contents (+5%; P = 0.03) were found in pigs offered the 13% CP diet and slaughtered at 115 kg BW. There was a genotype × CP interaction for MUFA concentration because of the higher MUFA content observed in IB pigs offered the highest protein content diet (P = 0.03). Our results suggest that genetic variation in de novo lipid synthesis and pattern of FA unsaturation might contribute to explain differences in back-fat FA profile of IB and LR × LW pigs under identical nutritional management. They could be also relevant to explain the low efficiency of nutrient and energy utilization in the IB pig.

Growth of body components and carcass composition of Iberian pigs of 10 to 150 kg body weight as affected by the level of feeding and dietary protein concentration

A total of 211 growing-finishing Iberian (IB) pigs from 4 separate and independent sets of trials were slaughtered at several stages of growth from 10 to 150 kg BW to determine growth and development of chemical and physical components of the cold eviscerated carcass (CC; without head, feet, and tail). Within each set of trials, a factorial arrangement of treatments, involving several concentrations of ideal protein in the diets as 1 factor and 2 or 3 levels of feed intake as the other, was used. The main objective of the present study was to provide information on the relative growth of physical and chemical components of the CC of IB pigs, which differed because of the dietary treatment imposed, involving a wide range of protein-to-energy ratios and feeding levels. Allometric relationships (P < 0.001) were established between the weight of a chemical component in the CC and empty BW or CC weight. Irrespective of the adequacy of the dietary protein-to-energy ratio, the growth coefficient for CC weight relative to empty BW was >1 (P < 0.001), whereas those for protein, water, and ash relative to empty BW or CC weight were <1 (P < 0.001). In contrast, relative growth coefficients >1 (P < 0.001) were obtained for fat mass and total energy, reflecting the increase in fat relative content that occurs with increasing weight. Multiple-regression equations (P < 0.001) were developed using a stepwise procedure, which estimates the chemical (g/kg) or energy (MJ/kg) composition of CC as a function of empty BW, dietary protein-to-energy ratio, and feeding level, expressed as a multiple of the ME required for maintenance. It is concluded that even if the pattern of developmental growth for the IB pig may show some similarities (increased fat content or decreased proportional weight of some primal cuts with BW or age) with that observed for pigs of different genetic background, relevant differences were detected. They are related to a much smaller relative size of the IB pig lean tissues and cuts, their slower rates of growth, and the increased total body fat, with marked changes in its distribution among depots. Consequently, relationships obtained for lean or conventional genotypes are not applicable to the IB pig.

Lysine concentration in dietary protein affects performance and pattern of nutrient retention of weaned Iberian piglets

The amino acid composition of dietary protein, specifically the essential amino acid composition, is a key factor that affects the efficiency of use of dietary protein and, therefore, growth and protein retention. The balance among essential amino acid for maintenance and production functions has been established in pigs, with some variations according to the physiological state of the animal (BSAS, 2003). Pig genotype is one the factors that might influence such balance, although limited information is available in the literature concerning this issue. The Iberian pig is an obese, slow-growing breed. In previous work we have shown that Iberian pig requirements for total protein differ markedly from those of pigs of conventional genotypes (Nieto et al., 2012), although dietary protein was formulated following the amino acid pattern (g amino acid/kg crude protein) established for conventional pigs. The present work aimed at establishing the dietary lysine (Lys) requirements (g Lys/kg crude protein) for optimum performance of post-weaned Iberian piglets.

Differential protein deposition in tissues of growing Iberian and Landrace × Large White pigs under identical nutritional management

The present work is part of an experimental program aimed at explaining the biological basis for the lower metabolic efficiency of the Iberian pig, a slow-growing, native obese pig, when compared to conventional lean pig types (Barea et al., 2011).