Background An essential component in the development of a sustainable pig production is the reduction of nitrogen excretion in fattening pigs. Pig feeds typically contain high levels of dietary crude protein, and due to incomplete conversion to muscle tissue, excess nitrogen is excreted, resulting in environmental problems such as nitrate pollution and greenhouse gas emissions. Therefore, improving protein efficiency (PE), i.e. the proportion of dietary protein that remains in the carcass and is thus available for meat production, is desirable. This study aimed to estimate the heritability (h2) of PE and its genetic correlations with phosphorus efficiency, three performance, seven meat quality and two carcass quality traits when pigs were fed a 20% protein-restricted diet, using a total of 1,071 Swiss Large White pigs. To determine PE, the intake of feed with known nutrient content was accurately recorded for each pig and the nitrogen and phosphorus content of the carcass was determined using dual-energy X-ray absorptiometry. Genetic analysis was performed with a Bayesian animal model. Results We found an average PE of 0.39 ± 0.04 and a heritability of 0.43 (0.29, 0.58). PE showed a low genetic correlation with phosphorus efficiency (0.12 [0.04, 0.21]) and moderate genetic correlations with feed conversion ratio (-0.40 [-0.50, -0.30]), average daily gain (-0.34 [-0.41, -0.23]) and average daily feed intake (-0.61 [-0.69, -0.50]). The genetic correlations between PE and meat quality traits were not significantly different from zero except for meat redness (-0.40 [-0.58, -0.09]) and meat yellowness (-0.27 [-0.45, -0.04]). In contrast, feed conversion ratio showed unfavourable genetic correlations with meat colour, drip loss and cooking loss. Conclusions Protein efficiency is heritable and can be considered in breeding to reduce the environmental impact of pig production without influencing meat quality traits, but the potential for coselecting improved phosphorus efficiency is rather small. Selecting nutrient efficiencies might be a more suitable strategy to reduce nitrogen pollution from manure than focusing on FCR because the latter shows genetic antagonism with meat quality in our population.

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Background An essential component in the development of sustainable pig production is the reduction of nitrogen excretion in fattening pigs. Pig feeds typically contain high levels of dietary crude protein, and due to incomplete conversion to muscle tissue, excess nitrogen is excreted, resulting in environmental problems such as nitrate pollution and greenhouse gas emissions. Therefore, improving protein efficiency (PE), i.e., the proportion of dietary protein that remains in the carcass, is desirable. The aim of this study was to estimate the heritability (h2) of PE and its genetic correlations with phosphorus efficiency, three performance, seven meat quality and two carcass quality traits when pigs were fed a 20% protein-restricted diet, using 1071 Swiss Large White pigs. To determine PE, the intake of feed with known nutrient content was accurately recorded for each pig and the nitrogen and phosphorus content of the carcass was determined using dual-energy X-ray absorptiometry. Results We found an average PE of 0.39 ± 0.04 and a heritability of 0.54 ± 0.10. PE showed a high genetic correlation with phosphorus efficiency (0.61 ± 0.16), moderate genetic correlations with feed conversion ratio (− 0.55 ± 0.14) and average daily feed intake (− 0.53 ± 0.14), and a low genetic correlation with average daily gain (− 0.19 ± 0.19). While PE has favourable genetic correlations with the performance traits and some meat quality traits, there is a potentially unfavourable correlation of PE with meat colour (redness [rg = − 0.27 ± 0.17]; yellowness [rg = − 0.31 ± 0.18]) and intra-muscular fat (IMF; rg = − 0.39 ± 0.15). Feed conversion ratio (FCR) also showed unfavourable genetic correlations with meat lightness, redness yellowness, IMF and cooking loss. Conclusions PE is a heritable trait that can be considered in breeding programs to reduce the environmental impact of pig production. We found no strong negative correlation of PE with meat quality traits, and that there is potential to indirectly select for improved phosphorus efficiency. Selecting nutrient efficiencies might be a more suitable strategy to reduce nitrogen pollution from manure than focusing on FCR because the latter also shows genetic antagonism with some meat quality traits in our population.

The objective of this study was to explore the potential of using automatically recorded feeding behaviour as a proxy for protein efficiency (PE) by investigating the relationship between feeding behaviour and PE. A total of 402 Swiss Large White pigs were used in this experiment (204 females and 198 castrated males). Pigs were fed ad libitum on a reduced protein diet (80% of standard) from 20kg to 100kg BW. Individual daily feed intake was monitored and carcass composition at slaughter was determined by dual-energy X-ray absorptiometry (DXA). The PE was calculated as the ratio of protein in the carcass (estimated by DXA) to the total protein consumed. Feeding behaviour traits monitored were daily feed intake (DFI; g/day), feed intake per visit (FIV; g/visit), number of daily visits (NDV; visits/day), duration of visits (DUV; min/visit), feeding rate (FR; g/min), and feeder occupation (FO; min/day). Regression analysis was used to estimate the relationship between PE and feeding behaviour, while correcting for the effects of sex, experimental series and age. Weak Pearson’s correlations (−0.25 to 0.12) were found between PE and feeding behaviour traits. Beta (β) estimates from this analysis for feeding behaviours were also very low (0.0093% to 0.087%). An increase in FR (g/min) will increase PE by 0.087% and an increase in DFI (g/day) will decrease PE by 0.0093%. In conclusion, feeding behaviours are not suitable for the identification of protein-efficient pigs, as estimates are negligible.ImplicationsThis study suggests that feeding behaviour traits recorded via automatic feeder are not reliable predictors of protein efficiency in Swiss Large White pigs receiving a protein-reduced diet. Despite the large differences in protein efficiency, only negligible changes in a range of feeding behaviours were observed. Hence, feeding behaviours are not suitable proxies for the high-throughput phenotyping of protein efficiency and the selection of live animals for use in nutrition experiments or for breeding.