Genetic analysis of protein efficiency and its association with performance and meat quality traits under a protein-restricted diet

Abstract

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.

Phenotypic link between protein efficiency and pig welfare suggests no apparent trade-offs for mitigating nitrogen pollution

“…This difference could be due to seasonality on the one hand and genetics on the other. Protein efficiency has been shown to be moderately heritable [22]; therefore, because mothers and fathers did not overlap in the series, it is likely that some of the differences in PE between groups are genetic. In the observation month of the first series, in August 2020, the outdoor temperature fluctuated between 21.2°C and 30.4°C during the observation hours, resulting in a temperature between 23.7°C and 27.1°C in the barn.…”

“…As the ideal temperature for fattening pigs is between 5 and 17°C [44], the high temperature in August might have affected the animals’ metabolism and thus slowed their activity. With increasing temperatures, PE decreases [22], which can be explained by the altered metabolism during heat stress. In general, pigs exposed to high temperatures have lower muscle and higher fat mass [45].…”

“…The pigs were part of a larger experiment comprising 14 farrowing series (681 pigs), with the goal of estimating genetic parameters of PE [22]. In this study, 95 non-tail-docked Swiss Large White pigs (53 females and 42 castrated males) were observed between August and December 2020.…”

Genome-wide association study and regional heritability mapping of protein efficiency and performance traits in Swiss Large White pigs

“…Although the environmental impact of pig production is lower than that of beef production, approximately 50% of the dietary protein consumed by pigs is excreted as waste [4,5]. Methods such as reducing dietary nitrogen [6,7] and selection to increase protein efficiency (PE; the proportion of total dietary protein intake retained in the carcass) in pigs [8] have been proposed to reduce the contribution of animal-based food production to environmental pollution. Varying heritability estimates between 0.21 and 0.59 have been recently reported for PE and related traits (e.g., nitrogen digestible coefficient), depending on the breed, fattening phase and diet type [8,9,10].…”

“…Methods such as reducing dietary nitrogen [6,7] and selection to increase protein efficiency (PE; the proportion of total dietary protein intake retained in the carcass) in pigs [8] have been proposed to reduce the contribution of animal-based food production to environmental pollution. Varying heritability estimates between 0.21 and 0.59 have been recently reported for PE and related traits (e.g., nitrogen digestible coefficient), depending on the breed, fattening phase and diet type [8,9,10]. The heritability (h 2 ) estimates for PE from these studies indicate that this trait can be genetically improved and thus presents a promising target towards a more sustainable pig production through reduced nitrogen excretion.…”