Phenotypic and genetic parameters of feed efficiency in Charolais bulls – Part 1. Correlations across test station and field conditions under contrasting fattening diets

Abstract

In the French Charolais breeding programme, feed efficiency traits are routinely evaluated in sires fed a cellulose-rich pelleted concentrate with a moderate energy density. However, this diet differs considerably from the silage-based diets commonly used in commercial farms. This study aimed to assess whether selection for feed efficiency under a cellulose-rich pelleted diet remains effective when progeny is fattened under alternative field feeding conditions. A total of 4 625 performance test bulls fed a pelleted diet were evaluated in a test station, with data collected for feed intake (FI), average daily gain (ADG) and final weight (FW). Between 2015 and 2020, 26 of these bulls were used as sires, producing 639 terminal bulls fattened in experimental farms on either corn- or grass-silage-based diets. Feed efficiency was assessed using three criteria: residual feed intake (RFI), residual gain (RG), and feed conversion efficiency (FCE). Carcass traits, including dressing percentage, fat trimmings weight (FTW) and internal fat weight (IFW), were also recorded at slaughter. Genetic parameters were estimated using animal mixed models. Feed efficiency traits were heritable in both populations. High genetic correlations between test and terminal bulls were found for RG (0.95 ± 0.35) and FCE (0.99 ± 0.42), while a moderate correlation was observed for RFI (0.58 ± 0.37), indicating a potential genotype-by-diet interaction specific to RFI. Moreover, unfavourable genetic correlations were identified between RFI and growth traits (0.57 ± 0.27 with ADG; 0.34 ± 0.31 with FW), raising concerns about possible trade-offs when selecting for RFI. Selection for RFI, RG or FCE would not have the same consequences for carcass traits as our results showed that RFI was genetically correlated with FTW (0.42 ± 0.27), whereas no genetic relationship existed between both fat traits and RG or FCE. Interestingly, RFI, RG and FCE were negatively correlated with dressing percentage, suggesting trade-offs in carcass yield. This study also highlighted that animals fed corn silage had better performances with greater FI (+0.40 kg/d), ADG (+0.23 kg/d), FW (+50 kg), FCE (+0.02 kg/kg) and more FTW (+0.5 kg) and IFW (+0.8 kg) in the carcass. To conclude, breeding programmes that rely on performance test station data to improve growth-related feed efficiency traits (RG and FCE) remain highly relevant for animals raised under commercial farming conditions. However, the observed unfavourable genetic correlations, particularly between RFI and growth traits, indicate a potential risk of inadvertently selecting for slower-growing animals.