RESUMO
Japanese black Wagyu cattle are renowned for producing some of the world's most highly valued and recognized beef with exceptional marbling. Therefore, the primary focus of genetic selection for Wagyu cattle has historically been on meat quality, particularly achieving high marbling levels. However, even when the price of the final product is high, production costs also remain high, especially considering that most of the feed has to be imported. The objective of this study was to evaluate phenotypic relationships between feed efficiency, specifically residual feed intake, as the most utilized efficiency index in cattle, and various meat quality parameters in Japanese black cattle in order to determine if a common phenotypic selection for these parameters could be feasible. For this, a total of 39 Wagyu cattle were evaluated for feed efficiency over their entire fattening period (900 days), with a focus on RFI as a key indicator. Animals were fed high-starch diets with vitamin A deprivation to achieve the desired marbling. Results revealed positive correlations between feed efficiency and meat quality in Wagyu cattle. Specifically, animals with higher feed efficiency exhibited superior meat quality traits, including firmness, marbling, and overall meat rating. When comparing the 20 most extreme RFI individuals (10 most and 10 least efficient), we observed that efficient RFI animals showed increased marbling levels (+13.2%, P=0.05) and ranking quality (+12%, P=0.06) of the meat. In conclusion, this research contributes to understanding the interplay between feed efficiency and meat quality in Japanese black Wagyu cattle. Phenotypic correlations observed suggest the possibility of incorporating RFI criteria into genetic selection programs without compromising the prized meat quality traits of Wagyu beef.
RESUMO
Beef industry needs alternative feeding strategies to enhance both economic and environmental sustainability. Among these strategies, adjusting the diet dynamically according to the change of nutritional requirements (multiphase diet) has demonstrated its economic and environmental benefits in pig production systems. Therefore, this retrospective study aims to assess, through simulation, the theoretical economic and environmental benefits of introducing a multiphase diet for crossbreed bulls feeding (one or more diet changes). For this, individual data of BW, BW gain, and daily intake were recorded from 342 bulls during the last fattening period (112 days). These data were used to estimate individual trajectory of energy and protein requirements, which were subsequently divided by individual intake to calculate the required dietary energy and protein concentrations. The area between two functions (i.e., ƒ1: constant protein concentration in the original diet during fattening and ƒ2: estimated protein concentration requirements) was minimised to identify the optimal moments to adjust the dietary concentration of energy and protein. The results indicated that both energy and protein intake exceeded requirements on average (+16% and +28% respectively, P < 0.001), justifying the adoption of a multiphase diet. Modelling the individual trajectories of required metabolisable protein (MP, g/kg DM) during the fattening period resulted in exponential decay model in relation to BW [32120 × exp(-0.026 × BW) + 59.9], while the dietary net energy concentration followed a slightly quadratic model [2.26-0.0026 × BW + 0.000003 × BW2]. Minimisation of the area between curves showed two optimal moments to adjust the diet: at 312 kg and 385 kg of BW, indicating three diet phases: (a) <312 kg, (b) 312-385 kg, and (c) 385-600 kg. For the second and third phases, the dietary energy and protein concentration should be 70 g MP/kg DM and 1.70 Mcal/kg DM and 61 g MP/kg DM and 1.65 Mcal/kg DM, respectively. These diet adjustments might improve economic profitability by 29 /animal, reduce estimated nitrogen excretions by 16% (P < 0.001), and maintain similar weight gain (P > 0.16) compared to the commercial diet. However, the decrease in dietary energy concentration led to increased fibre concentration, which in turn increased the estimated CH4 emissions of animals with the multiphase diet (+44%, P < 0.001). Hence, multiphase diet could theoretically reduce feeding cost and nitrogen excretion from fattening cattle. Further in vivo studies should confirm these results and find optimal nutritional strategies to improve economic profitability and environmental impact.
