Abstract :
[en] The Belgian Blue (BB) breed, originated from central and upper Belgium in the 19th century, is composed of two strains including Beef Belgian Blue (BBB) and Dual-Purpose Belgian Blue (DPBB). The BBB is the most important breed for beef production in Belgium, while the DPBB is the most important local dual-purpose cattle breed reared in dairy farms located in the Walloon Region of Belgium. Through their local identity and resilient characteristics, DPBB cows could be more popular on organic and direct sale-oriented farms in Belgium. In recent decades, human consumption patterns of dairy products have changed, and consumers are more aware of the effects of milk fatty acids (FA) on health. Furthermore, the milk FA composition plays an important role in the quality of butterfat. Therefore, interest in changing the milk FA profile is growing, which motivated researchers to define new traits related to milk FA profile and evaluate the feasibility of including them in selection programs of dairy cattle. In this study, two new traits related to milk FA profile were defined: butter softness (BSO) defined as the ratio of unsaturated to saturated FAs, and butter spreadability (BSP) defined as the ratio of C18:1 (cis-9) FA to C16:0 FA. Data of 69 369 test-day records of milk yield (MY), fat percentage (FP), protein percentage (PP), BSO, and BSP collected from 2007 to 2020 on 7 392 first parity, and 5 185 second parity cows distributed in 104 herds throughout Wallonia were used. Mean heritability estimates across lactation were 0.33 and 0.36 for BSO and 0.24 and 0.32 for BSP in the first and second parity, respectively. Mean genetic correlation estimates between BSO and MY, FP, and PP were, respectively, -0.30, -0.38, and -0.01 in the first and -0.31, -0.46 and -0.12 in the second parity. Mean genetic correlation estimates between BSP and MY, FP, and PP were, respectively, -0.27, -0.38, and -0.06 in the first and -0.27, -0.45 and -0.17 in the second parity. Observed moderate (negative) genetic correlations estimated between the examined traits and milk traits indicate that genetic selection for milk traits would decrease quality of butterfat. High positive genetic correlation was found between BSO and BSP; however, BSO showed a higher heritability than BSP. In addition, the prediction of BSO is more efficient than BSP. Therefore, when a choice must be made between these traits, the inclusion of BSO in selection programs appears to be more justified than BSP.
