Evaluation of the body conformation traits by system FleckScore and its relationship to longevity of Slovak Simmental cows

The relationship between the body conformation traits and longevity in dairy cattle has been explored of many authors by different approaches (Sewalem et al.; 2004, Zavadilová et al., 2011; Imbayarwo-Chikosi et al., 2016; Novotný et al., 2017 and others). Composite traits and udder type traits have been used as indicator for length of productive life (Morek-Kopec and Zarnecki, 2012; Novotný et al., 2017). FleckScore system is new quality factor in the exterior assessment. Evaluation of the body conformation traits reflects the optimisation of the length of productive life in Simmental breeds in the Europe (Anzenberger, 2012; Ondráková, 2014).


Introduction
The relationship between the body conformation traits and longevity in dairy cattle has been explored of many authors by different approaches (Sewalem et al.;2004, Zavadilová et al., 2011Imbayarwo-Chikosi et al., 2016;Novotný et al., 2017 and others). Composite traits and udder type traits have been used as indicator for length of productive life (Morek-Kopec and Zarnecki, 2012;Novotný et al., 2017). FleckScore system is new quality factor in the exterior assessment. Evaluation of the body conformation traits reflects the optimisation of the length of productive life in Simmental breeds in the Europe (Anzenberger, 2012;Ondráková, 2014).
The aim of this study was to evaluate relationship between longevity and the composite type traits in Slovak Simmental cows using Weibull proportional hazard model.

Data
The data were provided by the Breeding Services of Slovak Republic, s.e. and Association of Slovak Spotted Cattle Breeders -Cooperative. The data comprised of 2596 Slovak Simmental cows with the first calving between February 2018 and February 2020. All cows were scored for type traits by system FleckScore in the first lactation. The composite traits as frame, feet and legs, muscularity and udder were evaluated in the interval between 68 and 93 points. Longevity was characterised as length of productive life (LPL) expressed as the number of days between the first calving to culling or censored. 85% data were censored by reason that cows have not been yet culled at the end of study or did not reach milk production higher as 1,700 kg.

Model
The analyses were performed by the Survival Kit, v6.1 (Ducrocq et al., 2012). A Weibull proportional hazard model was used: where: Λ(t) -the hazard function for a given cow at time t; Λ 0 (t) -the Weibull baseline hazard function; p -parity (n = 2); m -the milk production classes, expressed as a standard deviation from within-herd-year average (n = 6); hs -the herd size expressed as increase or decrease number of cows in comparison with last year (n = 6); a -age at first calving (n = 5); hys -the random time-dependent effect of the herd-year-season interaction with change points at April 1 and October 1 in each year (n = 219); pedigree included of 109 sires of cows; trait -composite trait -analyse was performed four times, separately for each trait Traits were grouped to 5 classes. Relationship between LPL and level of composite traits were expressed as the relative risk of culling (ratio of the estimated risk of being culled under the influence environmental factors relative to the reference risk (= 1). Risk ratio >1 represents a higher culling risk and vice-versa.   Figure 1 shows relative risk of culling for the four composite traits. The highest number of records in class was given as the reference level. The lowest risk of culling was found at the score between 84 and 93 for muscularity (0.591), the score between 77 and 79 points for udder (0.879) and feet and legs (0.751) and at the 80 points for frame (0.816). Clear linear decreasing trend of relative risk culling was observed on muscularity trait with the highest risk of culling in class of the least muscular cows. Comparable trend was recorded also on udder trait. Zavadilová et al. (2011) found the lowest risk of culling at the score 80-84 points for udder and feet and legs in Holstein cows. The relationship between longevity and type trait confirmed also Sewalem et al. (2004) that reported linear relationship between mammary system and longevity. Udder traits, such as fore udder attachment, udder texture, and udder depth, were the most important, with a strong relationship with functional survival of cows. Sawa et al. (2013) calculated the highest phenotypic correlation between lifetime performance and udder score (r = 0.22) and legs and feet (r = 0.13). Imbayarwo-Chikosi et al. (2016) found that among the udder traits, fore teat placement had the greatest influence in the relative risk of culling cows. Novotný et al. (2017) confirm genetic correlations of udder depth and two composite traits -udder and feet and legs with functional longevity. Authors stated that selection for fore and rear udder length and high rear udder attachment may contribute to high length of productive life of Czech Fleckvieh cattle.

Figure 1
Risk ratio of culling for composite traits

Conclusions
Longevity and length of functional productive life of cows are result of many factors interaction such as health condition, management, environment, welfare and others. An indirect estimation of length of productive life by Fleckscore system evaluation of conformation traits reflects all factors mentioned above.