Genetic parameters of type traits in two strains of dual purpose autochthonous Valdostana cattle

Abstract

The main objectives of this study were (i) to investigate the best fitting model for the genetic analysis of type traits and (ii) to estimate the genetic parameters of 4 composite (body size, muscularity, body shape, and udder) and 22 individual type traits between and within the two strains of the Valdostana dual purpose breed: the Aosta Red Pied (ARP; n=25,183 records) and the Aosta Black Pied and Chestnut (ABP-CHES; n=14,701 records). All type traits were scored from 2000 to 2012 on primiparous cows using a 1 to 5-point scale system. A model comparison was undertaken by considering the Akaike Information Criterion values obtained from the analysis, producing a final model that took into account the effects of herd-year-classifier, days in milk, age at calving as fixed and the animal additive genetic effect as random. Heritability estimates obtained through single trait animal model analysis varied from 0.03 for thinness (in both strains) to 0.32 (ARP) and 0.29 (ABP-CHES) for stature. Medium-low heritability estimates were obtained for individual muscularity traits (0.22 for ARP and 0.13 for ABP-CHES), and for individual udder type traits (0.12 on average in both Valdostana strains). The highest genetic correlations between composite traits were for muscularity with body shape in both Valdostana strains (0.55 for ARP and 0.52 for ABP-CHES). Different and opposite values of genetic correlations were found for the composite body shape and the composite udder traits (0.13 for ARP and –0.25 for ABP-CHES; P<0.01), probably due to the different breeding purposes set up for the two Valdostana strains. Regarding the individual type traits, for the ARP strain the highest genetic correlation was 0.97 (between thigh, buttocks side and rear view), whereas for the ABP-CHES strain it was 0.98 (between stature and body length), meaning that improving one trait of each pair led to a positive variation in the other. Most of the genetic correlations between the individual muscularity traits and the individual udder traits were negative, especially those involving udder volume (from –0.19 to –0.42 in ARP, and from –0.17 to –0.41 in ABP-CHES; P<0.01), indicating a substantial antagonistic situation of type traits related to dairy and beef traits. In conclusion, the selection for the dual purpose in local breeds such as in Valdostana cattle implies a thorough consideration of opposite morphological traits.