Heritability and correlations among milk yield, Body Condition Score and type traits in the Italian Mediterranean Buffaloes (Bubalus bubalis)

The objective of the present study was to estimate variance components between milk yield and type traits, including Body Condition Score (BCS) in the Italian Mediterranean Buffaloes. Type evaluation in the Italian Mediterranean Buffaloes began in 2000 including thirty traits, namely seven composites, twenty-two linear and BCS. Composite traits included final score (FS), structure (ST), feet and legs (FL), dairy characters (DC), dairy strength (DS), udder (UT) and yield potential (YP). Linear traits included twelve, two and eight traits respectively, for structure, feet and legs and udder. In 2009, the first official genetic evaluation for type traits was introduced but it did not include milk yield and BCS as correlated traits. The data analysed included 6199 buffalo cows and a pedigree file with 17,773 animals. A multi-trait animal model was fitted using a Bayesian implementation via Gibbs sampling. The fixed part of model included the following effects: herd-year of evaluation-classifier, days in milk (30 days class), age nested within parity and number of lactations. Animal and residual effects were treated as random. Traits analysed included five composite traits (FS, ST, FL, YP, UT), BCS, nine linear scores (stature, body depth, body length, Foot angle, Fore Udder Attachment, Rear Udder Width, Udder Depth, Teat Placement and Teat Length) and milk yield at 270 days. Heritability estimates for the type traits varied from 0.09 to 0.43, the largest was for stature. Genetic correlation between type traits and milk yield ranged from -0.21 (Udder Depth) to 0.50 (Rear Udder Width). BCS had a null genetic correlation with milk yield at 270 days (-0.03). This result suggests that the possible inclusion of BCS in an aggregate index will not affect genetic response for milk yield. Rear Udder Width was positively correlated with both Fore Udder Attachment (0.75) and Teat placement (0.48) but negatively correlated with Udder Depth (-0.31) and Teat Length (-0.12). Fore Udder attachment had the same pattern. Teat length and Teat Placement had a mild negative correlation (-0.16). Excluding FL, foot angle and Teat Length, whose heritability was around 0.10, all the other traits showed moderate to high heritabilities suggesting reasonable and accurate response to selection. A multi-trait approach will help to cope with the expected low accuracy of some traits.