Comparison of milk-related traits’ heritability evaluated by functional controls vs Automatic Milking Systems

Heritability (h2) is one of the key attribute to be studied in order to assess the potential use of a trait in genomic selection. By definition, h2 is relative to the specific animal population in which it is evaluated and is highly influenced by the measurements of the phenotypes involved. Therefore, the technologies used to record data should be carefully selected. Milk-related traits are measured by monthly milk composition analyses (MCA) in which different phenotypes (i.e., milk yield, somatic cell count, and fat percentage) are measured and are therefore considered as a gold standard measurements. Nowadays, however, Automatic Milking Systems (AMS) are increasingly available in commercial dairy farms and can record the same traits as the functional controls on a daily basis. The measurement technology is, however, not the same. In this study we compared the h2 evaluated on different milk-related traits measured by functional controls and AMS in 5 Holstein Friesian dairy farms in a 6.35 years’ time period (18,813 observations, 1810 cows). Correlations between the same milk-related trait measured with both MCA and AMS were calculated. Lastly, pedigree-based h2 of the studied traits from the two different strategies was evaluated (using the breedR package for R) and then compared for each couple of traits. Milk yield h2 was similar comparing the two measurement technologies (28% AMS vs 25.3% MCA). Differently, h2 of the other milk-related traits differed when estimated on data from the two involved technologies. The results obtained in this preliminary study confirmed the importance of the methods used in phenotypes recording.