Genetic associations between milk ß-hydroxybutyrate and fatty acids in early first lactation of Canadian Holsteins

Abstract Text:

Hyperketonemia (or ketosis) is one of the most frequent diseases in dairy cattle. As clinical ketosis is not widely recorded, the level of milk ß-hydroxybutyrate is used as its indicator. Milk fatty acid profile is considered to be related to the energy balance of cows in early lactation. The objective of this study was, therefore, to investigate the genetic associations between milk ß-hydroxybutyrate and milk fatty acids in early first lactation of Canadian Holstein cows. Test-day data were available on milk ß-hydroxybutyrate and five fatty acid groups: short-chain (C₄-C₁₀), medium-chain (C₁₂-C₁₆), long-chain (C₁₇-C₂₂), saturated (no double bond) and unsaturated (one or more double bonds). Only the first cow’s test-day record between 5 and 40 DIM was considered for all traits, because most of the metabolic changes occur over this time period. The data set consisted of 23,345 cow records from 1,541 sires and 2,510 herds. Data were analyzed with a 6-variate linear sire model using the Average Information-Restricted Maximum Likelihood (AI-REML) procedure in the DMU package. Heritability of 0.13 was found for milk ß-hydroxybutyrate. Heritability estimates for fatty acids ranged from 0.10 to 0.29. Genetic correlations between milk ß-hydroxybutyrate and short chain, medium chain and saturated fatty acids were low and not significantly different from zero. Genetic correlations between milk ß-hydroxybutyrate and long chain and unsaturated fatty acids were 0.51 and 0.48, respectively. These results confirm the known relationship between milk ß-hydroxybutyrate and energy balance status in early lactation, explained by the release of long chain fatty acids from the mobilization of body fat reserves.

Keywords: milk ß-hydroxybutyrate, fatty acid, genetic correlation