Effects of Genetic and Non-Genetic Factors on Bovine Milk Cholesterol Content

Dairy products are rich in cholesterol (CHL), therefore monitoring CHL levels in cow milk may become an important factor. The study aimed to a) determine the factors that influence milk CHL content, b) estimate (co) variances and heritability for milk cholesterol, and c) estimate genetic correlations between milk CHL and other production traits. Milk samples were collected from 2,907 cows from 38 commercial herds in Quebec. Milk CHL content was determined by gas chromatography and expressed as mg of CHL in 100 g of total fat (CHL_fat) or in 100 mg of milk (CHL_milk). Test-day milk (Milk), fat (Fat) and protein (Prot) yields, fat (Fat%) and protein (Prot%) percentages and somatic cell counts (SCC) were also determined. A total of 2,418 cows were retained for analysis after editing for registration status, cow, sire/dam identification, breed, age at calving, and stage of lactation. Linear mixed models with fixed effects of test date, parity, age at calving and stage of lactation and random effects of herd-year-season of calving and residual were run to test the significance of fixed effects on CHL. Univariate models were used to estimate (co) variances and heritability; meanwhile bivariate models were used to compute phenotypic and genetic correlations. The mean values of CHL_fat and CHL_milk were 274.60±74.66 mg and 11.27±0.74 mg, respectively. Cholesterol content was significantly affected by stage of lactation but not by parity and age at calving, regardless of the scale of expression (P < 0.05). Heritability estimates for CHL_fat and CHL_milk were 0.09 ± 0.04, and 0.18 ± 0.05, respectively. Phenotypic and genetic correlations between CHL_fat and CHL_milk were 0.85± 0.01 and 0.33± 0.17, respectively. CHL_fat had no significant genetic correlations with Milk, Fat and Prot% (-0.17 to -0.37) and close to zero genetic correlation with Prot and Fat%. CHL_milk also had low non-significant genetic correlations with Fat (0.33) and Prot (-0.39), but moderate and significant genetic correlations with Milk (0.58) and Prot% (0.47) and high genetic correlation with Fat% (0.81). CHL_fat and CHL_milk also had no significant genetic correlations with SCC. This is the first study to estimate genetic parameters for milk CHL content. Further studies on response to selection and genomics are required to assess the possibility of genetically selecting cows with desired CHL content.