Genetic Parameters for Test-Day Electrical Conductivity of Milk for First-Lactation Cows from Random Regression Models

• Published in: Journal of dairy science Vol. 87; no. 6; pp. 1917 - 1924
• Main Authors: Norberg, E., Rogers, G.W., Goodling, R.C., Cooper, J.B., Madsen, P.
• Format: Journal Article
• Language: English
• Published: Savoy, IL Elsevier Inc 01.06.2004; Am Dairy Sci Assoc; American Dairy Science Association
• Subjects: Animal productions; Animals; Bayes Theorem; Biological and medical sciences; bovine mastitis; Cattle - genetics; Cattle - physiology; dairy cattle; dairy cows; disease detection; Electric Conductivity; electrical conductivity; environmental variance; Female; Food industries; Fundamental and applied biological sciences. Psychology; genetic correlation; genetic variance; heritability; indicator traits; Lactation - genetics; Lactation - physiology; mastitis; Mastitis, Bovine - diagnosis; Mastitis, Bovine - physiopathology; mathematical models; milk; Milk - chemistry; Milk and cheese industries. Ice creams; Models, Genetic; Models, Statistical; phenotypic variation; Predictive Value of Tests; quantitative traits; random regression model; Regression Analysis; repeatability; selection criteria; Sensitivity and Specificity; statistical analysis; Terrestrial animal productions; Vertebrates; RR; mastitis; COP; AG; random regression model; dairy cattle; MSEP; PE; AIC; electrical conductivity; BIC; EC; 2lnΛ; Farming animal; Electrical conductivity; Lactation; Dairy cattle; Dairy product; Ox; Genetic parameter; Cow; Vertebrata; Mammalia; Regression model; Dairy industry; Artiodactyla; Day; Ungulata; Milk
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(04)73350-0

Electrical conductivity (EC) of milk has been introduced as an indicator trait for mastitis during the last few decades. The correlation of EC to mastitis, easy access to EC data, and the low cost of recording are properties that make EC a good indicator trait for mastitis. In this study, EC was measured daily during the lactation and available from 2101 first-lactation Holstein cows in 8 herds in the United States. Data were analyzed with an animal model that included herd-test-day, age at calving and days in milk (DIM) as fixed effects, and random additive genetic and permanent environmental effects. A repeatability model and 5 random regression (RR) models with increasing order of Legendre polynomials were used. The goodness of fit for the different models was evaluated based on several tests. Our results indicate that the best model was a RR model with a fourth-order Legendre polynomial for both additive genetic and permanent environmental effects. Heritability estimates obtained with this model were from 0.26 to 0.36. Due to the relatively high heritability obtained for EC of milk, EC might be a potential indicator trait to use in a breeding program designed to reduce the incidence of mastitis.