Lactation Curves and Prediction of Daily and Accumulated Milk Yields in a Multibreed Dairy Herd in Thailand Using All Daily Records

Daily milk records of 88 cows in a multibreed dairy herd were used to describe lactation curves and test the ability of seven models to predict daily milk yields, and accumulated 100-d and 305-d milk yields. The seven mathematical models were a gamma function, a mixed log second-degree polynomial model, and five polynomial regression models. Cows were of three breed groups: Holstein Friesian (HF), 1/2HF-1/2RS (Red Sindhi), and 3/4HF-1/4RS. Lactation number was classified as first, second, third, and fourth-and-later lactations. Calving age was defined as age less than 30 months, and equal to or greater than 30 months for the first lactation; age less than 44 months, and equal to or greater than 44 months for the second lactation; less than 60 months, and equal to or greater than 60 months for the third lactation; and all ages for the fourth-and-later lactations. Seasons of calving were defined as winter (November to February), summer (March to June), and rainy (July to October). Four general types of lactation curves were found: convex, slightly convex, two-peaked, and flat. Types of lactation curves varied across breed group x lactation x calving season and breed group x lactation x calving age subclasses. The second-degree polynomial model was the best in terms of predicted minus actual daily and 305-d milk yields, and computational requirements. For 100-d milk yield the best model was the sixth degree polynomial model. The application of these results is limited to HF x RS multibreed herds in the Northeastern region of Thailand. To further help national genetic evaluation efforts, this study needs to be repeated with a data set that is representative of the national Thai dairy cattle population.