DIFFERENTIATION OF LINEAR PROFILES OF BULLS WITH DIFFERENT LEVELS OF MILK FAT AND PROTEIN CONTENT IN DAUGHTERS

Abstract

The paper presents the results of a study of the pattern of changes in the linear profiles of Holstein sires groups depending on the level of milk fat and protein in their first-calf daughters. The study was conducted at a breeding farm in the Novosibirsk Region from 2017 to 2023. Data on 18 linear exterior and productivity traits (milk fat and protein content over 305 days of lactation) of 1243 first-calf cows obtained from 28 sires, mainly of North American origin, were analyzed. The bulls were divided into 8 groups depending on the level of milk fat and/or protein in their daughters. Exterior profiles of the bulls were constructed and analyzed. It was found that all the animals studied had a pronounced milk body type. However, full compliance with the optimal scores in all groups was observed only for body strength and foot angle. It was found that selection of bulls based on daughters with high milk fat content was accompanied by improvement of udder features (udder cleft, rear udder height) and limbs, but decreased scores for body features (rump length, pin width, milk forms, stature) and some udder parameters (teat length, rear udder width). Similar changes (e.g., decreased height, pelvic position, nipple length) were observed during selection based on protein content. Selection for simultaneous increase of milk fat and protein (fifth group) showed the best results for udder attachment. Selection for increase of milk fat and/or protein content in daughters leads to regular changes in exterior profiles of sires. This emphasizes the need for an integrated approach to selection.