De invloed van erfelijkheid en milieu op de samenstelling van de melk bij Friese koeien en de praktische mogelijkheid van selectie op het eiwitgehalte

Abstract

The milk composition of individual cows was studied especially as to protein content. In total 729 cows were tested including 238 dam-daughter pairs, 6 large progeny groups of bulls used in artificial insemination and 20 small progeny groups of bulls in natural service. Milk production, and fat, protein, casein, lactose and solids-not-fat were estimated during lactation.Environmental influences on milk production and composition were studied, e.g. lactation curve, month of calving, age of cow, duration of lactation. The average percentages fat and protein of individual cows were only slightly influenced and generally in the same direction by environmental factors.The variation in protein percentage (σ= 0.17) was smaller than that of fat (σ = 0.27) but this variation was still enough to permit successful selection on percentage protein.The protein percentage was positive correlated with fat content (r = +0.54). The percentage fat and protein were both largely determined by genetic factors (h 2= about 0.7). Taking account of the purpose for which milk was used, e.g. cheese production, especially protein was an economically important component of milk.Protein analysis on a large scale was cheap. For the Netherlands, and for Friesland in particular, it was definitely warranted to base payment for milk on percentages fat and protein and to select both on fat and protein