Effect of linseed supplementation and the K232A polymorphism on milk composition of dairy cows
Summary
Abstract
The diacyl glycerolacyl transferase 1 (DGAT1) gene has been expected to influence milk yield and milk composition (Grisart et al.,2004) various polymorphism of this gene have been reported. One polymorphism of interest causes an amino acid substitution from lysine (K) to alanine (A) on the 232 amino acid place of the diacyl glycerolacyl transferase enzyme. The K allele has been associated with higher fat yield, higher protein and fat concentration and a milk fat composition with more saturated fatty acids. Whereas the A allele has been associated with higher milk and protein yield and a milk fat composition with a higher fraction of unsaturated fatty acids (Schennink et al.,2007). The milk fat composition of milk can be affected by the nutritional supplementation of unsaturated fatty acids to dairy cows like present in for example pasture and linseed oil (Bu et al.,2007). The present study investigated the effect of linseed oil supplementation and the DGAT1 gene on milk composition of dairy cows. Therefore a study was performed with 8 rumen-cannulated dairy cows. Four cows were genotyped homozygote KK and 4 cows were genotyped homozygote AA regarding the DGAT1 polymorphism.
The experiment had a change over design with 2 treatments. The dietary treatments were either the supplementation of 500 gram of linseed oil per day for the duration of 14 days, or the supplementation of 500 gram palm fat per day also for a period of 14 days. Cows were selected and blocked depending on milk yield and the DGAT1 polymorphism. The cows were fed a partial mixed ration composed of 49% grass silage, 33% corn silage, 11% soy bean meal, 5 % rapeseed meal and 2 % premix on a dry matter basis, concentrate mixture was given according to production level. Milk yield was reported and milk samples were taken during the last 4 milkings. The samples were used to determine milk fat, protein and lactose content. Data were analysed by using a two way ANOVA.
In comparison with AA cows KK cows had a higher milkfat and protein content respectively (P =0.02) and (P = 0.03). The KK cows also had a higher fat yield compared to AA cows (P = 0.04) Cows treated with linseed oil produced significantly less fat per day (P = 0.01) and also had a significantly lower fat content ( P = 0.01) No significantly genotype x fat source interactions were found based on the data