EFFECTS OF INTERACTION BETWEEN GENOTYPE AND FEEDING SYSTEM ON MILK-PRODUCTION, FEED-INTAKE, EFFICIENCY AND BODY TISSUE MOBILIZATION IN DAIRY-COWS

The objective of this study was to investigate genotype by feeding system interactions in Holstein-Friesian dairy cows. For this purpose, selection (S) and control line (C) cows, housed and managed at the Langhill Dairy Cattle Research Centre, were offered ad lib. complete mixed diets, with proportions (in total DM) of concentrates, silage and brewers grains of either 20:5: 75 (LC) or 45:5:50 (HC), over a full lactation. No significant feeding system x genetic line interactions were observed for a number of traits, describing milk production, feed intake, efficiency and body tissue mobilisation, when compared as treatment means (128 heifer lactations and 249 cow lactations). However, regression coefficients of milk yield (P < 0.01) and condition score (P < 0.05) on pedigree index for fat plus protein yield were significantly different between LC and HC. This indicates that G X E might become of importance in the future, with continued selection for fat plus protein yield.