A DAIRY RECORDS STUDY OF THE EFFECTS OF FEEDING LEVELS ON MILK YIELD AND COMPOSITION

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Abstract
A total of 139,720 Holstein and 17,259 Ayrshire 305-day lactation records from the Dairy Herd Analysis Service were studied to estimate linear and quadratic effects of net energy intakes from silage, hay, pasture and meal and effects of silage:hay ratio, roughage:meal ratio and energy concentration on milk yield and composition. Effects of correcting for feeding levels on estimates of herd and cow variance components were studied also. Linear effects of increased net energy intakes from silage, hay, pasture and meal on milk, fat and protein yields were positive (P <.01) for both breeds. For Holsteins, all quadratic effects on milk yield were also positive (P <.01). Quadratic effects of each roughage source on fat and protein yield were negative, but meal had a positive quadratic effect (P <.01). Quadratic effects were inconsistent for the Ayrshires. Both linear and quadratic effects of feeding levels on fat and protein percent were inconsistent for the two breeds. For both breeds, greater silage:hay ratios and energy concentrations increased yields, and greater roughage:meal ratios decreased yields and fat percent (P <.01). Correcting records for net energy intake reduced estimates of herd, cow and error variance components. Repeatability estimates of yield traits were also reduced, but percentage trait repeatabilities were not altered.