Verification of equations to predict dry matter intake of dairy heifers

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Virginia Tech

Diets of varying forage base were fed to dairy heifers to test the accuracy of an prediction equation to accurately predict dry matter intake (DMI). Heifers ranging from 120 to 430 kg body weight, were randomly assigned to treatments with forage bases of 1) 100% corn silage, 2) 75% corn silage : 25% alfalfa haylage, 3) 50 % corn silage : 50% alfalfa haylage, or 4) 25% corn silage : 75% alfalfa haylage. Diets were fed for an average of 187 days. Rations were formulated to meet NRC requirements for .68 kg ADG and reformulated monthly. Animals consistently gained an average of .8 kg per day. Statistical analysis showed actual DMI to be significantly less than predicted levels of DMI. The correlation coefficient of actual DMI to predicted DMI was .59. In spite of increased rates of gain, differences due to treatment, ration acid detergent fiber (ADF) and season were not significant. Depressed intake may be the result of metabolic control of intake as ADG approaches .8 kg. This suggests that current recommendations for TDN may be excessive for dairy heifers reared in confinement.