Input-Output of Dairy Cows Fed a Complete Ration of a Constant or Variable Forage-to-Grain Ratio

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Abstract
Dairy cows (20) were allotted to 2 treatment groups in a continuous feeding experiment over 2 lactation cycles. Cows in Group 1 were fed ad lib to assure 5% orts, a constant 60:40 forage-to-grain ratio (dry basis) while Group 2 cows were fed 50:50, 63:35 and 85:15 ratios during early (Period 1, 21 wk) and late (Period 2, 23 wk) lactation, and the dry period (Period 3, 8 wk). There was no significant difference between groups in the 2-yr average 308-day actual or 4% fat-corrected milk. The 4% fat-corrected milk production during lactations 1 and 2 for Group 1 was 6591, 6398 and for Group 2 was 6006, 6678 kg. Fat test was higher during early lactation in Group 1; other milk composition data were similar. The 2-yr average daily and yearly total dry matter intakes were not different between treatments. Digestible energy concentration of diets for Groups 1 and 2 during Periods 1, 2 and 3 were: 2.88, 2.93; 2.90, 3.08; and 2.99, 2.93 Mcal/kg dry matter. Cows in Group 2 had a more positive energy balance during early lactation, produced more actual milk, consumed more dry matter, lost less body weight, had higher blood glucose and lower ketone values, showed an earlier postcalving estrus and recovered lost postpartum weight faster than cows in Group 1.