Feed Intake Relative to Stage of Lactation for Dairy Cows Consuming Total Mixed Diets with a High or Low Ratio of Concentrate to Forage

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Abstract
This experiment examined the effect of feed quality on the relationship between intake and stage of lactation in dairy cows. Two total mixed diets composed of grass silage and concentrate were formulated. The high concentrate total mixed diet was designed to meet energy requirements, and the low concentrate total mixed diet was designed to limit intake. Twenty-four Holstein-Friesian cows were offered the total mixed diets in a full 2 x 2 change-over design with control treatments. The changeover was at 153 d in milk (DIM). For the statistical analyses, two periods of 13 wk, one period before and one period after the changeover, were used. Dry matter intake (DMI), milk yield, body weight, and body condition score were significantly greater for cows fed the high concentrate total mixed diet than for cows fed the low concentrate total mixed diet. Significant interactions between total mixed diet and period were observed for DMI and milk yield. However, no significant residual effects of changing from one total mixed diet to the other were observed. The interactions were due to substantially different slopes of DMI and milk yield relative to DIM for cows fed the two different total mixed diets. For cows fed the low concentrate total mixed diet, there was no effect of stage of lactation on DMI; the slope was 0. For cows fed the high concentrate total mixed diet, there was a significant decline in DMI as lactation progressed.