Effect of Low and High Fill Diets on Dry Matter Intake, Milk Production, and Reproductive Performance During Early Lactation

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Abstract
Feedstuffs analyzed for rate and extent of ruminal neutral detergent fiber disappearance were used to formulate 2 diets that differed for predicted time required for rumineal clearance of neutral detergent fiber. Diets with slow and fast estimated disappearance rate of neutral detergent fiber were termed high and low fill, respectively. For both diets, crude protein, acid detergent fiber, neutral detergent fiber, net energy of lactation, and soluble protein were similar. Lactating cows (28) were limit fed the rations 2 wk prior to calving, then fed for ad lib consumption until 8 wk after calving. Cows fed low fill produced more milk (30.3 vs. 26.3 kg) and milk protein (0.97 vs. 0.78 kg) and had higher incidence of short estrous cycles and fewer acyclic cows by 8 wk postpartum than cows offered high fill. Dry matter intake, fat-corrected milk yield, daily fat production, and solids-no-fat did not differ between diets. Rumen fermentation measurements for pH and NH3-N concentrations also did not differ between diets. Cows fed low fill tended to have higher rates of solids and liquid turnover and lower total dry matter in the rumen compared with cows fed high fill. Low ruminal pH on both diets as well as other physiological mechanisms may have been responsible for failure of rates of neutral detergent fiber disappearance to affect intake of dry matter.