Abrupt Changes in Forage-Concentrate Ratios of Complete Feeds Fed Ad Libitum to Dairy Cows

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Abstract
Effects of abrupt changes in energy of complete feeds offered individually ad lib to 68 lactating cows plus the effect of drying off on intake of diets in late lactation and early dry period were studied. Diets were 95:5, 80:20, 60:40 and 40:60 ratios of forage to concentrate dry matter. On day 84 postpartum, 17 of the cows on 60% forage were switched to 40%, and 17 of those on 40% were switched to 60%. Remaining cows on both diets continued without change. Abrupt increase in concentrate caused increased consumption of dry matter and energy, yield of milk and solids-corrected milk, percentage milk protein, and ruminal concentrations of propionate and total acids, and decreased percentages of milk fat, total solids, ruminal pH, decreased concentration of butyrate, and acetate:propionate ratio. Increased forage had opposite effects. On day 210 postpartum, cows were changed factorially from 60 and 40% to 95 and 80%. Increased forage reduced consumption of dry matter and energy and milk production. Ruminal changes suggested a slight disruption in fermentation due to abrupt changes of diet, but adaptation occurred within 15 days. Drying cows off at 305 days caused reduced intake of dry matter and energy, but cows fed 95 and 80% overconsumed calculated net energy requirements by 18.5 and 30.3%.