Digestion during continuous culture fermentation when replacing perennial ryegrass with barley and steam-flaked corn

• Published in: Journal of dairy science Vol. 92; no. 1; pp. 189 - 196
• Main Authors: Wales, W.J., Kolver, E.S., Egan, A.R.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.01.2009; American Dairy Science Association; Am Dairy Sci Assoc; Elsevier
• Subjects: Animal productions; Bacteria - metabolism; barley; Biological and medical sciences; concentrate supplementation; continuous culture fermentation; corn; cow feeding; crude protein; dairy cows; Diet - veterinary; dietary carbohydrate; Dietary Fiber - metabolism; Dietary Proteins - metabolism; digesta; digestibility; digestible protein; digestion; Digestion - physiology; dry matter content; fatty acid composition; Fatty Acids, Volatile - analysis; feed concentrates; feed grains; feed intake; feed supplements; Feeding. Feeding behavior; feeds; Fermentation; forage grasses; Fundamental and applied biological sciences. Psychology; Gastrointestinal Contents - chemistry; Gastrointestinal Contents - microbiology; highly digestible pasture; Hordeum - metabolism; Hydrogen-Ion Concentration; in vitro studies; Lolium - metabolism; neutral detergent fiber; Nitrogen - analysis; nutrient availability; Regression Analysis; rumen fermentation; rumen fluids; Terrestrial animal productions; Time Factors; Vertebrates; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Zea mays - metabolism; highly digestible pasture; concentrate supplementation; digestion; continuous culture fermentation; Barley; Corn; Digestion; Fermentation; Water vapor; Feeding; Pasture; Dairy industry; Cereal; Concentrate; Supplementation
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2008-1223

The objective of this study was to quantify the optimal inclusion rate of grain required to maximize nutrient digestion of a diet based on highly digestible pasture. It was hypothesized that maximum digestion would occur at a rate of grain inclusion that resulted in a culture pH of 6.0, reflecting the pH below which fiber digestion would be expected to be compromised. Four dual-flow continuous culture fermenters were used to establish the effects on digestion of replacing freeze-dried, highly digestible ryegrass with 0, 15, 30, and 45% of dry matter as 60% barley, 35% steam-flaked corn, and 5% molasses mix. The respective composite diets were fed twice daily to mimic intake patterns observed in dairy cows offered supplements during milking and offered half their daily allowance of pasture after each milking. Digesta samples were collected during the last 3 d of each of four 9-d experimental periods. Average daily culture pH decreased linearly as proportion of cereal grain in the diet increased, with average daily pH ranging from 6.29 to 5.74. Concentrations of neutral detergent fiber and total fatty acids decreased linearly with increasing proportion of cereal grain in the diet. Digestion of organic matter (OM) was maximized at an interpolated value of 24% grain inclusion and culture pH of 6.0, but the difference in the OM digestibility over the range of grain treatments from 0 to 45% was small (3 percentage units) despite pH changes over a range of 6.3 to 5.7. The relatively small change in OM digestibility was explained by reduced fiber and crude protein digestibilities being balanced by an increased digestion of nonstructural carbohydrate. Although different relationships between ruminal pH and digestibility appear to exist when cows are fed pasture alone compared with a total mixed ration, when starch supplements are included in pasture diets, the relationships associated with feeding a total mixed ration may then be more likely to apply.