Pasture Intake and Substitution Rate Effects on Nutrient Digestion and Nitrogen Metabolism during Continuous Culture Fermentation

• Published in: Journal of dairy science 2003-04, Vol.86 (4), p.1330-1340
• Main Authors: Bargo, F., Varga, G.A., Muller, L.D., Kolver, E.S.
• Format: Article
• Language: English
• Subjects: Ammonia - analysis; ammonium nitrogen; animal feeding; Animal Nutritional Physiological Phenomena; Animal productions; Animals; Bacteria - metabolism; Biological and medical sciences; Cattle - physiology; chemical composition; continuous fermentation; Diet; Dietary Fiber - metabolism; Dietary Proteins - administration & dosage; Digestion; dry matter intake; Eating; Energy Intake; Fatty Acids, Volatile - analysis; feed concentrates; Female; Fermentation; forage; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; in vitro digestibility; in vitro digestion; laboratory techniques; N metabolism; Nitrogen - analysis; Nitrogen - metabolism; nitrogen balance; nonprotein nitrogen; nutrient digestion; nutrient utilization; nutrition physiology; pasture; pasture plants; Rumen - metabolism; substitution rate; Terrestrial animal productions; Vertebrates
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(03)73718-7

A continuous culture system was used to investigate ruminal digestion in response to increased pasture intake and three different substitution rates (SR) in a 4×4 Latin square design. The treatments were 1) low pasture (55g dry matter (DM)/d, 2) medium pasture (MP, 65g DM/d), 3) high pasture (75g DM/d), and 4) pasture (45g DM/d) plus concentrate (PC, 30g DM/d). Treatments were designed to produce a low (0.33), medium (0.67), and high (1.00) SR (g of pasture/g of concentrate) by contrasting the low, medium, and high pasture intake treatments with the pasture plus concentrate treatment, respectively. Pasture was fed at 0630, 1000, 1730, and 2100h, and concentrate at 0600 and 1700h. Digestibility of DM and neutral detergent fiber were not affected by the amount of pasture. As the amount of pasture increased, pH decreased linearly, and total volatile fatty acid and NH3-N concentrations, and nonammonia N and bacterial N flows increased linearly. Concentrate supplementation did not affect DM digestibility at high SR but increased DM digestibility at low SR. Concentrate supplementation reduced pH and NH3-N concentrations at the three SR. Concentrate supplementation reduced the ratio of rumen degradable N to rumen degradable organic matter; however, the mechanism depended on the SR. High SR, concentrate supplementation reduced rumen degradable N, which reduced NH3-N concentration without affecting bacterial N flow. At low SR, concentrate supplementation increased rumen degradable organic matter, which reduced NH3-N concentration and increased bacterial N flow. Based on these results, at low SR, concentrate supplementation may enhance animal performance because of higher total DM intake and synthesis of microbial protein.