title: Short communication: Using diurnal patterns of (13)C enrichment of CO2 to evaluate the effects of nitrate and docosahexaenoic acid on fiber degradation in the rumen of lactating dairy cows.
abstract: Nitrate decreases enteric CH4 production in ruminants, but may also negatively affect fiber degradation. In this experiment, 28 lactating Holstein dairy cows were grouped into 7 blocks. Within blocks, cows were randomly assigned to 1 of 4 isonitrogenous treatments in a 2×2 factorial arrangement: control (CON); NO3 [21g of nitrate/kg of dry matter (DM)]; DHA [3g of docosahexaenoic acid (DHA)/kg of DM]; or NO3+DHA (21g of nitrate/kg of DM and 3g of DHA/kg of DM). Cows were fed a total mixed ration consisting of 21% grass silage, 49% corn silage, and 30% concentrates on a DM basis. Based on the difference in natural (13)C enrichment and neutral detergent fiber and starch content between grass silage and corn silage, we investigated whether a negative effect on rumen fiber degradation could be detected by evaluating diurnal patterns of (13)C enrichment of exhaled carbon dioxide. A significant nitrate × DHA interaction was found for neutral detergent fiber digestibility, which was reduced on the NO3 treatment to an average of 55%, as compared with 61, 64, and 65% on treatments CON, DHA, and NO3+DHA, respectively. Feeding nitrate, but not DHA, resulted in a pronounced increase in (13)C enrichment of CO2 in the first 3 to 4 h after feeding only. Results support the hypothesis that effects of a feed additive on the rate of fiber degradation in the rumen can be detected by evaluating diurnal patterns of (13)C enrichment of CO2. To be able to detect this, the main ration components have to differ considerably in fiber and nonfiber carbohydrate content as well as in natural (13)C enrichment.
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH, Wageningen, the Netherlands. Electronic address: geronda.klop@wur.nl.
authors.forename: G
authors.initials: G
authors.lastname: Klop
authors.affiliation: Wageningen UR Livestock Research, PO Box 338, 6700 AH, Wageningen, the Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Bannink
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH, Wageningen, the Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Dieho
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH, Wageningen, the Netherlands.
authors.forename: W J J
authors.initials: WJJ
authors.lastname: Gerrits
authors.affiliation: Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH, Wageningen, the Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: Dijkstra
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism*; D002417:Cattle; D004032:Diet / Q000662:veterinary; D004043:Dietary Fiber / Q000032:analysis*; D004063:Digestion / Q000187:drug effects*; D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D005260:Female; D005285:Fermentation; D007774:Lactation; D008697:Methane / Q000096:biosynthesis; D009566:Nitrates / Q000494:pharmacology*; D006109:Poaceae / Q000737:chemistry; D012417:Rumen / Q000187:drug effects* / Q000378:metabolism; D012820:Silage / Q000032:analysis; D013213:Starch / Q000032:analysis; D003313:Zea mays / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D004043:Dietary Fiber; D009566:Nitrates; D002245:Carbon Dioxide; D004281:Docosahexaenoic Acids; D013213:Starch; D008697:Methane
keywords: (13)C enrichment; feed additives; fiber degradation; methane