The influence of casein and urea as nitrogen sources on in vitro equine caecal fermentation

• Published in: Animal (Cambridge, England) Vol. 6; no. 7; pp. 1096 - 1102
• Main Authors: Santos, A. S., Ferreira, L. M. M., Martin-Rosset, W., Cotovio, M., Silva, F., Bennett, R. N., Cone, J. W., Bessa, R. J. B., Rodrigues, M. A. M.
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01-07-2012; Elsevier Limited; Published by Elsevier (since 2021) / Cambridge University Press (until 2020); Elsevier
• Subjects: acetates; adenine; adenosine triphosphate; amino-acids; ammonium nitrogen; Animals; caecal fermentation; cannulas; casein; Caseins - metabolism; cecum; Cecum - metabolism; Cecum - microbiology; Computer Science; diet; digestibility; Dose-Response Relationship, Drug; energy; equine hindgut; Fatty Acids - metabolism; fermentation; Fermentation - drug effects; gas-production; guanine; Horses; Humanities and Social Sciences; in vitro; in vitro studies; In Vitro Techniques; invitro; kinetics; Life Sciences; metabolism; Methane - biosynthesis; microbial biomass; microbial growth; Models, Statistical; nitrogen; Nitrogen - metabolism; Nitrogen - pharmacology; Nutrition; peptides; ponies; propionic acid; protein; rumen microbial-growth; urea; Urea - metabolism; urea nitrogen; volatile fatty acids; casein; equine hindgut; caecal fermentation; in vitro; urea; PROTEIN; INVITRO; PONIES; RUMEN MICROBIAL-GROWTH; PEPTIDES; METABOLISM; AMINO-ACIDS; KINETICS; GAS-PRODUCTION; DIGESTIBILITY
• ISSN: 1751-7311; 1751-732X; 1751-732X
• DOI: 10.1017/S1751731111002527

To access the fermentative response of equine caecal microbial population to nitrogen availability, an in vitro study was conducted using caecal contents provided with adequate energy sources and nitrogen as limiting nutrient. Two nitrogen (N) sources were provided, protein (casein) and non-protein (urea). Caecal fluid, taken from three cannulated horses receiving a hay–concentrate diet, was mixed with a N-free buffer–mineral solution. The influence of four N levels (3.7, 6.3, 12.5 or 25 mg of N in casein or urea) was studied using the gas production technique. Total volatile fatty acids (VFA), NH3-N and gas production were measured after a 24-h incubation period. Microbial biomass was estimated using adenine and guanine bases as internal markers, and ATP production was estimated stoichiometrically. Microbial growth efficiency (YATP) and gas efficiency (Egas) were estimated. Fermentation with casein as the sole N source was generally characterized by lower total VFA, NH3-N, total gas production and higher acetate : propionate (A : P) ratio and YATP than with urea. Results herein presented indicate that, under these in vitro conditions, caecal microbial population does in fact use urea N, but less efficiently than casein in terms of microbial growth.