The influence of casein and urea as nitrogen sources on in vitro equine caecal fermentation
A.S. Santos,
L.M.M. Ferreira,
W. Martin-Rosset,
M. Cotovio,
F. Silva,
R.N. Bennett,
J.W. Cone,
R.J.B. Bessa,
M.A.M. Rodrigues
Affiliations
A.S. Santos
Animal Production Group, Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
L.M.M. Ferreira
Animal Production Group, Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
W. Martin-Rosset
Institut National de la Recherche Agronomique, Center of Research of Clermont-Ferrand, Theix, 63122 Saint-Gene's-Champanelle, France
M. Cotovio
Animal Production Group, Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
F. Silva
Animal Production Group, Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
R.N. Bennett
Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
J.W. Cone
Animal Nutrition Group, Department of Animal Science, Wageningen University, Marijkeweg 40, 6709 PG Wageningen, The Netherlands
R.J.B. Bessa
Interdisciplinary Centre of Research in Animal Health (CIISA), Faculdade de Medicina Veterinária, Technical University of Lisbon, Lisboa, Portugal
M.A.M. Rodrigues
Animal Production Group, Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro, PO Box 1013, 5001-801 Vila Real, Portugal
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.
