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

The researchers aimed to understand the fermentation response of equine caecal microbial population to nitrogen availability. They used casein (a protein source) and urea (a non-protein source) as nutrient sources in an in vitro experiment and observed various effects on microbial growth.

Research Methodology

• The research team performed in vitro tests using caecal contents from three cannulated horses. The horses were fed a hay-concentrate diet before their caecal fluid was drawn.
• The caecal fluid was mixed with a nitrogen-free buffer-mineral solution, and nitrogen provision was controlled through the use of casein and urea.
• The fermentative response at four different nitrogen levels (3.7, 6.3, 12.5 or 25 mg of nitrogen in casein or urea) were studied using the gas production technique.

Observations and Measurements

• The team measured levels of Total volatile fatty acids (VFA), NH3-N and gas production after a 24-hour incubation period.
• They estimated microbial biomass using the internal markers adenine and guanine bases. The production of ATP was also estimated using stoichiometric methods.
• The researchers then estimated the microbial growth efficiency (YATP) and gas efficiency (Egas) based on these measurements.

Findings

• Results showed that the type of nitrogen source affected microbial activity. When casein was used as the sole nitrogen source, there was generally lower total VFA, NH3-N, total gas production. However, there was an increased acetate: propionate (A:P) ratio and higher microbial growth efficiency (YATP).
• The results indicated that while the caecal microbial population can use urea nitrogen, it does so less efficiently than it uses casein in terms of microbial growth. This suggests that the type of nitrogen source can significantly impact the health and function of the horse’s digestive system.