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Comparison of Techniques to Determine the Clearance of Ruminal Volatile Fatty Acids

J. C. Resende Júnior^*,1, M. N. Pereira, H. Bôer and S. Tamminga

^* Departamento de Medicina Veterinária, and
Departamento de Zootecnia Universidade Federal de Lavras, Lavras, MG, Brazil, 37200-000
Wageningen University, Animal Sciences, Animal Nutrition Group, Wageningen, The Netherlands

¹ Corresponding author: joaocrj{at}ufla.br

The objective of this experiment was to compare measurements of fractional clearance rates obtained by using an unlabeled valerate-CoEDTA technique with measurements obtained by using a ¹³C-labeled volatile fatty acids (VFA) technique. The exponential decay rate of the ¹³C/¹²C ratio after pulse-dosing ¹³C-acetate, ¹³C-propionate, or ¹³C-butyrate into the rumen was compared with the decay rate of rumen valerate concentration following a simultaneous pulse dose. The unlabeled valerate, CoEDTA, and each labeled VFA, one at a time, were concurrently mixed with the evacuated ruminal content of 6 lactating cows in two 3 x 3 Latin squares. The clearance of VFA by passage to the omasum was assumed to be equivalent to the decay in ruminal Co concentration and was around 50% of the total clearance. Acetate, propionate, and butyrate had similar fractional clearance rates (31.2, 33.4, 30.4%/h, respectively), but propionate had a higher absorption rate (19.2%/h) than butyrate (14.2%/h). Linear regression determination coefficients using the valerate clearance rate as an estimator for acetate, propionate, and butyrate rumen clearance were 0.51, 0.56, and 0.99, respectively. In a second experiment, the ¹³C-valerate fractional clearance rate estimate (33.7%/h) was similar to the estimate obtained with unlabeled valerate (35.0%/h) by the valerate-Co technique. No ¹³C enrichment of rumen microbes was noted 4 h after the intraruminal infusion of ¹³C-valerate. Fractional VFA absorption rate estimates obtained in both techniques were similar, although both were lower than estimates reported in the literature by other methods.

Key Words: volatile fatty acid • rumen • clearance rate • absorption

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