Four German Merino wethers were maintained on 1600 g of lucerne hay fed twice daily. A dilute solution of a labelled volatile fatty acid (VFA) marker was infused over a period of 22 h and 6 discrete rumen fluid samples were withdrawn at 2 h intervals over the last 12 h of infusion (08h00-20h00)
Total VFA production varied over the period of the feeding cycle, rising 89% from a basal rate of 3,32 moles/ 12 h to a peak of 6,38 moles/ 12 h at 4,5 hours after feeding. The concomitant rise in VFA concentration (39%) was not as great as that of the production and the disparity was ascribed to the dilution of the VFA pool by the intake of fodder and saliva into the rumen during the period of maximum production. VFA production rate cannot, therefore, be predicted with any confidence during this period from the VFA levels present in the rumen.
Pooled rumen fluid samples were constituted from equal aliquots of the 6 discrete samples and analysed together with the above individual samples. No statistical difference (P< 0, 9) was found between the average net total VFA production rate of 4 ,43 moles/ 12 h calculated from the pooled sample data and the arithmetic mean of 4,6 (range 3,32- 6,28) moles/12 h derived from the discrete sample data
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