The objective of this work was to develop a simple method for screening feeds for their potential to increase rumen acid load. It is difficult to undertake in vivo experimentation on this subject owing to the dangers of acidosis as well as the animals’ ability to avoid major changes in rumen conditions. Additionally, the large number of samples involved make it desirable to develop a simple in vitro technique.
A simple in vitro method was developed for estimation of the rumen acid load, based on the dissolution of calcium from calcium carbonate after a period of rumen fermentation. The method was based on the first stage of the method of Tilley and Terry (1963) with some modification to the buffer (which contained MgCl2 instead of MgSO4, 0.025% (w/v) Cystine monohydrochloride and was diluted to 20% in strength). At the end of each incubation, a 2 ml sample was taken, mixed with 0.05 g CaCO3 and centrifuged at 4000 rpm for 10 minutes. The supernatant was analysed for calcium using a Sigma kit (method No. 587) on a discrete analyser. The concentration of calcium (mg per 100 ml) in the supernatant has been termed the acidogenicity value (AV). A series of pilot experiments were conducted to investigate the effects of duration of incubation, buffer concentration, buffer pH and source of rumen liquor.