I saw many papers calculating the Acetic : Propionic acid ratio when they do experiment about ruminal fermentation, both in vitro and in vivo. But I don't fully understand about its meaning. Could you please tell me? Thank you in advance.
Acetic acid is milk fat precursor, it is produced more from fermentation of fodder, whereas, butyrate is produce more as a result of fermentation of grain, it reduces milk fat, hence more butyrate is not desirable.
The ratio has a significance both in milk fat synthesis as well as ruminal acidosis which are the major problems when rations are fed in disproportionate content of concentrate and roughage. as if the concentrate part is more it will produce more propionate and butyrate which could result acidosis and milk fat depression.
Even though VFAs produced by rumen fermentation are absorbed very rabidly from the GIT without significantly affecting rumen pH, the proportion of Acetate to propionate tell us the kind of diet that has been fermented by the animals (fed to the animal). The more roughage ingredients in the total ration then the more is the proportion of Acetate: propionate while increasing the proportion of concentrate in the total ration will reduce the absolute amount of Acetate and increase propionate but still the percent proportion of Acetate out of the total VFA is greater than propionate. Therefore, the proportion of Acetate:propionate in the diet is a good indicate of milk fat synthesis in ruminant as mentioned by other colleagues.
The proportion of acetate:propionate is not only a good indicator of milk fat synthesis, it equally affects the performance of an animal. Since propionate is glucogenic, lower acetate:propionate ratio indicates increased production and availability of energy for nutrient utilization, growth, milk production/lactation, foetal development in pregnant animals, etc. depending on the physiological state of the animal. Lower acetate:propionate improves ruminal fermentation efficiency as energy is available for rumen microbes activities. Conversely, higher acetate:propionate has some implications on the performance of an animal. For instance in dairy animals, higher acetate:propionate tends to result in higher butterfat than milk yield (i,e., increased milk fat at the expense of milk yield).
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