A data analysis on the effect of acetic acid on dry matter intake in dairy cattle

Silage is the main source of acetic acid in ruminant diets. In most silages, acetic acid is the fermentation product with the second highest concentration, after lactic acid. As it inhibits yeasts and therefore improves aerobic stability of silages, moderate concentrations of up to 30 g/kg dry matter (DM) are often recommended. However, acetic acid may impair the DM intake (DMI) by ruminants, most probably due to its sensory characteristics. The objective of this data-analysis was to evaluate the effect of the dietary content of acetic acid on the DMI in dairy cattle. Either rations containing silages inoculated with hetemfermentative Lactobacillus buchneri or rations treated with pure acetic acid were included in the dataset. Data analysis was performed with a mixed model, including random effects of experiment (intercept and slope) and fixed effects of acetic acid concentration (intercept, linear and quadratic terms). A broken-line regression showed the best goodness of fit (the lowest corrected Akaike's information criterion and the largest R-2 -adj = 0.77). Per 100 kg body weight (BW), an increase of 1 g acetic acid/kg DM led to a reduction of 1.2 g in DMI for acetic acid concentrations < 17.3 g/kg DM. From 17.3-60 g acetic acid/kg DM, DMI reduction was 5.6 g for each additional g of acetic acid in DM (per 100 kg BW). Therefore, dairy nutritionists should consider the content of acetic acid in fermented ingredients upon balancing the diet, to avoid DMI depression (< 17 g/kg DM). Considering typical proportions of silage in diet, current recommendations for the upper limit of acetic acid in silages might, from the perspective of maximizing DMI, be too high and therefore warranting reconsideration.