In vitro ruminal fermentation, methane production and nutrient degradability as affected by fruit and vegetable pomaces in differing concentrations

Pomaces are food industry by‐products and may serve as animal feed to increase sustainability of meat and milk production. The aim of the present study was to evaluate fermentation characteristics of dried fruit and vegetable pomaces in a short‐term in vitro experiment using the Hohenheim Gas Test. A selection of six fruit (apple, aronia, orange, pomegranate, red, white grape) and three vegetable (beetroot, carrot, tomato) pomaces was tested in three concentrations (150, 300, 500 g kg⁻¹ of dry matter (DM)) as supplement to the basal diet (hay, used as control). Three runs were performed, using rumen fluid from one of three different rumen‐cannulated cows in each run. Per run, each compound was tested in duplicate. After 24 h incubation, total gas production, methane and CO₂ concentration, short‐chain fatty acids, in vitro organic matter digestibility as well as microbial counts were determined. In addition, the pomaces' polyphenol content including the fractions non‐tannin phenols, condensed tannins and hydrolysable tannins were analysed. Most pomaces did not significantly affect rumen fermentation characteristics in any of the tested dosages and may thus be applied in ruminant nutrition without adverse effects. Aronia significantly decreased (−14.5%) the organic matter digestibility in the highest concentration whereas apple (+12%), carrot (+10%) and beetroot (+8%) increased gas formation related to digestible organic matter. The 500 g kg⁻¹ dosage of pomegranate significantly decreased methane formation by about 28% without impairing digestibility. Pomegranate was the only pomace of those high in total tannins that contained exceptionally high amounts of hydrolysable (90% of total tannins) and proportionally low amounts of condensed tannins (10% of total tannins), indicating that the hydrolysable tannins most likely reduced the methane production. Therefore, pomegranate pomace may be an interesting option for a methane mitigating feed supplement in ruminants and should be considered for following in vivo testing.