Effects of organic and inorganic nitrogen sources on in vitro degradability of citrus byproduct and milk thistle

Abstract

In order to evaluate rumen microbial activity, the effects of two nitrogen sources (organic and inorganic) were analyzed invitro by inoculating dairy cow rumen fluid and using citrus byproduct (CBP) and milk thistle ( Silybum marianum , MT) as energysource substrates. The experimental design was 2 × 3 where we used three different nitrogen sources (N1: no nitrogen added, N2:ammonium bicarbonate, N3: sodium glutamate) with a basic concentration of nitrogen (100 mg/1 L). Culture pH, dry matterdegradability %, ammonia-N (NH 3 -N), total volatile fatty acids (TVFAs), individual volatile fatty acid proportions, and acetatepropionate ratio (A:P) were measured after 24 h of fermentation. Culture pH values were in the optimal range with CBP and MTin all media. Supplementing nitrogen sources had similar tendencies to increase dry matter degradability (P < 0.01) and NH 3 -Nproduction in N2 and N3 with MT and CBP. Glutamate significantly (P < 0.01) increased TVFAs, which were twice as high than inN1 and N2 with MT. These results show that N supplementation had minor effects on in vitro rumen microbiota activity comparedto N1; however, it could be proposed to improve microbial biomass production in mixed rations of agricultural byproducts with localforages.