Effects of extruded tannin-enriched protein concentrates on nitrogen partitioning in sheep fed a corn silage-based diet

Abstract

Soybean meal has high ruminal degradability, which can reduce nitrogen utilization efficiency by increasing ammonia production. Excess ammonia not used by microbes is converted to urea and excreted, causing metabolic and environmental losses. Soybean expeller and tannin supplementation are used to reduce ruminal protein degradation. This study evaluate the impact of including tannin-treated protein concentrates during the extrusion process on N partitioning in sheep fed maize silage-based diets. A digestibility trial was conducted in metabolic cages using eight castrated male Santa Inês lambs. The experimental design was a 4×4 double Latin square, with four periods of 17 days each, including 10 days of adaptation and 7 days of sample collection. Four experimental diets were offered, consisting of 60% corn silage and 40% concentrate (dry matter (DM) basis) composed of corn grain and one of the following protein sources: soybean meal (SM), soybean expeller (SE), SE plus tannins diluted in water (TA) or in sodium hydroxide solution (TH). Tannins were added to 1% of the SE.  During the sample collection period, individual intake and fecal output were recorded. Samples of feeds, refusals, and feces were collected and analyzed for N, and digestibility was calculated. Statistical analysis was analyzed with the MIXED procedure of SAS. Nitrogen intake tended to be higher in SM than in other treatments (P = 0.09). Fecal N excretion was lower in TA and SE compared to TH (P < 0.05). Urinary N excretion was higher in SM than in SE, TA and TH (P < 0.01). Nitrogen retention and digestibility were similar among treatments. Expressed as a proportion of ingested N, treatments had no effect N excretion, or N retention. Replacing SM with SE reduced urinary nitrogen excretion, but the inclusion of tannins during the extrusion process of SE had no additional effect on nitrogen partitioning.