PS5-28. Effects of Ground Pecan Shell Supplementation on In Vitro Gas Production Kinetics and Ruminal Fermentation.

Abstract Pecan shells are an agro-industrial by-product rich in phenolics and antioxidants. Previous work reported reduced inflammation in endotoxin-challenged cattle fed a diet containing 10% ground pecan shells (PEC). This study evaluated the effects of PEC supplementation on in vitro ruminal gas production and fermentation. Rumen inoculum was obtained from four ruminally cannulated cows supplemented via the cannula with either PEC or cottonseed hulls (CSH) at 0.6 kg/d on a DM basis (5.5% of daily DM intake). Cows were adapted to treatments for 7 d before rumen inoculum was collected across six periods and used in 48-h in vitro incubations using the ANKOM RF gas production system. Each fermentation bottle (250 mL) contained 1.0 g of ground alfalfa hay (19.1% CP, 38.8% NDF, DM basis), 0.1 g of PEC or CSH corresponding to the inoculum source, 80 mL of buffer solution, and 20 mL of rumen inoculum. Data were analyzed using a randomized complete block design with six blocks (incubation periods) and eight experimental units (bottles) per block, yielding 24 replicates per treatment. Cumulative gas production did not differ between treatments from 0 to 26 h of incubation, tended to be lower for PEC at 28, 30, 34, 36, and 38 h, and was lower for PEC at 40, 46, and 48h compared with CSH (treatment × hour; P ≤ 0.01). Gas production from the slowly degradable fraction (b) and asymptotic gas production (a + b) were lower (P ≤ 0.01) for PEC than CSH, whereas gas production from the soluble fraction (a) and fractional rate constant (c) did not differ (P ≥ 0.14). After 48-h incubations, acetate tended (P = 0.08) to be greater, and the acetate:propionate ratio and butyrate were greater (P ≤ 0.01) for PEC than CSH; propionate did not differ (P = 0.83) between treatments. In vitro DM degradability, methane yield, ammonia-N concentration, and pH were not affected (P ≥ 0.25) by PEC. Pecan shells altered later-stage in vitro fermentation dynamics without affecting overall degradability, suggesting phenolics in pecan shells may redirect ruminal fermentation pathways and influence rumen microbial metabolism.