Effects of Cashew Nut Shell Extract on Nutrient Digestibility and Ruminal Fermentation Under in Vitro Batch Culture and Continuous Culture Conditions

The overall objective of this research was to determine the effects of cashew nut shell extract (CNSE; 59% anacardic acid and 18% cardol) on nutrient digestibility and rumen fermentation profile under in vitro batch culture (Chapter 2) and continuous culture conditions (Chapter 3). The second objective was to determine an optimal supplementation dosage for dairy cows. The batch culture study was organized as a randomized complete block design with 15 replicates per treatment incubated for 24 h during four incubation runs. Each incubation was inoculated with rumen contents collected from ruminally fistulated cows fed either a close-up (CU; 15.1% CP, 38.1% NDF, and 20.8% starch) or a fresh cow diet (FC; 16.4% CP, 31.8% NDF, and 28.0% starch). Diets fed to donor cows were the same as the substrate used in the batch culture incubations. Treatments consisted of four levels of granulated CNSE formulated to contain 50% CNSE (additional 50% representing the coating and carrier) and added to the cultures in increments equivalent to 0, 2.5, 5.0, and 10.0 g/head/d. Dietary treatments incubated to mimic CU conditions had no impact on in vitro dry matter digestibility (IVDMD), in vitro true dry matter digestibility (IVTDMD), in vitro neutral detergent fiber disappearance (IVNDFD), and total nitrogen digestibility (TNd). Under CU conditions, increasing CNSE level decreased the molar proportion of acetate (linear and quadratic effect), propionate (linear effect), increased isovalerate and valerate, and pH (linear and quadratic effect). When mimicking FC conditions, increasing the level of CNSE tended to linearly decrease IVDMD, IVTDMD, IVNDFD, and TNd. Acetate molar proportions tended to decrease (linear effect), whereas isovalerate and valerate showed dose-dependent increase (linear effect). Ammonia nitrogen (NH3N) decreased at all levels of supplemented CNSE in a linear and quadratic manner. Culture pH increased at 2.5 and 5.0 g of CNSE/head/d and decreased at 10 g of CNSE/head/d (quadratic effect). Under batch culture conditions, adding incremental levels of CNSE had no effect on nutrient digestibility in CU diets, but negatively impacted digestibility in FC diets. Under continuous culture conditions, four treatments were randomly assigned to eight fermenters for two periods of 10 d. Treatments consisted of four doses of granulated CNSE formulated to contain 50% CNSE, premixed with corn grain, and added to diets in stepwise increments equivalent to 0, 2.5, 5.0, and 10.0 g/head/d. Fermenters were fed 56.2 g/d of a total mixed ration (TMR; 17.0% crude protein (CP), 29.7% NDF, and 29.9% starch), divided between two feedings at 0800 and 2000 h. The apparent digestibility of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) were not affected by CNSE supplementation. Cashew nut shell extract had no effect on total volatile fatty acids (VFAs) or individual VFA molar proportions, culture pH, oxidation-reduction potential (Eh), or relative hydrogen score (rH). These results suggest that CNSE has no impact on nutrient digestibility and rumen fermentation profile under continuous culture conditions