Effects of humic acid on forage digestibility in ruminants

Abstract

Three experiments were conducted to determine the effects of purified humic acid (HA) on rate and extent of microbial digestion of various forages in ruminants. In Exp. 1 the in vitro dry matter disappearance (DMD) of Coastal Bermuda grass hay (CBH) was evaluated in the presence of HA at concentrations of .001, .01, .1, and 1% of the substrate and, following 12, 24, 36, and 48 h fermentation periods. In vitro DMD was increased (P<.05) by 8.7% and 10.9% by the . 1 and 1 % humic acid treatments, respectively at the 12 h time period. At the 24 h time period, HA increased in vitro DMD by 10.91, 5.86, 18.85, and 16.12% when incorporated at .001, .01, .1, and 1%, respectively. In Exp. 2, the effect of HA on rate of (DMD) and neutral detergent fiber digestibility (NDFD) was evaluated in situ at 3, 6, 12, 24, 48, 72, and 96 h on alfalfa hay (CP 26.27%) and 3 different qualities of CBH; low quality (LQCBH; CP 7.30%), medium quality (MQCBH; CP 10.40%), high quality (HQCBH; CP 12.01%) and alfalfa. The .10 level of HA increased (P<.01) 3, 6, and 12 h DMD of MQCBH by 9% at each time and increased NDFD of MQCBH by 97, 91, and 74% at 3, 6, 12 h respectively. In addition, the .10 level of HA increased (P<.Ol) the NDFD of alfalfa hay by 116, 118, 124, 152, and 35% at 3, 6, 12, 24, and 96 h respectively and the >001 level of HA increased (P<.01) NDFD of alfalfa hay by 146, 148, 156, and 196% at 3, 6, 12, and 24 h respectively. These results indicate that HA increased the initial rate of NDFD in situ. Experiment 3 consisted of a metabolism trial involving twelve crossbred wether lambs (avg. wt 41kg) and 3 HA treatment levels used in a 3 x 3 Latin square design. No changes (P<.01) in dry matter intake or in the digestibility of dry matter, NDF, hemicellulose, cellulose, lignin, ash and nitrogen were observed between treatments.