Effects of plant tannin supplementation on animal responses and in vivo ruminal bacterial populations associated with bloat in heifers grazing wheat forage1

Two experiments were conducted to 1) enumerate the effect of tannin supplementation on ADG, bloat frequency, in vitro gas, and biofilm and foam production, and 2) quantify the influence of tannin supplementation on ruminal bacterial populations of heifers grazing wheat forage. Twenty-six heifers (286 ± 26 kg) were randomly allocated to 1 of 3 treatments that included a control (nontannin group) and 2 types of tannins (mimosa and chestnut tannins). Plant tannins (1.5% of DMI) were supplemented once daily mixed with a textured feed (500 g/animal). Heifers were visually monitored daily for bloat score (0 = no bloat, 3 = severe bloat). In Exp. 1, supplementation of tannins reduced the rate of frothy foam and biofilm production with chestnut being more efficacious than mimosa tannins. There was no treatment × time interaction (P > 0.1) for ADG and bloat measurement. Chestnut tannin supplementation increased ADG (P < 0.05) with time (P < 0.01). Mean bloat score and bloat day were greater (P < 0.01) for the control diet than for tannin-supplemented treatment groups. In Exp. 2, Fibrobacter succinogenes, Streptococcus bovis, and Prevotella ruminicola strains were relatively stable with time (d 0, 10, and 25) in the rumen of animals not receiving tannin supplementation. However, with supplementation of chestnut and mimosa tannins, populations of P. ruminicola and strains of both F. succinogenes and Ruminococcus flavefaciens were increased, respectively. Results show that daily supplementing mimosa and chestnut tannins to heifers grazing wheat forage improved beef production and minimized bloat frequency with minimum impact to the microbial populations studied.