Pretanned leather shavings in a supplement mixture for steers: I. In situ and in vitro disappearance, ruminal fermentation, and organic matter, nitrogen, and fiber digestion

Two digestion studies were conducted to evaluate the use of pretanned leath er shavings as a component of a protein supplement. In Exp. 1, the in situ and in vitro disappearance of pretanned leather shavings and soybean meal w as evaluated. Results revealed that less than 18.4% of the pretanned leathe r shavings was solubilized and disappeared when exposed to McDougall's buff er for 48 h, but there was 90.0% disappearance with 48-h exposure to a .1 N HCl/pepsin treatment and 97.0% disappearance with exposure to a two-stage digestion. In situ disappearance following 72 h in the rumen allowed 6.8% d isappearance. Thus, leather shavings seem to be relatively indigestible in the rumen, but postruminal digestion may be possible. In Exp. 2, six Angus x Holstein steers, fitted with ruminal and duodenal cannulas, were used in a replicated 3 x 3 Latin square to evaluate ruminal and digestion effects o f the following supplements combined with fescue hay at 1.7% of BW (DM basi s): no supplementation (cont roll; supplementation intraruminally with soyb ean meal at .07% of BW las-fed basis); and supplementation intraruminally w ith a combination of soybean meal and pretanned leather shavings (17:8 rati o) at .05% of BW (isonitrogenous to soybean meal; as-fed basis). Ruminal fl uid passage rate was greater and fluid turnover time was shorter in steers fed leather shavings than in those fed soybean meal (P = .10). Ruminal pH w as lower (P = .04) for supplemented steers than for control steers and rumi nal NH3 N concentration was greater (P = .01) in steers fed soybean meal th an in those fed leather shavings. Total VFA concentration was increased (P = .02) by supplementation. Supplementation with soybean meal increased (P < .05) ruminal molar proportions of butyrate, valerate, and isovalerate comp ared with leather shavings. Duodenal OM flow and OM disappearing in the int estines were increased by supplementation (P < .10), but not by the type of supplement fed (P > .10). Ruminal digestion of OM and total tract OM diges tion were unaffected (P > .10) by supplementation and the type of supplemen t fed. Flow and digestion of NDF were unaffected (P > .10) by the treatment s. Flow of N and the quantity of N disappearing in the intestines were incr eased (P < .05) by supplementation but did not differ (P > .10) between sup plementation groups. Microbial N flow, N utilization for net microbial prot ein synthesis, and ruminal N disappearance were unaffected (P > .10) by sup plementation and the type of supplement provided. Combining pretanned leath er shavings with soybean meal seemed to have no deleterious effects on dige stion or fermentation and to allow for escape of some N to the lower tract.