Effects of tallow on the energy metabolism of wethers fed barley finishingdiets

A balance trial was conducted to titrate the effects of tallow on the energ y metabolism of wethers fed barley finishing diets. Six dietary levels of t allow (0, 2, 4, 6, 8, or 10%) in a barley finishing diet were fed to six cr ossbred wethers (35 +/- 1.1 kg) in a randomized complete block design. Diet s were 73% barley, 10% tallow and(or) bentonite, 10% alfalfa pellets, and 7 % supplement. There was no effect of tallow level on OM intake (1,103.1 +/- 51 g/d),OM digestibility (84 +/- 0.9%), GE digestibility (83 +/- 1.1%), or cell solubles digestibility (84.2 +/- 1.2%). The level of tallow quadratic ally decreased ADF digestibility (P < 0.05), methane emissions, and methane energy as a percentage of GE P <less than> 0.01). There were linear increa ses in:dietary GE (megacalories per kilogram of OM [P < 0.01]), dietary DE (megacalories per kilogram of:OM [P < 0.05]), and dietary ME (megacalories per kilogram of OM[P < 0.01]), as dietary tallow increased. Numbers of rumi nal protozoa (Entodinium spp. and Polyplastron sp.) decreased linearly (P < less than> 0.05) with increased level of tallow. The energy value of tallow (calculated by difference):was low. The tot al-tract fatty acid digestibil ity of tallow was calculated by linear regression, without intercept, after accounting for the fatty acids digested from the base diet (0% tallow fed to a wether in a period). Fatty acids of the same carbon length were pooled for the regression analysis. All linear regressions were significant (P < 0.10) indicating no effect of tallow level on fatty acid digestibility. Lau ric acid had low digestibility. The high digestibility of all C16 (89%) and C18 (104%) fatty acids suggests an effect of tallow on endogenous and micr obial fatty acid excretion. Fatty acid digestibility was probably a minor c ontributor to the low energy content of tallow, calculated by difference, i n these diets.