Effects of partial replacement of corn silage and oat silage with dried extracted stevia plant on production, feeding behavior, and digestibility in dairy cows.

The objectives were to determine the effects of partially replacing corn and oat silages with dried extracted stevia (Stevia rebaudiana) on production performance, behavior, ruminal fermentation, N metabolism, digestibility, and fecal characteristics of Holstein cows. Eighteen cows (133 ± 16 d postpartum) were assigned to a sextuplicate 3 × 3 Latin square design, with treatment sequence balanced for carry-over. Cows were assigned to squares based on ECM yield in the week preceding enrollment. Diets contained 60% of the total DM as forage and stevia replaced silages to represent 0% (ST0), 25% (ST25), or 40% (ST40) of dietary DM. Each period lasted 21 d, with data collected from d 16 to 21. Diet and fecal samples were analyzed for gross energy and diet digestible energy (DE) was calculated. Orthogonal polynomial contrasts evaluated linear [ST0 vs. (2/13 ST25 + 11/13 ST40)] and quadratic [ST25 vs. (3/8 ST0 + 5/8 ST40)] effects of stevia. Results are described in sequence as ST0, ST25, and ST40. Increasing dietary stevia linearly increased DMI (25.2 vs. 28.6 vs. 29.5 kg/d) but linearly decreased yields of milk (47.3 vs. 46.7 vs. 45.8 kg/d), ECM (49.6 vs. 48.4 vs. 47.4 kg/d), and true protein (1.40 vs. 1.32 vs. 1.25 kg/d). Stevia reduced milk true protein (2.97 vs. 2.84 vs. 2.74%) and urea N (17.1 vs. 16.4 vs. 15.0 mg/dL) concentrations, but increased the content of pre-formed fatty acids in milk (1.20 vs. 1.21 vs. 1.26%) without affecting other aspects of milk fat. Stevia increased concentrations of free fatty acids in plasma (0.14 vs. 0.14 vs. 0.20 mM). Stevia increased time spent eating (289 vs. 296 vs. 314 min/d) and meal size (2.94 vs. 3.21 vs. 3.32 kg/meal), but it did not affect intermeal interval. Although stevia increased DMI, cows spent less total time ruminating (586 vs. 570 vs. 516 min/d), which reduced ruminating time per kg of DM (25.0 vs. 21.2 vs. 19.3 min/kg) and NDF (75.6 vs. 60.8 vs. 53.8 min/kg) consumed. Nitrogen intake (656 vs. 710 vs. 748 g/d) and fecal N output (266 vs. 361 vs. 417 g/d) increased, whereas urinary N excretion tended to decrease (149 vs. 152 vs. 126 g/d) and milk N secretion decreased (227 vs. 214 vs. 203 g/d) with increasing stevia in the diet. Collectively, cows fed stevia had reduced efficiency of capturing dietary N as milk N. Diets containing stevia had increased contents of lignin and undigested NDF and a smaller proportion of particles > 8 mm, which likely contributed to the linear reductions in digestibility of OM, thus compromising the digestible energy content of diets (2.71 vs. 2.47 vs. 2.28 Mcal/kg). Collectively, partially replacing corn and oat silages with stevia reduced diet digestibility which resulted in reduced feed efficiency by increasing DMI while decreasing ECM yield in Holstein cows.