Table 6.
Ruminal responses of rumen-cannulated heifers receiving feedlot diets containing (2 × 2 factorial arrangement): 1) monensin + tylosin (360 mg/steer daily from Rumensin 90 and 90 mg/steer daily from Tylan 40; Elanco Animal Health, Greenfield, IN) and 2) Y. schidigera extract (4 g/steer daily, as-fed basis; Micro-Aid Feed Grade Concentrate; DPI Global, Porterville, CA)1,2
| Item | Monensin + tylosin (A) | Y. schidigera extract (B) | P-values | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Yes | No | SEM | Yes | No | SEM | A | B | A × B | |
| Rumen fluid ammonia, mM | 1.04 | 1.44 | 0.2 | 1.03 | 1.45 | 0.2 | 0.18 | 0.15 | < 0.01 |
| Rumen protozoa count, 103 per mL | 812 | 387 | 78 | 572 | 627 | 77 | <0.01 | 0.56 | 0.40 |
| Rumen fluid pH | 5.80 | 5.67 | 0.06 | 5.81 | 5.67 | 0.06 | 0.04 | 0.03 | 0.27 |
| Rumen fluid viscosity, mPa.s. | 13.8 | 19.7 | 9.9 | 3.1 | 29.9 | 10.0 | 0.65 | 0.04 | 0.80 |
| Total rumen volatile fatty acids, mM | 210 | 208 | 6 | 208 | 210 | 6 | 0.74 | 0.77 | 0.49 |
| Acetate, mol/100 mol | 49.6 | 51.4 | 1.1 | 49.7 | 51.3 | 1.1 | 0.16 | 0.23 | 0.15 |
| Propionate, mol/100 mol | 35.8 | 32.4 | 1.3 | 35.6 | 32.6 | 1.3 | 0.04 | 0.07 | 0.32 |
| Butyrate, mol/100 mol | 10.8 | 11.9 | 0.7 | 10.6 | 12.0 | 0.7 | 0.84 | 0.55 | 0.45 |
| Iso-valerate, mol/100 mol | 0.873 | 1.020 | 0.117 | 0.892 | 1.00 | 0.117 | 0.30 | 0.45 | 0.68 |
| Iso-butyrate, mol/100 mol | 0.581 | 0.591 | 0.029 | 0.573 | 0.599 | 0.029 | 0.80 | 0.52 | 0.88 |
| Valerate, mol/100 mol | 2.38 | 2.59 | 0.18 | 2.52 | 2.46 | 0.18 | 0.24 | 0.74 | 0.68 |
| Acetate:propionate ratio | 1.41 | 1.64 | 0.09 | 1.44 | 1.63 | 0.09 | 0.03 | 0.08 | 0.21 |
1Heifers were assigned to a 4 × 4 Latin square design, containing four periods of 21 d each and a washout interval of 14 d between periods. During each period, heifers were housed in drylot pens equipped with electronic feed bunks (GrowSafe Systems Ltd, Airdrie, AB, Canada) that measured individual feed intake.
2Rumen fluid was sampled prior to feeding (0700 h) on the first day of each period, and 4 h after feeding (1200 h) on the final day of each period. Rumen pH was measured using a pH meter concurrently with rumen fluid sampling. Rumen fluid samples were analyzed for viscosity assessment (Pitta et al., 2016), protozoa count (Caigle et al., 2020), ammonia (Broderick and Kang, 1980), and volatile fatty acid profile (Cappellozza et al., 2013). Results obtained on the first day of each period were used as independent covariate in each respective analysis.