Effects of Feeding Eragrostis Tef Hay Harvested at Different Stages of Maturity on Nutrient Intake, Ruminal Fermentation, and Nitrogen Utilization in Beef Cattle

Eragrostis tef (‘Tiffany’ teff), a warm-season annual grass, could be an excellent forage for beef cattle. However, there is limited information on its nutritive value at different stages of maturity. Therefore, our objective was to determine the effect of feeding teff hay harvested at the boot (BT), early-heading (EH), or late-heading (LH) stages of maturity on nutrient intake, ruminal fermentation, and nitrogen (N) utilization in beef cattle. Six ruminally-cannulated beef heifers (initial BW ± SD; 476 ± 32.6 kg) were used in a replicated 3 × 3 Latin square design with 28-d periods (18 d for adaptation and 10 d for measurements). Dietary treatments were BT, EH, or LH teff hay. Dry matter intake was measured daily and indwelling pH loggers were used to continuously measure ruminal pH from d 21 to 28. Ruminal fluid for ammonia determination and spot urine samples for measurement of urine output, N and urea-N excretion were collected from d 26 to 28. Blood samples for plasma urea-N (PUN) determination were collected 3 h post-feeding on d 28. The NDF and ADF content were similar across diets. However, CP content was greater for the BT than EH and LH hay (18.1, 14.1, and 11.5 %, respectively; DM basis). Dry matter intake was higher (P = 0.03) for heifers fed the LH (kg/d; 11.6) compared to the BT hay (10.9), whereas CP intake increased (P = 0.03) for heifers fed the EH (1.76) compared to the LH hay (1.65). There was no diet effect (P > 0.05) on mean, minimum and maximum pH, and the duration and area pH < 6.2 and 5.8, but ruminal ammonia concentration was greater (P < 0.05) for heifers fed BT (mg/dL; 14.04) than EH (8.82) and LH hay (5.01). Plasma urea-N concentration also tended to be higher (P = 0.08) for BT compared to EH and LH hay (19.1, 15.9, and 14.1 mg/dL, respectively). Urine output increased (P = 0.01) in heifers fed the BT (kg/d; 15.2) than EH (11.5) and LH (11.7) hay. Similarly, urine N and urea-N excretion increased (P < 0.01) for heifers fed the BT compared to the EH and LH hay. In conclusion, although there was no diet effect on ruminal pH, the decrease in CP content with advancing maturity resulted in a decrease in the ruminal ammonia and PUN concentrations, and urine N and urea-N excretion when teff hay was fed to beef cattle.