Effects of the interaction of forage and supplement type on digestibility and ruminal fermentation in beef cattle.

The objectives of this research were to test interactions of supplement type, liquid versus dry, and forage type, hay versus corn stover, on digestibility and ruminal metabolism of beef cattle. Ruminally fistulated steers were fed in a replicated 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments: 1) hay with liquid supplement, 2) hay with dry supplement, 3) corn stover with liquid supplement, and 4) corn stover with dry supplement. The liquid supplement was molasses and glycerin based (23.3% CP and 1.63 Mcal/kg NEm) whereas the dry supplement was ground corn based (16.8% CP and 1.81 Mcal/kg NEm). Each period, steers were adapted to diets for 14 d and samples were collected for 8 d. In situ disappearance was determined by a 24-h incubation of Dacron bags, containing soybean hulls, in the rumen. There were no interactions ( ≥ 0.25) of supplement and forage type on DMI, apparent total tract digestibility, or ruminal pH. There was a tendency ( = 0.08) for a forage × supplement type interaction for in situ NDF disappearance (ISNDFD). There were no differences in ISNDFD in steers fed hay, but liquid supplement increased ISNDFD in steers fed corn stover. There were no main effects ( ≥ 0.12) of supplement type on DMI, apparent total tract or in situ digestibility, or ruminal pH. There was a supplement × hour interaction ( = 0.04) for acetate concentrations. Although no effect occurred at 0 h after feeding, at 3 and 6 h after feeding, acetate concentrations were reduced in steers fed liquid supplements when compared with those fed dry supplements. In addition, there was a supplement × hour ( = 0.02) interaction for butyrate concentrations, where at all time points, butyrate concentrations increased ( ≤ 0.01) in steers fed liquid supplements when compared with those fed dry supplements. Steers fed hay had increased DMI ( < 0.01) and apparent total tract NDF digestibility ( = 0.07) when compared with steers fed corn stover, regardless of supplement type. At 0, 1.5, and 18 h after feeding, ruminal pH was greater ( ≤ 0.01) in cattle consuming corn stover when compared with those fed hay, regardless of supplement type. However, steers fed hay had increased ( < 0.01) concentrations of acetate and total VFA compared with steers fed corn stover, regardless of supplement. Feeding liquid supplement increased ISNDFD when steers were fed corn stover; however, these changes were not associated with differences in total tract digestibility. Regardless of forage type fed, the liquid supplement increased ruminal butyrate concentrations.

Use of soybean hulls as a replacement for dry rolled corn in beef cattle feedlot receiving diets.

Consecutive receiving studies were used to evaluate the replacement of starch (dry rolled corn; DRC) with a nonforage fiber source (soybean hulls; SBH) on performance, mineral, and blood metabolite status of newly arrived feedlot steer calves. Steers in yr 1 (Y1; 9 pens/diet, 8 to 10 animals/pen) and yr 2 (Y2; 6 pens/diet, 9 to 10 animals/pen) were blocked by weaning management, and then stratified by BW and randomly assigned to pens. Pens were randomly assigned to an oat silage-based diet containing starch (HS) from DRC or digestible fiber (HF) from SBH. Diets were formulated for 12% CP (DM basis) and to meet or exceed NRC (1996) nutrient requirements for Ca, P, and vitamins A and E. Mineral status was assessed in Y1 only via liver biopsies and serum samples collected on d 3 and 28. Mineral concentrations on d 28 were compared using d 3 concentrations as a covariate. Glucose, NEFA, and plasma urea N status were assessed in Y2 only via blood collections on d 0, 3, 7, 14, 28, and 59. Morbidity (<10%) and mortality rates were not different (P > 0.10) between treatments across years. Daily BW gain was similar (P > 0.10) between treatments both during the receiving period and cumulatively across years. Overall, feed intake was greater (P = 0.007) for steers fed HF compared with steers fed HS in Y1, but was not different in Y2 (P = 0.13). Steers consuming the HS diet tended (P = 0.07) to have better BW gain efficiency in Y1 only. Across years, BW gain efficiency and ADG were similar between treatments (P > 0.10), although DMI was greater for steers fed HF (P = 0.003). Based on 2 yr of performance, the calculated ME content of SBH was estimated at 92.5% of the ME value of DRC (2.74 vs. 2.96 Mcal/kg, respectively). Mineral concentrations on d 28 were similar (P > 0.10) for most minerals assayed. There was a steeper (P = 0.005) decline in hepatic Cu concentrations early in the feeding period for steers fed HF, resulting in decreased (P = 0.001) d 28 hepatic concentrations. Hepatic Mn was greater (P = 0.003) in steers fed HF on d 28 as a result of greater (P = 0.006) Mn accumulation during the initial 28 d on feed. Blood metabolites in Y2 (using d 0 values as a covariate) were similar (P > 0.10) across treatments, except for reduced (P = 0.025) plasma urea N concentrations on d 7 and greater (P = 0.050) NEFA concentrations on d 28 for steers fed HS. These studies indicate that the use of SBH in receiving diets can support BW gain similar to the use of DRC.