1701
Glycerol exacerbates effects of sorghum-based tannins extract on in vitro fermentative activity of mixed ruminal microorganisms
Tannins have been observed to impact ruminal metabolism, affecting protein degradation, predisposition to bloat, and production of methane and conjugated linoleic acid; however, these effects on rumen modulation and animal performance have not been consistent. Glycerin is a byproduct from biodiesel production and is a major component of distiller’s grains, and thus is frequently present in diets of finishing cattle. The aim of this work was to evaluate interactive effects of sorghum-derived tannins and glycerol on fermentative activity (in vitro dry matter digestibility, IVDMD; ammonia, NH3; and volatile fat acid, VFA profiles) of in vitro cultures of mixed ruminal microorganisms. Tannins were prepared from sorghum bran by extraction with acetone and lyophilized. For in vitro fermentations, 40 mL of modified McDougall’s buffer (no urea) were placed into 100 mL plastic bottles along with 20 mL of strained ruminal fluid and 2 grams of substrate. Ruminal fluid was obtained from fistulated cattle fed a diet consisting of approximately 50:50 forage:concentrate (alfalfa hay, corn silage, corn flake, dry distilled grain, mineral mix). Substrate for in vitro fermentations consisted of finely ground (<1 mm) corn and soybean meal in a 90:10 ratio (C) or partial replacement of corn with glycerol (G; 10% of substrate), tannin (T; 1%) or a mix (TG). After incubating 24 h at 39C, IVDMD and concentrations of NH3 and VFA were measured. Data were analyzed as a randomized complete block design by using the MIXED procedure of SAS, and results are summarized below. Shifts in concentrations of ammonia and VFA in cultures fed glycerol generally were exacerbated by the presence of tannins. The observed interaction between glycerol and tannin may explain the varying results found in studies that use glycerol as a substitute for cereals grains in diets of ruminants.
Table 1. Effect of glycerol and sorghum-based tannins extract on in vitrofermentative activity of mixed ruminal microorganisms
|
Treatment |
|
|
|
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Item |
C |
G |
T |
TG |
SEM |
P-value* |
|
||
IVDMD, % |
55.2 |
53.7 |
53.1 |
52.5 |
0.91 |
0.104 |
|
||
Ammonia, mM |
2.45ª |
2.31a |
1.96b |
1.59c |
0.157 |
<0.01 |
|
||
Acetate, mM |
34.86ª |
33.74b |
33.59b |
32.31c |
0.55 |
<0.01 |
|
||
Propionate, mM |
20.69b |
23.30a |
20.15c |
22.92a |
0.42 |
<0.01 |
|
||
Butyrate, mM |
6.57ª |
6.50a |
6.21b |
6.22b |
0.16 |
<0.01 |
|
||
*Means in the same row without a common superscript letter are different; P < 0.05. |
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Keywords: Glycerin, tannin, sorghum