The objective of the present work was to study the effects of the addition of increasing
levels of propylene glycol on the ruminal fermentation of diets with different forage:
concentrate proportions, by the semi-automatic in vitro gas production technique, and
in situ degradability of diets for cattle receiving water with or without infusion of
propylene glycol (PGLIC). Four rumen fistulated cattle was used, two for inoculum in
vitro test and two for incubation in situ test. Experimental diets were composed
included Mombaça grass silage and a commercial concentrate. In vitro experiments
were used on three diets with 100: 0, 50:50 and 0: 100 of ratios roughage: concentrate
and four proportions of PGLIC: 0, 2, 4 and 6%. This trial follow a randomized block
design (DBC) with a 3 x 4 factorial arrangement, making 12 treatments with 3 blocks.
1.0 g of sample, 10 mL of rumen inoculum, 90 mL of culture medium and low levels of
PGLIC were incubated in glass vials at 39 °C. Measurements of gas pressure and
volume were taken at times 2, 4, 6, 8, 10, 12, 15, 19, 24, 30, 36, 48, 72 and 96 hours.
There was a decrease in gas production, degradation of dry matter and organic matter,
as the percentage of PGLIC was increased (P <0.05). France parameters had the
greater effect of diets than PGLIC levels in all variables. PGLIC may have been
responsible for decreasing microbial activity and lower degradation rates, but provides
readily metabolizable energy. Adding up to 4% PGLIC can improves or provides
energy without severely reducing diet degradability. In situ experiments, animals
consumed water with PGLIC in the 0.0 and 4.0% samples as indicated in the gas
production test. Three forage: concentrated ratios were used: 100: 0, 75:25 and 50:50.
The experimental design was cross-over, with three diets and two levels of PGLIC: 0.0
and 4.0%, making 6 interventions with two animals and two periods. The incubation
times used were: 0, 6, 12, 24 and 96 hours. The degradability parameters were
followed by the nonlinear regression procedure adopted by Gauss-Newton. The mean
DM degradation of controls without PGLIC was higher than controls with PGLIC (P
<0.05). As fractions A and B presented higher values for the 100% roughage diet when
treated with PGLIC, and lower for diets with 75:25 and 50:50 roughage: concentrate
ratios. PGLIC improved the degradability of crude protein (CP) from the fibrous diet.
Higher acid detergent fiber (FDA) degradability was achieved in the 50V50C4
treatment. In general or PGLIC in water, the in situ degradation of dietary DM, fiber
and CP improves. The Ørskov parameters are the best fit for diet data with 50:50
volume: concentrate ratio and when treated with PGLIC.
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