Effect of sugarcane fiber digestibility and mode of conservation on intake and ruminal short chain fatty acids of growing steers

Abstract Text: Effect of sugarcane stalk fiber digestibility (NDFD) and method of conservation on intake and ruminal short chain fatty acids (SCFA) was evaluated. Eight ruminally cannulated steers (275 ±20 kg BW) were used in a duplicated 4x4 Latin square design with a 2x2 factorial arrangement of treatments. Two sugarcane genotypes with differing stalk NDFD were used: IAC86-2480 with higher NDFD (33.7% 30h-NDF digestibility), and SP91-1049 with lower NDFD (29.6% 30h-NDF digestibility). Treatment diets contained 40% sugarcane (DM basis) as sole roughage source given as freshly-chopped or as silage. All diets were formulated with 14.8 CP to provide daily gain of 1.2 kg/d. Animals were housed individually in tie-stalls with free access to water, and fed ad libitum allowing 10% orts. Periods lasted for 14d, being 10d for adaptation, and 4d for sample collection. Dry matter intake was determined on days 10, 11 and 12, and rumen fluid samples were collected at six times: 0, 1, 3, 6, 9 and 12 h after feeding on day 14. Samples were taken from three areas of the rumen, filtered through a 1 mm nylon mesh, and centrifuged at 6,500×g for 15 min. A two mL subsample of the supernatant was taken, mixed with 0.4 mL of formic acid for SCFA determination by gas chromatography. Main effects of sugarcane genotype (GEN), method of conservation (CONS), and their interaction were tested by PROC MIXED. Feeding sugarcane with higher NDFD increased DM intake (5.6 vs. 4.5 ± 0.5 kg/d, P=0.01), however the interaction GEN x CONS was significant (P=0.01). The effect of greater NDFD on DMI was only significant when feeding sugarcane as silage (P<0.01), having no effect on DMI when sugarcane was fresh (P=0.53). Total concentration of SCFA was higher for fresh sugarcane compared with silage (114 vs. 99 ± 12 mM, P=0.05). Conserving sugarcane as silage resulted in greater acetate proportion in the rumen, when compared with fresh sugarcane (58.7 vs. 55.8 ± 1.6 % of total SCFA, P=0.01). Proportion of propionate was also effect by conservation method, with greater proportion for diets with fresh sugarcane than sugarcane silage (24.2 vs. 20.6 ± 1.6 % of total SCFA, P=0.01). There was no effect of GEN of SCFA in the rumen. Increased in vitro NDFD improved intake, but only when given as silage. Feeding sugarcane ensiled decreased total SCFA and propionate proportion and increased acetate proportion.

Keywords: Sugarcane silage, Cattle, NDF digestibility, Short chain fatty acids.