5622 Effect of fber digestibility and conservation method on feed intake and the ruminal ecosystem of growing steers 1 D. O. Sousa,* B. S. Mesquita,† J. Diniz-Magalhães,* I. C. S. Bueno,‡ L. G. Mesquita,* and L. F. P. Silva* 2 *Department of Animal Science, School of Veterinary Medicine, Universidade de São Paulo, Pirassununga, São Paulo, Brazil; †Ouro Fino Saúde Animal, Cravinhos, São Paulo, Brazil; and ‡Department of Animal Science, Faculty of Animal Science and Food Engineering, Universidade de São Paulo, Pirassununga, São Paulo, Brazil ABSTRACT: Fiber digestibility is an important factor regulating DMI in ruminants. Additionally, the ensil- ing process can also affect digestibility and chemical composition of the forage. The objective of this study was to investigate effects of sugarcane NDF digestibil- ity (NDFD) and conservation method on intake, rumen kinetics, and the ruminal ecosystem of steers. Eight rumi- nally cannulated Nellore steers (275 ± 22 kg BW) were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Two sugarcane genotypes divergent for stalk NDFD were used: IAC86- 2480 with high NDFD and SP91-1049 with low NDFD. Experimental diets were formulated with 40% sugarcane, either freshly cut or as silage, and 60% concentrate on a DM basis. Each experimental period lasted for 14 d, with the last 4 d used for determination of intake, rumi- nal evacuation, and ruminal fuid collection. The effect of fber digestibility on DM and NDF intake was depen- dent on the forage conservation method (P = 0.01). High NDFD increased (P < 0.01) DMI only when sugarcane was offered as silage, having no effect (P = 0.41) on DMI when offered as freshly cut. Conservation method had no effect on total ruminal mass, with only a tendency (P < 0.10) for greater NDF and indigestible NDF ruminal mass in steers fed the low-NDFD genotype. The NDF turnover and passage rates were greater (P < 0.05) for the genotype with high NDFD but only when offered as silage. Liquid turnover rate in the rumen was greater (P = 0.02) for diets containing silage, with no effect of genotype (P = 0.87). There was no effect of NDFD genotype on ruminal pH (P = 0.77); however, diets containing sugarcane as silage increased (P < 0.01) ruminal pH. Total concentration of short chain fatty acids (P = 0.05) and proportions of propionate (P = 0.01) were greater for diets containing fresh sugarcane. Diets with fresh sugarcane increased the ruminal population of Streptococcus bovis (P < 0.01) and Ruminococcus albus (P = 0.03). The relative population of R. albus was also greater (P = 0.04) for diets contain- ing the sugarcane genotype with high NDFD. Feeding diets containing the sugarcane genotype with high NDFD increased Fibrobacter succinogenes population but only when sugarcane was fed as freshly cut (P = 0.02). Using sugarcane genotypes with high NDFD can increase intake and beneft fber-degrading bacteria in the rumen. Key words: cellulolytic bacteria, conservation method, fber digestibility, intake, passage rate, sugarcane © 2014 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2014.92:5622–5634 doi:10.2527/jas2014-8016 INTRODUCTION Feed intake in cattle can be limited by 2 main fac- tors: ruminal fll and an excess of ruminal fermentation (Allen, 2000). When forage is conserved as silage, the accumulation of fermentation end products can fur- ther limit feed intake (Huhtanen et al., 2007; Weiss et al., 2003). Sugarcane can be an inexpensive source of nutrients during the low rainfall season; however, the main limitation of using sugarcane as the only roughage source to high-producing animals is the low fber digest- ibility and the low CP concentration (Santos et al., 2011). Similar to corn silage, advanced maturity has little effect on DM digestibility of sugarcane, but DM di- gestibility is maintained by greater sugar accumulation in the stalk associated with a linear decrease in fber di- gestibility (Carvalho et al., 2010). Therefore, ensiling of sugarcane has been used as a conservation method that, apart from other advantages, can increase NDF 1 This study was funded by FAPESP (Proc. 2009/00976-2). 2 Corresponding author: lfpsilva@usp.br Received May 1, 2014. Accepted October 8, 2014. Published December 12, 2014