Abstract
The aim of this study was to investigate the effects of sugarcane neutral detergent fiber digestibility (NDFD), conservation method, and concentrate level on the ruminal microbial population of steers. Eight ruminal-cannulated Nellore steers were distributed in two contemporary 4 × 4 Latin Square design with a 2 × 2 factorial arrangement of treatments. Experiment 1: diets were formulated with 60% of concentrate level, and two sugarcane genotypes (high or low NDFD) either freshly cut or as silage. Experiment 2: diets were formulated with two levels of concentrate (60 or 80%), and two sugarcane genotypes (high or low NDFD) offered as freshly cut. Each experimental period lasted for 14 d, with the last 4 d used for ruminal fluid collection. Three cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus albus, Ruminococcus flavefaciens), two amylolytic (Streptococcus bovis, Ruminobacter amylophilus), and a lactate fermenting microorganism (Megasphaera elsdenii) were quantified by qPCR. Experiment 1: diets with fresh sugarcane increased the population of S. bovis, and M. elsdenii. Sugarcane with high NDFD increased F. succinogenes population only when sugarcane was offered as freshly cut. Experiment 2: increasing concentrate in the diet decreased S. bovis population, and increased R. amylophilus. Sugarcane with high NDFD increased the population of cellulolytic bacteria only at the 60% concentrate diet. Providing sugarcane with high NDFD favored the growth of fibrolytic bacteria, and this effect were dependent on the conservation method and on diet concentrate level. In addition, sucrose appears to have great effect on the composition of ruminal microflora, especially S. bovis.
Highlights
Feedlot diets have high inclusion of concentrate and low roughage, usually resulting in low ruminal pH that directly affects the digestibility of the fiber, and may lead to metabolic disorders (Anderson et al 2016)
Study 1 In the first study, the effect of fiber digestibility on F. succinogenes population was dependent on the forage conservation method, as there was a significant neutral detergent fiber digestibility (NDFD) × CONS interaction (P = 0.01; Table 2)
The sugarcane genotype did not affect the population of S. bovis (P = 0.53) and M. elsdenii (P = 0.61)
Summary
Feedlot diets have high inclusion of concentrate and low roughage, usually resulting in low ruminal pH that directly affects the digestibility of the fiber, and may lead to metabolic disorders (Anderson et al 2016). On the other hand, increasing the digestibility of carbohydrates in the rumen results in pH to drop below 6.0 due to the greater production of short-chain fatty acids (SCFA). In this situation, there is a reduction in the activity of fibrolytic bacteria, affecting the digestibility of fiber, while there is increased activity of amylolytic bacteria, such as Streptococcus bovis and Ruminococcus amylophilus, and lactate users, as Megasphaera elsdenii (Tajima et al 2001; Nagaraja and de Souza et al AMB Expr (2017) 7:55. The excess of ruminal fermentation of NFC, combined with low inclusion of roughage in the diet, can lead to acidosis, decreasing fiber digestibility, dry matter intake and, causing a reduction in weight gain of animals (Gonzalez et al 2012)
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