Effect of sources of non fiber carbohydrates on intake, body gain, carcass characteristics, rumen kinetics and ecosystem of finishing bulls

Abstract

Beef cattle finishing diets have high energy contents, which represents a challenge for the stability of ruminal ecosystem. With the increasing popularity of sugarcane silage by farmers, it becomes essential to understand the effect of supplementing with different levels and sources of non-fiber carbohydrates (NFC) on rumen metabolism and animal performance. The main objective of this study is to quantify the effect of parcel substitution of flaked corn or citrus pulp for ground corn on body weight gain, feed intake and carcass characteristics of finishing Nellore bulls. It is also our aim to quantify the effect of feedings different levels and sources of NFC on rumen fermentation, kinetics of fiber degradation and passage, and total DM and starch digestibility. Finally, we intend to characterize changes in rumen bacterial population caused by the increase in concentrate levels and by the NFC sources, determining the relative quantity of amylolytic, cellulolytic, and lactate utilizing bacteria. For determining animal performance and carcass characteristics, 54 young Nellore bulls weighting approximately 350 kg will be used. Animals will be housed in 18 concrete stalls, in a randomized block design with six replicates. Intake will be regulated for each stall by daily weighting of diet and orts. For measuring ruminal kinetics and ecosystem, six rumen cannulated Nellore steers will be used at a 6x6 Latin Square design. Experimental diets for the performance assay will be formulated with 80% concentrate with sugarcane silage as roughage. As NFC sources, flaked corn or citrus pulp will be partially substituted for ground corn. Animal performance will be evaluated by periodic weighing of the animals after 16h starvation, to estimate average daily gain and feed efficiency. Fat deposition and muscle growth will be evaluated by ultrasonography at the beginning and end of the experimental period. Blood samples will be collected for dosage of serum glucose, urea nitrogen, total protein and albumins. Using the cannulated animals, total rumen mass and volume will be determined by rumen emptying. Samples will be taken from both, solid and liquid phases, for determining the size of the rumen pool and digest components. Samples from the diet, orts and rumen digest will be measured for nutrient content. Indigestible NDF will be estimated as NDF content after 264h of in situ incubation. Rumen liquid volume and rate of passage will be calculated using polyethylene glycol 4,000 MW. The relative quantification of cellulolytic, amylolytic and lactate utilizing bacteria will be determined by real-time PCR after total DNA extraction. (AU)