Effect of feeding growing heifers with corn silages with high or low fiber digestibility on intake, body gain, rumen kinetics and ecosystem

Abstract

Forages are the basis of ruminant nutrition, and cell wall digestibility is the main factor limiting animal performance. Therefore, improving cell wall digestibility should be the focus of breeding programs aiming to improve the quality of tropical forages. Among forages, corn silage is commonly used by farmers, especially in production systems exploring the maximum genetic potential of the animals. The identification of a parameter for fiber quality evaluation that effectively has an impact on animal performance is of great importance for corn silage breeding programs, and for selection of hybrids by farmers. Our objective with this study is to evaluate the effect of feeding growing heifers with diets containing corn silages with either high or low stem NDF digestibility, over the following parameters: 1) dry matter intake; 2) body weight gain and variation in body condition score; 3) age and body weight at puberty, 4) ruminal digestion and passage rate of NDF; 5) ruminal fermentation parameters; and 6) quantification of amylolytic, cellulolytic and lactate utilizing bacteria. Forty eight pre-pubertal Nelore heifers, approximately 250 kg of BW, will be used. Heifers will be housed in groups of three per pen, and the intake will be controlled in each pen. Experimental diets will be composed either 20 or 60% concentrate in the dry matter basis, and the roughage will be corn silage with either high or low stem NDF digestibility, in a total of four experimental diets. Sixteen heifers will surgically fistulated for fitting of rumen cannulas, and used for determination of fiber ruminal kinetics: NDF passage and digestibility rates. The experimental design will be that of random blocks with 8 repetitions (performance) or 4 repetitions (rumen metabolism and kinetics). The occurrence of puberty will be evaluated by weekly ultrasound analysis of the ovaries for detection of a functional corpus luteum, confirmed by the plasma progesterone content. The total rumen content mass and volume will be determined by the flux and pool method. Samples will be taken from both solid and liquid phases for determining the size of the rumen pool for diet components. Diet, orts and ruminal digesta will be analyzed for nutrient contents. Indigestible NDF will be estimated by the FDN content of samples after 264 h of in situ incubation. Polietilenoglicol with molecular weight of 4,000 will be used for determination of liquid volume and liquid passage rate at the rumen. The relative quantification of rumen bacteria will be performed by real-time PCR after total DNA extraction. (AU)