Abstract
Two experiments were carried out to evaluate the effects of corn and sorghum with different processing methods on the expression of genes involved in volatile fatty acids transport and pH regulation, and ruminal keratinization in rumen epithelium of finishing bulls. For Exp. 1, five rumen cannulated Nellore bulls were used in a 5x5 Latin square arrangement, with 14 d for adaptation and 9 d for sample collection. Treatments were: dry ground corn, dry ground sorghum, reconstituted corn, reconstituted sorghum, and control (forage-based diet). Samples of rumen epithelium from ventral sac were excised, rinsed, snap-frozen and stored at -80°C until total RNA isolation and quantitative real-time PCR analysis. In the Exp. 2, 24 Nellore bulls were assigned to a completely randomized design lasting 168 d. Experimental treatments were similar to those at Exp. 1, but without the control treatment. After the experimental period, bulls were slaughtered and rumen epithelium samples were rapidly excised for further histological analysis. Rumen epithelial tissue from animals fed reconstituted corn had lower expression of downregulated-in-adenoma (P = 0.03) and Na+/H+ exchanger 2 (trend; P = 0.09). The expression of Na+/ H+ exchanger 1 (P = 0.10) and putative anion transporter (P = 0.06) tended to be lower in rumen epithelium of bulls fed reconstituted grains. Ruminal concentration of valerate was greater for animals fed reconstituted grain (P = 0.01). Likewise, animals fed reconstituted corn tended to have greater butyrate ruminal concentration (P = 0.08). Keratinized layer thickness did not differ among treatments (P > 0.10). Therefore, reconstituted grains (especially corn) decrease the mRNA expression of genes involved in volatile fatty acids transport and pH control in the rumen epithelium.
Highlights
Corn and sorghum are typically the primary grains used for finishing cattle in South American feedlots [1]
Digestibility variables were affected by ingredients; sorghum treatments tended (P = 0.08) to have higher organic matter (OM) ruminal digestibility than corn
We hypothesized that the animals fed reconstituted grains would present greater mRNA expression of key genes involved in volatile fatty acids (VFA) transport in their ruminal epithelium than animals fed dry ground grains
Summary
Corn and sorghum are typically the primary grains used for finishing cattle in South American feedlots [1]. Due to their high costs, these grains are usually processed to enhance the efficiency of digestion, reducing waste and improving livestock profitability. The main objective of grain processing is to increase the energy availability by facilitating access to grain starch for rumen microorganisms or/and intestinal digestion [2, 3]. Typical grain processing methods such as; dry corn, may enhance digestibility, there are still high starch losses when animals are fed high-grain levels diets [4]. High ruminal fermentation diets can increase microbial yield [9] and energy available to the animal, there is a risk of developing acidotic epithelial damage, affecting nutrient absorption
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