Impacts of corn processing and urea source on enzyme activities and gene expression levels of carbohydrate - and nitrogen-metabolism related in tissues of Nellore bulls

Abstract

The aim of the study was to evaluate how different urea sources associated with corn processing influence the expression of genes related to urea, glucose, volatile fatty acids transport, ruminal maintenance, and pH, as well as genes linked to the urea cycle in the liver of finishing Nelore steers. Four treatments were tested: ground corn with conventional urea (GC+UC), ground corn with post-ruminal release urea (GC+PRU), rehydrated corn with conventional urea (REC+UC), and rehydrated corn with post-ruminal release urea (REC+PRU), over a 100-day period. The diet comprised 28% corn silage, 63% corn (ground or rehydrated), 6.3% soybean meal, 0.1% ammonium sulfate, and 3% mineral vitamin supplement and monensin. Samples from the rumen, jejunum, kidneys, and liver were collected for gene expression analyses via RT-qPCR and enzymatic activity. Steers fed rehydrated corn showed higher final weight, average daily gain, feed efficiency, and carcass gain. Cattle fed ground corn had higher nitrogen intake, fecal nitrogen excretion, lower nitrogen utilization efficiency, resulting in reduced nitrogen retention (P ≤ 0.04). The inclusion of post-ruminal release urea in the diet also increased final body weight, feed efficiency, and nitrogen utilization efficiency (P ≤ 0.004). In terms of gene expression, in the rumen, there was an interaction between corn type and urea source for genes AE2 and GPR41, with enhanced expression observed with the combination of ground corn and conventional urea (P = 0.01). AQP7 and TRPV3 expression was higher with ground corn feeding (P < 0.04). In the jejunum, genes AQP3 and AQP10 were more expressed with rehydrated corn consumption (P < 0.04), while AQP7 and ARG1 tended to be more expressed (P < 0.09). In the liver, CPS1 gene expression increased with rehydrated corn consumption (P = 0.02), and there was also a trend towards increased ASL1 mRNA expression (P = 0.09). In the kidneys, UT-B mRNA was higher with post-ruminal release urea feeding (P = 0.001). Additionally, the activity of several enzymes, such as α-amylase, chymotrypsin, urease, and maltase, was influenced by the type of corn and urea source in the diet, showing different metabolic responses in the evaluated tissues (P ≤ 0.04). In summary, the use of rehydrated corn and post-ruminal release urea improved steer performance without affecting dry matter intake, and nutrient transport-related genes responded differently to diet variations.