Rumen papillae morphology of beef steers relative to gain and feed intake and the association of volatile fatty acids with kallikrein gene expression

Abstract

Feed costs are the most expensive input in beef production. Improvement in the ability of beef cattle to convert feed into meat would lower feed inputs and reduce the cost of production. The rumen epithelium is responsible for absorption and metabolism of nutrients and microbial by-products, and may play a significant role in gain or feed intake. Our objective was to determine the relationships among rumen papillae morphology, gene expression, volatile fatty acid concentrations, and gain and feed intake. Average daily gain (ADG) and average daily feed intake (ADFI) were collected on a crossbred population of beef steers over three feeding trials. Based on feed intake and weight gain differences, 48 steers were selected for the project (16 from each feeding study). At harvest, rumen epithelial samples were taken from three locations in the rumen of each animal. The number of papillae on 1 cm2 of epithelium was counted to determine density. Papillae (n=30) from each sample were measured for length and width. The density, length, and width were combined to determine surface enlargement factor (SEF). None of the morphological characteristics of the papillae (length, width, density or SEF) were associated with feed intake or gain (P≥0.10). Ruminal fluid was collected from steers (n=15) in the third trial for volatile fatty acid (VFA) analysis to determine if a relationship between VFA and ADG or ADFI existed. No differences in volatile fatty acid (VFA) concentrations were associated (P≥0.17) with ADFI or ADG. VFA variation was also evaluated for a relationship with kallikrein (KLK) genes since ruminal butyrate concentrations have previously been associated with the transcript abundance KLK genes. Additionally, qRT-PCR data showed that variation in the transcript abundance of KLK6,8-10, and 13 associated with feed intake in our first trial of steers. Thus, we evaluated the transcript abundance of eight KLK genes in rumen papillae from steers in the third trial (n=16). Expression levels of KLK5 correlated with valerate concentrations in the rumen (P<0.05), KLK10 correlated with acetate concentrations in the rumen (P<0.05), KLK12 correlated with acetate and butyrate concentrations in the rumen (P<0.05), and the expression levels of KLK9 and KLK10 were associated with gain. While rumen papillae morphology was not associated with beef steer gain or intake, our data suggests members of the kallikrein gene family have a relationship with the VFA environment in the rumen, and also appear to play a role in the highly correlated traits of ADG and ADFI.