Abstract
Compensatory growth (CG) is utilised worldwide in beef production systems as a management approach to reduce feed costs. However the underlying biology regulating the expression of CG remains to be fully elucidated. The objective of this study was to examine the effect of dietary restriction and subsequent re-alimentation induced CG on the global gene expression profile of ruminal epithelial papillae. Holstein Friesian bulls (n = 60) were assigned to one of two groups: restricted feed allowance (RES; n = 30) for 125 days (Period 1) followed by ad libitum access to feed for 55 days (Period 2) or (ii) ad libitum access to feed throughout (ADLIB; n = 30). At the end of each period, 15 animals from each treatment were slaughtered and rumen papillae harvested. mRNA was isolated from all papillae samples collected. cDNA libraries were then prepared and sequenced. Resultant reads were subsequently analysed bioinformatically and differentially expressed genes (DEGs) are defined as having a Benjamini-Hochberg P value of <0.05. During re-alimentation in Period 2, RES animals displayed CG, growing at 1.8 times the rate of their ADLIB contemporary animals in Period 2 (P < 0.001). At the end of Period 1, 64 DEGs were identified between RES and ADLIB, with only one DEG identified at the end of Period 2. When analysed within RES treatment (RES, Period 2 v Period 1), 411 DEGs were evident. Genes identified as differentially expressed in response to both dietary restriction and subsequent CG included those involved in processes such as cellular interactions and transport, protein folding and gene expression, as well as immune response. This study provides an insight into the molecular mechanisms underlying the expression of CG in rumen papillae of cattle; however the results suggest that the role of the ruminal epithelium in supporting overall animal CG may have declined by day 55 of re-alimentation.
Highlights
In beef cattle production, profitability is driven by the efficient conversion of feed to carcass growth
Feed conversion ratio was better in restricted feed allowance (RES) animals during re-alimentation induced Compensatory growth (CG) in Period 2 compared to RES Period 1 and ADLIB animals across both periods, (Period 1: RES: 9.5 (0.45); ADLIB: 6.71 (0.48); Period 2: RES: 4.87 (0.63); ADLIB: 9.98 (0.69); P < 0.0001)
During subsequent re-alimentation induced CG, our data suggest that greater nutrient intake is consistent with an upregulation in transcriptional activity of ruminal epithelial tissue, which may in turn lead to greater nutrient uptake through an increase in papillae surface area and contribute to increased feed efficiency typical of CG, supporting the accelerated growth phenomenon of both the rumen as well as the animal
Summary
Profitability is driven by the efficient conversion of feed to carcass growth. Given that feed inputs typically account for up to 75% of the variable costs [1] any improvement in lifetime nutrient utilization will enhance economic efficiency of beef production systems. Enhanced feed efficiency can lead to improved profitability but has been shown to result in a reduction in ruminal methane emissions [2, 3] reducing the carbon footprint of beef production. The exploitation of the CG phenomenon is one management strategy implemented by producers to reduce the overwintering feed costs of cattle production [5, 6] and is utilised worldwide [7,8,9,10,11]. The underlying molecular mechanisms controlling the expression of CG, remain to be determined
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