title: Examination of the molecular control of ruminal epithelial function in response to dietary restriction and subsequent compensatory growth in cattle.
abstract: BACKGROUND
  The objective of this study was to investigate the effect of dietary restriction and subsequent compensatory growth on the relative expression of genes involved in volatile fatty acid transport, metabolism and cell proliferation in ruminal epithelial tissue of beef cattle. Sixty Holstein Friesian bulls (mean liveweight 370 ± 35 kg; mean age 479 ± 15 d) were assigned to one of two groups: (i) restricted feed allowance (RES; n = 30) for 125 d (Period 1) followed by ad libitum access to feed for 55 d (Period 2) or (ii) ad libitum access to feed throughout (ADLIB; n = 30). Target growth rate for RES was 0.6 kg/d during Period 1. At the end of each dietary period, 15 animals from each treatment group were slaughtered and ruminal epithelial tissue and liquid digesta harvested from the ventral sac of the rumen. Real-time qPCR was used to quantify mRNA transcripts of 26 genes associated with ruminal epithelial function. Volatile fatty acid analysis of rumen fluid from individual animals was conducted using gas chromatography.
  
  
  RESULTS
  Diet × period interactions were evident for genes involved in ketogenesis (BDH2, P = 0.017), pyruvate metabolism (LDHa, P = 0.048; PDHA1, P = 0.015) and cellular transport and structure (DSG1, P = 0.019; CACT, P = 0.027). Ruminal concentrations of propionic acid (P = 0.018) and n-valeric acid (P = 0.029) were lower in RES animals, compared with ADLIB, throughout the experiment. There was also a strong tendency (P = 0.064) toward a diet × period interaction for n-butyric with higher concentrations in RES animals, compared with ADLIB, during Period 1.
  
  
  CONCLUSIONS
  These data suggest that following nutrient restriction, the structural integrity of the rumen wall is compromised and there is upregulation of genes involved in the production of ketone bodies and breakdown of pyruvate for cellular energy. These results provide an insight into the potential molecular mechanisms regulating ruminal epithelial absorptive metabolism and growth following nutrient restriction and subsequent compensatory growth.
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, 4 Ireland ; Animal and Bioscience Research Department, Animal & Grassland Research and Innovation Centre, Teagasc Grange, Dunsany, Co. Meath, Ireland ; UCD Earth Institute, University College Dublin, Belfield, Dublin, 4 Ireland.
authors.forename: Emma
authors.initials: E
authors.lastname: O'Shea
authors.affiliation: Animal and Bioscience Research Department, Animal & Grassland Research and Innovation Centre, Teagasc Grange, Dunsany, Co. Meath, Ireland.
authors.forename: Sinéad M
authors.initials: SM
authors.lastname: Waters
authors.affiliation: Animal and Bioscience Research Department, Animal & Grassland Research and Innovation Centre, Teagasc Grange, Dunsany, Co. Meath, Ireland.
authors.forename: Kate
authors.initials: K
authors.lastname: Keogh
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, 4 Ireland.
authors.forename: Alan K
authors.initials: AK
authors.lastname: Kelly
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, 4 Ireland ; Animal and Bioscience Research Department, Animal & Grassland Research and Innovation Centre, Teagasc Grange, Dunsany, Co. Meath, Ireland.
authors.forename: David A
authors.initials: DA
authors.lastname: Kenny
keywords: Beef cattle; Compensatory growth; Feed efficiency; Nutrient restriction; Rumen epithelium