Form of calf diet and the rumen. I: Impact on growth and development

摘要

Preweaning diet is known to affect rumen tissueappearance at the gross level. The objectives of thisexperiment were to investigate effects of different preweaningdiets on the growth and development of therumen epithelium and on putative rumen epithelialstem and progenitor cell measurements at the gene andcell levels. Neonatal Holstein bull calves (n = 11) wereindividually housed and randomly assigned to 1 of 2diets. The diets were milk replacer only (MRO; n = 5)or milk replacer with starter (MRS; n = 6). Diets wereisoenergetic (3.87 ± 0.06 Mcal of metabolizable energyper day) and isonitrogenous (0.17 ± 0.003 kg/d of apparentdigestible protein). Milk replacer was 22% crudeprotein, 21.5% fat (dry matter basis). The textured calfstarter was 21.5% crude protein (dry matter basis).Water was available ad libitum and feed and water intakewere recorded daily. Putative stem and progenitorcells were labeled by administering a thymidine analog(5-bromo-2′-deoxyuridine, BrdU; 5 mg/kg of bodyweight in sterile saline) for 5 consecutive days and alloweda 25-d washout period. Calves were killed at 43± 1 d after a 6 h exposure to a defined concentrationof volatile fatty acids. We obtained rumen tissue fromthe ventral sac and used it for immunohistochemicalanalyses of BrdU (putative stem and progenitor cells)and Ki67 (cell proliferation), gene expression analysis,and morphological measurements via hematoxylin andeosin staining. Epithelial stem and progenitor cell genemarkers of interest, analyzed by real-time quantitativePCR, were β1-integrin, keratin-14, notch-1, tumor proteinp63, and leucine-rich repeat-containing G proteincoupledreceptor 5. Body growth did not differ by diet,but empty reticulorumens were heavier in MRS calves(MRS: 0.67 ± 0.04 kg; MRO: 0.39 ± 0.04 kg). The percentageof label-retaining BrdU basale cells was higherin MRO calves than in MRS calves (2.0 ± 0.3% vs. 0.3± 0.2%, respectively). We observed a higher percentageof basale cells undergoing proliferation in MRS calvesthan in MRO calves (18.4 ± 2.6% vs. 10.8 ± 2.8%,respectively). Rumen epithelial gene expression wasnot affected by diet, but the submucosa was thicker inMRO calves and the epithelium and corneum/keratinlayers were thicker in MRS calves. Presumptive stemand progenitor cells in the rumen epithelium were identifiableby their ability to retain labeled DNA in thelong term, changed proliferative status in response todiet, and likely contributed to observed treatment differencesin rumen tissue thickness.