Light microscopic observations of the ruminal papillae of cattle on diets with divergent forage to cereal ratios

Abstract

High levels of supplementation with cereal increases production rates in cattle but can increase incidence of disease, ranging from mild indigestion to acute ruminal acidosis and death. Therefore, there is motivation to determine biological markers which can be used to identify whether animals have been, or are being fed, sufficient or excessive cereals. This study aimed to describe light microscopic findings from animals being fed diverse dietary cereal proportions and to test the performance of a novel rumen epithelial scoring system. Rumen wall tissue samples were obtained from the abattoir from 195 cattle from 11 Scottish farms and processed for histological examination. Light microscopic examination was used to characterise ruminal epithelial response to dietary challenge. Secondary objectives included describing the distribution of immune-related cells in bovine ruminal epithelium and assessing the use of a modified Elastin Martius Scarlet Blue stain (EMSB) for histological examination of the rumen epithelium. Cells staining positive for cluster of differentiation 3 were distributed mainly in the lower layers of the stratum basale and were found in higher densities in animals offered lower cereal proportion diets. Cells staining positive for major histocompatibility complex class 2 (MHCII) were most common in perivascular locations and in the junction between the lower stratum basale and the propria-submucosa. The density of MHCII positive staining cells was higher in animals on lower cereal diets. The level of supplementation with cereal was also associated with the thickness of the stratum corneum (SCT) and stratum granulosum (SGT), the integrity of the stratum corneum and sloughing of cornified cells. There were no advantages in using EMSB stain over haematoxylin and eosin (H&E) in this scoring system. We concluded that a scoring system that included only SCT, SGT and a measure of the loss of appearance of intercellular space allowed differentiation of groups of animals according to the level of cereal supplementation.

Keywords: Acidosis; Bovine; Epithelium; Histology; Rumen.

Fig. 1

Representative section of bovine rumen papilla stained with (A–B) Haematoxylin and Eosin (H&E) or (C–D) Elastin Martius Scarlet Blue (EMSB) at ×10 and ×40 magnifications, respectively.

Fig. 2

Bovine rumen papillae showing measurements and derivation of (A) stratum corneum thickness (SCT), shown in lines 1–5 (L1–L5), and stratum granulosum thickness (SGT), shown in L6–L10, both at ×40 magnification; and (B) vessel diameter (VASCD) at ×40 magnification on sections stained with haematoxylin and eosin (H&E) (L1–L2).

Fig. 3

Representative examples of categorical data type shown in bovine rumen papillae. (A) Low and (B) high cytoplasmic swell score where the loss of cellular definition is evident, with arrows pointing to intercellular spaces. (C) Low and (D) high perinuclear vacuolation score with arrowheads pointing to perinuclear vacuoles. (E) Low and (F) high clefting scores; (G) Low and (H) high stratum corneum integrity scores; and (I) Low and (J) high slough scores. Magnification at ×4 (E–F), ×10 (G–J) and ×40 (A–D) with the scale bars on the last image of each magnification.

Fig. 4

Representative immunohistochemical staining for myeloperoxidase, cluster of differentiation 3 (CD3) and major histocompatibility complex 2 (MHCII) in bovine rumen papillae. (A) Myeloperoxidase-stained microabscess between stratum corneum and granulosum. (B) CD3-stained papilla showing the typical distribution of CD3 positive staining cells, mainly at the junction between the lower stratum basale and the propria-submucosa. (C) MHCII-stained papilla showing the typical, predominantly perivascular, distribution of MHCII positive staining cells, particularly in the lower stratum basale and the propria-submucosa. Magnification at ×40.