Comparative analysis of bovine abomasal mucosal immune responses resulting from pasture/grass or grain feeding

Authors: Tuo, Wenbin; LI, LEI - University Of Maryland; LV, YINGJUN - University Of Maryland; BROWN, DEDRA - Texas A&M University; DAVIS, WILLIAMS - Washington State University; SONG, JIUZHOU - University Of Maryland; Zarlenga, Dante; XIAO, ZHENGGUO - University Of Maryland

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2016
Publication Date: 1/15/2016
Citation: Tuo, W., Li, L., Lv, Y., Brown, D., Davis, W., Song, J., Zarlenga, D.S., Xiao, Z. 2016. Comparative analysis of bovine abomasal mucosal immune responses resulting from pasture/grass or grain feeding. Veterinary Parasitology. 229:118-125.

Interpretive Summary: Beef cattle raised under grass-fed or organic conditions reach a desired market weight later than the grain-fed cattle. The current explanation for this delay in growth is that grass-feeding alone provides lower levels of nutrition when compared to cattle fed with grain. In addition to nutrition, we believe that pasture-transmitted gastrointestinal (GI) nematode parasites may play an important role in reducing feed conversion and weight gain. A comparative study was performed to understand the difference in levels of inflammation and pathology in the cattle abomasum, the 4th stomach of ruminants which functions similar to that of the mono-gastric animals, between grain-fed (with limited or no parasite exposure) and grass-fed cattle. Our results showed that cattle raised on grain had very low levels of inflammation and essentially no pathology, whereas cattle allowed to graze on pasture had high levels of inflammation and pathology in the abomasum. Based on the immunological characteristics of the nematode parasite identified in the tissue, the inflammation and pathology in the abomasum of grass-fed cattle was likely caused by the cattle-specific stomach worm, Ostertagia ostertagi. The inflammation and pathology can affect the efficiency of nutrient digestion in the stomach and may in part be responsible for further reduced feed conversion and weight gain. Due to the endemic and highly pathogenic nature of O. ostertagi in temperate regions, the productivity of cattle having access to pastures with reduced or prohibited use of anthelmintics is negatively impacted. Understanding of immune responses to pasture-borne nematode parasites will facilitate development of vaccines which are allowed to use in organically raised cattle. These results are useful to the cattle industry.

Technical Abstract: Differences in the nutrient composition of beef derived from cattle fed with grass or grain has been documented, where meat from grass-fed animals afford specific nutritional benefits to human health. However, the effects of these two different cattle rations on abomasal mucosal immunity have never been investigated particularly in light of the potential exposure of pasture-fed animals to environmentally-transmitted gastrointestinal nematode parasites. In the present study, the abomasal mucosal immune responses resulting from grass- or grain-fed animals were compared. Our results indicate that grass-fed cattle displayed inflammed abomasal tissues accompanied by enlarged draining lymph nodes in the presence of acquired O. ostertagia larvae along with detectable Ostertagia-specific antibodies in circulation. The level of B cells was elevated in the abomasal mucosa in the presence (nodular) or absence (non-nodular) of Ostertagia-specific pathology, where B cells were 4-fold higher in the nodular mucosa. Foxp3+ CD4 T cells were also noticeably elevated in both the abomasal mucosa and in peripheral blood, but were only slightly higher in non-nodular mucosa than in the nodular mucosa. In contrast, grain-fed animals presented no enlargement of abomasal draining lymph nodes and exhibited little to no immune cell infiltration in the abomasal mucosa as analyzed microscopically and by flow cytometry. Further, grass-fed animals had higher numbers of mucosal mast cells when compared to grain-fed animals, though mucosal mast cells were high in all animals. Overall, grass-fed cattle displayed significantly higher levels of inflammation and pathology in the abomasum and may explain in part, reduced feed conversion and weight gain relative to grain-fed animals. The results of this study emphasize the need for parasite control using host immune-based strategies which are compatible with the organic cattle production system.