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Livestock Management impacts on disease risk and control -- Assessment 1

Tsiouris et al[1] used a 2x2 experimental design to investigate effects of stocking density (15 or 30 birds/m2) and of direct challenge with Clostridium perfringens (4x108 cfu per inoculation) on the prevalence and severity of subclinical necrotic enteritis in Cobb broiler chicks. In addition to gross and histologic pathology, ingesta pH and viscosity, caecal C.perfringens counts, and productivity measures were compared between groups using ANOVA.

Higher stocking density was associated with increased disease prevalence and increased gross intestinal lesion scores in challenged but not unchallenged birds, suggesting stocking density and pathogen exposure act synergistically to induce disease. This is consistent with other studies that demonstrate that necrotic enteritis is multifactorial.[2.3] The current experiment provided equivocal evidence that higher stocking density increases favorability of the gut environment  (low pH, high viscosity) to C.perfringens growth, although higher stocking density was associated with higher C.perfringens caecal counts in unchallenged birds. This could warrant further investigation such as quantification of faecal shedding and microbial analysis of litter; however, any further investigations should distinguish between virulent and avirulent C.perfringens strains. Additionally, bird immune competence could be measured using immunohistochemistry and gene expression studies[4,5].

Farmers may resist the argument that stocking density jeopardizes welfare, not only because the disease is subclinical, but because birds show increased weight gain at higher stocking densities. Moreover, more efficient feed conversion translates to increased profitability. Strategies to reduce the prevalence of necrotic enteritis at higher stocking density may include manipulation of diet and feeding strategies, litter management, temperature control, anti-coccidial vaccination, and using resistant slower-growing chicken breeds. [6-9]

Schewe et al[10] collect data via voluntary mail surveys from dairy farms in Michigan, Pennsylvania, and Florida on sociodemographics, milking proficiency and systems, cow environment, infected cow monitoring and treatment, farm labor, and attitudes towards mastitis. The effect of these variables on reported bulk tank somatic cell count (BTSCC) was analyzed using principal component analysis and linear regression.

The data may be skewed by the fact that response to a survey may reflect overall farm organization and farmer attitude. Indeed, a higher threshold of concern for BTSCC was associated with higher BTSCC. Comparison of the current data set to that from the USDA, however, indicated that it was representative. Ideally, reported BTSCC and farm practices would be confirmed by some direct observation.

Unsurprisingly, proven preventative practices, such as use of internal teat sealants and blanket dry cow therapy, were associated with lower BTSCC. The survey could be expanding to include information on nutrition and cow breeds/genetics as factors contributing to milking immunity [11,12].

Importantly, large herd size was associated with higher BTSCC while several management variables, such as ensuring compliance with milking protocols, were associated with lower BTSCC. The authors thus conclude that management challenges associated with expansion of herd size have affected BTSCC. This supports the general understanding that dairy farm management is rapidly evolving and that labour relations are increasingly complex[13]. Possible expansion on the study would be to survey the managers’ openness to management intervention and to survey employee attitudes directly.

'''REFERENCES '''

1. Tsiouris, V., Georgopoulou, I., Batzios, C., Pappaioannou, N., Ducatelle, R., & Fortomaris, P. (2015). High stocking density as a predisposing factor for necrotic enteritis in broiler chicks. Avian Pathology, 44(2), 1-31.

2. Moore, R. (2016). Necrotic enteritis predisposing factors in broiler chickens. Avian Pathology, 45(3), 275-281.

3. Timbermont, L., Haesebrouck, Ducatelle, & Van Immerseel. (2011). Necrotic enteritis in broilers: An updated review on the pathogenesis. Avian Pathology, 40(4), 341-347.

4. Bar Shira, Enav, & Friedman, Aharon. (2018). Innate immune functions of avian intestinal epithelial cells: Response to bacterial stimuli and localization of responding cells in the developing avian digestive tract. PLoS ONE, 13(7), E0200393.

5. Athanasiadou, S., Russell, K., Kaiser, P., Kanellos, T., Burgess, S., Mitchell, M., Sparks, N. (2015). Genome wide transcriptomic analysis identifies pathways affected by the infusion of Clostridium perfringens culture supernatant in the duodenum of broilers in situ. Journal of Animal Science, 93(6), 3152-63.

6. Tsiouris, V., Georgopoulou, I., Batzios, C., Pappaioannou, N., Ducatelle, R., & Fortomaris, P. (2018). Heat stress as a predisposing factor for necrotic enteritis in broiler chicks. Avian Pathology, 47(6), 616-624.

7. Tsiouris, V., Georgopoulou, I., Batzios, C., Pappaioannou, N., Diakou, A., Petridou, E., Fortomaris, P. (2013). The role of an attenuated anticoccidial vaccine on the intestinal ecosystem and on the pathogenesis of experimental necrotic enteritis in broiler chickens. Avian Pathology, 42(2), 163-170.

8. Tsiouris, V., Georgopoulou, I., Batzios, C., Pappaioannou, N., Ducatelle, R., & Fortomaris, P. (2015). The effect of cold stress on the pathogenesis of necrotic enteritis in broiler chicks. Avian Pathology, 44(6), 430-435.

9. Tsiouris, V., Georgopoulou, I., Batzios, C., Pappaioannou, N., Ducatelle, R., & Fortomaris, P. (2014). Temporary feed restriction partially protects broilers from necrotic enteritis. Avian Pathology, 43(2), 1-27.

10. Schewe, Kayitsinga, Contreras, Odom, Coats, Durst, Erskine. (2015). Herd management and social variables associated with bulk tank somatic cell count in dairy herds in the eastern United States. Journal of Dairy Science, 98(11), 7650-7665.

11. Ingvartsen, K., & Moyes. Nutrition, immune function and health of dairy cattle (2013). Animal, 7(1), 112-122.

12. Mallard, B. A., Emam, M., Paibomesai, M., Thompson-Crispi, K., & Wagter-Lesperance, L. (2015). Genetic selection of cattle for improved immunity and health. Japanese Journal of Veterinary Research, 63, S37-S44.

13. Findeis, J., & Ovid Technologies, Inc. (2002). The dynamics of hired farm labour constraints and community responses. Wallingford, U.K. ; New York, N.Y.: CABI Pub. �