The importance of the immunological competence of the mink dam for the development of pre-weaning diarrhea in mink kits

Abstract

Mink are bred in captivity in Denmark for their pelts. During their lifecycle on the farms, the mink can get affected by different diseases. One of the common diseases during the pre-weaning period is the pre-weaning diarrhea (PWD) syndrome also referred to as “wet”/”sticky”/“greasy” kits. It affects all the kits in a litter and severely compromises the welfare of the kits and can lead to huge financial losses for the mink farmer. Morbidity is high and if the kits are severely affected it can lead to dehydration and eventually death. It is considered multifactorial with no specific cause, and no cure or preventive measures are currently available. During this period the usage of antimicrobials are at their highest, increasing the risk of developing resistant bacteria. Alternative disease prevention and treatment could be found in the protective immunological factors delivered by the mink dam, as it has been shown that cross-fostering kits affected by PWD to another litter improved the health of the kits. Furthermore, 1-year-old dams are more likely to produce kits with PWD than 2-year-old dams, indicating the delivery of a more naïve immune system of the 1-year-old dams to the offspring. During this PhD the overall aim was to investigate a possible association between the dam’s immune factors and the protection against PWD. As the mink kits are born with very low levels of circulating immunoglobulin G (IgG) our hypothesis is that the mammary secretions of IgG and the IgG uptake in mink kits are crucial in preventing PWD. To analyze the IgG concentration from both serum and milk, a sensitive and robust assay is needed. As there are no commercially available methods for quantifying mink IgG, we developed and validated a sandwich enzyme-linked immunosorbent assay (ELISA). Analysis of serum derived from healthy mink kits revealed a within litter effect of IgG, enabling the use of only one kit from each litter in subsequent studies as a proxy measure for all the kits in the litter. Additionally, the kits IgG concentration in serum reached a plateau after 8 days, after which there was only minor changes in the concentration until the kits were 23 days old. Analyzing the species-specific uptake of IgG in 3-day-old kits by oral gavage with either mink enteritis virus (MEV) specific IgG or porcine IgG, revealed an increased uptake of MEV-IgG compared to porcine IgG after 3 hours. The serum IgG concentration from kits affected by PWD showed a reduction in concentration compared to healthy controls when the kits were 13/15 days old, indicating an association between serum IgG concentration and development of PWD. We investigated the serum concentration of a biomarker for inflammation; the acute phase protein-serum amyloid A (SAA), in both healthy kits and kits affected by PWD and found increased SAA levels in kits affected by PWD. In the same kits we demonstrated a difference in bacterial isolates between healthy and kits affected by PWD, which was also observed in the intestinal sections during histopathology. Kits affected by PWD showed disrupted gut architecture with, vacuolated enterocytes, atrophy of the villi in the small intestine, and mucosal atrophy in the large intestine. Furthermore, adherence of coccoid bacteria to the intestinal wall was most frequently observed in PWD-affected kits, which could be associated with the increased SAA concentration. Mink astrovirus has frequently been observed in kits affected by PWD, however also in healthy kits. We investigated the presence of specific antibodies against astrovirus in mink dams and kits, but found no astrovirus specific IgG in the milk and serum of the dams and serum of the kits. These combined findings are important for developing new preventative immunoglobulin supplement-based strategies for protecting mink kits against outbreaks of PWD. Future studies should focus on and investigate the possible usage of IgG as an immune boost or as treatment out on the farms. In addition, the usage of SAA as a biomarker for the health status of the mink should also be researched.