A case-control study of herd- and cow-level risk factors associated with an outbreak of Mycoplasma mastitis in Nemuro, Japan

Highlights

• Risk factors of Mycoplasma mastitis were evaluated by case-control studies.

• Conscious teat wiping before milking was negatively associated with Mycoplasma mastitis.

• Introduction of cattle was a herd level risk factor.

• Cows with a high milk yield were more susceptible against Mycoplasma mastitis.

• Previous acute mastitis without isolation of causal pathogens was a risk factor.

Abstract

The objective of this case-control study was to determine the herd- and cow-level risk factors associated with an outbreak of Mycoplasma bovine mastitis in the winter of 2014–2015 in Nemuro, Hokkaido, Japan. Two questionnaire surveys were sent to all 40 Mycoplasma-infected farms in the area and 73 non-infected farms for the farm-level analysis. Infected cows were matched to twice the number of non-infected cows in the same herds by parity and days after calving. Movement records, dairy herd test records, and clinical records of infected cows and matched non-infected cows were collected for the cow-level analysis. Risk factors for Mycoplasma infection were explored by multivariable analyses at both levels. In the herd-level analysis, tie stall housing for milking cows (odds ratio [OR] = 0.20, 95 % confidence interval [CI]: 0.07-0.60, p =  0.004), consciously wiping of teat openings before milking (OR = 0.15, 95 % CI: 0.02-0.76, p =  0.030), and use of paper towels to wipe teats (OR = 0.31, 95 % CI: 0.09-0.92, p =  0.045) were identified as preventive factors, whereas introduction of cattle (OR = 3.43, 95 % CI: 1.14–10.86, p =  0.030) was identified as a risk factor. In the cow-level analysis, a history of presence in livestock markets (OR = 10.80, 95 % CI: 1.12–104.38, p =  0.040), higher milk yield 2 months prior to Mycoplasma infection (OR = 1.09, 95 % CI: 1.02–1.18, p =  0.014), and previous diagnosis of acute mastitis without isolation of the causal pathogen (OR = 3.14, 95 % CI: 0.86–11.41, p =  0.082) were identified as risk factors. These results highlight the importance of proper milking hygiene control and quarantine of introduced cattle to prevent Mycoplasma infection.

Introduction

Bovine mastitis caused by Mycoplasma spp. is a highly contagious disease and a major problem in the global dairy industry (Nicholas et al., 2016). The economic impact of Mycoplasma mastitis is high because the disease is considered untreatable with antibiotics, and thus, culling of infected cows is commonly recommended for within-farm control. Several Mycoplasma species have been linked to bovine mastitis, with Mycoplasma bovis being the most important (González and Wilson, 2003). In addition to mastitis, Mycoplasma spp. also cause a variety of other diseases, including pneumonia, otitis media, and arthritis (Maunsell et al., 2011).

The primary route of Mycoplasma infection is udder-to-udder spread by milking equipment, hands, or teat dipping (Maunsell and Donovan, 2009). Calves can be infected by ingestion of contaminated colostrum or waste milk and through aerosols (Foster et al., 2009; Maunsell et al., 2011). Intra-uterine or intra-mammary transmission of Mycoplasma from a dam to a calf has also been reported (Pfutzner and Schimmel, 1985; Fox et al., 2008). Contaminated semen is also a route of Mycoplasma infection (Haapala et al., 2018). Several risk factors for Mycoplasma mastitis have been reported as well. Commonly identified risk factors include large herd size and introduction of cattle (González and Wilson, 2003). Potential reasons larger herds have a higher risk of contracting mastitis are that they tend to have more introduced cattle and a higher chance of a rare infection event (Fox et al., 2003). In addition, a higher frequency of Mycoplasma infection in winter has been reported (Maunsell and Donovan, 2009).

Hokkaido is the largest dairy production area in Japan, producing more than half of the cow milk in the country (Ministry of Agriculture‚ Forestry and Fisheries, 2018). Hokkaido is the northernmost prefecture in Japan and typically covered in deep snow in winter. Mycoplasma mastitis is a major dairy issue in Japan, with an estimated herd-level prevalence of 3.8 % in the Tokachi area of Hokkaido (Ministry of Agriculture‚ Forestry and Fisheries, 2018; The Federation of Agricultural Cooperatives in Nemuro, 2018). An increase in the occurrence of Mycoplasma mastitis cases was noted from 2014 to 2015 in the Nemuro area (the eastern part of Hokkaido) by the Nemuro Mycoplasma Mastitis Control Committee (NMMCC), which consists of local agricultural cooperatives, the Federation of Agricultural Cooperatives in Nemuro (FACN), the Hokkaido Dairy Milk Recording and Testing Association, veterinarians in the Hokkaido Higashi agriculture mutual aid association (AMAA) and Nemuro Prefectural Livestock Hygiene Service Center, agriculture extension officers in the prefectural agriculture extension office, and the prefectural livestock research institute. Three to six times per year, the committee conducts PCR-based bulk tank milk screening tests (Higuchi et al., 2011) for Mycoplasma spp. for all of the member dairy farms of the agricultural cooperatives. Although possible risk factors have been reported in the literature, little is known regarding the relative importance of these factors in Japan.

In the present case-control study, we conducted separate analyses of both cow- and herd-level risk factors for Mycoplasma mastitis by (1) comparing infected and non-infected farms, and (2) investigating the records of cattle movement, milk testing, and clinical services regarding infected and non-infected cows at the infected farms.