Sheep and farm level factors associated with contagious ovine digital dermatitis: A longitudinal repeated cross-sectional study of sheep on six farms

Abstract

Contagious ovine digital dermatitis (CODD) is a cause of severe lameness in sheep in the UK currently affecting approximately 50% of farms. Six farms were studied in North Wales to investigate (1) the prevalence dynamics of CODD, (2) the association between sheep with CODD and potential risk factors and (3) the impact of CODD on lameness in sheep. The farms were visited at approximately two-month intervals between June 2012 and October 2013 and 6515 sheep were examined. The mean sheep level prevalence of CODD varied between farms (2.5-11.9%). Within farms, prevalence may increase in the late summer/early autumn and after housing. Environmental risk factors included larger flocks, lowland pasture, lush pasture and poached pasture. Co-infection of a foot with footrot was strongly associated with CODD in that foot (OR: 7.7 95% CI: 3.9-15.5 P<0.001) but negatively associated with co-infection of a foot with interdigital dermatitis (OR: 0.04 95% CI: 0.02-0.1 P<0.001). Reinfection with CODD was observed in 78 individual sheep but there was no re-infection at foot level. Lameness on all farms reduced during the study and seasonal changes in lameness followed similar patterns to those for CODD. Infection with CODD leads to a greater increase in locomotion score compared to footrot or interdigital dermatitis and CODD lesion grade was strongly associated with being lame. Sheep with CODD in more than one foot were more likely to be lame (OR: 25.0 95% CI: 12.5-49.9 P<0.001) than those with just one foot affected (OR:10.0 95% CI: 8.6-11.6 P<0.001). The biggest risk factor for CODD is co-infection with footrot and therefore control of footrot should help reduce the risk of CODD on affected farms. Furthermore environmental risk factors for CODD are similar to those for footrot adding weight for control strategies that target both diseases in tandem. The routine repeated gathering of sheep for the purposes of treating all lame sheep might be an effective control strategy for lameness on some sheep farms. Effective systemic immunity to CODD in sheep appears to be lacking, as 78 sheep were observed to be re-infected with CODD during the survey. However, there is epidemiological evidence that there may be some local immunity within the foot warranting further investigation.

Welfare Assessment on Pasture: A Review on Animal-Based Measures for Ruminants

“…Animal-based measures (ABMs) evaluated on small ruminants concerning the comfort principle. Fleece fleece condition score 0-2 sheep DA AUS [79,82] dag score score 0-5 sheep DA AUS [79,82] Mastitis physical inspection of the udder (presence of fibrosis, swelling, inflammation, abscesses) score 0-4 sheep DA AUS [82] Tail length tip of the vulva covered by the tail yes/no sheep DA AUS [79,82] Claw alterations foot-wall integrity score 0-3 sheep DA AUS [79] hoof overgrowth score 0-2 sheep DA AUS [79] contagious ovine digital dermatitis yes/no sheep DA GBR [76,77] footrot yes/no sheep DA GBR [76,77] Interdigital dermatitis yes/no sheep DA GBR [76,77] white line yes/no sheep DA GBR [76,77] overgrown claws yes/no sheep DA GBR [76,77] foot abscess yes/no sheep DA GBR [76] granuloma yes/no sheep DA GBR [76] interdigital hyperplasia yes/no sheep DA GBR [76] injury yes/no sheep DA GBR [76] joint infection yes/no sheep DA GBR [76] 1 direct assessment: DA; recording (audio and/or video): R; sensor: S.…”

“…Although not described in detail in this paper, both body weight and BCS probably implied restraining the individual animals, and were therefore time-consuming. The same time constraints apply to body condition scoring carried out by other authors [76,77,82,[85][86][87].…”

“…Furthermore, for other ABMs, such as cleanliness [76,77,79,82], or health indicators (e.g., integument alterations, fleece conditions, or foot lesions [76,77,79,82]), the evaluation was carried out by assessors, and the animals had to be restrained in small holding pens to allow individual examination; for the evaluation of mastitis, restraining the animals in a crate was also required [82]. These operations were therefore time-consuming and probably induced some level of stress in animals that were not used to being handled due their extensive living conditions.…”

“…The selection of appropriate sampling schemes is very important, especially when dealing with large herds (as sheep often are) and when animals have to be herded for the inspection, which is a common situation in extensive farming systems. Angell et al [76,77] also included the evaluation of lameness, that was scored by a trained assessor in a holding pen, while Munoz et al [79,82] used a similar locomotion score but evaluated it when the sheep were released from the holding pen.…”

Understanding contagious ovine digital dermatitis

“…D nodosus is believed to be the causative agent of footrot in sheep. However, frequent isolation from CODD lesions and evidence from several epidemiological studies suggests an important association between footrot and CODD (Duncan and others 2012, Angell and others 2015e). …”