Keynote Message

Cohort studies have the ability to further scientific knowledge, through the analysis of prospectively collected data whereby exposure data are collected prior to outcome data, thus avoiding the problem of reverse causality, which can occur in studies based on retrospective data. Despite the strength of evidence generated from cohort studies, and relatively short generation intervals of animals, few animal cohort studies have been reported. The financial investment needed to set up and run a cohort study is relatively large, particularly if a life-long study is planned. However, the wealth of data that can be collected, particularly in relation to the management of animals, means that cohort studies are ideal for extending our knowledge of environment/management-related, and early-life factors in the subsequent development of health, behaviour, and welfare outcomes within cohort animals. Cohort studies also enable outcomes that do not result in a visit to a veterinarian to be studied using prospective data. In this session, aspects of designing and running cohort studies will be discussed with reference to resource implications, recruitment and retention of study participants, sources and quality of data collected, and validation of data. Sampling bias arising from self-selection of participants and loss to follow-up will also be discussed, together with suggestions for minimising the effects of this bias. Two cohort studies - the Bristol Cats Study and the Generation Pup study - will be used to provide examples and provide evidence of the effectiveness of different strategies.

Key References

1.  Boyd A, Golding J, Macleod J, et al. Cohort profile: the 'children of the 90s' - the index offspring of the Avon Longitudinal Study of Parents and Children. International Journal of Epidemiology. 2013;42(1): 111–127. DOI: 10.1093/ije/dys064

2.  Casey RA, Murray JK, Tasker S, et al. Longitudinal birth cohort study investigating risk factors for behaviour and disease in dogs. Journal of Veterinary Behaviour Clinical Applications and Research. 2015;10(5):444.

3.  Ireland, JL, Clegg PD, McGowan CM, et al. Factors associated with mortality of geriatric horses in the United Kingdom. Preventive Veterinary Medicine. 2011;101(3–4):204–218. DOI: 10.1016/j.prevetmed.2011.06.002

4.  Murray JK, Casey RA, Gale E, et al. Cohort profile: The 'Bristol Cats Study' (BCS) - a birth cohort of kittens owned by UK households. International Journal of Epidemiology. 2017 Jun 22. doi: 10.1093/ije/dyx066. [Epub ahead of print]

5.  Pugh CA, Bronsvoort BM, Handel IG, et al. What can cohort studies in the dog tell us? Canine Genetics and Epidemiology. 2014;1:5. DOI: 10.1186/2052-6687-1-5

6.  Wylie CE, Collins SN, Verheyen KL, et al. A cohort study of equine laminitis in Great Britain 2009–2011: estimation of disease frequency and description of clinical signs in 577 cases. Equine Veterinary Journal.2013;45(6):681–687. DOI: 10.1111/evj.12047.