Table 25.

Sources of uncertainty on the relationship between group size and prevalence of respiratory disorder estimated via EKE

Sources of uncertainty	Reason
Housing type (e.g. igloo vs closed barn), including presence or absence of ventilation	Whether the animal is reared indoors or has access to an outdoor run; total air volume and the degree of ventilation can have an impact on the prevalence of respiratory diseases (Moser et al., 2020)
Humidity and temperature (temperature humidity index)	Seasonal effects are possible (e.g. colder temperatures may be associated with higher rate of respiratory disorders)
Stocking density	Larger stocking density can be associated with higher rate of respiratory disorders
Regrouping	Less stable groups (with higher rate of groups being rearranged, with animals being moved in and out) can be associated with a higher rate of respiratory disorders (Pedersen et al., 2009)
Immune system of the calf	A higher immune competence is thought to be associated with a lower prevalence of respiratory diseases (Langel et al., 2015). This will depend on the quality and quantity of colostrum ingested by the calf and on the vaccination status of the dam
Antibiotic use (metaphylactic)	Prevalence of respiratory disease can depend on whether metaphylactic application of antibiotics is carried out (Pardon et al., 2012; Lava et al., 2016)
Feeding system (bucket versus shared teats)	Automatic systems (with competition and teat sharing) can be associated with higher prevalence of disorders