Risk factors associated with colibacillosis outbreaks in caged layer flocks

Figures & data

Table 1. Potential risk factors for colibacillosis outbreaks in caged layer flocks: descriptive data of categorical variables, significant in the bivariate analysis

Variable	Control flocks	Affected flocks	Bivariate P value
Type of animal with access to hen house			0.02
None	3	2
Cats	6	1
Rodents	7	13
More than one species	4	4
Regular treatment against flies			0.02
No	9	7
Yes	11	13
Pattern light increase at the beginning of the batch			0.0003
More than 30 min per week	7	12
30 min per week	13	8
Pre-lay feed offered before layer feed at the beginning of the batch			0.005
No	8	17
Yes	12	3
Number of other poultry farms (commercially kept layers or broilers) within a 1 km radius			0.005
None	20	15
1 to 3	0	4
More than 3	0	1
Percentage in lay at 22 weeks versus target			0.005
Below the target	10	13
On the target	6	1
Above the target	4	6

Table 2. Potential risk factors for colibacillosis outbreaks in caged layer flocks: descriptive data of continuous variables, significant in the bivariate analysis

	Mean (minimum to maximum)
Variable	Control flocks	Affected flocks	Bivariate P value
Biosecurity measures
Visitors entering hen house (n/month)	0.8 (0 to 2)	1.4 (0 to 4)	0.004
Frequency of water disinfectant use (n/year)	43.4 (0 to 365)	84.3 (0 to 365)	0.04
Infrastructure
Number of hens in the flock (n)	26 996 (11 005 to 44 000)	36 157 (23 400 to 50 000)	0.0003
Well depth (m)	82.2 (7 to 250)	181.2 (18 to 300)	0.04
Farm situation
Distance to the nearest poultry farm (km)	3.3 (0 to 10)	1.0 (0 to 3)	0.0006
Rearing period
Age of beak trimming (days)	25.4 (7 to 42)	13.6 (9 to 42)	0.03

Table 3. Risk factors for colibacillosis outbreaks in caged layer flocks not found significant in the bivariate analysis: categorical variables

Variable
Hygienic preventive measures
Dead hen removal from the house (daily or not daily)
Use of contract cleaners between batches (yes or no)
House cleaning method between batches (high pressure hose, compressed air, broom, or combination)
Disinfectant used on house between batches (formalin, commercial combination products containing quaternary ammonium compounds, aldehydes and alcohol, or other)
Cleaning of silos (using water, compressed air or broom, or silos never cleaned)
Frequency of cleaning silos (never, less than every batch, or at least once per batch)
Disinfectants used as water additive (yes or no)
Flock health
Previous illness in other contemporary flock (other disease than colibacillosis, colibacillosis, or none)
Management factors
Use of feed supplements (extra vitamins, minerals) (never, sometimes or always)
Duration house empty between two batches (1 to 2 weeks or more)
Only poultry kept on the farm (yes or no)
Infrastructure
Drinking nipples shared between cages (yes or no)
Water mixing system (dosing pump or other)
Ventilation system (natural ventilation, fans, or a combination of both)
Fan orientation (natural ventilation only, width, or length)
Manure drying system (within the house or none within the house)
Farm situation
Distance from farmer's house to hen house (≤50 m or >50 m)
Production parameters
Percentage in lay at sampling (below, on, or above the target)
Rearing period
Extra vaccinations (E. coli, Salmonella, M. gallisepticum and/or avian pneumovirus) besides ‘standard scheme’ (yes or no)
Salmonella vaccine administered (yes or no)

Table 4. Risk factors for colibacillosis outbreaks in caged layer flocks found not significant in the bivariate analysis: continuous variables

Variable	Units
Biosecurity measures
Treatment frequency against D. gallinae	n/year
Frequency of dead hen removal from the house	n/week
Score on biosecurity measures	–
Management factors
Age at delivery	weeks
Light regime	h/day
Feeding frequency	n/day
Manure removal from the house	n/week
Infrastructure
Number of flocks on the farm	n
Total number of hens on the farm	n
Hen density in the house	n/m^3
Cage space per hen	l
Battery floors	n
Age of the hen house infrastructure	years
Rearing period
Vaccinations against Salmonella	n

Table 5. Significant risk factors in the final model^a

Variable	Odds ratio (95% confidence interval)	P value^b
Distance to nearest poultry farm (km)	0.16^c (0.05 to 0.55)	0.0035
Volume in cage (l/hen)	0.75^d (0.63 to 0.89)	0.0010
^a This model yielded a deviance of 16.11 from the null model (degrees of freedom=2, P=0.00032).
^b P values for the estimates of the odds ratios.
^c Increase in the distance by 1 km.
^d Increase in the volume per hen by 1 l.