Table 2.

Final multivariable mixed-effects Poisson regression results for risk factors associated with dead-on-arrival rate in 17,179 single-flock trailer loads of broiler chickens transported to slaughter in 2019. Flock ID was included as a random effect (n = 6,603).

Risk factor	IRR	Wald P-value	Lower 95 CI	Upper 95 CI	LRT P-value	Risk factor	IRR	Wald P-value		Lower 95 CI		Upper 95 CI	LRT P-value
Loading temperature					<0.001	Loading temperature							<0.001
Humidity ≤80%						Humidity >80%
<0°C	1.14	0.451	0.81	1.60		<0°C	1.43	<0.001		1.35		1.52
0°C–5.0°C	1.14	0.001	1.05	1.23		0°C–5.0°C	1.05	0.029		1.01		1.11
5.1°C–10.0°C	1.21	<0.001	1.15	1.27		5.1°C–10.0°C	1.02	0.392		0.98		1.06
10.1°C–15.0°C	1.00					10.1°C–15.0°C	1.00
15.1°C–20.0°C	0.98	0.490	0.94	1.03		15.1°C–20.0°C	0.94	0.033		0.89		1.00
20.1°C–25.0°C	1.20	<0.001	1.13	1.29		20.1°C–25.0°C	2.02	<0.001		1.65		2.46
25.1°C–30.0°C	3.93	<0.001	3.60	4.28		25.1°C–30.0°C	-	no observations in sample
>30.0°C	16.89	<0.001	15.25	18.70		>30.0°C	-	no observations in sample
Reported journey time					0.004
≤60 min	1.00
>60 min	1.06	0.004	1.02	1.11
Reported journey distance					<0.001
≤50 km	1.00
>50 km	1.13	<0.001	1.08	1.18
Catch method					<0.001
Manual	1.00
Mechanical	1.32	<0.001	1.23	1.42
Thin or depletion					<0.001
Deplete	1.00
Thin	1.09	<0.001	1.06	1.13
Time in lairage					0.002
≤90 min	1.00
>90 min	1.07	0.002	1.05	1.10
Breed					<0.001
Ross	1.00
JA	0.27	<0.001	0.19	0.40
Cobb	0.94	0.015	0.90	0.99
Catch age					<0.001
≤38 d	1.00
>38 d	1.15	<0.001	1.11	1.20
Parent flock age					0.003
Young	1.01	0.629	0.97	1.06
Peak	1.00
Old	1.04	0.116	0.99	1.09
Mixed ages	1.13	<0.001	1.06	1.21
7-d mortality					0.079
≤1.50%	1.00
>1.50%	0.97	0.078	0.93	1.00
Late period mortality					<0.001
≤0.80%	1.00
>0.80%	1.26	<0.001	1.22	1.31
between flock variance	0.41		0.39	0.43

Abbreviation: LRT, likelihood ratio test.