Manipulation of the phenotypic appearance of individuals in groups of laying hens: effects on stress and immune-related variables

Figures & data

Table 1. Experimental design for phase I and II regarding phenotypic appearance (PA) assignment within groups (flocks) for each group size (10 or 40 birds per pen, flock).

		PA composition phase II (34–46 weeks of age)
Original marking condition (%)	PA composition phase I (1–34 weeks of age)	30% changed (34 weeks of age)	50% changed (38 weeks of age)	70% changed (44 weeks of age)
0	100 UM	30 M and 70 UM	50 M and 50 UM	70 M and 30 UM
30	30 M and 70 UM
50	50 M and 50 UM
70	70 M and 30 UM
100	100 M	30 UM and 70 M	50 UM and 50 M	70 UM and 30 M

UM = unmarked; M = marked. 750 chicks were randomly assigned among 30 pens and housed in groups of 10 or 40 birds (15 pens per group size, 3 pens per original marking condition). Number of birds sampled per group/phenotype condition = 9; total number of birds studied = 180. Data were analyzed by mixed-model ANOVA.

Figure 1. Plasma corticosterone concentrations in adult hens with different artificial phenotypic appearance (PA) from day one of age. Basal = birds reared in regular husbandry conditions; Stressed = same birds submitted to 5 min acute stress consisting of individual isolation in a novel environment. Bars represent the mean ± SE (number of birds per homogeneous or heterogeneous group/phenotype condition = 9, total number of birds in the study = 180). Data were analyzed by mixed-model ANOVA; p = 0.001, stressed > basal; no significant effects of PA or GS. M = marked; UM = unmarked; 100, 30, 50 and 70 = 100, 30, 50 and 70% of the birds within a flock either marked or unmarked. Group size 10 = birds reared in groups of 10 individuals. Group size 40 = birds reared in groups of 40 individuals.

Table 2. Immune-related variables measured (mean ± SE) in adult laying hens with different artificial phenotypic appearance (PA) from day one of age.

	Phenotypic appearance
									p values
Variables	100 M	100UM	30 M	70UM	50 M	50UM	70 M	30UM	PA	GS	PA × GS
H/L ratio	1.54 ± 0.25	1.69 ± 0.24	1.59 ± 0.28	1.81 ± 0.45	1.34 ± 0.32	2.21 ± 0.42	1.44 ± 0.36	1.33 ± 0.16	0.21	0.65	0.17
Innate/adaptive	1.57 ± 0.24	1.82 ± 0.24	1.61 ± 0.31	1.98 ± 0.54	1.48 ± 0.30	2.33 ± 0.46	1.58 ± 0.37	1.44 ± 0.16	0.24	0.50	0.22
Antibody titer	5.58 ± 0.91	5.79 ± 0.80	6.33 ± 0.84	6.25 ± 1.10	5.86 ± 0.86	6.37 ± 1.11	5.28 ± 0.82	5.67 ± 0.61	0.89	0.36	0.59
Inflammation	46.0 ± 11.7	45.7 ± 11.1	36.9 ± 6.1	33.7 ± 13.7	42.4 ± 10.2	32.8 ± 12.1	44.3 ± 8.7	44.3 ± 15.3	0.81	0.51	0.41

UM = unmarked; M = marked; GS = group size; 100, 30, 50 and 70 = percentage of birds within a flock (group) either marked or unmarked; H/L: heterophil/lymphocyte; innate/adaptive: (number of basophils + number of heterophils + number of monocytes) / (number of eosinophils + number of lymphocytes). Antibody titer: primary antibody response against sheep red blood cells using a microagglutination assay; Inflammation: percentage of change in the wing web thickness 24-h postlocal injection of phytohemagglutinin-p (PHA-P). Data from GS 10 and 40 birds were pooled together to facilitate visualization within each PA condition. Number of birds per homogeneous or heterogeneous group / phenotype condition = 18 (9 from each group size). Data were analyzed by mixed-model ANOVA.

Figure 2. Plasma corticosterone concentrations after changing the phenotypic appearance (PA) of 70% of a flock during adulthood. Basal = birds reared in regular husbandry conditions; Stressed = same birds submitted to 5 min acute stress consisting of individual isolation in a novel environment. Bars represent the mean ± SE (number of birds per treatment = 9, total number of birds in the study = 144). Data were analyzed by mixed-model ANOVA. M = marked; UM = unmarked; 30 and 70 = 30% and 70% of the birds within the flock (i.e., group/pen) either marked or unmarked. Flocks with nonaltered PA: PA of all birds within the flock remained unchanged from day 1 of age. Flocks with altered PA = PA of birds was either changed during adulthood or remained unchanged from day 1 of age. Group size 10 = birds reared in groups of 10; Group size 40 = birds reared in groups of 40. ^a,cStressed groups with no common letters differ significantly (p < 0.05; Fisher least significant difference test).

Table 3. Immune-related variables measured (mean ± SE) after changing the phenotypic appearance (PA) of 70% of a flock during adulthood.

	Flocks with unchanged PA (from day 1 of age)				Flocks with changed PA (PA of birds was either changed during adulthood or remained as changed on day 1 of age)				p Values
Variables	70 M	30UM	70UM	30 M	Changed to 70 M	Unchanged 30UM	Changed to 70UM	Unchanged 30 M	PA	GS	PA × GS
H/L ratio	(1.30 ± 0.3	1.37 ± 0.4	1.31 ± 0.2	1.34 ± 0.0)^a	(2.18 ± 0.5	2.67 ± 0.1	2.27 ± 0.4	2.39 ± 0.6)^b	0.01	0.28	0.91
Innate/adaptive	(0.38 ± 0.0	0.39 ± 0.1	0.38 ± 0.1	0.39 ± 0.0)^a	(0.51 ± 0.1	0.55 ± 0.1	0.54 ± 0.1	0.54 ± 0.1)^b	0.04	0.22	0.93
Antibody titer	6.38 ± 0.7	6.44 ± 0.7	6.88 ± 0.6	5.83 ± 0.4	6.22 ± 0.6	6.38 ± 0.8	5.97 ± 0.6	5.88 ± 1.0	0.81	0.08	0.54
Inflammation	20.1 ± 4.1	22.3 ± 4.8	20.0 ± 8.2	25.9 ± 11.0	18.6 ± 5.9	23.4 ± 8.5	20.1 ± 4.8	19.9 ± 7.3	0.98	0.13	0.93

M = marked; UM = unmarked; GS = group size; 70 and 30 = percentage of birds within a flock (i.e., group in a pen) either marked or unmarked; H/L ratio: heterophil/lymphocyte counts; innate/adaptive: (number of basophils + number of heterophils + number of monocytes) / (number of eosinophils + number of lymphocytes). Antibody titer: primary antibody response against sheep red blood cells using a microagglutination assay; inflammation: percentage change in the wing web thickness 24-h postinjection of phytohemagglutinin-p (PHA-P). Data from GS 10 and 40 birds were pooled together to facilitate visualization within each PA condition. Number of birds per heterogeneous group/ phenotype condition = 18 (9 per each group size). Data were analyzed by mixed-model ANOVA.

^a,bWithin the same row, grouped data from birds within unaltered pens differed from birds within altered pens at p < 0.05.