K.A. Uitdehaag

Effects of genetic origin and social environment on behavioral response to manual restraint and monoamine functioning in laying hens.

Purebred laying hen lines of White Leghorn (WL) origin have been found to be more flighty and to show more feather pecking than lines of Rhode Island Red (RIR) origin. It has been found, however, that when RIR birds were housed together with WL birds, RIR birds became more flighty and those mixed groups developed more feather damage than pure-line cage-housed groups. It is unknown, however, whether this effect of social environment is accompanied by changes in stress-related behavior and neurophysiological activity, which are assumed to be associated with increased feather damage. The objective of this study was therefore to investigate the effects of genetic origin (WL or RIR) and social environment (mixed or pure groups) on behavioral response to manual restraint and monoamine functioning. Monoamine functioning was measured by brain serotonin (5-HT) and dopamine turnover. Furthermore, correlations between 5-HT turnover in the brain and peripheral measures of 5-HT in the blood were calculated. Experimental birds, housed either with other birds from the same genetic origin (pure groups) or with both RIR and WL birds (mixed groups) from hatching onward, were subjected to a manual restraint test at 47 wk of age. The WL birds struggled less during restraint and had higher dopamine and 5-HT turnover levels after restraint than did RIR birds. The WL birds also showed higher levels of platelet 5-HT uptake than did RIR birds. No effects of social environment were found. Blood and brain 5-HT measures were found to be correlated, with correlations ranging from 0.34 to 0.57, which seems to offer opportunities for less invasive peripheral indicators of 5-HT activity. In conclusion, genetic origin, but not social environment, affected the behavioral response to manual restraint and monoamine functioning in laying hens.

The association of response to a novel object with subsequent performance and feather damage in adult, cage-housed, pure-bred Rhode Island Red laying hens.

In laying hens, behavioral responses measured late in the laying period are associated with decreased performance. If measured early in the laying period, these behavioral responses could be used to predict performance later in life. The main objective of the present study was to investigate the association of the behavioral response toward a novel object at 23 wk of age with subsequent performance during the laying period. A total of 1,251 hens from 6 different pure-bred Rhode Island Red lines (208 hens per line on average) were housed in 318 cages (56 cages per line on average). Performance variables included egg production (both per hen-present and hen-housed); BW at 19, 51, and 69 wk of age; mortality; and feather damage at 63 wk. Hens from cages with an approach response realized greater total egg production (hen-day and hen-housed) and greater egg production in the middle (hen-housed) and end of the laying period (per hen present and hen housed) compared with hens from cages with a passive response toward the novel object. Approach responses were also associated with more feather damage, but not with BW or mortality. Low correlations were found between greater egg production and more feather damage. These results suggest that an approach response toward a novel object measured early in the laying period is associated with better performance later in the laying period. The novel object test early in the laying period can be used to predict subsequent performance, although possible causal mechanisms for this association remain to be investigated.