Relations between peripheral and brain serotonin measures and behavioural responses in a novelty test in pigs.

Pigs differ in their behavioural responses towards environmental challenges. Individual variation in maladaptive responses such as tail biting, may partly originate from underlying biological characteristics related to (emotional) reactivity to challenges and serotonergic system functioning. Assessing relations between behavioural responses and brain and blood serotonin parameters may help in understanding susceptibility to the development of maladaptive responses. The objective of the current study was, therefore, to assess the relationship between the pigs' serotonergic parameters measured in both blood and brain, and the behaviour of pigs during a novelty test. Pigs (n=31) were subjected to a novelty test at 11weeks of age, consisting of 5-min novel environment exposure after which a novel object (a bucket) was introduced for 5min. Whole blood serotonin, platelet serotonin level, and platelet serotonin uptake were determined at 13weeks of age. Levels of serotonin, its metabolite and serotonin turnover were determined at 19weeks of age in the frontal cortex, hypothalamus and hippocampus. The behaviour of the pigs was different during exposure to a novel object compared to the novel environment only, with more fear-related behaviours exhibited during novel object exposure. Platelet serotonin level and brain serotonergic parameters in the hippocampus were interrelated. Notably, the time spent exploring the test arena was significantly correlated with both platelet serotonin level and right hippocampal serotonin activity (turnover and concentration). In conclusion, the existence of an underlying biological trait - possibly fearfulness - may be involved in the pig's behavioural responses toward environmental challenges, and this is also reflected in serotonergic parameters.

Maternal care and selection for low mortality affect post-stress corticosterone and peripheral serotonin in laying hens.

The aim of the present study was to investigate the effect of brooding and group selection for low mortality on post-stress corticosterone and peripheral serotonin in laying hens. Birds in the experiment originated from the same population and were either group-selected for low mortality (low mortality line) or randomly selected (control line) for two generations. Twelve groups of seven birds from each line were used. Within each line, six groups were brooded by a foster mother and six groups were non-brooded. At 33 weeks of age, birds (n=42/treatment) were manually restrained for 5 min, during which their behavioral response (number of struggles) was studied. Fifteen minutes after the start of the manual restraint, blood samples were drawn for assessment of plasma corticosterone and whole blood serotonin (5-HT) concentration. In the low mortality line, 80% of the birds struggled and vocalized vs. 72% in the control line (non significant). Birds from the control line had a higher plasma corticosterone concentration after manual restraint than birds from the low mortality line (7.7 vs. 6.0 nmol ml(-1)). Furthermore, birds from the control line that were reared without a mother had a lower whole-blood 5-HT concentration than birds from the other treatments (45 vs. 48 nmol ml(-1)). These results indicate that both brooding and selection for low mortality affect post-stress corticosterone and peripheral serotonin concentration, which may result in a reduced propensity to develop feather pecking.

Effects of genetic group selection against mortality on behavior and peripheral serotonin in domestic laying hens with trimmed and intact beaks.

Severe feather pecking is a maladaptive behavior in laying hens that may result in cannibalism and ultimately death of the victims. Selection methods in which the genetic effect of an animal on the survival of its group members is taken into account, i.e. 'group selection', have been shown to be very effective in reducing mortality due to feather pecking and cannibalism in laying hens. It has been suggested that fearfulness and serotonergic functioning are involved in the causation and development of feather pecking. We investigated effects of selection based on survivability in non-beak trimmed groups on fear-related behavior and peripheral 5-HT concentration and uptake in hens with trimmed or intact beaks, in a 2 x 2 factorial arrangement. Hens from the second generation of the low mortality line showed less fear-related behavior than control line hens. In addition, they displayed higher whole blood 5-HT concentrations and a lower platelet 5-HT uptake, indicating differences in functional activity of the 5-HT system. Beak trimming resulted in lowered levels of fear, and in a reduction of feather damage. Hens with trimmed and intact beaks did, however, not differ in peripheral 5-HT. The results imply that fearfulness and 5-HT activity are related to feather pecking without distinguishing between cause and effect. However, given that selection altered fear-related behaviors and peripheral 5-HT concentration and uptake, whereas beak trimming affected fearfulness and feather damage, but not 5-HT parameters, we suggest that peripheral 5-HT activity might reflect the predisposition to develop severe feather pecking under adverse conditions in laying hens.

Application of a [13CO2] breath test to study short-term amino acid catabolism during the postprandial phase of a meal.

A [13CO2] breath test was applied as a non-invasive method to study the catabolism of ingested amino acids shortly after a meal. This test requires the ingestion of a [1-13C]-labelled amino acid and the analysis of expired air for [13C] enrichment and CO2. The recovery of label as [13CO2] reflects the catabolism of the [1-13C]-labelled substrate. Such a non-steady state approach provides information that is complementary to the information obtained by steady-state methods using a primed continuous infusion of tracer amino acids during the fed state. In a model study with twenty adult male rats, two groups of animals were fed twice a day with one of two semi-synthetic iso-energetic diets. One diet contained egg white protein (EW) as the sole amino acid source. The second diet contained a mixture of free amino acids with a pattern similar to that of the EW diet. On day 5 of the dietary treatment, L-[1-13C]leucine, either bound in EW protein or in free form, was ingested as part of the morning meal. The expired air was sampled at 30 min intervals for 5 h. The rate of recovery ranged from 0% to 6% of the dose/h. Up to 120 min after the onset of the meal, the recovery values for the free amino acid diet were higher than those for the EW diet. Differences in recovery reflect differences in postprandial utilisation. The differences in label recovery were mainly determined by the [13C] enrichment of the expired air. As a consequence, CO2 measurements are not mandatory when CO2 production is comparable.