Effects of Serotonin on the Food Intake in Chickens in the Early Post-hatching Period

Abstract

Baranyiova Eva: Effects of Serotonin on the Food Intake in Chickens in the PostHatching Period. Acta vet. Brno, 59, 1990: 23-33. The effect of serotonin (5-HT) on food intake in the post-hatching period was studied in 360 Hybro broilers from 1 to 25 days of age in 3 experimental series. They were reared in batteries and had free access to food and water. The experimental chickens (4 groups of 10 or 20 birds) were each intraperitoneally given single doses of 1 or 2 mg 5-HT (Sigma Corp., USA), four groups were sham-injected with saline, and four groups were left untreated. The food intake of experimental and control groups was measured 30 and 60 min post injection and then at 1-h intervals till 1400 h. Cumulative food intake for the interval 0700 to 1400 h and per 24 h was also recorded. The 5-HT administration did not affect the food intake of chickens 1 and 2 days of age. On day 3, however, the birds began to respond to 5-HT administration in that its higher dose stopped eating in the first post-injection hour, the lower dose (1 mg . kg-I) suppressed it significantly as compared to sham-injected (P < 0.01) and intact controls (P < 0.02). The food intake of experimental chickens at all other ages under study (i. e. on days 4, 5, 9,11,17 and 25) was similarly suppressed in the first post-injection hour compared to either control groups. No dose-dependent effect of 5-HT was detected. In older birds, consuming increasingly larger portions in the first morning hour, the 5-HT induced abstinence was also manifested in cumulative food intake from 0700 to 1400 h. Their actual food consumption was lower at 17 (P < 0.01) and 25 (P < 0.01) days of age, the relative food intake at 17 (P < 0.01) days. Expressed in terms of 24-h consumption the 5-HT inhibited eating during the first morning hour became apparent especially in 25-d-old birds (P < 0.05). It is noteworthy that no differences in food consumption of sham-injected and intact controls were found. The fact that the ingestive response to peripheral administration of 5-HT did not occur until day 3 suggests that maturation of some components of the serotoninergic system in the fowl continues after hatching. Age, broiler, intraperitoneal administration, 5-HT In birds, serotoninergic mechanisms are involved in the regulation of numerous physiological functions. Their morphological substrates and the presence of serotonin (5-HT) in various tissues have been demonstrated (Juorio and Vogt 1967; Epstein et al. 1980; Gershon et al. 1980; Cassone et al. 1983; Wallace 1985). In the blood plasma of cocks 3-7 mg. kgl have been found (Freeman 1984). A number of studies on 5-HT have shown that this neurotransmitter affects the cardiovascular and respiratory systems of pigeons and poultry, exerts an excitatory effect on the electromyographic activity of the esophagus of the adult pigeon, and is involved in energy metabolism and thermoregulation affecting their circadian rhythms in chickens (Cogburn et al. 1976; Freeman 1979; Hillman et al. 1980; Fileccia et al. 1987; Hohtola et al. 1989). Serotonin administered centrally or peripherally also affects the behaviour of birds; in chickena