Performance, incidence of metabolic disturbances and endocrine variables of food-restricted male broiler chickens

1. This experiment was carried out to evaluate the productive and physiolog ical consequences of a slight but long term food restriction of male broile r chickens from 2 commercial strains. 2. Cobb-500 and Ross chickens were submitted to a 20% food restriction from 8 to 21 d of age. Strain, food programme and their interactive effects wer e analysed in terms of consequences upon performance, mortality, incidence of sudden death syndrome (SDS) and ascites syndrome (AS), index of right ca rdiac hypertrophy and plasma concentrations of hormones related to metaboli sm and growth (T-3, T-4, T-3:T-4 ratio, IGF-I and GH). 3. Although some catch-up growth was observed by refeeding previously restr icted birds after 22 d of rearing, food restriction decreased (P less than or equal to 0.05) body weight at market age (42 d) irrespective of the stra in, but improved (P less than or equal to 0.05) food conversion. 4. The incidence of mortality was not high in non-restricted birds but SDS and AS caused more than 50% of deaths. Hypertrophic cardiac index was obser ved in chickens of both strains after 4 weeks of age and was higher in ad l ibitum fed birds. 5. During the period of food restriction, plasma T-3 and IGF-I concentratio ns decreased whereas plasma T-4 and GH concentrations increased compared to those of the age-matched ad libitum fed counterparts. During the subsequen t ad libitum feeding period, few differences in circulating hormone concent rations were observed, except for the higher mean CH litres in previously f ood-restricted chickens at 35 d of age. 6. These results indicate that even a non-severe food restriction negativel y affects body weight of 42-d-old male broilers but these are benefits with improved food efficiency and diminished mortality from metabolic disturban ces. The hormone results suggest that the degree of food restriction applie d was not severe because there was a very fast adaptive response with small and transient alterations in T-3, T-4 and GH plasma concentrations during the period of compensatory growth.