Resumo

REQUENA, Fanny; LEON, Alicia  e  DE BASILIO, Vasco. Effects the food restriction on early-age thermal conditioning of male broiler chickens. Zootecnia Trop. [online]. 2004, vol.22, n.4, pp.371-385. ISSN 0798-7269.

Early age thermal conditioning (TC) by exposing chicks to 40 ± 1°C for 24 hours with 5 days of age arise as an alternative to improve resistance of broilers chickens to heat stress and reduces mortality (M) during the finishing period. However, TC efficacy could be affected by several factors such as feed consumption. A design with a 2x2 factorial arrangement (2 feeding status: ad libitum (AL) and feed restriction (R) for 23 h during the TC and two environmental conditions: chicks exposed to TC and not exposed (N) was used. A total of 288 male day-old broiler chicks (Cobb) were housed in a semi controlled tropical environment chamber (SCE). Heat stress was applied at 42 days of age by increasing ambient temperature (TA) to 40°C for 8 hours in SCE. Body temperature (Tb) and body weight (BW) were recorded individually at 4, 5, 7 d of age and weekly from 14 to 42 d of age, as well as feed intake (FI). Mortality was recorded daily. The results showed that before TC, there were not differences of Tb among treatments. After TC (7 d of age), mean Tb of the TC chickens was significantly (P<0,0001) lower than those no exposed (N) (40.87°C vs. 41,15ºC). A significant effect of feeding status was evident on Tb. Average Tb of fed ad libitum chicks was 40.94°C when compared to R chicks (41.08°C). Although interactions between the feeding status and TC were not significant, Tb variations associated with TC were greater when chicks were fed compared to their counterparts whose food was withdrawn. Feed restriction reduced body weight gain in chicks exposed to TC (-10.56 g) and not exposed (-9.69 g). After TC (6-7 d) compensatory weight gain was appreciated. From 7-42 days, there were not significant differences among treatments for Tb, mortality (<1%), neither productive parameters. After heat stress at 42 days of age, Tb was lower in acclimatized chickens (42.48°C) compared to N chicks (43.07°C). Early age thermal conditioning to 40°C for 24 h at 5 days of age reduced the body temperature. Feeding restriction did not have effect in reinforcing the changes of Tb induced by TC.

Palavras-chave : Feed restriction; thermal conditioning; broilers.