Incidence of ascites syndrome and related hematological response in short-term feed-restricted broilers raised at low ambient temperature

Ascites is a major cause of mortality and morbidity in modern broiler production. Reduction of early growth, followed by compensatory gain, seems a practical and viable method to minimize losses caused by ascites. An experiment was conducted to determine if early feed restriction can reduce the incidence of ascites in broilers exposed to cool temperatures. Ross 308 cockerels (N = 180) were assigned to 5 diet treatments and 2 temperature regimes, with 3 replicate pens of 6 birds per treatment and temperature. A standard grower diet was diluted by adding rice hulls at 0, 15, 30, 45, and 60% by weight from 7 to 14 d of age. On d 21 through 42, the temperature was maintained at 20 to 25 degrees C (thermoneutral), or at 11 to 15 degrees C (cool). Broilers exposed to cool temperatures developed higher right ventricle (RV) to total ventricle (TV) and RV to BW ratios, increased plasma triiodothyronine (T-3) and thyroxine (T-4) concentrations, and elevated blood values for hemoglobin concentration, mean cell volume, and hematocrit (P < 0.05) but did not develop clinical ascites. Diluting the feed with rice hulls from d 7 to 14 resulted in proportional reductions in BW by d 14 (P < 0.001) that tended to persist through d 28 (P = 0.005), after which compensatory growth eliminated all differences in BW between diet treatment groups by d 35 (P = 0.099) and d 42 (P > 0.1). Exposure to cool temperatures increased key indices of ascites susceptibility, and these preascitic changes were partially prevented by diluting the feed to reduce growth performance.