The continuous selection for rapid growth has been accompanied by an increasing occurrence
of ascites syndrome (AS), which develops in broilers failing to supply the increasing
demand for O(2) in their bodies. Moderate heritability has been reported for AS in
broiler populations, suggesting that selection against AS is feasible. However, direct
selection based on AS mortality requires exposure of candidate birds to AS-inducing
conditions (AIC), which hinder selection for performance traits. Noninvasive indicators
of AS, expressed under standard husbandry, may facilitate the integration of selection
against AS into breeding programs. This study was designed to look for differences
in heart rate, hematocrit, O(2) saturation of hemoglobin in arterial blood (SaO(2)),
BW, and weight gain, all measured at early ages under standard brooding conditions,
between birds that later developed AS and those that remained healthy under AIC, and
to estimate the heritability of these AS-related parameters and their genetic correlation
with the tendency of broilers to develop AS. The experimental population was derived
from a broiler dam line. Male progeny of 34 half-sib sire families were reared under
standard brooding conditions to 19 d of age, then under an AIC protocol consisting
of housing in individual cages, cool air high-speed ventilation, and growth enhancement
using high-energy pelleted feed and 23 h/d of light. Birds were necropsied upon mortality
or at the end of the trials and were recorded as being susceptible, with manifestations
of AS (SUS), or resistant and healthy (RES). About 44% developed AS, confirming the
efficacy of the novel AIC protocol. The SUS and RES chicks did not differ in BW and
weight gain up to 19 d of age, suggesting that there was no association between AS
susceptibility and rapid early growth. The SUS chicks exhibited lower SaO(2) and heart
rate than the RES chicks. Moderate heritability was estimated for all traits, but
only SaO(2) exhibited consistently significant genetic correlation (-0.5) with AS,
suggesting that it may serve as an early indicator for selection against AS, albeit
with a limited efficacy.