Haematological characteristics predicting susceptibility for ascites. 1. High carbon dioxide tensions in juvenile chickens

Abstract

1. Male broilers of two different genetic stocks, a pure broiler sire line (A) and commercially available Ross broilers (B), were used to study the effect of haematological characteristics in juvenile chickens on the development of clinical ascitic signs. Production performance (body weight gain (BWG), feed intake (FI), feed conversion ratio (FCR)) from 448 birds per stock was measured from 2 to 5 weeks of age. Mortality was recorded from 2 to 6 weeks of age. The birds were housed at a low ambient temperature to stimulate the incidence of ascites. 2. From each stock, 32 birds with the highest (high risk: HRc) and 32 birds with the lowest (low risk: LRc) carbon dioxide tensions (pCO2) in venous blood were selected at 11 d of age. These birds were marked for future blood sampling to determine changes in pCO2 with age to relate these values to ascites susceptibility. 3. At 2 weeks of age all birds (including HRc and LRc birds) were allotted to 32 floor pens (one HRc and one LRc in each pen) per stock. Venous blood samples were collected weekly from HRc and LRc birds for blood gas analysis and haematocrit, and at week 5 also for thyroid hormone (T3, T4) concentrations in plasma. At 5 weeks of age all HRc and LRc birds were examined post-mortem, relative heart, lung, and liver weights and arterial pressure index (API) values were recorded. 4. Birds from stock A showed a lower BWG and FCR and notably higher ascites mortality compared with stock B. An effect of pCO2 tensions at d 11 was found on the incidence of ascitic signs in selected birds of both stocks up to week 5. From the HRc groups 30% of the birds showed ascitic signs, whereas this was only 8% in the LRc group. LRc birds of stock B in particular showed constant low API values (20 +/- 3%) and none of these birds showed signs of ascites. 5. Our results suggest that the ascites problem in Ross birds can be eliminated by selection for low pCO2 tensions in venous blood. Stock effects on API, liver weight, lung weight, and plasma thyroid hormone independent of pCO2 showed a more complex picture of the ascitic signs in stock A compared with B. 6. We concluded that in this experiment a high pCO2 tension in venous blood measured at d 11 was a reliable predictor for ascites susceptibility observed at 5 weeks of age. A low pCO2 tension provides an appropriate criterion for genetic selection, whereas a high pCO2 tension emphasises the necessity for intensive management in poultry houses.

Ascites and venous carbon dioxide tensions in juvenile chickens of highly selected genotypes and native strains

“…Mean pvCO 2 values of HRc birds differed markedly between modern breeds and old native strains. A convincing effect of high pvCO 2 values on API values found in this experiment in modern lines, confirmed results obtained in a previous study (Scheele et al, 2003a). Respecting all stocks we observed in this study a critical range of mean pvCO 2 values in high pvCO 2 -risk groups from 45 to 50 mm Hg at 12 days of age.…”

“…Fast growing LRc BC birds showed at wk 5 similar API values than ascites resistant breeds LR and MK. The latter confirms results of Scheele et al (2003a) showing constant low API values and no signs of ascites within fast growing LRc Ross chickens.…”

“…On the contrary, different experiments at sea level showed that hypercapnia is an evident feature in ascites susceptible broiler populations (Buys et al 1999;Olkowski et al 1999;Scheele et al 2003a). These experiments confirmed results from Reeves et al (1991) who discovered hypoventilation as an important feature in ascites susceptible chickens at sea level.…”

“…A previous study (Scheele et al, 2003a) with two stocks of fast growing broiler chickens demonstrated a substantial variability in CO 2 concentrations in venous blood at 11 days of age between birds within stocks. Moreover, high pvCO 2 values detected at day 11 predicted high values for API values, which is a reliable indicator for ascites susceptibility, at 5 wk of age.…”

“…These genetic components may have relationships to some aspects of production performances. Scheele et al (2003a) suggested that a high feed efficiency (i.e. a reduced heat production) can be realised in selection programmes by an unintended selection for a reduced physical activity, induced by an impaired respiratory activity.…”