Eddy Decuypere

Ascites in broiler chickens: exogenous and endogenous structural and functional causal factors

Broiler chickens and laying hens are intensively selected for productive traits. The management of these highly productive animals must be optimal to allow their full genetic potential to be expressed. If this is not done, inefficient production and several metabolic diseases become apparent. The causes of the latter are multifactorial but diet and, particularly, interactions between diet, other environmental and genetic factors play an important role. An imbalance between oxygen supply and the oxygen required to sustain rapid growth rates and high food efficiencies causes ascites in broiler chickens. It is clear that several nutritional factors, the amount of food given, its physical form and the composition of the diet have a major impact on the occurrence of ascites and sudden death syndrome in broiler chickens. Furthermore, the possible involvement of structural endogenous factors such as proportional changes in the respiratory and cardiovascular systems, shifts in the glycolytic:oxidative muscle metabolism ratio, and structural changes within the lung capillary system cannot be excluded. In addition, functional causal factors, such as the hypothyroid state associated with decreased maintenance metabolism as a result of the selection for fast growth rate and improved food efficiency, are likely to be involved. Both structural and functional causal mechanisms may already be initiated during the embryonic stage.

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 physiological consequences of a slight but long term food restriction of male broiler 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 were analysed in terms of consequences upon performance, mortality, incidence of sudden death syndrome (SDS) and ascites syndrome (AS), index of right cardiac hypertrophy and plasma concentrations of hormones related to metabolism and growth (T3, T4, T3:T4 ratio, IGF-I and GH). 3. Although some catch-up growth was observed by refeeding previously restricted birds after 22 d of rearing, food restriction decreased (P < or = 0.05) body weight at market age (42 d) irrespective of the strain, but improved (P < or = 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 observed in chickens of both strains after 4 weeks of age and was higher in ad libitum fed birds. 5. During the period of food restriction, plasma T3 and IGF-I concentrations decreased whereas plasma T4 and GH concentrations increased compared to those of the age-matched ad libitum fed counterparts. During the subsequent ad libitum feeding period, few differences in circulating hormone concentrations were observed, except for the higher mean GH litres in previously food-restricted chickens at 35 d of age. 6. These results indicate that even a non-severe food restriction negatively affects body weight of 42-d-old male broilers but these are benefits with improved food efficiency and diminished mortality from metabolic disturbances. The hormone results suggest that the degree of food restriction applied was not severe because there was a very fast adaptive response with small and transient alterations in T3, T4 and GH plasma concentrations during the period of compensatory growth.

Effect of chronic hypoxia during embryonic development on physiological functioning and on hatching and post-hatching parameters related to ascites syndrome in broiler chickens

The present study was designed to investigate the effect of different atmospheric pressure on the endogenous functions of broiler chickens during embryonic, hatching and growing periods related to ascites. Eggs from a commercial broiler line were incubated in two similar commercial incubators at high and low altitudes. The effect on embryonic development and physiological functions including hatching parameters, incidence of ascites and growth performance were examined. Embryos incubated at high altitude had higher plasma tri-iodothyronine, thyroxine, corticosteroid and lactic acid levels, and hatched earlier than those incubated at low altitude. Embryonic mortality was higher at high altitude. Chickens that had been incubated at high altitude showed less right ventricular hypertrophy and ascites mortality than those incubated at low altitude. It was concluded that different atmospheric pressure during incubation interacts with the endocrine functions of the embryo and hence affects hatching parameters, thereby influencing ascites susceptibility.

Metabolic rate and its relationship with ascites in chicken genotypes

1. Male chickens of 7 genetic lines, consisting of two pure sire and two pure dam populations, a commercial broiler cross and two slow-growing chicken lines (Label Rouge, LR and Mechelse Koekoek, MK) were reared from 1 to 37 d of age. The chickens received a two-phase dietary regime and were subjected to low ambient temperature. 2. The experimental aim was to investigate relationships between susceptibility to ascites and heat production. 3. Body weight gain (BWG), food intake and food conversion ratio (FCR) were determined. Ascites mortality, arterial pressure index (API=right ventricular/total ventricular weight ratio), haematocrit values, proportional lung weight (lung weight/body weight × 100), plasma thyroid hormones (thyroxine, T4 and triiodothyronine, T3) and arterial blood gas pressures ( pCO2 and pO2) were determined. The heat production per kg metabolic body weight (H/W0·75) and total heat production (H) were calculated for the period 16 to 33 d using an energy balance study according to the comparative slaughter method. 4. The two breeder sire lines had high BWG and low FCR and high but different incidences of ascites compared with the slow-growing ascites resistant LR and MK lines with notable high FCR. The broiler cross and slower-growing breeder dam lines had a similar and relatively lower incidence of ascites mortality. 5. The fast-growing chickens had low H/W0·75 values compared with slow-growing lines. 6. These fast-growing breeder sires had lower plasma thyroid hormone, reduced proportional lung weights, low arterial pO2 and high arterial pCO2 pressures compared with the slower-growing lines. 7. In conclusion, ascites incidence was associated with lower heat production per metabolic body weight and therefore a lower oxygen requirement per metabolic weight.

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

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.

The use of blood gas parameters to predict ascites susceptibility in juvenile broilers

Ascites syndrome is a metabolic disorder found in modern broilers that have insufficient pulmonary vascular capacity. Commercial breeding programs have heavily focused on high growth rate, which led to fast-growing chickens, but as a negative consequence, the incidence of ascites syndrome increased. However, not all birds with a high growth rate will suffer from ascites syndrome, which might indicate a genetic susceptibility to ascites. Information on blood gas parameters measured early in life and their relation to ascites susceptibility is expected to contribute to identification on the cause of ascites syndrome. In this study, several physiological parameters, such as blood gas parameters [pH, partial pressure of CO(2) in venous blood (pvCO(2)), and partial pressure of O(2) in venous blood], hematocrit, electrolytes (Na(+), Ca(2+), and K(+)), metabolites (lactate and glucose), were measured at d 11 to 12 of age from 100 female and 100 male broilers. From d 14 onward, the birds were challenged to provoke the development of ascites syndrome. Our results showed that high pvCO(2) values together with low pH values (males) or high pH values (females) in the venous blood of juvenile broilers coincided with ascites. Therefore, blood pvCO(2) and pH in both juvenile male and female broilers seem to be critical factors in ascites pathophysiology and can be used as phenotypic traits to predict ascites susceptibility in juvenile broilers at d 11 to 12. A prediction model was built on a subpopulation of the broilers without any loss in sensitivity (0.52) and specificity (0.78) when applied to the validation population. The parameter sex was included in the prediction model because levels of pvCO(2) and pH that associated with ascites susceptibility are different between males and females. Commercial breeders can include these phenotypic traits in their genetic selection programs to reduce the incidence of ascites syndrome.