| | Introduction
Ascites in Alberta
Ascites is a significant production problem in Alberta. Condemnations due to ascites related conditions at the time of processing are commonly in the range of 1% of all Alberta birds shipped; 4% worldwide. Upwards of 3% of all mortality in broiler chicken flocks prior to shipping may be due to ascites. The incidence of ascites appears to be higher in Alberta than in any other Canadian or American region (McMillan 1994), and increasing. There are several reasons for this. Alberta water typically contains high levels of sodium. Many of Alberta's broilers are raised 2900 feet above sea level. Because air pressure is lower at high altitudes, ascites is found more often at high altitudes. Open flame brooding can also contribute to ascites (remember that a flame uses up oxygen, so open flames actually compete with the birds for oxygen). Harsh winter environments mean that ventilation rates are usually quite low in the winter. Oxygen is used up by the birds and brooders, and must be replaced.
Ascites research
Dr. John Feddes has completed a major research project on ascites. The objectives of the project were to investigate the effects of environmental factors such as temperature, CO2, O2, dust, and growth rate on the incidence of ascites in broiler chickens.
Feed restriction
Short term feed restriction at an early age (day 7 to day 15) may reduce the incidence of ascites (Robinson et al. 1992). This is because the early growth rate is slowed, thereby reducing the early demand for oxygen. Feed intake can be restricted by a lighting program that will also slow the initial growth rate. Classen (1993) reported that an increasing photoperiod resulted in improved bird health with little or no effect on final weight or efficiency of feed utilization.
Dust
Respirable dust in the airspace of the broilers may also increase the incidence of ascites. Previous research in turkey housing (Feddes et al. 1992), indicated that the majority of airborne dust is in the respirable size range and consists mostly of faecal and urate particles. Being biologically active, these respirable particles may develop a sensitization within the lung tissue and cause a restriction in the bronchii similar to that of an allergenic reaction. This reduces the efficiency of oxygen uptake by the lungs. Adding canola oil to the litter (2% of the litter by volume) has been very effective in reducing the generation of respirable dust.
Temperature
Cold temperatures increase the oxygen requirement, cardiac output, and blood flow of the broiler chicken. As a result, pulmonary arterial pressure may increase, resulting in damage to the right ventricle (Julian et al., 1989). Research results have shown that exposure to cold temperatures increased the heart weight of chickens, probably as a result of the increased work-load on both the ventricles.
Experiment #1. Do dust and feed restriction affect ascites in broilers?
The effect of feed restriction and application of canola oil to straw litter on broiler growth and the incidence of ascites syndrome was evaluated in four pens over two cycles. Four hundred male broilers were housed, 100 per pen, in each cycle.
Feed intake - of birds in two pens was restricted to 18 g of feed/bird/day from 7 to 16 days of age. Birds in the other two pens had ad libitum access to feed throughout each growing period.
Litter oiling - Canola oil was added to the litter twice per week in one restricted and one ad libitum-fed pen (to control dust). Over the six week period, a total of 0.8 litres of oil were added to each square metre of litter.
Ascites score - At 6 wk of age, all birds were scored for the incidence of ascites syndrome at the processing plant. Hearts were removed and dissected. A cross sectional image of each heart analysed to determine the area of the right ventricle (RVA - the right ventricle is the chamber in the heart which pumps blood to the lungs).
Results
Birds fed ad libitum from 7 to 16 days of age
- were significantly heavier at 40 days (2.07 vs. 1.86 kg),
- showed more evidence of ascites
- had a higher ascites score, (0.87 vs. 0.61)
- had higher RVA values (0.40 vs. 0.35 cm2)
The ascites syndrome score was significantly correlated to RVA values (r=0.52).
Birds reared in pens where oil was added to the litter (ad libitum-fed birds)
- did not affect body weight
- showed less evidence of ascites
- reduced the RVA values (0.44 and 0.37 cm2)
Experiment #2. Do dust and fluctuating temperatures affect ascites in broilers?
The effect of temperature fluctuations and the application of canola oil to broiler straw litter (to remove airborne respirable dust) on growth performance, carcass characteristics, and the incidence of ascites was evaluated over two cycles. Six hundred male Hubbard HiY broilers were housed in four pens of 150 birds each in each cycle.
Temperature - Two pens had temperature fluctuations 3C above the required temperature during the day and 3C below the required temperature at night. All pens had the same mean temperature.
Litter oiling - Twice per week, the litter in one control temperature pen and one temperature fluctuation pen was sprayed with canola oil to reduce respirable dust levels. A total of 1.1 L/m2 of oil was added over the 6 week growing period).
Results
Temperature fluctuation resulted in
- no difference in 40 day body weight (2277 g) compared to the control (2265 g)
- significantly greater breast muscle (pectoralis major) weight (285.6 g) compared to birds in the non-fluctuating temperature treatment (273.6 g)
- significantly greater tenders (pectoralis minor) weight (67.4) compared to the control (64.4 g)
- significantly greater right ventricle weight (2.45 vs. 2.34 g).
- increased appetite (increased feed consumption)
Oiling
- had no significant affect on carcass conformation.
- The amount of oiling (1.1 L/m2) was excessive. The birds were oily, and had reduced growth performance because the insulative value of the feathers was reduced by the oil.
- The volume of 0.8 L of oil per m2 is adequate, and should not be adjusted for increased stocking density.
The area of the right ventricle was not significantly different between any of the treatments.
The mean ascites score was not different between the two treatments. There was a relatively low incidence of ascites in the flock.
So what?
- Feed restriction from 7 to 16 days decreased the incidence of ascites, but also decreased body weight gain.
- Litter oiling reduced indicators of ascites. Oiling resulted in a reduced RVA, and a reduced ascites score in the first trial. The same trend was not seen in the second trial because too much oil was applied to the litter.
- Oil applied to litter at the rate of 0.8 L/m2 appears to lower the challenge to the lung and improve oxygen transfer.
- Diurnal (day and night) temperature fluctuations caused higher mortality and resulted in significantly larger right ventricle weight (associated with ascites) and appeared to stimulate appetite.
- Temperature fluctuations resulted in greater breast muscle yield.
M. Zuidhof1, J. Feddes2, R. McGovern1, F. Robinson2, and J. Hanson1
1Alberta Agriculture, Food and Rural Development
2University of Alberta
Poultry Research Centre News - Vol. 6 No. 2, October 1997 |
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