Improved performance in commercial broiler flocks with subclinical infectious bursal disease when fed diets containing increased concentrations of vitamin E.

The economic effects of increased vitamin E supplementation in 79 commercial broiler flocks incorporating over 1.5 million birds was assessed. Approximately half of the flocks were fed on either a high (178 IU/kg) or normal (48 IU/kg) vitamin E-containing diet. In addition, in approximately half of the flocks subclinical infectious bursal disease (IBD) was present. Analysis of the performance data demonstrated that flocks with subclinical IBD were consistently worse (P< 0.001) for net income, feed conversion ratio and average weight per bird than flocks without the subclinical disease. The trial also indicated that the average net income of flocks with subclinical IBD and fed a high vitamin E-containing diet was 10% better (P < 0.05) than flocks with subclinical IBD and fed a normal vitamin E-containing diet. However, the trial also demonstrated that the difference between the average net income achieved by flocks without subclinical IBD and being fed on either a high or a normal vitamin E-containing diet was only 2% and not significantly different. It is suggested that the increased improved performance from high vitamin E-containing diets recorded in flocks with subclinical IBS is due to enhanced immunocompetence and increased resistance to disease. It is also suggested that under field conditions, high dietary inputs of vitamin E are most beneficial where there is a challenge to the host's defence system and significantly improved performance will occur more predictably under such conditions.

Prevalence of pleurisy and pneumonia in pigs in Northern Ireland (1969-1989).

A database of condemnation data from abattoirs was combined with a meteorological database to investigate the relationship between the prevalence of pleurisy and pneumonia in pigs in Northern Ireland and prevailing weather conditions. Between 1969 and 1989 three significant trends were found in the occurrence of condemnations due to pleurisy and pneumonia, and significant correlation coefficients were found between the percentage condemnations and air temperature.

Economic effects of clinical chicken anemia agent infection on profitable broiler production.

An outbreak of anemia dermatitis syndrome caused by chicken anemia agent (CAA) occurred in 15 broiler flocks. An average of 29% of chickens in these flocks were derived from a common breeder flock. The breeder flock had no antibody to CAA at 20 weeks of age but had seroconverted by 31 weeks. Diseased broiler flocks were derived from eggs laid by the breeder flock between 25 and 30 weeks of age. CAA infection in the breeder flock was subclinical, with no apparent effects on mortality or performance. A strategic program of therapeutic and/or prophylactic antibiotic therapy was begun in affected broiler flocks as soon as the disease was diagnosed. Nevertheless, when the cost of therapy was taken into account, affected broiler flocks had a net income 17.3% to 19.6% lower than normal flocks. Average bird weights were 3.3% to 3.5% lower in affected flocks than in unaffected flocks, and affected flocks had a significantly greater proportion of lighter birds. Average mortality in affected flocks was 2.0% to 2.3% higher than in normal flocks, with peak mortality occurring in the third week of life. There was no apparent effect on feed-conversion ratio.

The cost benefit of vaccinating broiler flocks against subclinical infectious bursal disease.

In an attempt to reduce economic losses due to subclinical infectious bursal disease (IBD), broilers reared in 23 houses known to have been infected with IBD virus were vaccinated with live, attenuated IBD virus vaccine at 20 days of age. Vaccination of either one, two or three consecutive flocks resulted in significant increases in net income and average bird weight, and in a decrease in mortality. An improvement in broiler performance was not restricted to vaccinated flocks, but was also apparent for at least 1 year following placing of the first vaccinated flock in subsequent flocks reared in the same houses.

Economic effects of subclinical chicken anemia agent infection in broiler chickens.

To evaluate the economic effects of subclinical chicken anemia agent (CAA) infection on broiler performance, clinically normal broiler flocks were grouped into two categories: A) flocks in which none of 10 birds sampled at slaughter had antibody to CAA, and B) flocks in which six or more of 10 similarly sampled birds had CAA antibody. Production and performance parameters of 25 flocks in each category were compared. No statistically significant differences were found between category A and category B flocks in major production parameters such as sex, feed manufacturer, type of litter, stocking density, and age at slaughter. However, category A flocks achieved 13% (P less than 0.05) greater net income per 1000 birds, 2.0% better feed-conversion ratio (P less than 0.05), and 2.5% (P less than 0.05) greater average weight per bird than category B flocks. No significant differences in hockburn bonus per 1000 birds (a bonus payable to growers whose broilers have the lowest prevalence of contact dermatitis lesions on the hocks) and mortality were found between category A and category B flocks. These results show that subclinical CAA infection has a substantial, statistically significant effect on commercial broiler performance and profitability.

Epidemiology of a contact dermatitis of broilers.

A computerised information retrieval system of broiler production data has been used to study the epidemiology of contact dermatitis. The results of the analyses of broiler production data for the period 1984/85 were compared and contrasted with those for the period 1986/1987. The prevalence of breast lesions recorded in the latter period was 33% less than in the former. The prevalence of hock lesions was similar in both periods, but the degree of variation in the prevalence of lesions recorded by individual flocks was substantially reduced in 1986/87. Stocking density, average age of removal and the sex of birds all had an effect on the prevalence of the condition in broiler flocks in both time periods. The condition was more frequently recorded in flocks during the winter and a strong correlation with ambient relative humidity, obtained.

Control, prevention and eradication of Salmonella enteritidis infection in broiler and broiler breeder flocks.

Salmonella enteritidis was identified by serological and bacteriological techniques in two clinically normal breeder flocks in an integrated broiler organisation in Northern Ireland. The organism was transmitted vertically to clinically affected progeny flocks. The infected breeder flocks were slaughtered and the infection throughout the organisation controlled and subsequently eradicated. A working group, consisting of the senior management of the broiler organisation and veterinary staff from the Veterinary Research Laboratories at Stormont, was formed to establish procedures to minimise the risk of the reintroduction of salmonella infection, by preventing vertical transmission from grandparent flocks, or lateral transmission from personnel, other animal species and fomites, or transmission through the feed. All feed was heated to a minimum of 70 degrees C for 12 minutes immediately before it was pelleted and subsequently transported to the flocks through a dedicated system of conveyor belts, bins and lorries. A comprehensive system for monitoring the efficacy of the preventive procedures was established and is now used throughout the poultry industry of Northern Ireland.

Economic effects of subclinical infectious bursal disease on broiler production.

A survey of the infectious bursal disease (IBD) status of 85 clinically normal broiler flocks was carried out. Flocks were grouped into three categories: flocks without IBD lesions (category A), flocks with typical acute IBD lesions (B) and flocks with typical chronic IBD lesions (C). Category A flocks achieved a net income per 1,000 birds which was 11% better (P<0.05) than category B flocks and 14% better (P<0.01) than category C flocks. The 85 broiler houses used by the surveyed flocks during production were similarly grouped into the three categories. Analysis of production data from 991 flocks comprising 14 million birds demonstrated that flocks reared in category A houses achieved a similar superiority in net income per 1,000 birds over those flocks reared in both category B and category C houses. Food conversion ratio and average weight per bird were also superior in flocks reared in category A houses. These findings suggest that IBD virus persisted from flock to flock in category B and category C houses. The differences in performance were greatly accentuated during the winter months. The results indicate that the presence of IBD virus infection accounts for about two-thirds of the reduced profitability achieved by broiler flocks in Northern Ireland during the winter.

Rain and windchill as factors in the occurrence of pneumonia in sheep.

A computerised information retrieval system of abattoir pathology and meteorological data has been used to investigate the effect of prevailing weather conditions on the occurrence of pleurisy and pneumonia in the sheep population of Northern Ireland. Significant correlation coefficients were found between the percentage condemnations due to pleurisy and pneumonia in sheep and rainfall, windspeed, temperature and humidity. The most significant correlation was found with windspeed. The paper describes the calculation of a new meteorological variable, the rain/windchill factor. Very highly significant correlation coefficients were found between the percentage lung condemnations in sheep and the rain/windchill factor prevailing during the same month and both one and two months previously. The paper discusses the practical implications of these findings for sheep production and highlights the desirability of protecting sheep from adverse climatic conditions during the winter months.

Type C botulism in cattle being fed ensiled poultry litter.

A botulinum toxin from ensiled poultry litter which caused a major outbreak of bovine botulism was characterised as type C1. The litter produced transient ataxia when fed to two experimental calves and the clinical signs were accompanied by a transient appearance of serum toxin. Type C1 toxin was demonstrated in muscle tissues which had been taken during the outbreak from an affected animal with high circulating serum toxin, and held frozen for seven months. Clostridium botulinum type C organisms were demonstrated in faeces from another affected animal and also in kidney tissue from a third animal. These observations have implications for the diagnosis and management of future outbreaks of botulism and for the potential health risk from the meat of affected animals.

A contact dermatitis of broilers--epidemiological findings.

Lesions of a contact dermatitis have resulted in serious downgrading of broiler carcases in the Northern Ireland poultry industry. A longitudinal survey was initiated to identify the important epidemiological factors involved in the occurrence of the condition. The results from the analysis of data from 986 flocks containing 12.6 million birds over a 2 year period, have quantified the effects which the major aspects of production have on the incidence of the condition in individual flocks. The stocking density, feed manufacturer, average age of removal and the sex of birds all had a profound effect. Lesions were more frequently recorded in flocks during the winter months and a strong correlation with the weather variable, relative humidity, obtained. Individual producers and houses varied in the incidence of the condition which was closely associated with the presence of poor litter conditions in the flocks.

Pulmonary lesions and Mycobacterium bovis excretion from the respiratory tract of tuberculin reacting cattle.

Although it is generally recognised that tuberculous lesions are present in lymph nodes associated with the respiratory tract in approximately 90 per cent of reactors with confirmed infection, lung lesions are found in only 1 to 2 per cent of such cases during abattoir examination. When lung lesions are not detected, it has been claimed that such cattle are non-excretors and thus unimportant in the epidemiology of the disease. In this study the lungs of 55 reactor cattle were sliced into sections approximately 0.5 cm thick. Tuberculous lesions were evident in over 70 per cent of lungs from reactors with concurrent lesions in lymph nodes of the respiratory system. Further, M bovis was isolated from single samples of nasal and, or, tracheal mucus taken at slaughter in 19 per cent of confirmed cases. Several of these reactors had a clear tuberculin test less than six months previously indicating recent infection. This study confirms the continued importance of the infected bovine in the epidemiology and current eradication of bovine tuberculosis. It is suggested that all tuberculous cattle with lesions in respiratory lymph nodes, rather than being regarded as non-excretors, should be considered as possible excretors and thus important sources of infection for other cattle both within and between herds.