Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Tibial Dyschondroplasia in "Stunted" Broiler Chickens Sandra Stephens Western College of Veterinary Medicine University of Saskatchewan
Introduction Poultry Extension at the University of Saskatchewan as approached by a local poultry slaughter facility about a problem they were having with birds that were too small to put through the evisceration equipment. The company had installed a high speed line in February of 1996. It had been noted that very small carcasses tended to get caught up in the machinery, but the low numbers of these carcasses meant that this was not usually a problem. In late August 1996, they reported an increase in the number of these very small carcasses in some flocks. The numbers were so high that it became a problem for the plant in that the line had to be stopped frequently to "unplug" equipment. Canadian Food Inspection Agency (CFIA) veterinarians determined that there were no pathological lesions in these very small carcasses that would warrant condemnation. The carcasses were therefore discarded prior to evisceration as plant rejects or discards so as to avoid line stoppages. Investigation The plant was asked to submit birds from flocks that had significant numbers of these small bird discards ("Affected") and birds from flocks with no small bird discards ("Normal") for examination. The findings from the two groups would be compared to determine if there were any significant differences. Affected flocks (9 flocks) examine 10 average size birds examine 10 stunted birds (discards) Normal flocks (6 flocks) examine 10 average size birds examine 10 small birds (not discards) Findings Affected flocks: (9 flocks)
No other gross pathological lesions. Bursa % of body wt. = 0.13% (range 0.06 – 0.2). 4 out of 9 flocks had a ratio < 0.10%. Birds "discarded" ranged from 0.2% to 4.8%. Average condemns – 2.33% Ascites – 0.42 Cellulitis – 0.58 Cyanosis – 0.56 Emaciation – 0.19 It was determined from this examination that a "Stunted" bird was one weighting < 1.14 kg (live wt.). The "cut off" weight for the plant to discard birds was < 1.33kg (live wt.). This appeared to be the weight where company employees would start to pull birds from the line as potentially being to small to go through the evisceration equipment properly. Normal Flocks: (6 flocks)
No other gross pathological lesions. Bursa % body wt. = 0.17% (range 0.05 – 0.2). 5 out of 6 flocks had burs ratios >0.17. Birds "discarded" ranged from 0 to 0.2%. Average condemns – 1.49% Ascites – 0.24 Cellulitis – 0.21 Cyanosis – 0.26 Emaciation – 0.06 The most significant finding was the unusually high incidence of tibial dyschondroplasia in these very small birds. A protocol was developed to survey a number of flocks in an attempt to determine the following: Which came first the tibial dyschondroplasia or the stunting? What was the role of nutrition? What was the role of infectious agents? Survey Format All feed companies supplying the broiler chicken industry in Saskatchewan were approached to aid in this investigation. They were to delegate three farms as survey flocks and fund feed analysis. Analyze starter ration from each flock. (sample collected in the barn – one cup collected every other day for one week) Gross and Histological examination at 9-10 days of age. (small, but active chicks) 21 day average weight. 35 day individual weight of 300 birds (one farm per feed company). Blood samples from each flock at 35 days. 35 day necropsy – 5 average males, 5 average females, 5 culls Flocks Statistics – weekly mortality -- questionnaire Findings (A total of sixteen flocks were surveyed) All Starter rations had > 1.0% Ca All were adequate for other elements. A high incidence of yolk sac infection was seen in submitted chicks from the majority of farms. One flock had histological lesions consistent with "infectious stunting". 21 days – weight on target – 738 g 35 day findings (weights and bursa scores were normal) -avg. wt. = 1.660 kg (1.600kg) - Bursa/Body wt. = 0.21% - TD avg birds = 45% Average weights at 21 days: 697g (mash and pellet rations) no correlation between 21 day weight and the incidence of TD 35 day individual weights of 300 birds to predict the number of small and "stunted" birds occurring in normal flocks. Small birds <1.33 kg Stunted birds <1.14kg
It appears that in any given flock, regardless of how heavy they are, there will be a small percentage of the birds (0.33%) that will be very small (<1.14 kg). Four flocks had low Bursa/Body weight ratios all had positive IBD titers 3 had <20% incidence of TD 1 had 26% incidence of TD Incidence of TD Average 20.6% (range 0.0% - 50%) Males – 26.8% Females – 13.3% Flocks reported to have poor uniformity at 21 days had a higher incidence of TD 32% (13% for uniform flocks). Shortly after the survey was completed, two flocks diagnosed with rickets were followed in the same manner as the survey flocks.
Flock #1
Slaughter - Live wt. At 39 days - average birds – 1.653 kg - stunted birds – 1.074 kg - 1.8% of birds slaughtered discarded as stunts
Flock #2
Slaughter - Live wt. At 41 days – average birds – 1.83 kg - stunted birds – 1.33 kg - 1.8% of birds slaughtered discarded as stunts
Conclusions
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