Cell death in avian tibial dyschondroplasia.

Tibial dyschondroplasia (TD) is a local defect of growth plates in fast-growing poultry where the transitional zone cartilage fails to resorb and persists as an avascular plug that prevents endochondral bone formation. We compared the differences in the cartilages from normal and TD-affected growth plates using the reduction of MTS to assess cartilage viability. Chondrocyte apoptosis was determined using biochemical measurement of DNA fragmentation, and in situ labeling of nuclei with fluorescein-dUTP using terminal deoxynucleotide transferase (TdT)-mediated nick end labeling (TUNEL) of isolated chondrocytes and growth plate sections. The TD-affected cartilage showed a significantly lower level of MTS reduction and a decrease in trichloroacetic acid (TCA)-precipitable DNA content. The TD cartilages had a higher percentage of fragmented DNA, which was also evident with agarose gel electrophoresis. A significantly higher number of chondrocytes isolated from TD-affected cartilages had condensed morphology, shrunken nuclei with little cytoplasm, and were TUNEL positive as identified by the incorporation of fluorescein-dUTP into the nuclei. In vivo results similarly showed a significant population of chondrocytes in transition zones undergoing condensation and apoptosis as determined by in situ TUNEL staining of growth plate sections. Normal growth plates, under similar conditions, showed no significant apoptosis of chondrocytes from hypertrophic and chondrolyzing zones. The condensation and apoptotic cell death may be responsible for the reduction of growth plate viability as well as the reduction in DNA content and increased DNA fragmentation. While the cause of the pathogenesis of TD is unknown, it appears that the aberrant death of chondrocytes in hypertrophic regions of growth plates may be responsible for the accumulation of cartilage and the arrest of endochondral bone formation.

Variation in toe-web response of turkey poults to phytohemagglutinin-P and their resistance to Escherichia coli challenge.

One thousand 5-wk-old male turkeys from each of two commercial strains (A and B) were grouped into low, medium, and high responders based on the cutaneous basophil hypersensitivity (CBH) response obtained 24 h after toe-web inoculation with 100 micrograms of phytohemagglutinin-P (PHA-P). The CBH response for Strain A was higher than strain B (P = 0.00001) and ranged from 0 to 1.95 mm, with a mean of 0.66, whereas the CBH response for Strain B ranged from 0 to 1.67 mm with a mean of 0.38. At 6 wk of age, 36 birds from each of the six response groups were inoculated into the left thoracic air sac with 1.5 x 10(7) cfu of an early log phase broth culture of Escherichia coli. Samples of 5 or 10 birds were necropsied from each of the six groups at 7, 14, 28, and 42 d postinfection (PI). Birds were scored for air-sacculitis/pericarditis (AS) and turkey osteomyelitis complex (TOC). Overall mortality of birds inoculated with E. coli was 31%. There were no mortalities in unchallenged controls. Strain A had significantly higher Week 1 mortality, marginally higher overall mortality (P = 0.1), and higher AS scores than Strain B. There were no TOC lesions detected until 7 d PI, after which all mortalities had TOC lesions in multiple sites. The differences in CBH response within each strain were not clearly correlated to E. coli susceptibility. However, these data suggest that air sac inoculation of E. coli can provide a useful model for the study of TOC. The greater incidence of disease in Strain A indicates that an enhanced inflammatory response may increase susceptibility to E. coli septicemia.

Histologic study of hepatic lesions in two turkey flocks.

Hepatic lesions were studied in two turkey flocks by euthanatizing 50 birds a week from the ages of 1 through 15 wk. Samples of liver that contained lesions and samples of duodenum, pancreas, ileum, and cecal tonsil were examined histologically. Lymphocytic infiltrations made up 82% and 75% of the hepatic lesions, and granulomas occurred in 18% and 25% of the livers. Nematode larvae were present in 12% and 15% of the hepatic lesions.

Matrix metalloproteinase activities in avian tibial dyschondroplasia.

Tibial dyschondroplasia (TD) in poultry is a disorder of growth plate cartilage that fails to resorb and consequently prevents bone formation. Matrix metalloproteinases (MMP) contribute to the process of resorption through the degradation of extracellular matrices and facilitating vascularization, growth plate remodeling, and maturation. In order to understand the cause of the failure of cartilage degradation in TD, the gelatinase and collagenase activities, and the levels of collagen and glycosaminoglycans of conditioned media derived from cartilage-explant cultures of normal and TD growth plates were measured. Substrate zymography exhibited two prominent gelatinolytic and collagenolytic bands corresponding to MW 63, 59, and a broad but fuzzy band of activity between 100 and 200 kDa. On treatment with 4-aminophenylmercuric acetate, a compound that converts proenzyme forms of MMP, the 63 kDa MW gelatinolytic band migrated as a approximately 60 kDa band and contributed to the broadening of the 59 kDa band. The TD-growth plate-conditioned media had significantly lower collagenolytic-gelatinolytic activities. The sulfated glycosaminoglycans, but not the collagen contents of the conditioned media from TD-explant cultures, were also reduced significantly. It is likely that the decreased matrix metalloproteinase activities of growth plate chondrocyte may contribute to a reduced turnover of extracellular matrices (ECM), leading to the retention of cartilage and its lack of vascularity in TD-affected growth plates.

Immune and physiological responses of turkeys with green-liver osteomyelitis complex.

A study of field turkeys was undertaken in order to determine the involvement of relative immunological differences in the etiology of turkey osteomyelitis complex (TOC). Lame and normal turkeys were sampled from commercial flocks just prior to processing in two separate trials. After testing for functions of both humoral and cellular immunity, the turkeys were necropsied and examined for lesions of TOC. There were significantly higher relative spleen and over weights and significantly lower body weights and relative bursal weights in birds with TOC. The birds with TOC had lower response to phytohemagglutinin-P in both in vivo and in vitro tests as well as lower circulating lymphocyte counts and higher monocyte, heterophil, and total white blood cell counts. There was a significantly higher antibody response to sheep red blood cells in turkeys with TOC, whereas antibody response to Salmonella pullorum antigen was not different. There were no significant differences in the percentages of mononuclear cells or heterophils able to phagocytize bacteria or latex particles, or kill bacteria; however, the heterophils from turkeys with TOC lesions did phagocytize significantly fewer latex particles per cell than did those of the healthy turkeys. Total serum protein, uric acid, and blood urea nitrogen levels were higher in birds with TOC, whereas hemoglobin, iron, alkaline phosphatase, and gamma-glutamyl-transferase levels were lower. Although many of the differences in birds with TOC could be caused by the normal host reaction to infection, further study may reveal innate differences that contribute to susceptibility to TOC.

Effect of the genetic selection of turkeys for increased body weight and egg production on immune and physiological responses.

Selection of poultry for fast growth rate is often accompanied by a reduction in specific immune responses or increased disease susceptibility. In this study, 17-wk-old male turkeys from each of four closed genetic lines, a randombred control (RBC) line and its subline (F) selected for increased 16-wk BW, and another RBC and its subline (E) selected for increased egg production, were tested for in vivo response to toe web inoculation with phytohemagglutinin-P (PHA-P), in vitro response of lymphocytes in whole blood to PHA-P and concanavalin A (Con A), hemolytic complement activity, differential white blood cell counts, hematology, and serum chemistry values. Fifteen male turkeys from each of two commercial lines, Com A and Com B, were also tested. The large-bodied F line birds had a lower toe web response to PHA-P, lower lymphocyte counts, and lower relative spleen weights than their smaller parent line. Body weights, total erythrocyte counts, blood urea nitrogen (BUN) levels, and in vitro mitogenic response to PHA-P and Con A were higher in the F line birds. Line E had lower hemolytic complement levels, lower relative spleen and relative bursal weights, and a higher in vitro mitogenic response to PHA-P than its parent line. The Com B line had a lower toe web response to PHA-P, and lower serum levels of gamma-glutamyltransferase and bilirubin than Com A. Line Com B had higher total RBC counts and higher levels of alanine aminotransferase (ALT) than Com A. These results support the concept that some changes in the cell-mediated immune response, as well as other physiological changes that may potentially affect immune response, appear to accompany selection for faster growth.

Effect of intermittent activity on broiler production parameters.

The use of intermittent lighting in broiler production has been shown to result in spurts of activity that appear to reduce lameness. Because intermittent lighting is difficult to achieve in curtain-sided houses, the objective of this study was to determine whether simple equipment used to increase activity in broilers would improve production variables. At 1 d of age, 840 male broiler chicks were placed in 24 floor pens. The four treatments (six replicates of 35 chicks each) were as follows: 1) Control-standard feeders, 2) Ramps and Toys-birds had to climb a slight incline ramp to reach feeder and had a hanging mobile, 3) Ramps only, and 4) Toys only-standard feeders. Two trials were conducted. Weekly group weights and feed consumption were recorded. Mortality was recorded daily. At 6 wk of age, birds were bled, euthanatized, weighted, and scored for ascites and tibial dyschondroplasia (TD), and relative heart, liver, and spleen weights were obtained. Blood samples were analyzed for blood gases, hemoglobin, red blood cell count, and clinical chemistries were performed. In Trial 1, during Weeks 2, 3, and 4, treatments with ramps had significantly heavier average bird weight and significantly lower feed:gain ratios. In Trial 2, treatments with ramps had no difference in average BW; however, these groups consumed less feed, resulting in significantly lower feed:gain ratios. Cumulative mortality was decreased by ramp treatment in Trial 2. Toys decreased the incidence and severity of TD in Trial 2. In general, organ weights, blood gases, hematologies, and clinical chemistries were not affected by treatments. However, birds in treatments with ramps had significantly lower serum calcium and smaller hearts in Trial 1, and significantly lower serum cholesterol and smaller hearts in Trial 2.

Evaluation of the toxicity of alum (aluminum sulfate) in young broiler chickens.

Two experiments were conducted to characterize the toxicity and evaluate the efficacy of alum to increase intestinal strength in young broiler chicks. Cobb x Cobb male broiler chicks were placed in an experimental design consisting of six dietary treatments of alum (control, 0.23, 0.47, 0.93, 1.9, and 3.7%) with four replicate pens of 10 broilers per pen. The chicks were housed in electrically heated batteries and provided the treatments for ad libitum consumption from 1 d to 3 wk of age. Alum significantly (P < or = 0.05) decreased body weights at 1.9 and 3.7% in Experiment 1 and at 0.93, 1.9, and 3.7% in Experiment 2. Feed conversion and the relative weight of the gizzard were increased in both experiments at 3.7%. Serum phosphorus was decreased at 1.9 and 3.7% in Experiment 1 and at 3.7% in Experiment 2. Intestinal and bone strength were decreased in both experiments at 3.7%. Bone ash was reduced at 3.7% in Experiment 2, bone S levels increased at 1.9 and 3.7% in Experiment 1 and at 3.7% in Experiment 2, and bone Al levels were elevated in both experiments at 3.7%. Muscle levels of P and S decreased, and that of Ca increased at 3.7%. Aluminum levels were not elevated in muscle tissues. These data indicate that alum can be toxic to young broiler chicks, but at levels that would not be expected to be reached through litter consumption, and that alum did not increase intestinal strength.

Pathogenicity studies of an Arkansas variant infectious bursal disease virus.

A variant infectious bursal disease virus (IBDV), IBDV-s977, was blind passaged in cell culture, plaque purified, and attenuated by serial passage at a high multiplicity of infection (MOI) in chick embryo fibroblasts (CEF). Cell culture passages of virus caused less bursal atrophy and splenomegaly than did the original isolate and retained immunogenicity; however, virus tended to persist for a longer time in the bursa and spleen of birds infected with the highest CEF passages. Antibody to both low MOI and high MOI passages of IBDV-s977 poorly neutralized virus that was isolated from bursal tissue 28 days postinfection (PI). The spleens of chickens infected with the eighteenth CEF passage were negative for virus at 3 and 7 days PI but had high titers of virus at 14 and 28 days PI. There was also more virus in the bursa of birds infected with the fifteenth and eighteenth CEF passages at 28 days PI than at 7 or 14 days PI. Defective interference (DI) was demonstrated when cell cultures were coinfected with a constant amount of low MOI virus and serial dilutions of high MOI virus. There was an increase in interference score with increased passage number in CEF, and there was more interference in virus passaged at a high MOI. There was an inverse relationship between interference score and bursal lesion score and splenomegaly at 7 days PI, indicating that DI particles may be involved in virus attenuation. There was a positive relationship between interference and viral persistence in the bursa and spleen at 28 days PI. Antiserum to s977 was shown to enhance the nonlytic replication of s977 in CEF, presumably within macrophages, providing a possible mechanism for the pathotypic variation seen in emerging strains of IBDV.

Antigenic characterization of an Arkansas isolate of infectious bursal disease virus.

The s977 strain of infectious bursal disease virus (IBDV) was isolated in northwest Arkansas in 1977 from the bursae of young broilers with high maternal antibody titers to the Moulthrop strain of IBDV (BursaVac). The comparison of a plaque-purified isolate of s977 with other IBDV serotype 1 and serotype 2 strains using virus neutralization indicates that s977 is a subtype of serotype 1 vaccine viruses and the MD variant strain of IBDV and has no relatedness to the Delaware Variant A (VarA) virus. In vivo cross-protection studies in specific-pathogen-free white leghorn chickens showed that an inactivated vaccine using s977 antigen was 2.5 times more protective against challenge with s977 than was an inactivated IBDV Variant E (VarE) vaccine. The vaccination of maternally immune broiler chicks with live s977 did not provide protection against subsequent challenge, indicating that s977 does not have enough antigenic difference to break through maternal immunity. Analysis of denatured viral polypeptides using polyacrylamide gel electrophoresis showed that s977 and two reported variant strains, 51 and VarE, share three protein bands, 90 kD (VP1), 40 kD (VP2), and 31 kD (VP3), that were not observed in BursaVac. BursaVac and s977 shared a 74 kD precursor band that was absent or very faint in the VarE and 51 strains. The most unique characteristic of s977 was the relative abundance of a wide, 56-63 kD band that contained two distinct immunoreactive bands when blotted with antiserum to s977. BursaVac contained a 56 kD band that failed to react with s977 antiserum. Analysis of polypeptide bands using laser densitometry indicated the presence of a number of bands between 20 kD and 25 kD in the s977, 51, and VarE preparations but only a 25 kD band in BursaVac. The number of bands decreased with the degree of relatedness to standard vaccine strains. It appears that, antigenically, S977 may hold an intermediate position between the classic virus strains and the more recently reported serotype 1 variants.

Effect of gonadal steroids on bone and other physiological parameters of male broiler chickens.

Comparative studies of the effects of estradiol, progesterone, testosterone, cholesterol, and megestrol on juvenile chickens were carried out to determine their effects on bone and other physiological parameters. The chickens were implanted at 6 wk of age with ethylene-vinyl acetate copolymers containing steroids equivalent to a weekly dose of 10 mg/kg body weight for 3 consecutive wk. Estradiol caused a gain in body weight and relative liver weight but suppressed the growth of comb and testis. It also increased several serum variables, including triglycerides, cholesterol, calcium, phosphorus, and iron, and reduced testosterone levels. Testosterone produced an increase in comb weight and decreased both testicular and bursal weights. Growths of testis and comb were suppressed in progesterone-implanted chickens, as was the level of serum testosterone. Megestrol stimulated liver growth and increased serum testosterone levels. The lengths, relative weights, diaphyseal diameters, and ash percentages of both femur and tibia did not change significantly due to any treatment except that estradiol reduced tibial weight. Both progesterone and megestrol increased fibular growth plate alkaline and tartarate-resistant acid phosphatase activities. Other steroids did not affect these or the levels of calcium and of phosphorus of the fibular growth plate. Only testosterone caused a marked increase in the breaking strengths of both femur and tibia in all three parameters, i.e. load at yield, Young's modulus, and stress at yield responses. These findings suggest that the effects of steroids on bone in juvenile chickens may be limited.

Effect of feed and water withdrawal on green liver discoloration, serum triglycerides, and hemoconcentration in turkeys.

Turkey poults at 1 d of age were obtained from a local hatchery (Experiment 1), or at 14 wk of age from a local grower (Experiment 2), and kept in floor pens with feed and water available for ad libitum consumption. When the turkeys reached 16 wk of age (Experiment 1) and 18 wk of age (Experiment 2), the treatments were established within a 2 x 2 factorial arrangement and consisted of ad libitum consumption of feed and water (control), or feed, water, or both feed and water withdrawal. In Experiment 1, 1 turkey per pen, 6 turkeys per treatment, were killed every 4 h for 32 h, and in Experiment 2, 10 turkeys per treatment were killed at 24, 30, 36, 42, 48, and 54 h after feed, or water, or both had been withdrawn. The turkeys were bled at sampling times 16 and 32 h in Experiment 1 and at each sampling time in Experiment 2. Serum was collected and hematological and clinical chemistries performed. The turkeys were examined for green liver discoloration and turkey osteomyelitis complex lesions. Withdrawal of feed, water, or both feed and water for up to 54 h did not affect the incidence of green liver discoloration in these studies. Serum triglyceride concentrations were the most sensitive blood constituent to either water or feed withdrawal, with reductions (P < or = 0.05) occurring at 16 h after feed withdrawal. Hemoconcentration resulted in an increase in hematocrit and hemoglobin levels 30 h after water withdrawal.

The effect of dietary copper sulfate on infectious proventriculitis.

Oral inoculation of day-old broiler chicks with a crude homogenate of affected proventricular tissue, or the same homogenate filtered through a .2 micron filter caused proventricular lesions similar to those responsible for carcass contamination of broilers at processing. Dietary copper sulfate (CUS) has also been shown to produce similar lesions. In this study, we investigated the interaction between crude proventriculus homogenate or filtered proventriculus homogenate and 1 g/kg CUS added to a standard chicken diet. Cobb x Cobb female broiler chicks were distributed into six groups with four replicate battery pens per group. Birds were fed either a standard broiler starter diet or the same diet with 1 g/kg CUS. Each dietary treatment was inoculated per os with 1 mL of either sterile saline, unfiltered homogenate, or filtered homogenate. Both crude and filtered homogenates had a much stronger affect on proventriculus score than did Cu by itself, resulting in no interaction between either homogenate or filtrate and CUS. There was a significant and possibly antagonistic interaction on proventriculus relative weights in the CUS by filtrate group during Week 1 and a synergistic interaction in the CUS by homogenate group during Week 4. Body weights were decreased in birds fed homogenate or CUS, but not in birds fed filtrate. There was a protective effect shown by filtrate on body weight of birds fed both filtrate and CUS only during Week 1. There was a synergistic decrease in body weight of birds fed homogenate and CUS during Week 2. Overall feed conversion efficiency was significantly decreased in the homogenate treatment (P = .04) and decreased in the birds fed CUS (P = .1). There was a (4.2 vs 2.3) (P = .1) decrease in feed conversion efficiency in birds fed both homogenate and CUS. Natural exposure to low levels of the infectious agent present in the homogenates may interact with excess dietary CUS, resulting in increased proventriculus size and decrease in body weight and feed conversion efficiency.

Experimental reproduction of proventriculitis using homogenates of proventricular tissue.

Proventriculitis is a problem affecting the processing of broiler carcasses, particularly those processed at 4 to 5 wk of age. The proventriculus and the gastric isthmus connecting the proventriculus to the gizzard are enlarged and swollen and often rupture during processing, causing carcass contamination. This study suggested that a filterable agent found in homogenated proventriculi can cause lesions similar to those seen in field cases. Proventriculitis was produced independently of an effect on growth, and only unfiltered homogenate caused stunting. Field birds with severe proventriculitis were shown to have increased body weights compared with birds without proventriculitis or with milder lesions. Intestinal weakness was not associated with proventriculitis and field birds with the most severe proventriculitis had stronger intestines. Although infectious proventriculitis has generally been reported as one of the lesions associated with stunting syndrome, these data suggest that it may have an independent etiology.

Identification of transforming growth factor-beta and interleukin-6 in chicken ascites fluid.

Ascites fluids from chickens were analyzed for the occurrence of transforming growth factor-beta (TGF-beta) and interleukin-6 (Il-6) using the mink lung epithelial cell inhibition and B9 hybridoma proliferation assays, respectively. Both of these cytokines were significantly elevated in ascites fluids (TGF-beta, 0.129 +/- 0.017 ng/mg protein; Il-6, 0.054 +/- 0.011 ng/mg protein) relative to serum (TGF-beta, 0.005 +/- 0.003 ng/mg protein; Il-6, < 0.002 ng/mg protein) derived from the same individual birds. TGF-beta occurred in a latent form and required activation by heat or acid (heat, 100%; non-activated, 5.2 +/- 1.1%; acid-activated, 89.5 +/- 12.3%). Heat treatment destroyed Il-6 activity. Both TGF-beta and Il-6 activities could be neutralized by antibodies directed against the recombinant human counterpart of these cytokines. Increasing dilutions of ascites fluid caused proportionate decreases in cytokine activities. Il-6 activity was further characterized by gel filtration using high-pressure liquid chromatography, which yielded a peak of biological activity corresponding to an approximate molecular weight of 35,000. These data suggest that ascites fluid may be an interesting biological model and source for studying avian cytokines and their physiological relevance.

Effect of thiram on chick chondrocytes in culture.

The effect of thiram, a fungicide that increases the incidence of tibial dyschondroplasia (TD) in poultry, was studied in vitro using growth plate chondrocyte culture. Thiram caused a significant reduction in alkaline phosphatase, acid phosphatase, and lactate dehydrogenase (LDH) activities at concentrations of 5 microM and above. It was highly cytotoxic to chondrocytes at and above this concentration as determined by their ability to reduce 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (triazolyl blue, MTT), a marker of cellular viability. An increase in the leakage of LDH into culture media was evident at concentration as low as 1 microM. Very few differences were noticed in the electrophoretic migration profiles of cell-extract proteins at any treatment level relative to control. The cytotoxic effect of thiram is possibly due to its damaging effect on the cell membrane, which may be responsible for chondrocyte death.

The effect of microaerosolized hydrogen peroxide on bacterial and viral poultry pathogens.

The effect of microaerosolized H2O2 on bacterial and viral poultry pathogens was investigated. Bacterial cultures and viruses were dried on sterile glass Petri dishes and subjected to direct and indirect 5% (H2O2) microaerosol mist. In the trials using Escherichia coli and Staphylococcus aureus, there was complete inactivation following exposure to H2O2. Using Salmonella typhimurium, indirect exposure resulted in only partial inactivation whereas direct exposure to H2O2 gave complete inactivation. For the viruses studied, 5% H2O2 microaerosol mist completely inactivated infectious laryngotracheitis virus. Newcastle disease virus, infectious bronchitis virus, and avian influenza virus showed reduced infectivity but were not completely inactivated. Avian reovirus susceptibility varied with the method of exposure and infectious bursal disease virus was highly resistant. The use of 10% H2O2 mist, however, resulted in total inactivation of infectious bursal disease virus. The effect of 10% H2O2 on equipment and selected materials representative of a hatcher or poultry house was investigated. A solar cell calculator, a thermostat containing a microswitch, and samples of uncoated steel, galvanized steel, and uncoated aluminum were subjected to 10 fumigation cycles. No damage was detected in the calculator and the thermostat. Both the uncoated steel and the galvanized steel showed signs of oxidation. The aluminum did not show signs of oxidation.

A longitudinal study of green-liver osteomyelitis complex in commercial turkeys.

Two flocks of Nicholas tom turkeys from separate farms with histories of above-average condemnations for turkey green-liver osteomyelitis complex (TOC) were studied throughout a 16-week growout. Fifty birds from each farm were necropsied each week for 15 weeks, and birds that had green livers, osteomyelitis in the proximal tibia, or swollen joints were cultured for aerobic bacteria along with an equal number of control birds. At processing, TOC lesions and green livers were obtained for bacterial culture and histopathology. Green-liver-associated TOC was not observed until the turkeys were 9 or 10 weeks of age. The incidence of TOC was higher on one farm, which also had a higher incidence of airsacculitis, higher early and weekly mortality, seroconversion to Newcastle disease virus and Mycoplasma meleagridis, and significantly higher average body weights, relative spleen weights, and relative liver weights. Both farms had a high incidence of intestinal lesions and infestation with Ascaridia dissimilis. Histological evaluation of green livers revealed hyperplasia of bile ducts, dilation of sinusoids, and pigment-containing Kupffer's cells, some of which stained positive for iron. The bacterial isolates most frequently cultured from bones and livers were pleomorphic gram-variable coccobacilli, which grew visible colonies only after a series of subcultures and extended incubation.

A survey of two commercial turkey farms experiencing high levels of liver foci.

Two turkey farms that had previously experienced high levels of liver condemnations at slaughter were monitored through one complete growout cycle. Liver foci appeared at both farms by week 2. More than 80% of the liver foci sampled did not have any aerobic or facultative bacteria isolated from the lesions. Low numbers of Ascaridia dissimilis larvae were found on both farms by week 3 in the growout. The patterns for the ascaridiasis at both farms were similar, although one of the farms had a higher number of ascarids earlier than the other. Neither farm had high levels of adult ascarids present, although the average larval burden was high. Piperazine was administered at both farms on multiple occasions, but there were no significant decreases in the level of adult ascarids following administration. There was no apparent development of immunity, since all stages of the life cycle remained stable, even late in the growout. The simultaneous appearance of the liver foci and the A. dissimilis indicate that the ascarids may be responsible for the hepatic pathology.

Age-related changes in the incidence of tibial dyschondroplasia in turkeys.

Age-related changes in the incidence and severity of tibial dyschondroplasia (TD) and its relationship to body weight and other bone pathologies were studied in turkeys from ages 2 through 15 wk. A steady increase in the incidence and severity of TD was observed from 11 wk onwards. Whereas there was no correlation between the body weight and TD in early ages, during Weeks 14 and 15 the turkeys with severe TD had significantly higher body weight relative to those without or with mild lesions. Starting from Week 13, hemorrhage was evident in the base of TD-affected growth plates of many turkeys, which increased linearly during the following weeks. Histological examination of these areas revealed mild necrosis with erosion in TD tissues accompanied by occasional bone formations, fibrosis, and the presence of multinucleate chondroclasts and large number of erythrocytes adjacent to lesions. Sporadic rod-like bacterial colonies were discernible in TD tissues and cartilage canals. These studies show 1) whereas the onset of TD may have an independent etiology, the severity of the disease may be influenced by a higher body weight; and 2) subepiphyseal hemorrhages possibly facilitate a healing-type response that leads to replacement of TD tissue by way of resorption, bone formation, and fibrosis, but simultaneously makes the tissue accessible to bacteria.