J. Comp. Path. 1997 Vol. 116, 303 320 Expression of Growth Factors in Chicken Growth Plate with Special Reference to Tibial Dyschondroplasia P. Ren, G. N. Rowland III* and J. Halper~ Departments of Pathology and *Avian Medicine, Collegeof VeterinaryMedicine, University of Georgia, Athens, Georgia 30602-7388, USA Summary Immunoreactive growth factors were identified in chick embryonic cartilage and bone, and in the growth plate of normal tibiotarsi and tibiotarsi affected with tibial dyschondroplasia (TD). A specific pattern of temporal and spatial expression was observed for each growth factor. Transforming growth factor [3 and ~ (TGF~ and TGF~) and epidermal growth factor (EGF) were briefly expressed in chondrocytes of early chick embryos. Immunolabelling for TGFI3 then gradually shifted into cartilaginous matrix and was not observed in cytoplasm of hypertrophic chondrocytes until the late embryonic and post- hatch stages. The distribution and intensity of TGF[3 labelling was the same in chondrocytes of the TD and normal growth plate. Insulin-like growth factor I (IGF-I) labelling persisted from the early embryonic stage to the end of the mid-stage and then disappeared from chondrocytes. IGF-I appeared again in chondrocytes 1-2 days before hatching. After hatching, the labelling intensified in prehypertrophic and hypertrophic chondrocytes. TD lesions displayed IGF-! in the distal region, mainly in chondrocytes around small blood vessels. EGF reappeared in proliferative and hypertrophic chondrocytes of the mid-embryonic stage. By day 18 after hatching, EGF was present mainly in prehypertrophic and hypertrophic chondrocytes. EGF was dem- onstrated only in distal proliferative and early prehypertrophic chondrocytes of the dyschondroplastic growth plate. TGFct was identified in hypertrophic chondrocytes adjacent to the periosteum and in the distal tip of the mid- embryonic growth plate. With progressing ossification, TGFa labelling in- tensified in the embryonic hypertrophic chondrocytes. In the TD growth plate at day 18 after hatching, TGF0~ expression was limited to 1-3 concentric layers of chondrocytes surrounding blood vessels. 9 1997 W.B. Saunders Company Limited Introduction Tibial dyschondroplasia (TD) of broiler chickens is characterized by an abnormal plug of nonvascularized, unmineralized cartilage persisting in the proximal metaphysis of the tibiotarsus (Fig. 1A) (Riddell, 1987), The lesion is thought to be the result of failure of maturation and subsequent lack of mineralization of prehypertrophic chondrocytes (Orth and Cook, 1994). The disorder bears some similarity to osteochondrosis (Poulos, 1978a, b), a cartilage defect in rapidly growing mammals (Rejno and Stromberg, 1978), and to J"Corresponding author. 0021 9975/97/030297 + 18 $12.00/0 9 1997 W.B. Saunders Company Limited