Hip dysplasia in a 6-year-old Salz ram

Abstract

A 6-year old Salz ram was presented with a history of poor body condition, progressive gait abnormalities, pelvic limb lameness, and difficulty with copulation. Based on the history, clinical signs, hip palpation, and radiography, a diagnosis of hip dysplasia, previously unreported in sheep, was made.

A 6-year old Salz ram was admitted to the Veterinary Faculty Hospital, University of Zaragoza, Spain, with a history of poor body condition, more than 1 y of progressive gait abnormalities with pelvic limb lameness, and inability to copulate during the last 18 mo.

The Salz breed (females: 50–60 kg, males: 65–75 kg) is a meat sheep developed by crossing Romanov rams of 2 strains with Rasa Aragonesa ewes. Rasa Aragonesa is the local breed, which is characterized by white, medium-short wool; sturdiness; longevity; and the production of high-quality light lambs. Nowadays, the Salz strain is considered fixed, containing equal proportions of Rasa Aragonesa and Romanov genes. The introduction of the Romanov breed improved the prolificity of the local breed (1).

The animal came from a flock of 506 sheep (484 females and 22 males) of the Salz breed. The animals were housed mainly in pens and allowed to graze occasionally on pasture. Ewes were fed barley, maize, glutenfeed, and straw, supplemented with vitamins and minerals. Tupping was controlled in order to concentrate the date of lambing.

On examination at the Veterinary Faculty Hospital, the ram was in poor body condition (score 1.5; range 1 to 5; 55 kg bodyweight), and showed weakness, gait abnormalities with unstable hips, severe pelvic limb lameness, muscular atrophy, and low exercise tolerance. Particular attention was given to a neurological evaluation (assessment of behavior, posture, mental status, gait, spinal reflexes, conscious proprioception, and cranial nerve function). No other animal from the flock showed the same clinical signs. Results from hematological and biochemical assessment of a blood sample obtained by jugular venipuncture were within the normal reference ranges. The ram's temperature was not elevated either on the farm or at the hospital. A sample of fluid from the hip joint was obtained and inoculated onto blood agar (normal atmosphere and CO₂), Columbia colostin-nalidixic acid agar, MacConkey agar, Chapman agar for the isolation of streptococci, and onto isolation culture medium for Mycoplasma spp. No growth of microorganisms was observed.

No abnormalities were detected on neurological evaluation. Differential diagnoses were other nervous and muscular locomotor disorders that may affect sheep, such as spinal column trauma, pelvic limb trauma or luxation, lumbosacral spondyloarthrosis, and peripheral pelvic nerve damage; metabolic disorders (hypocalcemia, hypomagnesemia); intoxication by organophosphates; and plant-associated toxicities (ryegrass, phalaris).

Evaluation of the hip joint was carried out using Ortolani's (2) and Bardens and Hardwick's maneuvers (3), methods used for assessing canine hip dysplasia. Ortolani's maneuver revealed a palpable “clunk” while the ram was positioned in lateral recumbency. The Bardens and Hardwick's maneuvers showed increased hip joint laxity. The animal showed pain during the hip joint manipulation. Although these tests have not demonstrated clear diagnostic value and even less prognostic value in evaluating canine hip dysplasia, they are valuable in locating pain and malfunction of the hip joint (4).

Hip dysplasia is defined by many authors as a congenital, bilateral, degenerative joint disease. Hip dysplasia is a dynamic proccess; in the luxated hip, the femoral head resides outside the acetabulum, and there is no congruence of the hip joint. A definitive diagnosis is dependent on characteristic signs of hip dysplasia (hip joint subluxation and degenerative joint disease (DJD)) on pelvic radiographs. Radiographs were taken according to the recommendations of the Orthopedic Foundation for Animals (4) with the ram sedated in dorsal recumbency with legs fully extended and stifles internally rotated. Radiographs showed similar changes in both hemipelves: flattened acetabulum, sclerosis of subchondral bone in dorsal and craniolateral acetabular rims, osteophytes and new bone formation around both the femoral necks and the craniolateral acetabular rims, lysis and sclerosis in both femoral heads and necks, and subluxation in both hips (Figures 1–3).

Figure 1. Ventrodorsal radiographic projection of the hip joints of a 6-year-old Salz ram with severe hip dysplasia.

Figure 2. Enlarged image of the right hip joint.

Figure 3. Enlarged image of the left hip joint.

On the basis of the history, the clinical findings, their progressive development, the radiographic observations, and the fact that only 1 animal from the farm was affected ruled out most of the above mentioned differential diagnoses. A definitive diagnosis of hip dysplasia was made.

Hip dysplasia has been described in humans and dogs, but no reports could be found of a similar disease in sheep. The etiology of canine hip dysplasia (CHD) remains in question. It is known that CHD is an inherited, developmental condition, characterized by a lack of conformity between the femoral head and the acetabulum, leading to laxity of the hip joint. The severity of the clinical signs and the time of onset of disease progression, and the degree of pain and impaired mobility are quite variable. Hip laxity frequently results in radiographic signs of degenerative joint disease and clinical lameness. Breeding animals are selected to improve the breed, but when CHD is diagnosed the animal is discarded from the selection scheme because of CHD́s hereditability.

The treatment of hip dysplasia is mainly palliative, restricted activity, and analgesic drugs. In dogs with more advanced disease, orthopedic surgery is indicated.

The importance of this clinical report lies in the genetic value of this ram for breeding. During the first years of his life, there was no problem with tupping. However, the degeneration of the hip joint led to a progressive worsening of being unable to remain on his pelvic limbs. The owner of the ram had no information about predecessors and offspring of this animal. Almost all Salz male lambs are traditionally marketed between 70 and 100 d, before clinical signs of hip dysplasia have had an opportunity to develop. Consequently, it is difficult to find hip dysplasia in these animals. The main problem appears when one of these animals is maintained as a breeding sire.

In spite of the great genetic value of this animal, because of the difficulty in tupping and, above all, because of the possibility that the offspring might inherit this disease, the owner decided to have the ram euthanized. CVJ