Leg weakness in pigs : a review.

Abstract

LEG WEAKNESS I N PIGS 1 A REVIEW F.X. Aherne SUMMARY Leg weakness is a broad term used to describe lameness of pigs caused by cartilage or skeletal abnormality or foot lesions. Though most market-weight hogs show some degree of joint cartilage damage a t time of slaughter, the problem i s of no economic significance for slaughter hog production. In contrast, approximately five percent of sows and 10 to 20% of boars are culled because of lameness. Rapid growth rate does not contribute to the problem of lameness. There i s no convincing evidence to suggest that nutrition i s implicated as a causative factor in the lameness of swine. The heritability of leg weakness is low to moderate and, therefore, some progress could be expected through judicious selection of breeding stock. Though floor type does influence the incidence of foot pad lesions, it does not contribute t o let weakness in market weight hogs or breeding animals. A t present there is no known cure for the disease and recovery of affected animals by movement to non-confinement situations is unlikely. Until the actual cause of joint damage i s clearly understood, l i t t l e progress in the cure or prevention of the disease is likely. INTRODUCTION Leg weakness is a broad term used to describe lameness of pigs caused by cartilage or skeletal abnormality or foot lesions. Several reports have indicated that virtually a l l pigs of slaughter weight have lesions in one or more joints (Grondalen 1974; Aherne et al. 1984). Frequently the presence of these joint lesions does not cause lameness and even when it does it i s rarely severe enough to reduce animal performance or lead to condemnation after slaughter Wells (1986). In breeding stock lameness is sccond to reproductive failarr as a cause of culling. In his review, Wells (1986) cites several reports in which it was reported that in intensive units, 10-12% of sows are culled because of locomotor disturbances. In a recent Canadian study of 30 swine herds conducted over a 2 year period, foot and leg problems accounted for approximately 10 to 15% of a l l sows culled (Friendship et al. 1986). If culling rates are 30-40%, then the proportion of sows culled for lameness is only 4-5% (Penny 1985). For boars there have been reports from several countries that 20-402 of boars in performance test stations are culled because of locomotor problems (Smith 1965; Sabec et al. 1980; Hilley 1982). Many tissues contribute to locomotory ability but today's discussion w i l l focus mainly on cartilage and bone integrity. *Address: Department of Animal Science, University of Alberta, Edmonton, Alberta There are two types of degenerative joint disease. The f i r s t i s osteochondrosis ( ~ i g . 1) which is manifested as a disturbance of endochondral ossification (Nakano et al. 1979a). Cartilage i s thickened and retained in L.-L.-. As bone grurth coiiiiiilies, Done aecuuse normal ossification does not occur. the lesion enlarges and cartilage sep~irat ion and trrlhccular collapse IURY occur as a result. The second lesion category is tt.tnred ostecwrtl~rosis(k'is. 2). In this case ossification is normal but the articular cartilage surfzice iu irregular, grooved, or superficially fractured (Nakano et al. l979a). The articular cartilages most commonly affected are those of the distal humerus and distal femur which form the elbow and knee joints, respectively (Grondalen 1974a,b). The distal ulnar growth plate also has a very high incidence of osteochondrosis (Empel et al. 1980). Several reports indicate that virtually a l l pigs of slaughter weight have lesions a t some bone site (Grondalen 1974a; Nakano et al. 1984). Mild articular cartilage lesions have been observed in pigs as early as four weeks of age (Perrin 1978). However, severity and incidence of joint lesions increases with age and weight especially during the period 60 to 120 kg. Articular cartilage i s devoid of nerves and only severe lesions result in clinical lameness. Reiland (1978) and Fredeen and Sather (1978) reported no significant correlation between joint lesion severity and lameness. Nakano et al. (1981a) found that if a pig has lesions on the distal humerus, proximal ulna and distal femur, then there i s a high probability that the pig w i l l be lame. Van der Valk et al. (1981) also reported considerable agreement between femoral osteochondrosis and the degree of lameness of the hind limbs. Many researchers have suggested that modern intensive methods of production and confinement housing of swine have increased the incidence of leg weakness (Grondalen 1977). Rapid growth rate, feed intake, lack of exercise, conformational changes, genetics and nutritional factors have been implicated in the etiology of this condition. Growth rate Duthie and Lancaster (1964) were among the f i r s t to suggest that rapid weight gain of pigs might lead to joint lesions. Pigs today can reach a market weight of 100 kg at 140 days or less. Such rapid growth may result in considerable mechanical stress on the joint cartilage which may be too immature to support such weight. Grondalen (1974a1, and more recently Lundeheim (1987) have reported a significant relationship between rapid growth rate up to 60 kg body weight and impaired gait of pigs. However, Perrin et al. (1978) and Nakano et al. (1984) have suggested that normal variations in growth rate of swine populations fed ad libitum are not significantly correlated with the severity of joint lesions (Table 1). Feed intake It has been suggested that reducing growth rate by restricted feeding w i l l reduce the incidence of cartilage lesions (Reiland 1978; Grondalen 1976). Reiland (1978) observed a very low incidence of osteochondrosis in swine fed less than 60% of ad libitum feed intake. However, milder restriction of feed or energy intake did not significantly reduce the incidence of osteochondrosis in 90 kg boars (Nakano et al. 1979; Perrin et al. 1978) (Table 2) or boars, g i l t s and castrates slaughtered between 55 and 118 kg ell et al. 1970; Grondalen 1974a; Nakano et al. 1984). Hanssen and Grondalen (1979) reported that in five of six experiments, restriction of energy intake of pigs from 25 to 100 kg liveweight did not significantly affect either gait score or cartilage soundness of the elbow or knee joints* Normal Cal i i ***** ********* rCg ************ 1 1 Osl:eochondrotic ********* kge -. . 1 . 1 1 < ;I' : , b ,o.:'n' 1 6 I , I ' , 1 ' . I :: ' ' , , , '' I , , , I , .. .*.. ; :b:~: ...** ' ' -*a**e.- cartilage .* ** , 1 .*****. I , I ' ,a . # I r , * 1 , :e: ' * I 1 I , , ', ' ' ' I 1 1 :: , ' . I # ' . *. : 1 Figure 1. Normal and osteochondrotic joint cartilage. Figure 2. Osteoarthrotic joint cartilage. Figure 3. Leg joints of swine. TABLE 1 Average scores for soundness of the medial hunwral and the niedial fenloral condylar cartilage from fitst-, intcni~ediatt- and s low-growing pigs. Intermediate 14 0.74-0.76 2.61 1.68 Growth rate Standard Slow error 14 0.53-0.67 2.82 2.32 0.15 0.24 NS Fast Number of Animals Average daily gain from weaning to slaughter weight (kg) Medial humeral condyle Medial femoral condyle 14 0.82-1.00 2.61* 2.28 Sig. NS '1, normal; 2-4, slight to moderate lesion; 5-7, moderate to severe lesion. NS, no significant difference (P>0.05). TABLE 2 Sex Feed Intake Daily gain, kg Walking condit ion Cartilage damage Front legs Hind legs Nakano et al. (1984) Lack of exercise It has been suggested that ad libitum fed pigs raised in confinement spend in excess of 80% of their time lying down. However, it i s a1 so known that exercise is essential for normal growth of cartilage. Therefore, lack of exercise may lead to retarded growth of cartilage and also result in muscle weakness or lack of muscle tone, and thereby contribute to instability of the joint. Several studies have shown that leg or joint soundness was less in pigs confined individually than in pigs housed in groups. Perrin and Bowland (1977) and Grondalen (1974) conducted long term studies with pigs on a treadmill and observed improved locomotory ability of these pigs. However, the enforced exercise did not reduce the incidence and severity of joint lesions. Effects of sex and restricted feeding on lameness. Boars Restricted 0.63a Barrows ad lib 0.86b Gilts ad lib 0.79~ Boars ad lib 0. 90b no significant difference no s ignif icant difference no significant difference Conformation Grondalen (1977) suggested that abnormal exterior conformation and joint shape induce local overloading in the joint and precipitate cartilage lesions. Conformation of body and feet and legs has been emphasized by many observers as a critical factor in the has been suggested that the incidence judicious visual selection of breeding topline, are longer and have pasterns each foot. incidence of feet and leg problems. It of osteochondrosis could be reduced by stock, i.e. animals that have a level tlrat are sloping with even-size toes on Genetics The low incidence of osteochondrosis in wild pigs ell et al. 1970) and the absence of the disease in Yucatan pigs (~arnumet al. 1984) suggests that genetically slow growing pigs are less susceptible to the condition. Grondalen and Vangen (1974) in a study of genetically fast and slow growing lines of pigs observed a significantly lower incidence of joint lesions in the slower growing line. However, the incidence of lesions in this line was 95%. Reiland and Anderson (1979) reported that total lesion score in the joints they examined was not significantly affected by breed. Several studies have reported heritability estimates for osteochondrosis that have ranged from low (10%) to moderate (30%) (Reiland 1978; Lundeheim 1987). These same authors reported that leg soundness score also has a low to moderate heritability. Therefore, some progress could be expected through the judicious selection of breeding stock. Floor type The performance of pigs has generally been similar on different types of floors (~ornegayet al. 1981; Lindvall 1981). Small differences in foot and pad lesions of starter pigs have been noted (Table 3), but the long term significance of these to subsequent leg weakness has not been evaluated. TABLE 3 Effect of floor type on performance criteria and foot and joint lesion scores (8.5 to 93 kg). Plastic coated Starter period daily gain, kg Foot pad score 20 to 93 kg daily gain, kg Feed: gain Foot pad score Cartilage score Fem-Hum Rad-Urn Brennan-Adherne (1987). Woven wire Sip;. Aluminum slats, sharp edged concrete slats and rough concrete floors can result in severe foot injuries and could result in changes in the way the pig walks. Such changes could alter the angles a t which bones meet in the joints and thus lead to a shift in the areas of the articular cartilage upon which the greater degree of pressure i s exerted. If such areas of the cartilage are not suited to this increased weight load, the result may be damage to the cartilage or subchondral bone. The surface area of the claw increases by only 7% from 55 to 95 kg while the weight mass bearing down on this area increases * by 40%. This may explain why lesions to tl~csole of t h t - c1:lw show up IIIOI.~\ frequently in the finishing period. Vaughan (197 1) suggests that soft cr flooring, such as grass and earth, provides a more secure footing than does slippery concrete for limbs with defective posture and may prevent severe clinical lameness. However, in our experiments (Perrin et al. 1978) there was no significant difference in the incidence or severity of arthrotic lesions between pigs raised on concrete floors and earth floors covered with straw. Several researchers have reported that floors which are abrasive or have a high percentage of void space increase the severity of foot lesions, especially in the post-weaning period (~ritschen1976; Kornegay et al. 1981; Brennan and Aherne 1987). However, the condition of the foot pads did not influance the incidence or severity of joint lesions (Brennan and Aherne 1987). Nutrition Calcium and vhosphorus Because of the importance of calcium (Ca) and phosphorus (P) in bone structure, it is often. suggested that current (NRC 1979) recommended dietary levels of Ca and P for growing pigs and sows may not be adequate for normal skeletal development. It has also been suggested that the rapid growth rate and improved feed to gain ratio of modern confined pigs may lead to inadequate daily intake of calcium and phosphorus. Similarly, for sows with poor appetites and large milk yields, the daily intake of Ca and P may be inadequate. It has been suggested that maximum mineralization of bone during growth and development may be necessary if swine are to remain structurally sound ( ~ o r n e ~ a y Thomas 1981). and It i s well established that Ca and P intake required for maximum mineralization or bending moment of bone is in excess of that which i s required for maximum growth rate of growing and finishing pigs (Nimo e t al. 1980; lfaxson and Mahan 1983; Koch et al. 1984; Brennan and Aherne 1986). However, there was no association between bending movement or ash content of bone and severity of osteochondrotic lesions in finishing pigs when Ca and P intakes exceeded NRC ( 1979) recommendat ions. Brennan and Aherne ( 1986 ) ; Pond et al. 1978; Duthie and Lancaster (1964) reported that dietary Ca and P levels within a range adequate for maximum performance and producing a wide range in bone mineralization did not reduce the incidence or severity of cartilage lesions or in bone structure or degree of lameness (Table 4) and osteochondrotic joints. In normal Ca and P levels were similar in subchondral bone adjacent to the s i t e of osteochondrot ic lesions (Nakano et al, 1981a). Therefore, there is considerable evidence that elevated dietary Ca and P intakes for growing-finishing swine do not reduce the severity of joint damage or improve structural soundness of pigs up to 130 kg liveweight (Duthie and Lancaster 1964; Hanssen and Grondalen 1979; Kornegay 1981a, 1981b; Calabotta et al. 1982; Kornegay et al. 1983; Lepine 1985; Brennan and Aherne 1986). In several recent studies the feeding of dietary levels of Ca and P sufficient to maximize bone mineralization in gilts during early growth and development did not improve reproductive longevity (Arthur e t al. 1983a,b; Kornegay et al. 1983). As mentioned previously, the second most common reason for culling sows after reproductive failure is lameness (Wells 1986). In many cases the lameness i s due to foot or leg injuries and not related to dietary inadequacies. Posterior paralysis or the 'downer' sow syndrome may result during late gestation or during lactation if dietary calcium, phosphorus or vitamin D supplementation is inadequate. In posterior paralysis, the TABLE 4 Effect of dietary calcium and phosphorus levels on leg soundness, cartilage condition and bone ash content of swine (100-130 kg). NRC % CalX P (20-55 kg) % Ca/% P (55-100 kg) .58/. 50 .54/ .65 .74 3.21 68.78 Ca and P level AKC .S3/.63 .80/.60 130X ARC 1.041.82 .93/. 74 Daily gain (kg) Feed :gain (20-100 kg) % ash in femur .75 3.21 69.43 no difference no difference .75 3.20 69.86 NS NS PC .001 Walking cond i t ion Cartilage condition Brennan and Aherne (1986) vertebrae slips from its normal position and pinches the causing paralysis in the hind quarters. Kornegay et al. long term study evaluating two dietary levels of calcium 5). Reproductive performance over five parities did not dietary mineral levels provided, but there was a higher locomotor problems for sows fed the lower Ca-P levels. TABLE 5 spinal cord, thus (1973) conducted a and phosphorus able differ from the two culling rate due to Data from the Ohio Calcium and phosphorus levels for gestating sows. Calcium, g/d Phosphorus, g/d No. Sows X Completing 5 cycles No. pigs born weaned 10.3 11,O 55 56 15.5 15.0 54 70 Causes of culling Crippled Other causes Kornegay et al. (1973) 6 18 Station demonstrated that sows fed various dietary Ca and different bone ash contents a t the end of the third parity performance was not affected by treatment but the rib and some evidence of demineralization. Consequently, because are demineralized before the other bones, the symptoms of are understandable. P levels had (Table 6). Sow vertebrae did show vertebrae and ribs posterior paralysis TABLE 6 Effect of calcium-phosphorus on sow bone ash (3rd parity). Ca/P levels. % Bone Reprod. State .h5/.50 .8O/ .60 66 67 62 61 901.70 Femur PregILact. Open PregfLact. Open 66 67 59 62 67 68 62 62 Rib Mahan and Fetter (1982). Other minerals Dietary manganese, zinc, copper and magnesium concentrations in excess of the requirement for optimum performance of swine did not reduce the incidence of joint cartilage lesions (Walker et al. 1966; Grondalen 1974a; Grondalen 1977). Maternal nutrition The recent diagnosis of osteochondrotic lesions in swine a t birth (Hill et al. 1985) suggests the possibility that maternal nutrition may influence endochondral ossification in the fetus. However, our recent studies of the offspring of sows fed only 3 kg feed per day during three consecutive lactations revealed no effect of maternal nutrition on the incidence of osteochondrosis in their offspring slaughtered at 100 kg liveweight. Vitamins Vitamins A and D are essential for bone growth. However, increasing dietary levels of vitamins A, D and E above the usual recommended levels for swine did not prevent development of joint lesions (Walker et al. 1966). Vitamin C is essential for biosynthesis of collagen which contt-ibutcs to the tensile strength of cart ilnge. Walker et ~ 1 (1966) reported that . supplementation of swine diets with vitmiin C could not prevent the development of ulnar osteochondrosis. Pigs with joint damage had normal plasma ascorbic acid concentrations and normal urinary secretion of ascorbic acid. Nakano et al. (1983) reported that dietary supplementation of 350 or 750 ppm vitamin C did not significantly reduce the incidence of elbow or knee joint lesions (Table 7). Also, collagen content of knee joint articular cartilage was not increased by supplemental vitamin C. Brooks et al. (1977) described a type of lesion often found in swine herds. It consists of extensive cracks and ulceration of hooves which may lead to lameness, These symptoms are similar to those described for biotin deficiency by Cunha et al. (1946). They also reported that biotin supplementation reduced the incidence of such lesions and improved the reproductive performance. These results are consistent with those of Bryant et al. (1983). Similar cracks and lesions in the feet of g i l t s or sows have been reported by Grandhi and Strain (1980). However, biotin supplementation (200-300 pg/kg) did not prevent the incidence of these lesions (Table 8). TABLE 7 Performance and leg soundness of pigs (7 to 90 kg) fed various levels of vitamin C. 0 Suvvlementary vitamin C (vvml 350 700 0.68 0.67 NS Daily gain 0.65 Walking condition Cartilage abnormalities Front legs Hind legs Nakano e t al. (1983) no difference no difference no difference TABLE 8 Effect of biotin supplementation on the incidence of severity of claw lesions. Control Biotin added Claw lesion scores: Front legs no difference no difference no d if f erencr no difference no difference Hind legs Inside claws Outside claws Mean leg scores Grandhi and Strain (1980) Similar results have been reported by Bane et al. (1980) and Hamilton and Veum (1984). Penny et al. (1980) reported that a herd in which foot lesions were already established did not benefit from biotin supplementation of their diet. However, replacement gilts fed biotin supplemented diets developed fewer and less severe foot lesions. Bryant et al. (1983a,b) reported not significant effect of biotin supplementation on heel and toe erosion in growing-f inishing swine but heel cracks were reduced. It is obvious that the role of biotin in claw tissue integrity is not clear. Since there is a near limitless l i s t of environmental or mechanical factors that cause lesions to the various areas of the claw, it is extremely risky to use the claws as indications of a nutrition deficiency. Recovery from osteochondrosis Severai researchers have stated that the gait of lame pigs improved when they were transferred from confinement housing to pasture (~aughan1971; McPhee 1976; Freeden and Sather 1978; Sather and Freeden 1982) but no evidence of improved locomotory ability score, joint lesion score or altered biochemical composition of cartilage of synovial fluid was presented. However, Nakano et al. (1981) penned boars which had been culled in a performance test station because of lameness in extensive pasture lots. Gait did appear to improve but there was no improvement in the severity of joint cartilage lesions or in the composition of joint cartilage or subchondral bone. Some repair tissue was evident but it was very minimal. Because of the absence of known preventative or therapeutic practices, there i s a demand for a pharmacological agent to control the problem of degenerative joint disease in swine. 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