Relationship between the extent of vascular injury and the evolution of surgically induced osteochondrosis lesions in a piglet model

Ostechondritis dissecans (OCD) is an orthopaedic disease characterized by formation of osteochondral defects in developing joints. Epiphyseal cartilage necrosis (osteochondrosis [OC]) caused by focal failure of vascular supply is the known precursor lesion of OCD, but it remains to be established how the severity of vascular failure drives lesion healing or progression. In the current study we have implemented a novel piglet model of induced osteochondrosis of the lateral trochlear ridge of the femur to determine the role that the extent of ischemia plays in the development and progression of OC/OCD lesions. Ten 4-week-old Yorkshire piglets underwent surgical interruption of the vascular supply to the entirety (n = 4 pigs) or the distal half (n = 6 pigs) of the lateral trochlear ridge of the femur. At 2, 6, and 12 weeks postoperatively, distal femora were evaluated by magnetic resonance imaging (MRI) to determine the fate of induced OC lesions. At 12 weeks, piglets were euthanized, and the surgical sites were examined histologically. After complete devascularization, lesion size increased between the 6- and 12-week MRI by an average of 24.8 mm2 (95% CI: [-2.2, 51.7]; p = 0.071). During the same period, lesion size decreased by an average of 7.6 mm2 (95% CI: [-24.5, 19.4]; p = 0.83) in piglets receiving partial devascularization. At 12 weeks, average ± SD lesion size was larger (p<0.001) in piglets undergoing complete (73.5 ± 17.6 mm2) vs. partial (16.5 ± 9.8 mm2) devascularization. Our study demonstrates how the degree of vascular interruption determines lesion size and likelihood of healing in a large animal model of trochlear OC.

Naturally occurring osteochondrosis latens lesions identified by quantitative and morphological 10.5 T MRI in pigs

Juvenile osteochondritis dissecans (JOCD) is a pediatric orthopedic disorder that involves the articular-epiphyseal cartilage complex and underlying bone. Clinical disease is often characterized by the presence of radiographically apparent osteochondral flaps and fragments. The existence of early JOCD lesions (osteochondrosis latens [OCL] and osteochondrosis manifesta [OCM]) that precede the development of osteochondral flaps and fragments is also well recognized. However, identification of naturally occurring OCL lesions (confined to cartilage) using noninvasive imaging techniques has not yet been accomplished. We hypothesized that 10.5 T magnetic resonance imaging (MRI) can identify naturally occurring OCL lesions at predilection sites in intact joints of juvenile pigs. Unilateral elbows and knees (stifles) were harvested from three pigs aged 4, 8, and 12 weeks, and scanned in a 10.5 T MRI to obtain morphological 3D DESS images, and quantitative T2 and T1ρ relaxation time maps. Areas with increased T2 and T1ρ relaxation times in the articular-epiphyseal cartilage complex were identified in 1/3 distal femora and 3/3 distal humeri and were considered suspicious for OCL or OCM lesions. Histological assessment confirmed the presence of OCL or OCM lesions at each of these sites and failed to identify additional lesions. Histological findings included necrotic vascular profiles associated with areas of chondronecrosis either confined to the epiphyseal cartilage (OCL, 4- and 8-week-old specimens) or resulting in a delay in endochondral ossification (OCM, 12-week-old specimen). Future studies with clinical MR systems (≤7 T) are needed to determine whether these MRI methods are suitable for the in vivo diagnosis of early JOCD lesions in humans.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

Associations among individual gilt birth weight, litter birth weight phenotype, and the efficiency of replacement gilt production

Selection for larger litter size has increased the number of low individual birth weight (BWi) pigs and produced sows with a repeatable low average litter birth weight phenotype (BWP). Using an average of 3.6 litters records per sow, BWP was established in 644 nucleus-multiplication sows producing replacement gilts in a large commercial operation and classified as low (L-BWP, <1.18 kg, n = 85), medium (M-BWP, ≥1.18 to ≤1.35 kg, n = 250), or high (H-BWP, >1.35 kg, n = 309) on the basis of a BWi of 1.18 kg below which there was a high risk of early mortality and the average BWi (1.35 kg) for the population. In subsequent litters, potential replacement gilts born to these sows (n = 7,341) received a unique identification tag that allowed the impact of BWi, BWP, and their interactions on the efficiency of replacement gilt production to be evaluated. Negative effects of BWi on mortality until day 4 after birth were confirmed (P < 0.05) and cumulative losses to weaning, to day 70 of age, and to final pre-selection at 165 d of age were affected (P ≤ 0.05) by the interaction between BWP and BWi. Among the 2,035 gilts for which records for selection efficiency and production to fourth parity were available, a lower BWi decreased the probability of gilts reaching pubertal estrus (P < 0.05) after 21 and 28 d of boar stimulation starting at 180 d of age, with no effect of BWP. Overall, neither BWi, BWP, nor their interaction affected age at puberty. After breeding, only the main effect of BWP affected productivity and retention in the sow herd. In parities 1 and 2, percent stillborn was higher in litters born to gilts from H-BWP compared with L-BWP dams (P < 0.05), and in parity 2, total born and born alive were lower in sows derived from H-BWP compared with other BWPs. There were no differences in retention based on BWP classes until parity 2, after which retention tended (P ≤ 0.09) to be lower in sows derived from H-BWP compared with L-BWP dams. These results provide evidence that sow BWP is an important factor in the overall efficiency of replacement gilt management. This study also confirms that effective gilt selection and pre-breeding management protocols support excellent sow lifetime productivity and mitigate the risk of a high BWP in the litter of origin affecting retention in the breeding herd.

Alleged predisposing dietary factors fail to increase the incidence of osteochondrosis-like lesions in growing pigs at 14 and 24 wk of age

Early lesions of osteochondrosis (OC) are exhibited by regions of cartilage retention along the growth plate and articular cartilage. Progression of OC lesions may impair locomotion and necessitate euthanasia in adherence to animal welfare guides. Little is known about the role of nutrition in the initiation and early stages of OC. However, dietary components are commonly implicated as predisposing factors. In this study, diets were altered as an attempt to induce early stage OC lesions under controlled conditions. At 8 wk of age, 96 crossbred gilts (body weight [BW] = 17.4 ± 0.18 kg) were randomly assigned to one of four corn-soybean meal-based diets (four pens per diet, six pigs per pen) to assess diet effects on the number and volume of OC lesions in the distal femur. Diets included a non-pelleted control diet (Ctl); Ctl plus 20% glucose (Glc); the Ctl with increased concentrations of lysine, Ca, and P (+CaP); and the +CaP diet in a pelleted form (PEL). Femurs were collected from pigs euthanized at either 14-wk (Wk 14) or 24-wk (Wk 14) of age for assessments of OC lesions. Based on a mixed model analysis with pen as the experimental unit, dietary treatments did not affect final BW (129.3 ± 3.8 kg) or average daily gain (ADG) (1.00 ± 0.03 kg/d) over the trial. As expected, pigs fed PEL and Glc diets were more efficient (P < 0.05) in feed conversion compared with Ctl and +CaP. Using femurs as the experimental unit at Wk 14 (collected from two of the six pigs per pen), bone mineral content, determined by dual-energy x-ray absorptiometry scans, was greater (P < 0.05) in pigs fed +CaP and PEL than Ctl or Glc diets; however, only +CaP group differed (P < 0.05) at Wk 24 (collected from four pigs per pen). Computed tomography (CT) scans of femurs were reconstructed as three-dimensional images to allow detection of the number, volume, and surface area of lesions in distal growth plates. At Wk 14, pigs fed Ctl had fewer number of lesions (P < 0.05); however, no differences were detected among dietary treatments in lesion volume or lesion surface area. Pigs had fewer lesions at Wk 24 than Wk 14; however, differences were not detected among dietary treatments. At Wk 24, pigs fed Ctl diets had the greatest lesion volume among dietary treatments (P < 0.05). In conclusion, none of the pigs exhibited symptoms of lameness regardless of dietary treatment or OC lesion traits. Diet modifications due to pelleting or inclusion of rapidly digestible ingredients, such as glucose, did not increase prevalence or size of OC lesions. Image analysis of CT scans was a reliable method to quantify the number, size, and location of OC lesions.

Evaluation of the Suitability of Miniature Pigs as an Animal Model of Juvenile Osteochondritis Dissecans

Juvenile osteochondritis dissecans (JOCD) is a developmental disease characterized by formation of intra-articular (osteo)chondral flaps or fragments. Evidence-based treatment guidelines for JOCD are currently lacking. An animal model would facilitate study of JOCD and evaluation of diagnostic and treatment approaches. The purpose of this study was to assess the suitability of miniature pigs as a model of JOCD at the distal femur. First, stifle (knee) joints harvested from three juvenile miniature pigs underwent magnetic resonance imaging (MRI) to establish the vascular architecture of the distal femoral epiphyseal cartilage. Second, vessels supplying the axial or abaxial aspects of the medial femoral condyle were surgically interrupted in four additional juvenile miniature pigs, and the developing epiphyseal cartilage lesions were monitored using three consecutive MRI examinations over nine weeks. The miniature pigs were then euthanized, and their distal femora were harvested for histological evaluation. Vascular architecture of the distal femoral epiphyseal cartilage in the miniature pigs was found to be nearly identical to that of juvenile human subjects, characterized by separate vascular beds supplying the axial and abaxial aspects of the condyles. Surgical interruption of the vascular supply to the abaxial aspect of the medial femoral condyle resulted in ischemic cartilage necrosis (a precursor lesion of JOCD) in 75% (3/4) of the miniature pigs. Cartilage lesions were identified during the first MRI performed 3 weeks post-operatively. No clinically apparent JOCD-like lesions developed. In conclusion, miniature pigs are suitable for modeling JOCD precursor lesions. Further investigation of the model is warranted to assess induction of clinically apparent JOCD lesions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2130-2137, 2019.

Effects of supplementing organic microminerals and methionine with or without limiting growth during the rearing phase of replacement gilts on lameness, growth, and body composition

Previous research suggested that lameness in growing pigs could be reduced using feeding strategies, such as limiting growth rate and supplementing trace minerals (TM) and (or) methionine (Met). The present study evaluates effects of 1) TM and Met and 2) limiting total lysine (Lys) during the rearing phase (90 d) of gilts (as a means to limit growth rate) on lameness, performance, and sow claw health and productivity (to first parity). Gilts (n = 240; 58.0 ± 11.1 kg body weight [BW]) were blocked, distributed into pens of 10 gilts, and pens were allocated to a 2 × 2 factorial arrangement. Factors were: 1) control or TM plus Met, which provided additional 10, 20, and 50 mg/kg of chelated copper, manganese, and zinc, respectively (0.1%, Aplomotec Plus, Tecnología & Vitaminas, S.L.; Alforja, Spain), and a 1.01 Met:Lys ratio and 2) standard Lys was formulated to meet growth requirements or low Lys to 19% below growth requirements. Feeding was provided through two phases, first between 119 and 163 d of age (phase I) and the second between 163 and 209 d of age (phase II). Diets had 2.43 and 2.31 Mcal net energy/kg for phases I and II, respectively, and were offered ad libitum. Low Lys did not affect feed intake but rather reduced average daily gain (ADG) by 6.35% and the final BW by 3.80% compared with standard Lys (P < 0.001). Low Lys reduced ADG (P < 0.001) and gain:feed (P = 0.012) during phase I but not during phase II. Lameness prevalence was 7.92% during rearing and increased with time (P < 0.001). Final BW (151 kg) and ADG (989 g) were similar (P > 0.05) whether gilts displayed lameness or not. Lameness was low in severity and not affected by dietary factors. However, TM- plus Met-fed gilts were 19.2 kg heavier (P = 0.016) than were control at lameness detection. On the sow farm, there was no evidence for differences in lameness or claw lesions among previous dietary treatments. In conclusion, lameness prevalence during the rearing phase was similar, independent of TM plus Met supplement, low Lys, or the interaction. Insufficient reduction of ADG and low severity in lameness may have limited the potential of dietary treatments. Moreover, a greater deficiency of Lys would be needed to achieve the degree of growth reduction previously reported to lessen lameness through feed restriction.

Identification of Areas of Epiphyseal Cartilage Necrosis at Predilection Sites of Juvenile Osteochondritis Dissecans in Pediatric Cadavers

BACKGROUND

The pathogenesis of human juvenile osteochondritis dissecans (JOCD) remains poorly understood, with multiple factors implicated, including ischemia, repetitive trauma, and genetic predisposition. Similarities in the predilection site and the diagnostic and clinical features of JOCD to the well-characterized veterinary counterpart, osteochondrosis dissecans, suggest that, similar to the animal disease, the pathogenesis JOCD may also be initiated in the first few years of life, when disruption of blood supply to the epiphyseal growth cartilage leads to failure of endochondral ossification. To gather data in support of the hypothesis that JOCD and osteochondrosis dissecans have a shared pathogenesis, biopsy specimens obtained from predilection sites of JOCD in juvenile human cadavers were histologically examined to determine whether they contained lesions similar to those found in animals diagnosed with subclinical osteochondrosis dissecans.

METHODS

In this descriptive laboratory study, 59 biopsy specimens (6 mm in diameter) were harvested from the central aspect (i.e., the notch side) of the femoral condyles of 26 human cadavers (1 month to 11 years old). Specimens were histologically evaluated for the presence of areas of cartilage necrosis and the morphology of cartilage canal blood vessels.

RESULTS

Locally extensive areas of necrotic epiphyseal cartilage were identified in 4 specimens obtained from 3 donors (ages 2 to 4 years). Areas of cartilage necrosis accompanied by focal failure of endochondral ossification or surrounded by subchondral bone were identified in biopsy specimens from 4 donors (ages 4 to 9 years).

CONCLUSIONS

The identification of epiphyseal cartilage necrosis identical to that described in animals with subclinical osteochondrosis, found in biopsy specimens obtained from femoral predilection sites of JOCD in pediatric cadavers, suggests a shared pathogenesis of JOCD in humans and osteochondrosis dissecans in animals.

CLINICAL RELEVANCE

These findings imply that the pathogenesis of human JOCD likely starts 5 to 10 years prior to the development of clinical symptoms. Enhanced understanding of the temporal features of JOCD pathogenesis provides an opportunity for earlier diagnosis and treatment, likely resulting in improved outcomes for this condition in the future.

Effects of supplementing organic microminerals and methionine during the rearing phase of replacement gilts on lameness, growth, and body composition

Lameness is a primary reason for culling and mortality within a sow herd. This study evaluated the impact of feeding organic trace minerals and methionine (Met) to growing gilts (134 d) on lameness, performance, body composition and claw health (to first parity), productivity (to second parity), and reproductive performance through 2 parities. Young gilts (28.8 ± 8.8 kg of body weight [BW], n = 360) were BW blocked (10 gilts/pen) and randomly allotted to 1 of 4 dietary treatments: control (CON, basal diet); CON plus organic minerals (MIN, at 10, 20, and 50 mg/kg of Cu, Mn, and Zn, respectively; Aplomotec Plus, Tecnología & Vitaminas, S.L, Alforja, Spain); additional Met (MET, at 102% Met: Lys); and MET plus MIN (MM). Feed was provided ad libitum. Lameness, BW, and body composition were measured 7 times during rearing, at gilt service, day 109 of gestation, and first weaning. Gilts fed the MM diet had lower average daily feed intake (5.1%) and final BW (2.1%) than CON gilts (P < 0.05), whereas MIN and MET were intermediate and not different from each other. Similarly, final backfat (BF) was greatest in CON (P < 0.05), whereas CON and MIN increased final loin depth compared with MM (P < 0.05) with MET not being different. During rearing, 7.7% of all gilts presented lameness, which appeared between 106.8 and 129.7 kg BW confidence interval. Gilts that had been or were lame had reduced BW and average daily gain compared with never lame gilts (P < 0.05). Lameness during rearing was highest (P < 0.01) in gilts fed CON diet (14.8%), with no differences amongst MIN (2.0%), MET (5.3%), or MM (6.5%). In the sow herd, 21% of sows showed lameness and 24% of those were associated with claw lesions. At weaning, gilts fed CON diet had highest (P < 0.01) prevalence of lameness (20.8%) with no differences amongst MIN (6.5%), MET (11.1%), or MM (7.6%). Over the first 2 parities, 27.3% of gilts were culled. On farm, lameness was associated with 0.7 more stillborn piglets (P < 0.10), 1 mm more BF loss in first lactation (P < 0.05), and increased weaning-to-estrus by 3 d (P < 0.05). In conclusion, lameness during rearing was decreased by supplementing organic trace minerals, methionine, and their combination, which also reduced lameness during lactation.