P. F. Fennessy

Articular / epiphyseal osteochondrosis in Thoroughbred foals at 5 months of age: influences of growth of the foal and prenatal copper supplementation of the dam.

Abstract AIMS: To determine the influence of copper (Cu) supplementation by injection of mares in late gestation on the frequency and severity of osteochondrosis (OC) lesions in their foals at around 160 days of age. To determine if there was any influence of the concentration of Cu in the liver, growth rate, birthweight, weight at 160 days of age, fatness, sex, or year of birth of the foal on the frequency and severity of OC lesions. To determine the influence of dams age, and sex and birthweight of the foal on the growth rate from birth to 160 days of age, and weight at 160 days of age. METHODS: Thirty-three Thoroughbred foals, born in two consecutive years, were weighed every 2 weeks from birth. The dams had been supplemented with parenteral Cu or saline during late gestation, and the supplementation regimens were different in each year. Foals had liver biopsies harvested at birth for determination of Cu concentration. Pasture samples were collected every 4–8 weeks for analysis of concentration of Cu and zinc (Zn). At 160 days of age, articular cartilage of long bones was examined. Gross lesions were counted and scored, then sawn and radiographed, and processed for histopathology. Lesions were given radiographic scores and histopathological scores. Maximum scores for each lesion were combined to give a total OC score for each joint and each foal. The fatness of 20 foals (10 each from Years 1 and 2) at 160 days of age was determined chemically. RESULTS: Supplementation of dams with Cu had no significant effect on the concentration of Cu in the liver of foals at birth, or on the frequency or severity of lesions in articular cartilage at 160 days of age. The Cu and Zn concentrations of pasture were similar in Years 1 and 2, and were lower than current recommendations. All foals in Year 2, and 9/10 foals in Year 1 had irregularities in cartilage that was confirmed histologically to be indicative of OC. The average number of lesions per foal was 4.7 (SD 1.1) and 5.7 (SD 1.1) in Years 1 and 2, respectively. However, the severity of the lesions was considered mild, and no foals showed any clinical evidence of OC while alive. The number of lesions in the tarsocrural (TC) joint and the TC OC score at 160 days were positively associated with average daily weight gain (ADG) in the previous 4 weeks (p=0.005 and p=0.001, respectively). There was no significant effect of sex, fatness, birth-weight, weight at 160 days of age, or year of birth of the foal on the frequency and severity of OC lesions. CONCLUSIONS: Many of the lesions classified as OC, using classification systems described by other authors, were likely to be normal variations of the process of endochondral ossification. Despite the high frequency of such lesions, they were considered to be of minor significance and none were clinically evident. The distribution of lesions was not typical, and most probably reflected the subtlety of the lesions. These results support the hypothesis that Cu is an over-emphasised factor in the aetiopathogenesis of OC. The relationship between subtle macroscopic lesions and lesions resulting in clinical signs of disease requires further investigation.

Chemical body composition of 20 Thoroughbred foals at 160 days of age, and preliminary investigation of techniques used to predict body fatness.

Abstract AIMS: To determine the chemical body composition of Thoroughbred foals born in two consecutive years, and to investigate several techniques used to predict body composition in foals born in the second year, with particular reference to fat. METHODS: The chemical composition of 20 foals at around 160 days of age, born in two years, was determined. In vivo techniques to predict body composition were assessed in 23 foals born in Year 2, before and after euthanasia; 10 of these foals were used for chemical body composition analysis. Techniques to assess body composition in vivo included liveweight (LW), overall and regional condition scores, ultrasonic fat thickness measurements over the ribs and rump, linear measurements and bioelectrical impedance analysis. Correlations were determined between ultrasonic fat thickness, and bioelectrical impedance analysis, before and after euthanasia. Stepwise regression analysis was used to determine the relationships between in vivo techniques used to assess body composition and the chemical body composition of 10 animals. RESULTS: Foals used for analysis of chemical composition weighed between 220.5 and 260.0 kg before euthanasia. Fat content ranged from 5.5-13.0% of the partial empty body-weight (LW less head, gastrointestinal contents, distal limbs and skin). Fillies had significantly more fat mass and percentage fat than colts (p=0.031 for both measurements). The mean chemical composition of the fat-free partial empty body was 73.2% (SD 0.6) water, 22.7% (SD 0.9) protein and 4.1% (SD 0.4) ash. Most of the variation in the concentration of empty body water was associated with variation in the concentration of fat (p<0.001). The live animal overall condition scores were correlated with fat mass and concentration (p=0.006 and p=0.013, respectively; n=10). Condition score over the rib region was highly correlated with fat mass and fat concentration (p=0.004 and p<0.001; n=10). Ultrasound measurements taken 10 cm cranial to the tailhead and 4 cm from midline, used to assess the thickness of rump fat, were correlated with condition score (p=0.001), and explained 71% of the variation in body fat mass (p=0.002; n=10). Nearly 50% of the variation in fat-free mass and partial empty body water mass were associated with variation in the impedance indices calculated from length and bioelectrical impedance analysis measurements (p=0.023 and p=0.026, respectively; n=10). CONCLUSIONS: At around 42% of expected mature weight, fillies were significantly more fat than colts. Condition scores were correlated with partial empty body fat mass, and there was a trend for higher scores in fillies compared to colts. Much of the variation in water or protein mass of the partial empty body could be explained by variations in LW. CLINICAL RELEVANCE: Measurements of LW, rump fat and condition score are useful predictors of the chemical composition of foals at 5 months of age.

Enlargements of the distal third metacarpus and metatarsus in Thoroughbred foals at pasture from birth to 160 days of age.

Abstract AIMS: To assess the relationship between the radiographic and microscopic appearance of the physeal regions of the distal third metacarpal (Mc3) and metatarsal (Mt3) bones of Thoroughbred foals at 160 days of age, and to clinically assess changes in contour of the distal Mc3 and Mt3 physeal regions from birth to 160 days of age. To assess relationships between maximum clinical physis scores and age, time of year, foals sex, condition score, growth rate, copper (Cu) concentration in the liver of the foal, and supplementation of the dam with Cu in late gestation. METHODS: Dams were given Cu (n=5 and n=11, in Years 1 and 2, respectively) or saline (n=5 and n=12, in Years 1 and 2, respectively) injections in late gestation. Liver biopsies were harvested from foals in the first week of life, and the whole liver homogenised after the animals were euthanised at around 160 days of age, to determine Cu concentrations. Pasture samples were collected every 4–8 weeks for analysis of mineral composition. During Year 1, 10 foals were weighed and examined every 2 weeks from birth to 160 days of age for evidence of pain and lameness in the distal Mc3/Mt3. In Year 2, 23 foals were weighed, condition-scored and examined for evidence of pain and lameness weekly for the first 5 weeks of life, then every 2 weeks from birth to 160 days of age, and a clinical physis score for the distal Mc3/Mt3 given. Cabinet radiographs of frontal slices of the physeal region of the distal Mc3/Mt3 at around 160 days of age were given a radiographic physis score. Physes were then examined histologically for evidence of abnormal en- dochondral ossification. RESULTS: Gross enlargements of the distal Mc3 and Mt3 were observed in all foals in this study, but were not associated with lameness, pain or inflammation. The most severe clinical physis scores occurred over 2 months in late summer/autumn, and were not influenced by the foals growth rate, sex, or Cu concentration in the liver, or treatment of dams with Cu in late gestation. The clinical physis score was highly correlated to radiographic evidence of shouldering in the forelimb and hindlimb (both p<0.001). Focal disturbances in endochondral ossification were evident radiographically and histologically in the some of the physes at 160 days of age. The mineral composition of pasture was similar in Years 1 and 2, and concentrations of Cu and zinc were below those currently recommended for growing horses. CONCLUSIONS: Gross enlargements of the distal Mc3 and Mt3 were not consistent with previous descriptions of physitis. Results suggest that while many Thoroughbred foals at pasture will have visible boney enlargements of the distal Mc3/Mt3 in the first 5 months of life, few have physeal cartilage abnormalities or significant compromise of endochondral ossification. The importance of these clinical swellings may be overestimated, and they may more appropriately be called physiological enlargements associated with remodelling of bone.

Liver copper kinetics in Thoroughbred foals at pasture from birth to 160 days of age

Abstract Pregnant mares in New Zealand are often kept at pasture with inadequate copper (Cu) concentrations according to National Research Council (1989) recommendations. Many authors recommend Cu supplementation of pregnant mares to reduce the degree and severity of developmental orthopaedic disease (DOD) in their foals. Few data exist on the efficacy of Cu injections in mares in raising liver Cu concentration in pregnant mares or their foals, or the pattern of normal decline in liver Cu concentration of foals after birth. In this study pregnant mares were treated with injectable Cu, or saline, in two different regimens, in 2 consecutive years. Mares and foals had liver biopsies harvested to determine the effect of mare Cu supplementation on liver Cu concentration, and to identify normal patterns of decline in foal liver Cu concentration from birth to 160 days of age. Injectable Cu supplementation had no significant effect on dam or foal liver and plasma Cu concentration. A mathematical model to describe the decline in liver Cu concentration of foals was constructed. In foals the concentration of Cu in liver biopsies showed high repeatability (87%), and was strongly correlated with total liver Cu concentration. Cu injections do not improve Cu status in mares and foals, and liver biopsies are highly re‐peatable and highly correlated with total liver Cu, thus are a useful tool to evaluate liver Cu stores.

The effect of high pasture molybdenum concentrations on the copper status of grazing horses in New Zealand

Abstract The objective of this study was to determine whether Mo causes secondary Cu deficiency in pasture‐fed horses. Twelve Thoroughbred weanling fillies were divided into two groups and fed either high Mo pasture (8 to 15 mg Mo kg−1 DM) or a low Mo pasture (0.6 to 1.2 Mo kg−1 DM) for 84 days. Both pastures contained 6 to 9 mg Cu kg−1 DM. The animals were challenged with Cu over the last 14 days to determine change in their Cu status to 1.0 mg Cu kg−1 liveweight d−1 given orally three times a week. Copper status was assessed from liver, plasma, blood cell, and plasma trichloroacetic acid‐insoluble Cu concentrations as well as the enzyme activities of plasma caeruloplasmin and red blood cell superoxide dismutase. None of these indices was affected by the increase in Mo intake. Horses grazing pasture high in Mo responded no differently to Cu challenge than did those on low Mo pasture. The results of this study suggest that Mo is unlikely to increase dietary Cu requirements and induce secondary Cu deficien...

The effect of removal technique and post‐removal handling on velvet antler colour

Abstract Asian markets for velvet antler perceive the colour of the core as a primary indicator of quality. The factors which influence colour are not known, but the market preference in Korea is for an even mid‐red colour. The aim of the present study was to determine whether removal technique and post‐removal handling influence velvet colour. Investigations took place at AgResearch Invermay and at Mount Hurt Station in mid Canterbury, New Zealand. The influences on velvet antler colour of sedative drug, mild stress, local anaesthetic administration, timing of tourniquet application, and restraint of the stags in a crush or workroom for velvet antler removal were investigated. The effects of antler orientation post‐removal and post‐removal environmental temperature on velvet antler colour were also investigated. In all studies, velvet antler was frozen and held at ‐20°C before being dried either by freeze drying or commercially. In all trials, a consistent pattern of both lightness and hue angle was shown from the tip of the velvet antler stick to the base; the tip was lighter and browner, the mid section was darker and redder, and the base was lighter and browner. There were no significant overall effects of drug treatment on colour, but there were significant differences among sections. Specifically, sedative drug treatments resulted in less red velvet antler than in control antlers removed using local analgesic only. Mild stress and method of local analgesic administration had no effect on any aspect of velvet antler colour. Placing the velvet at an angle of 15° (tip down) gave a darker and redder antler than the typical fully inverted position. There were no significant differences in colour whether the velvet antler was frozen immediately after removal or held at 4°C or ambient temperature for up to 6 hours prior to freezing. Overall, the use of sedative drugs produces velvet antler that is lighter and less red, and post‐removal handling technique can influence colour.