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Proudman, C., Pinchbeck, G., Clegg, P., & French, N. (2004). Equine welfare: risk of horses falling in the Grand National. Nature, 428(6981), 385–386.
Abstract: As in other competitive sports, the famous Grand National steeplechase, which is held at Aintree in the United Kingdom and is watched by 600 million people worldwide, sometimes results in injury. By analysing data from the past 15 Grand National races (consisting of 560 starts by horses), we are able to identify several factors that are significantly associated with failure to complete the race: no previous experience of the course and its unique obstacles, unfavourable ground conditions (too soft or too hard), a large number of runners, and the length of the odds ('starting price'). We also find that there is an increased risk of falling at the first fence and at the jump known as Becher's Brook, which has a ditch on the landing side. Our findings indicate ways in which the Grand National could be made safer for horses and illustrate how epidemiological analysis might contribute to preventing injury in competitive sport.
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Berger, J. (1983). Induced abortion and social factors in wild horses. Nature, 303(5912), 59–61.
Abstract: Much evidence now suggests that the postnatal killing of young in primates and carnivores, and induced abortions in some rodents, are evolved traits exerting strong selective pressures on adult male and female behaviour. Among ungulates it is perplexing that either no species have developed convergent tactics or that these behaviours are not reported, especially as ungulates have social systems similar to those of members of the above groups. Only in captive horses (Equus caballus) has infant killing been reported. It has been estimated that 40,000 wild horses live in remote areas of the Great Basin Desert of North America (US Department of Interior (Bureau of Land Management), unpublished report), where they occur in harems (females and young) defended by males. Here I present evidence that, rather than killing infants directly, invading males induce abortions in females unprotected by their resident stallions and these females are then inseminated by the new males.
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Williams, D. O., Boatwright, R. B., Rugh, K. S., Garner, H. E., & Griggs, D. M. J. (1991). Myocardial blood flow, metabolism, and function with repeated brief coronary occlusions in conscious ponies. Am J Physiol, 260(1 Pt 2), H100–9.
Abstract: Studies were performed in the conscious pony instrumented with a Doppler flow probe and hydraulic occluder on the left anterior descending coronary artery (LAD), sonomicrometry crystals and intraventricular micromanometer in the left ventricle, and catheters in the left atrium and anterior interventricular vein. Two-minute LAD occlusions were performed every 30 min continuously or during working hours. Data on release of catabolites (potassium, hydrogen ions, and lactate) and norepinephrine from the initially dysfunctional region were obtained periodically during a regimen of 445 +/- 56 occlusions in six animals. Regional myocardial blood flow was measured (microsphere method) before and after an occlusion regimen in four animals. Marked release of catabolites and norepinephrine from the initially dysfunctional region was noted in association with early occlusions when myocardial segment function was severely reduced. With further occlusions, release of these substances decreased while segment function improved. Blood flow was markedly decreased in the initially dysfunctional region during an early occlusion but was at the control level during a later occlusion. Although the metabolic findings are consistent with protection due to “ischemic preconditioning” and no increase in collateral perfusion, the inverse relationship noted between catabolite release and segment function is best explained by flow-dependent mechanisms. These results, together with the myocardial blood flow data, serve to validate a previous assumption that protection against regional myocardial dysfunction under these conditions is due to increased collateral perfusion.
Keywords: Animals; Consciousness/*physiology; Coronary Circulation/*physiology; Coronary Disease/pathology/*physiopathology; Disease Models, Animal; Hemodynamic Processes/physiology; Horses/*physiology; Hydrogen/metabolism; Lactates/metabolism; Myocardium/*metabolism/pathology; Norepinephrine/metabolism; Potassium/metabolism; Regional Blood Flow
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Dallmeyer, M. D., Turner, R. M., McDonnell, S. M., Sertich, P. L., Dolente, B. A., Parente, E. J., et al. (2006). Theriogenology question of the month. Behavior problems in a stallion caused by a nephrolith. J Am Vet Med Assoc, 229(4), 511–513.
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Arnold, W., Ruf, T., & Kuntz, R. (2006). Seasonal adjustment of energy budget in a large wild mammal, the Przewalski horse (Equus ferus przewalskii) II. Energy expenditure. J Exp Biol, 209(Pt 22), 4566–4573.
Abstract: Many large mammals show pronounced seasonal fluctuations of metabolic rate (MR). It has been argued, based on studies in ruminants, that this variation merely results from different levels of locomotor activity (LA), and heat increment of feeding (HI). However, a recent study in red deer (Cervus elaphus) identified a previously unknown mechanism in ungulates--nocturnal hypometabolism--that contributed significantly to reduced energy expenditure, mainly during late winter. The relative contribution of these different mechanisms to seasonal adjustments of MR is still unknown, however. Therefore, in the study presented here we quantified for the first time the independent contribution of thermoregulation, LA and HI to heart rate (f(H)) as a measure of MR in a free-roaming large ungulate, the Przewalski horse or Takhi (Equus ferus przewalskii Poljakow). f(H) varied periodically throughout the year with a twofold increase from a mean of 44 beats min(-1) during December and January to a spring peak of 89 beats min(-1) at the beginning of May. LA increased from 23% per day during December and January to a mean level of 53% per day during May, and declined again thereafter. Daily mean subcutaneous body temperature (T(s)) declined continuously during winter and reached a nadir at the beginning of April (annual range was 5.8 degrees C), well after the annual low of air temperature and LA. Lower T(s) during winter contributed considerably to the reduction in f(H). In addition to thermoregulation, f(H) was affected by reproduction, LA, HI and unexplained seasonal variation, presumably reflecting to some degree changes in organ mass. The observed phase relations of seasonal changes indicate that energy expenditure was not a consequence of energy uptake but is under endogenous control, preparing the organism well in advance of seasonal energetic demands.
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Skedros, J. G., Dayton, M. R., Sybrowsky, C. L., Bloebaum, R. D., & Bachus, K. N. (2006). The influence of collagen fiber orientation and other histocompositional characteristics on the mechanical properties of equine cortical bone. J Exp Biol, 209(Pt 15), 3025–3042.
Abstract: This study examined relative influences of predominant collagen fiber orientation (CFO), mineralization (% ash), and other microstructural characteristics on the mechanical properties of equine cortical bone. Using strain-mode-specific (S-M-S) testing (compression testing of bone habitually loaded in compression; tension testing of bone habitually loaded in tension), the relative mechanical importance of CFO and other material characteristics were examined in equine third metacarpals (MC3s). This model was chosen since it had a consistent non-uniform strain distribution estimated by finite element analysis (FEA) near mid-diaphysis of a thoroughbred horse, net tension in the dorsal/lateral cortices and net compression in the palmar/medial cortices. Bone specimens from regions habitually loaded in tension or compression were: (1) tested to failure in both axial compression and tension in order to contrast S-M-S vs non-S-M-S behavior, and (2) analyzed for CFO, % ash, porosity, fractional area of secondary osteonal bone, osteon cross-sectional area, and population densities of secondary osteons and osteocyte lacunae. Multivariate multiple regression analyses revealed that in S-M-S compression testing, CFO most strongly influenced total energy (pre-yield elastic energy plus post-yield plastic energy); in S-M-S tension testing CFO most strongly influenced post-yield energy and total energy. CFO was less important in explaining S-M-S elastic modulus, and yield and ultimate stress. Therefore, in S-M-S loading CFO appears to be important in influencing energy absorption, whereas the other characteristics have a more dominant influence in elastic modulus, pre-yield behavior and strength. These data generally support the hypothesis that differentially affecting S-M-S energy absorption may be an important consequence of regional histocompositional heterogeneity in the equine MC3. Data inconsistent with the hypothesis, including the lack of highly longitudinal collagen in the dorsal-lateral ;tension' region, paradoxical histologic organization in some locations, and lack of significantly improved S-M-S properties in some locations, might reflect the absence of a similar habitual strain distribution in all bones. An alternative strain distribution based on in vivo strain measurements, without FEA, on non-Thoroughbreds showing net compression along the dorsal-palmar axis might be more characteristic of the habitual loading of some of the bones that we examined. In turn, some inconsistencies might also reflect the complex torsion/bending loading regime that the MC3 sustains when the animal undergoes a variety of gaits and activities, which may be representative of only a portion of our animals, again reflecting the possibility that not all of the bones examined had similar habitual loading histories.
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Bobbert, M. F., & Santamaria, S. (2005). Contribution of the forelimbs and hindlimbs of the horse to mechanical energy changes in jumping. J Exp Biol, 208(2), 249–260.
Abstract: The purpose of the present study was to gain more insight into the contribution of the forelimbs and hindlimbs of the horse to energy changes during the push-off for a jump. For this purpose, we collected kinematic data at 240 Hz from 23 5-year-old Warmbloods (average mass: 595 kg) performing free jumps over a 1.15 m high fence. From these data, we calculated the changes in mechanical energy and the changes in limb length and joint angles. The force carried by the forelimbs and the amount of energy stored was estimated from the distance between elbow and hoof, assuming that this part of the leg behaved as a linear spring. During the forelimb push, the total energy first decreased by 3.2 J kg(-1) and then increased again by 4.2 J kg(-1) to the end of the forelimb push. At the end of the forelimb push, the kinetic energy due to horizontal velocity of the centre of mass was 1.6 J kg(-1) less than at the start, while the effective energy (energy contributing to jump height) was 2.3 J kg(-1) greater. It was investigated to what extent these changes could involve passive spring-like behaviour of the forelimbs. The amount of energy stored and re-utilized in the distal tendons during the forelimb push was estimated to be on average 0.4 J kg(-1) in the trailing forelimb and 0.23 J kg(-1) in the leading forelimb. This means that a considerable amount of energy was first dissipated and subsequently regenerated by muscles, with triceps brachii probably being the most important contributor. During the hindlimb push, the muscles of the leg were primarily producing energy. The total increase in energy was 2.5 J kg(-1) and the peak power output amounted to 71 W kg(-1).
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Dutto, D. J., Hoyt, D. F., Clayton, H. M., Cogger, E. A., & Wickler, S. J. (2004). Moments and power generated by the horse (Equus caballus) hind limb during jumping. J Exp Biol, 207(Pt 4), 667–674.
Abstract: The ability to jump over an obstacle depends upon the generation of work across the joints of the propelling limb(s). The total work generated by one hind limb of a horse and the contribution to the total work by four joints of the hind limb were determined for a jump. It was hypothesized that the hip and ankle joints would have extensor moments performing positive work, while the knee would have a flexor moment and perform negative work during the jump. Ground reaction forces and sagittal plane kinematics were simultaneously recorded during each jumping trial. Joint moment, power and work were determined for the metatarsophalangeal (MP), tarsal (ankle), tibiofemoral (knee) and coxofemoral (hip) joints. The hip, knee and ankle all flexed and then extended and the MP extended and then flexed during ground contact. Consistent with our hypothesis, large extensor moments were observed at the hip and ankle joints and large flexor moments at the knee and MP joints throughout ground contact of the hind limb. Peak moments tended to occur earlier in stance in the proximal joints but peak power generation of the hind limb joints occurred at similar times except for the MP joint, with the hip and ankle peaking first followed by the MP joint. During the first portion of ground contact (approximately 40%), the net result of the joint powers was the absorption of power. During the remainder of the contact period, the hind limb generated power. This pattern of power absorption followed by power generation paralleled the power profiles of the hip, ankle and MP joints. The total work performed by one hind limb was 0.71 J kg(-1). Surprisingly, the knee produced 85% of the work (0.60 J kg(-1)) done by the hind limb, and the positive work performed by the knee occurred during the first 40% of the take-off. There is little net work generated by the other three joints over the entire take-off. Velocity of the tuber coxae (a landmark on the pelvis of the animal) was negative (downward) during the first 40% of stance, which perhaps reflects the negative work performed to decrease the potential energy during the first 40% of contact. During the final 60% of contact, the hip, ankle and MP joints generate positive work, which is reflected in the increase of the animal's potential energy.
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Witte, T. H., Knill, K., & Wilson, A. M. (2004). Determination of peak vertical ground reaction force from duty factor in the horse (Equus caballus). J Exp Biol, 207(Pt 21), 3639–3648.
Abstract: Measurement of peak vertical ground reaction force (GRFz) from multiple limbs simultaneously during high-speed, over-ground locomotion would enhance our understanding of the locomotor mechanics of cursorial animals. Here, we evaluate the accuracy of predicting peak GRFz from duty factor (the proportion of the stride for which the limb is in contact with the ground). Foot-mounted uniaxial accelerometers, combined with UHF FM telemetry, are shown to be practical and accurate for the field measurement of stride timing variables, including duty factor. Direct comparison with the force plate produces a mean error of 2.3 ms and 3.5 ms for the timing of foot on and foot off, respectively, across all gaits. Predictions of peak GRFz from duty factor show mean errors (with positive values indicating an overestimate) of 0.8+/-0.04 N kg(-1) (13%; N=42; mean +/- S.E.M.) at walk, -0.3+/-0.06 N kg(-1) (3%; N=75) at trot, -2.3+/-0.27 N kg(-1) (16%; N=18) for the non-lead limb at canter and +2.1+/-0.7 N kg(-1) (19%; N=9) for the lead limb at canter. The substantial over- and underestimate seen at canter, in the lead and non-lead limbs, respectively, is attributed to the different functions performed by the two limbs in the asymmetrical gaits. The difference in load experienced by the lead and non-lead limbs decreased with increasing speed.
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Hodgson, D., Howe, S., Jeffcott, L., Reid, S., Mellor, D., & Higgins, A. (2005). Effect of prolonged use of altrenogest on behaviour in mares (Vol. 169).
Abstract: Erratum in:
Vet J. 2005 May;169(3):321. Corrected and republished in: Vet J. 2005 May;169(3):322-5. Oral administration of altrenogest for oestrus suppression in competition horses is believed to be widespread in some equestrian disciplines, and can be administered continuously for several months during a competition season. To examine whether altrenogest has any anabolic or other potential performance enhancing properties that may give a horse an unfair advantage, we examined the effect of oral altrenogest (0.044 mg/kg), given daily for a period of eight weeks, on social hierarchy, activity budget, body-mass and body condition score of 12 sedentary mares. We concluded that prolonged oral administration of altrenogest at recommended dose rates to sedentary mares resulted in no effect on dominance hierarchies, body mass or condition score. Keywords: Administration, Oral; Anabolic Agents/adverse effects/*pharmacology; Animals; Behavior, Animal/*drug effects; Body Constitution/drug effects; Body Weight/drug effects; *Doping in Sports; Female; Horses/*physiology; Social Behavior; Social Dominance; Time Factors; Trenbolone/adverse effects/*analogs & derivatives/*pharmacology
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