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The breeding of sport horses to compete in the Olympic disciplines of show jumping, eventing, and dressage is fast becoming a global industry with the increased use of reproductive technologies, including artificial insemination and embryo transfer. Reproductive technologies have facilitated the dissemination of genetics from elite horses across multiple countries and breeds as breeders are no longer limited by location. Due to this increased level of crossbreeding, there is an increased need for estimated breeding values (EBVs) for sport horse performance that can be compared across breeds and countries. However, the implementation of across-breed or across-country genetic evaluations has been limited by the differences in each studbook's individual breeding programs and genetic evaluations. Consequently, the aim of this review was to compare the genetic evaluations for show jumping of sport horse studbooks worldwide. The top sport horse studbooks in the world according to the World Breeding Federation for Sport Horses Studbook Rankings 2019 were contacted by email to request information on their current breeding programs and genetic evaluations. Twenty-six of the 51 studbooks contacted replied to this request but only 18 of these studbooks conducted their own genetic evaluations or were part of a larger genetic evaluation in their country of origin. The other eight studbooks were not involved in genetic evaluations at present but expressed an interest in the implementation of such in the future. Overall, many differences were identified among the genetic evaluations of each studbook or each country. The definition of show jumping performance differed within each evaluation and the methods and models utilized also differed. Despite some stallions and mares being registered in multiple studbooks or having progeny in multiple studbooks, these differences make comparison of EBVs across studbooks difficult. Further transparency and collaboration of sport horse studbooks with organizations such as Interstallion, will be essential to facilitate any future implementation of international genetic evaluations for show jumping performance. [ABSTRACT FROM AUTHOR]

The breeding of sport horses to compete in show jumping is fast becoming a global industry with the increased use of reproductive technologies, including artificial insemination and embryo transfer, facilitating the dissemination of genetics from elite horses across multiple countries and breeds. Due to this increased level of crossbreeding, there is an increased need for estimate breeding values for sport horse performance that can be compared across breeds and countries. However, the implementation of a cross-breed or across-country genetic evaluations has been limited by the differences in individual breeding programs and genetic evaluations in each studbook. Consequently, the aim of this study was to compare the genetic evaluations for show jumping of sport horse studbooks worldwide. An email was sent to the studbooks included in the World Breeding Federation for Sport Horses Studbook Rankings for show jumping in 2019 to request information on their current breeding programs and genetic evaluations. Twenty-six of the 51 studbooks contacted replied to this request. Only 18 of these studbooks conducted their own genetic evaluations or were part of a larger genetic evaluation in their country of origin. Overall, many differences were identified among the genetic evaluations of each studbook or each country. The definition of show jumping performance differed within each evaluation and the methods and models utilized also differed (Table 1). Despite some stallions and mares being registered in multiple studbooks or having progeny in multiple studbooks, these differences make comparison of estimated breeding values across studbooks difficult. Further transparency and collaboration of sport horse studbooks with organizations such as Interstallion, will be essential to facilitate any future implementation of international genetic evaluations for show jumping performance. [ABSTRACT FROM AUTHOR]

The current genetic evaluations of the Irish Sport Horse are undertaken on a single trait called the Lifetime Performance Rating (LPR). The LPR represents the highest level a horse has achieved two double clear rounds in show jumping in both national and international performances. The objective of this study was to compare the method currently used in these evaluations (Model 1, Table 1) to a modified methodology to determine the most accurate method for estimating breeding values (EBV) for the LPR. Genetic parameters and EBVs were generated based on the LPR of 30,355 horses using eight different animal models. Each of the eight models considered the additive genetic variance as the random effect and a combination of following fixed effects: sex, year the highest level was first achieved, age the highest level was achieved, maximum age of the animal in the competition data, Thoroughbred percentage (TB%), and TB% divided into eights. (Table 1). The goodness-of-fit of each model was evaluated using the Akaike's information criteria and the genetic parameters produced by each model. Heritability estimates for LPR ranged from 0.26 to 0.32 depending on the model used (Table 1). The inclusion of age or maximum age in the model decreased the residual variances, and thus, increased the heritability estimates of LPR; these models also performed better than those that did not consider age in any form. The models that considered the effect of TB% were not a significantly better fit than those that did not consider this effect. In conclusion, future genetic evaluations of LPR in the Irish Sport Horse would benefit from using a model that considers either the age or maximum age of performance of each horse, alongside the year the highest level was achieved, and the sex of the horse. [ABSTRACT FROM AUTHOR]

Persistent elevation in shear stress within conduit or resistance arteries causes structural luminal expansion, which serves to normalize shear stress while maintaining increased flow to the downstream vasculature. Although it is known that this adaptation involves cellular proliferation and remodeling of the extracellular matrix, the specific cellular events underlying these responses are poorly understood. Matrix metalloproteinases (MMPs) contribute to extensive remodeling of the extracellular matrix in conduit vessels and vein grafts exposed to high flow. However, involvement of MMPs in remodeling of small muscular collateral arteries, which are exposed to less severe increases in shear stress, has not been tested. We utilized an established model of outward remodeling in mesenteric collateral arteries to determine whether MMPs were upregulated during the remodeling response and to test whether MMP activity was required for luminal expansion. By 4 days, MMP-2 and membrane type 1 MMP (MT1-MMP), but not MMP-9, protein levels were significantly elevated in collateral arteries, as assessed by gelatin zymography and immunostaining. MMP-2 and MT1-MMP proteins, together with their respective transcriptional activators c-Jun and Egr-1 were localized predominantly to the smooth muscle layer of the collateral arteries. The general MMP inhibitor doxycycline prevented luminal expansion of collateral arteries but did not affect the endothelial cell proliferative or medial growth responses. In conclusion, this study provides evidence that MMP-2 and MT1-MMP are upregulated in collateral arteries exposed to elevated shear stress and that MMP activity is essential for the full remodeling response that leads to outward luminal expansion.