Bertrand Langlois

Mutations in the agouti (ASIP), the extension (MC1R), and the brown (TYRP1) loci and their association to coat color phenotypes in horses (Equus caballus)

Abstract. Coat color genetics, when successfully adapted and applied to different mammalian species, provides a good demonstration of the powerful concept of comparative genetics. Using cross-species techniques, we have cloned, sequenced, and characterized equine melanocortin-1-receptor (MC1R) and agouti-signaling-protein (ASIP), and completed a partial sequence of tyrosinase-related protein 1 (TYRP1).The coding sequences and parts of the flanking regions of those genes were systematically analyzed in 40 horses and mutations typed in a total of 120 horses. Our panel represented 22 different horse breeds, including 11 different coat colors of Equus caballus. The comparison of a 1721-bp genomic fragment of MC1R among the 11 coat color phenotypes revealed no sequence difference apart from the known chestnut allele (C901T). In particular, no dominant black (ED) mutation was found.In a 4994-bp genomic fragment covering the three putative exons, two introns and parts of the 5′- and 3′-UTRs of ASIP, two intronic base substitutions (SNP-A845G and C2374A), a point mutation in the 3′-UTRs (A4734G), and an 11-bp deletion in exon 2 (ADEx2) were detected. The deletion was found to be homozygous and completely associated with horse recessive black coat color (Aa/Aa) in 24 black horses out of 9 different breeds from our panel. The frameshift initiated by ADEx2 is believed to alter the regular coding sequence, acting as a loss-of-function ASIP mutation. In TYRP1 a base substitution was detected in exon 2 (C189T), causing a threonine to methionine change of yet unknown function, and an SNP (A1188G) was found in intron 2.

Inter-breed variation in the horse with regard to cold adaptation: a review

Abstract The scientific literature on adaptation to cold in the horse is scant. Yet, if one considers the geographical range of horse rearing around the world one can see that much of it lies in cold-climate zones or those with a cold winter. An examination of the literature on thermoregulation in mammals brings out a number of questions relevant to horse breeds. The answers to some of these questions may be of practical value in horse husbandry. An animal adapts to cold first and foremost by reducing thermolysis, and also by increasing thermogenesis. These are achieved through a variety of mechanisms, examined in this paper both in the individual animal and at the level of the population to which the individual belongs. Seasonal reproduction, for example, can be interpreted as a form of cold adaptation. The mechanisms involved often combine resistance to cold with resistance to food shortage, and body reserves play an important part. Aerobic metabolism, in which fatty acids are broken down, tends to take precedence over anaerobic metabolism, in which glycogen is broken down. The former is suited to prolonged, low-intensity effort, while the latter is suited to intense exertion of short duration. By examining all these phenomena one can work out the archetypes of the horse adapted to cold conditions and, conversely, those adapted to heat. These prove to match up quite well with the traditional classification into cold blood and warm blood. Most breeds can be placed somewhere between the two extremes. However, it is worth noting that the various breeds of trotters found in the cold climatic countries are the most northerly form of warm-blooded horses. Improving environmental conditions would therefore seem to have some economic limits.

Analyse statistique et génétique des gains des pur sang anglais de trois ans dans les courses plates françaises

Pour disposer de variables susceptibles d’être soumises aux calculs statistiques classiques, une transformation logarithmique a été appliquée aux gains de chaque cheval et à son gain moyen par départ. Pour les parents une actualisation à l’année 1973 selon le mode multiplicatif habituel a été réalisée au préalable. L’analyse de la variance sur les variables transformées portant sur les 5 235 descendants gagnants a permis de révéler l’absence d’un effet significatif de l’année et un effet hautement significatif du sexe en faveur des mâles. Par ailleurs l’absence d’interactions entre ces deux fac-

Genetic problems in horse breeding

Abstract The purpose of this paper is to give a short survey of the present problems concerning the genetic improvement of horse breeds. The evolution of these populations in Europe, characterized by a deep change from production of draught horses towards that of leisure horses, is described and the influence of the demographical parameters on the selection of these horse populations, is discussed. The generation interval represents an important handicap only surmounted in the case of racing breeds where a high selection intensity can be practised since all animals are subjected to performance testing. In the other cases, the farmer usually does not use modern breeding techniques, but uses crosses instead, which lead more easily to visible results. The available selection criteria are also dealt with. A distinction is made between direct estimates evaluating the abilities of the animals in practice and the indirect estimates measuring a character in correlation to previous ones. For the former estimates, a distinction is made between those resulting from competitions (handicap, records or earnings) and those resulting from direct in-station measurements (saddle, jumping, dressage abilities, draught power). For the indirect estimates, often used especially for the selection of mares, the most important analysis is obviously that of the conformation. However, in the future early selection criteria according to more physiological data should be sought and developed. Estimation of the breeding value according to a given ability is thereafter pointed out. There are two situations: “the panmictic case” concerning sport and draught horses and “the non-panmictic case” corresponding to racing horses, which give rise to some problems. The setting up of breeding plans is discussed. Due to the different economic situations and various objectives of horse production, conclusions are drawn about the role played by geneticists in the present development of this sector.

Genetic parameters of racing merit of Thoroughbred horses in steeplechase races

Abstract The aim of this study was to estimate variance components of racing ability in Thoroughbreds involved in steeplechase races. Race results were collected from steeplechase races in France (n=9041), in the United Kingdom and Ireland (n=8314) and contained the results of overall 106 020 runs from 1998 to 2003. Performance was measured by two criteria: earnings and ranks after mathematical transformation. The effects of year, sex, age, and race were considered as fixed, animal, permanent environment and maternal as random. Maternal environmental component for ranks were 0.021 in France and 0.000 in the United Kingdom and Ireland. Estimated heritabilities for the ranking criteria were 0.18 (repeatability 0.33) in France and 0.06 (repeatability 0.19) in the United Kingdom and Ireland. The high genetic correlation between the two traits (0.94 and 0.97) gives the opportunity to find out the most suitable criteria for breeding value estimation.

A new scheme for describing horse coat colour

Abstract A new descriptive scheme of horse colours is proposed with four dimensions: (1) pigmentary pattern (which deals with the symmetric partition of eumelanic — black or brown — and phaeomelanic — red — pigmented areas (five different types)); (2) eumelanic type (black or brown); (3) pigment alteration (a modification of pigmentary appearance inside the hair or an intermixing of white and pigmented fibres); and (4) white designs (when the white patches are clearly distinct from the coloured ones). The advantage of this new descriptive scheme are: (1) a better connection with the biological and genetic realities; (2) a more accurate description of the very numerous different colour phenotypes: and (3) a more assimilable international language.

Horse breeding problems

« all lactations ») have been compared. For cow evaluation : the index with and without paternal half-sibs and the direct comparison (BLUP « all lactations »). 3 600 lactations corresponding to 1800 daughters of 30 sires distributed in three groups recorded in 62 herds were generated by routines using 0.20 as value of h, 0.45 as value of repeatability and a phenotypic « within herd » variance equal to .60. Two versions were built differing by the presence (version 1) or not (version 2) of a great number of connections between groups of sires. The efficiency was measured by the rank correlation between true values and values estimated by the different methods. All these correlations are higher for the Blup method. Furthermore the superiority of the direct comparison is also well illustrated when comparing the average true breeding values of the 150 best cows seleced on the basis of the three methods.