Intermandibular width as a selection criterion for Thoroughbreds |
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| Institution: | 1. Facultad de Veterinaria, Universidad de Zaragoza, Instituto Agroalimentario de Aragón (IA2) (Universidad de Zaragoza-CITA), c/Miguel Servet 177, 50013 Zaragoza, Spain;2. Escuela de Medicina Veterinaria, Facultad de Ecología y Recursos Naturales, Universidad Andrés Bello, Av. República 440, Santiago 8370251, Chile;3. ADL Diagnostic Chile Ltda., Laboratorio de Diagnóstico y Biotecnología, Puerto Montt, Chile;4. Department of Veterinary Population Medicine, College of Veterinary Medicine University of Minnesota Saint Paul, MN, USA;1. Department of Dairy Science, University of Wisconsin-Madison, 1675 Observatory Drive, Madison, WI 53706, USA;2. Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, 1550 Linden Drive, Madison, WI 53706, USA;3. Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Drive, Madison, WI 53706, USA;4. Department of Animal Sciences, Michigan State University, 484 S Shaw Lane, E. Lansing, MI 48824, USA;1. Departamento de Ciencias Agroforestales, Universidad de Sevilla, Ctra. Utrera km 1, 41013 Sevilla, España;2. Departamento de Genética, Universidad de Córdoba, Ctra. Madrid-Cádiz Km.396ª, 14071 Córdoba, España;3. Departamento de Producción Animal, Universidad de Córdoba, Ctra. Madrid-Cádiz Km.396ª, 14071 Córdoba, España;1. Department of Stomatology, School of Dentistry, University of São Paulo, São Paulo, Brazil;2. School of Pharmacy, University of Paraná-Unicentro, Paraná, Brazil;3. Adolfo Lutz Institute, Section of Biomedical Sciences, Mycology Laboratory, Bauru, São Paulo, Brazil;4. Pontifical Catholic University, São Paulo, Brazil;5. University Brasil, São Paulo, Brazil;6. Rural Federal University of Rio de Janeiro, Rio de Janeiro, Brazil;7. Adolfo Lutz Institute, Section of Biomedical Sciences, São Paulo, São Paulo, Brazil |
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| Abstract: | The intermandibular width (IMW) was measured on 3042 Thoroughbreds ranging in age from 12 to 319 months and subsequently compared to their racing performance. IMW had a near normal distribution for both males and females and mean IMW was similar (P>.05) between both groups as yearlings and two-year-olds. However, after 36.5 months the mean IMW of males (9.63 cm) was greater (P<.002) than females (9.29 cm) and continued to become more pronounced with age. Males had an IMW growth rate of 9.1% compared to a 5% growth rate for females. For both males and females, grown IMW (GIMW) was weakly correlated (r−.08, P=.01) to grown height (GHT). Male GIMW had a small inverse relationship (r=−.062, P=.0412) to highest racing performance (HP) and a somewhat stronger inverse relationship (r=−.130, P=.0001) to highest racing distance (HD). For females, the correlation of GIMW with HP was essentially zero, but again a negative relationship (r-−.076, P=.0147) was found between GIMW and HD. Surprisingly, when individual GHT of males and females was divided by individual GIMW, there was a greater (P<.02) percentage of graded stakes winners in the groups with the highest (narrower IMW) ratio. Similarly, horses with the highest ratio were more (P<.0001) successful at racing distances over eight furlongs while horses with lower ratios (wider IMW) were more (P<.05) successful at sprint distances. The reason(s) for these findings remain the focus of further research. However, IMW may well be more reflective of individual body shape, than anything else, since narrower bodied horses, in general, tend to be best suited for distance racing, whereas wider bodied individuals tend to be best suited for sprint racing. Although IMW was not a useful indicator of Thoroughbred racing potential, the former claim that horses (particularly tall individuals) with ‘narrow’ IMW are at a racing performance disadvantage was unfounded. |
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