Veterinary Research Communications https://doi.org/10.1007/s11259-018-9712-6
ORIGINAL ARTICLE
Genetic parameter estimation and implementation of the genetic evaluation for gaits in a breeding program for assisted-therapy in donkeys Francisco Javier Navas González1,2 · Jordi Jordana Vidal2,3 · Jose Manuel León Jurado2,4 · Amy Katherine McLean2,5 · Gabriela Pizarro Inostroza1,2 · Juan Vicente Delgado Bermejo1,2 Received: 21 November 2017 / Accepted: 31 January 2018 © Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Genetic analyses in donkeys are likely to face compromises in terms of sample size and population structure. This study aims at implementing a suitable model to estimate breeding values and genetic parameters for gaits in Andalusian donkeys. Empirical observation revealed that ambling donkeys (showing a slightly uneven, non-isochronous 1–2, 3–4 lateral sequence gait) did not walk (i.e. presented an isochronous, even 1-2-3-4 sequence gait) and vice versa. However, the two donkey groups could trot, equally. In this study, 2700 gait records were registered from 300 donkeys. The sample included 1350 gait records from 169 ambling/trotting donkeys and 1350 gait records from 131 walking/trotting donkeys. Fixed effects included year, season, sex, farm/owner, husbandry system, weather, ground type and appraisers. Weight and age were included as covariates. MTDFREML software was used to estimate (co)variance components, genetic parameters and predict breeding values and their accuracies in both sets, separately. Gaits’ heritability ± SE estimates were 0.56 ± 0.155, 0.53 ± 0.317 and 0.67 ± 0.166 for amble, walk and trot, respectively. Genetic correlations were 0.31 ± 0.216, 0.42 ± 0.115 and 0.28 ± 0.178, for amble and walk, amble and trot and walk and trot, respectively. Not all gaits are suitable to treat every human sensomotor condition. We developed a locomotion selection index, assessing the relative loss/gain in index accuracy when each gait modality was excluded to develop different gait specific therapeutic lines to genetically select the best performing donkeys from each gait modality. Our results suggest that gait genetic lines could be developed and may be potential selection criteria to consider in assisted-therapy donkey breeding programs. Keywords Donkey · Restricted maximum likelihood · Genetic parameters · Amble · Walk · Trot
Introduction * Francisco Javier Navas González
[email protected] 1
Department of Genetics, Faculty of Veterinary Sciences, University of Córdoba, Córdoba 14071, Spain
2
The Worldwide Donkey Breeds Project, Faculty of Veterinary Sciences, University of Córdoba, Córdoba 14071, Spain
3
Departament de Ciència Animal i dels Aliments, Facultat de Veterinària, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain
4
Centro Agropecuario Provincial de Córdoba, Diputación Provincial de Córdoba, Córdoba 14071, Spain
5
Department of Animal Science, University of California Davis, Davis, CA 95616, USA
The smooth riding characteristics of donkeys were already reported in text fragments by Al-Maqrīzī dating back to the thirteenth Century. He would report the custom of riding on donkeys was widespread among Egyptian notables (Alkhateeb-Shehada 2008). The Andalusian donkey breed is believed to be closely related to or even the direct descendent of the ‘White’ Egyptian donkey breed, also known as Hassawi riding donkeys (Porter et al. 2016). Unfortunately, functional traits in donkeys have been overlooked over time. The technological improvement in agricultural machinery and the modernisation of transport facilities and networks ended relegating the role of these valuable animals to an afunctional secondary place within society. Donkeys can perform all the gaits that other affine species such as the horse develop. However, these gaits should be considered
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analogous variations as donkeys are conditioned by their anatomical and physiological characteristics (Navas et al. 2016). These facts together with the close bonds that they form with humans, the application of each gait modality in the treatment of specific human conditions and their kinetic versatility are key advantages when setting the base for their sustainable functional future. Genetic analyses for gaits and functional skills have long and deep been studied in horses by several authors such as Vicente et al. (2014b). However, genetic analyses in donkeys are likely to face compromises in terms of sample size and population structure. The objective of this study was to estimate (co)variance components and genetic parameters, and to predict breeding values and their accuracies for amble, walk and trot gait modalities in donkeys using MTDFREML software. Then, we computed different possible combinations of these gait modalities in selection indexes to find the best fitting selection methods when the breeding goal was locomotion, aiming at developing different therapeutic kinetic lines, considering the gait modalities for which every donkey assessed may be better suited.
Materials and methods Institutional animal care and use committee statement All farms included in the study followed specific codes of good practices for equids and particularly donkeys and therefore, the animals received humane care in compliance with the national guide for the care and use of laboratory and farm animals in research. The Spanish Ministry of Economy and Competitivity through the Royal Decree Law 53/2013 permitted the application of the protocols present in this study as cited in the 5th section of its 2nd article, as the animals assessed were used for credited zootechnical use. This national Decree follows the European Union Directive 2010/63/UE, from the 22nd of September of 2010.
Study sample and study background We studied a sample of 300 stud-book registered Andalusian donkeys (78 jacks and 222 jennies). Empirical observation revealed that ambling donkeys (showing a slightly uneven, non-isochronous 1–2, 3–4 lateral sequence gait) did not walk (i.e. presented an isochronous, even 1-2-3-4 sequence gait) and vice versa. However, the two donkey groups could trot, equally (Table 1). For this reason, two different kinds of donkeys were studied, ambling/trotting donkeys and walking/trotting donkeys. Ambling/trotting donkeys were those that could amble and trot, but could
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Veterinary Research Communications Table 1 Summary of the frequencies for slow gaits found in the Andalusian donkey sample Item
N = 300
Animals with unknown sire Animals with unknown dam Animal with both unknown parents Ambling males Walking males Ambling females Walking females Ambling offspring from ambling dam Ambling offspring from ambling sire Walking offspring from ambling sire Walking offspring from ambling dam Ambling offspring from walking sire Ambling offspring from walking dam Walking offspring from walking sire Walking offspring from walking dam
117 116 111 26 52 105 117 24 32 0 11 17 25 40 54
Accessed from Navas and Delgado (2016)
not walk, while walking/trotting donkeys were those that could walk and trot, but could not amble, respectively. The sample included 169 ambling/trotting donkeys (52 jacks and 117 jennies) and 131 walking/trotting donkeys (26 jacks and 104 jennies). The mean age of ambling/trotting donkeys was 97.63 ± 61.43 months while the mean age of walking/trotting donkeys was 73.39 ± 61.43 months (Fig. 1). Empirical visual observation and video recordings highlighted the fact that 100% ambling jacks produced ambling offspring in all cases, while the offspring of ambling jennies and walking jacks and jennies could either amble or walk, equally (Table 1). Parentage tests for each offspring had previously been performed with microsatellite molecular markers to ensure the reliability of the information in the pedigree as a way to counteract the small size of the sample tested. All tests were carried out using a pedigree file provided by the Union of Andalusian Donkey Breeders (UGRA). The pedigree file included 1017 animals (272 males and 745 females) born between January 1980 and July 2015 from which only 914 donkeys, 246 males, and 668 females, were alive during the development of the study. The pedigree of the donkeys in the sample was traced back six generations providing indirect information from 724 connected ancestors (71% of the historical population registered) and accounting for an average inbreeding of 1%.
Record description and scales Animals belonged to 22 different farms located in Andalusia (southern Spain). The donkeys were recorded on four randomly chosen days from June to November per
Veterinary Research Communications Fig. 1 Age distribution of the sample of Andalusian donkeys (N = 300)
year from 2013 to 2015. The 2700 records included direct information on the performance of 300 donkeys when developing two gait modalities, slow-moving gaits (walk or amble), and a fast-moving gait (trot). By slow gaits we refer to the movement patterns that the donkeys use to move without exerting an extra effort aimed at increasing their speed. All donkeys were scored by three trained appraisers. Another appraiser simultaneously videotaped (1080 p, 50 Hz, shutter speed: 1/250 s) the experiences to assess the donkey’s performance after the field experiences. The donkeys were led on a neck collar and lead rope, while the 3 trained appraisers watched them in a straight line from the side. Each donkey was assessed according to a 1 to 5 linear scale. A score number of 1 was assigned to gaits that lacked uniformity (likely meaning lacked balance) and cadence or harmony and were poorly developed, as the limbs involved did not move in synchrony. Animals scoring a 5 moved at a harmonic, rhythmic and smooth pace and their body reflected such synchrony. On the one hand, the field experiences revealed that donkeys that ambled did not walk and vice versa. On the other hand, no donkey reported the intermedium scores of the scale (2 or 4) for slow gaits (i.e. their amble or walk score was either 1, 3 or 5). Based on these two findings, we decided to reduce the scale into a 0 to 3 scale to fit the variation found in the population sample. When donkeys were assessed for ambling, a score of 0 was given to those donkeys presenting a walking gait, as they were unable to amble. In the same way, when donkeys were assessed for walking, a score of 0 was given to those who ambled, as ambling donkeys did not walk. Then a score of 1 was assigned to donkeys whose slow gaits lacked uniformity and cadence or harmony and were poorly developed, as the limbs involved did not move in synchrony. By contrast,
animals scoring a 3 moved at a harmonic, rhythmic and smooth pace and their body reflected such synchrony.
Statistical analysis First, a Shapiro–Wilk test was applied to check the fitness of the variables in the model to a normal distribution. Second, as the elements in the model did not fit to a normal distribution (P
