Summary: Computation of inbreeding rate (ΔF) must consider that inbreeding is delayed with one generation with respect to the idealized population when addressed using individual inbreeding coefficients. The expression relating inbreeding in generation t with inbreeding rate F_t = 1 – (1–ΔF)^t should be more correctly written in real animal populations as F_t = 1 – (1–ΔF)^t−1, as changes in allele frequencies occur in the equivalent co‐ancestries in the previous generation. This simple approach is tested on simulated and real pedigrees thus demonstrating that: (i) the adjusted individual increase in inbreeding becomes stable in populations under random mating while the unadjusted parameter does not; (ii) regression of the unadjusted parameter over generations in pedigrees under random mating is highly significant while after correction it is not significant; and (iii) the variance of the adjusted parameter is reduced with the generations.

The aims of this study were, first, to evaluate eye temperature (ET) with infrared thermography and heart rate (HR) to measure stress in horses during show jumping competitions and their relationship with competition results, and second, to evaluate the influence of different extrinsic and intrinsic factors of the horse on the stress measurements analysed. One hundred and seventy-three Spanish Sport Horses were analysed for ET and HR, and these measurements were taken 3 h before the competition, just after and 3 h after it. Two interval measurements were also assessed for each parameter. Positive significant correlations were found between ET and HR, measured before (r=0.23), just after competition (r=0.28) and for the later interval (r=0.26), whereas negative correlations with competition results were found only for ET when measured just after competing (r=−0.25). Two intrinsic factors (genetic line and age) and no extrinsic factors showed significant differences for ET, whereas one intrinsic factor (age) and two extrinsic factors (journey duration and number of training hours) showed significant differences for HR. The marginal means showed significantly higher ET values for the Anglo-Arab genetic line and for 5-year-old animals. HR values were significantly higher for 4-year-old animals, for horses which had travelled 4 to 6 h and for horses that had 3 to 6 h of daily training. This study suggests that, although ET and HR seemed to share a similar physiological basis, the factors that most influenced each parameter were different. Finally, ET seems to be a suitable tool for assessing stress during show jumping competitions in horses.

Summary: The objective of this study was to test the performance of a recently proposed methodology for the estimation of realized effective size (N_e) based on individual increase in inbreeding (ΔF_i) on several real pedigrees: (a) an experimental mice population; (b) a closed pedigree of fighting bulls; (c) the Spanish Purebred (SPB, Andalusian) horse pedigree; (d) the Carthusian strain of SPB pedigree; (e) the Spanish Arab horse pedigree; and (f) the Spanish Anglo‐Arab horse pedigree. Several reference subpopulations were defined on the basis of generation length in order to consider only animals in the last generation, to assess the influence of the pedigree content on the estimates of N_e. The estimates of realized N_e computed from ΔF_i () tended to be higher than those obtained from regression on equivalent generations. The new parameter remained approximately stable when pedigree depth achieved about five equivalent generations. Estimates of take into account the genetic history of the populations, the size of their founder population, and the mating policy or bottlenecks caused by poor use of reproducing individuals. The usefulness of the realized N_e computed from individual increase in inbreeding in real pedigrees is also discussed.

We present here a simple approach to obtain reliable estimates of the effective population size in real world populations via the computation of the increase in inbreeding for each individual (delta Fi) in a given population. The values of delta Fi are computed as t-root of 1 - (1 - Fi) where Fi is the inbreeding coefficient and t is the equivalent complete generations for each individual. The values of delta F computed for a pre-defined reference subset can be averaged and used to estimate effective size. A standard error of this estimate of Ne can be further computed from the standard deviation of the individual increase in inbreeding. The methodology is demonstrated by applying it to several simulated examples and to a real pedigree in which other methodologies fail when considering reference subpopulations. The main characteristics of the approach and its possible use are discussed both for predictive purposes and for analyzing genealogies.

The studbook of the Spanish Arab Horse was analysed in order to assess the available genetic variability in the population via genealogical analyses and to ascertain the influence of different countries in the formation of the population. The Spanish Arab horse studbook could be traced back to the late 19th century with a total of 18,880 animals. A 15.7% (2965) of the registered individuals were Arab horses imported from foreign populations. The total number of founders was 1626: from these, 1495 individuals were identified as imported from foreign countries. The sum of the genetic contributions of the founders to the population revealed that those imported from the ‘Middle East’, Poland, the United Kingdom and Egypt had a higher importance in the formation of the Spanish Arab Horse, contributing, respectively, 36.4%, 18.7%, 11.9% and 9.1% of the genetic variability. The effective number of founders was 38.6 and the effective number of ancestors was 19 thus characterising the abusive use of a little number of individuals for reproduction. This was due to a breeding policy that included mating between relatives, but also due to the limited availability of reproductive individuals after the Spanish Civil War. The average inbreeding of the population was 7.0% (9.8% for the individuals born during 1995–2004). Individuals with very high levels of inbreeding (≥ 12.5%) were 17.7% in the whole population and 26.7% of the individuals born in the last decade. Positive genealogical F IS near 2% characterised a breeding policy including matings between relatives. No clear within-population differentiation (inferred via genealogical F ST ) could be assessed between sire lines ( F ST = 0.01) and no differentiation between geographical areas existed. Overall, the Spanish Arab Horse can be described as a population without genetic subdivision and with a mating policy and historical constraints that reduced the available genetic variability regardless of the relatively large size of its founder population. The obtained information will be useful to implement a selection program in the Spanish Arab Horse. Keywords Spanish Arab horse Genetic variability Pedigree analysis Population history Within-population differentiation 1 Introduction The Arab breed is one of the most influential horse breeds in the World ( Bowling and Ruvinsky, 2000a ). It is distributed worldwide and has been involved in the formation of many other horse breeds, such as the Thoroughbred ( Bowling and Ruvinsky, 2000b ) or the Lipizzan ( Zechner et al., 2002 ). At present, the Arab horse breed has the third census size in Spain, totalling 8.1% of the horses in our country and when the Arab and the Arab crossbreed horse breeds (Hispano-Arab and Anglo-Arab) are considered it moves up to the second place among horse populations in Spain after the Andalusian (Spanish Purebred) horse ( MAPyA, 2003 ). The Spanish Arab studbook was founded in 1847 by the Spanish Ministry of War using, mainly, individuals imported from the Middle East and from various European countries ( Maxwell, 1995 ). During the first third of the 20th century a number of private studs were formed in Southern and Central Spain from individuals purchased in the Military Stud of Jerez de la Frontera and foreign countries such as Poland, the United Kingdom, France, Egypt and the area of the Arabian Peninsula ( Fenaux, 1995; Maxwell, 1995 ). Since the 70′s a significant number of Spanish Arab Horse studs have been founded in other Spanish regions such as Catalonia, Balearic Islands and the Cantabrian provinces. The Spanish Arab studbook remains open to include Arab horses from foreign countries that are not always registered with full genealogies in the Spanish Arab Studbook. As what happened in other Spanish horse breeds ( Valera et al., 2005 ) the interest in the Spanish Arab Horse has increased during the past decades with the number of registrations in the studbook. Currently, the Spanish Arab Horse Breeder Association (AECCA) is developing a selection scheme with the aim of improving conformation traits and horse performance, mainly, in endurance rides. The assessment of the within-population genetic variability, population structure and gene flow is necessary during the implementation of selection programs to establish an appropriate management of the genetic stock in order to enlarge genetic basis for selection. In this respect genealogical tools are important to describe these subjects ( Moureaux et al., 1996 Głażewska and Jezierski, 2004 ). Moreover, demographical analyses may also help to understand important circumstances affecting the genetic history of the population ( Zechner et al., 2002; Valera et al., 2005 ). The aim of this work is to analyse the pedigree information of the Spanish Arab Horse included in its studbook in order to quantify the available genetic variability in the population in terms of inbreeding levels and founder contributions to the present population. The study will also focus on analysing the influence of animals from foreign countries in the Spanish Arab Horse and to assess a possible population structure. The implications on the genetic history of the Spanish Arab Horse population over a century of breeding will also be discussed. 2 Materials and methods Information registered in the studbook of the Spanish Arab Horse from its foundation in 1847 to December 2004 has been analysed. Data included 18,880 (8893 males and 9987 females) registered animals. Current and older studbooks of major Spanish Arab studs were primary sources of information for the identification of the origin of the individuals imported from foreign countries (FC). Important secondary sources were the books of Fenaux (1995) , Maxwell (1995) and Steen (2006) . Altogether, FC individuals included those animals actually imported, their ancestors included in the Spanish Arab Horse studbook regardless of location in the Spanish...