AN ASSESSMENT OF THE CORRELATION BETWEEN STABILITY OF THE SEXUAL CYCLE AND THE BREEDING VALUE OF PUREBRED ARABIAN MARES USED FOR BREEDING IN THE NATIONAL STUDS IN POLAND

Dorota Sobczuk
Department of Animal Breeding and Use, Faculty of Agricultural Science, University of Life Sciences in Lublin, Poland

ABSTRACT

The present survey is based on the investigation of 397 purebred Arabian mares used for breeding in the period of 1970–1996, which came from the primary broodmare band in the Białka, Janów Podlaski, Kurozwęki and Michałów Stud Farms. Mares that had been used for 5 and more breeding seasons were selected from the total number of animals. For such mares, their oestrus periods were investigated in the breeding documentation. On the basis of our investigation the following regularities can be observed:

• the differences in average sexual cycles, periods of anoestrus and the oestrus length between the various stud farms were significant or highly significant, which can attributed to the differences in breeding environments of those stud farms;

• the length of the complete sexual cycle, oestrus, and anoestrus was characterised by a low or negative correlation to the racing performance of both the mares under investigation, as well as their progeny;

• in the population of purebred Arabian horses farmed in Poland one can distinguish genetic lineages that vary significantly as to their length of oestrus periods;

• characteristic differences were observed in the average length of the oestrus cycle, the oestrus itself, and the periods of anoestrus in specific coefficient of success ranges.

Key words: Arabian mares, racing performance, sexual cycle.

INTRODUCTION

It has often been concluded in the studies of purebred Arabian horses that the inheritance mechanisms of certain desired traits of such horses were at variance from similar processes in other breeds of horses [11]. Therefore, we see a need to investigate whether there are any characteristic regularities for this breed in the length of oestrus, the complete breeding cycle and periods of anoestrus, features of extreme importance for the breeding value of such mares [8]. The mutual influences among the features of the breeding cycle, as well as their genetic conditioning, are still relatively unresearched. However, certain known regularities [10] prove that there are links between the length of gestation and the breeding value of mares or their progeny. Nevertheless, the patterns and correlations in the length of the sexual cycle, periods of anoestrus and oestrus in Arabian mares and the genetic conditioning of such features has been studied fragmentarily [9,12]. An understanding of the correlation of the important features of the breeding cycle in mares can positively influence the breeding of mares, the use of stallions, and lead to a better choice of breeding partners with a view to acquiring desired breeding traits.

MATERIAL AND METHODS

The investigation comprised 397 purebred Arabian mares used for breeding in the period of 1970–1996, which came from the primary broodmare band of Arabian Stud Farms in Białka, Janów Podlaski, Kurozwęki and Michałów.

The research material was obtained from mating records in: Białka, Janów Podlaski, Kurozwęki, Michałów, Poland conducted by the Studs [13]. From all the mares under investigation, those that had been used for 5 or more breeding seasons were selected. For such mares, data about their oestrus periods recorded by farms were collected. Overall, between 1970 and 1996, 397 mares were investigated, among which 42 mares from the Białka Stud (10.58%), 153 mares from the Janów Podlaski Stud (38.54%), 71 mares from the Kurozwęki Stud (17.88%), and 131 mares from the Michałów Stud (33.00%).

In order to systematize the results and to conduct a full and viable interpretation of the influences such as farm origin, genealogical lineage, each researched feature (length of the sexual cycle, length of oestrus and anoestrus, length of gestation, and the influences thereof), we divided the population under investigation into particular farm groups. We also distinguished paternal groups (9 groups) and maternal lineages (16 lineages).

The most significant criterion for assessing racing and riding performance of purebred Arabian horses are their results achieved during trials at race courses [2,15,16,20]. The main criterion adopted for the assessment of racing performance of the population of horses under investigation was the index scoring developed [3,4,5]. In order to establish the stability of the Arabian mares sexual cycle correlated with their breeding value, we divided the mares under investigation into 5 groups according to the coefficient of success (Wp).

Wp – is the rate expressing performance of a given horse in relation to its peers, arrived at by the following formula:

where:

Wp – coefficient of success,
a – number of horses born in a given year,
∑ x – sum of races won by a given horse,
∑ a – sum of races won by all horses born in a given year.

We also calculated a percentage amount, in particular groups, of horses characterized by a given value of features being investigated. For all defined groups of horses, the following indexes were calculated: arithmetical mean (), extreme values: (Min – minimum and Max – maximum). We also investigated the correlation between particular features and we indicated the significance of the calculated values [17,18,19]. In order to determine the significance of differences in the researched features among particular groups, we applied a single factor variation analysis and Duncan's multiple range test [21].

RESULTS AND DISCUSSION

The sexual cycle in mares normally lasts for 19–22 days. It is the period which starts on the first day of the oestrus and finishes on the last day before the following oestrus [23]. The fluctuations of the cycle may amount to the range from 9 up to 124 days [1].

Thanks to a better understanding of secretory functions in mares, the initial definition of the oestrus cycle as the interval from the beginning of the oestrus to the beginning of the next oestrus has recently been changed [14]. Define the oestrus cycle in mares as the period between ovulations. During that time there are notable behavioural changes in mares, as well as in their internal and external sex organs. Such changes occur due to hormones present in the blood system of mares, and the purpose of the hormonal changes is to enable conception and gestation. The cycles are multiple, as horses are seasonally polyestral. A factor that stimulates the annual occurrance of sexual activity of mares seems to be the prolonged duration of daytime. Among all the other factors, it is the only entirely constant environmental factor [22].

The fluctuations of the sexual cycle in purebred Arabian horse farming investigated in mares with multiple oestrus in the breeding season are the following (Table 1): the longest average sexual cycle was shown by mares from the Michałów Stud Farm, and it amounted to 27.20 days, the extreme values being: 9 days minimum, 112 days maximum, and the shortest average sexual cycle was shown by mares from the Białka Horse Farm (Fig. 1) and the value amounted to 22.87 days with fluctuation from 16 to 52 days. The differences among the farms in the length of the average sexual cycle, periods of anoestrus, and the length of oestrus are significant or highly significant, the reason for which can be attributed to the difference in the farms' environmental conditions.

From the population of mares with multiple oestrus in one breeding cycle 16 female sublineages were chosen with 5 to 15 individual horses, on average with 9.2, and 9 paternal groups with 5 to 22 horses, with 11 mares on average.

In female sublineages the highest values of the sexual cycle and periods of anoestrus were shown by mares from Manilia and Piewica sublineage, where the values were 33.80 and 27.93 and 30.11 and 26.06 days respectively. The lowest values of both features were shown by Ela sublineage mares, where the average length of oestral cycle was 23.42 and the anoestrus 17.30 days and for Forta, where the average length of oestral cycle was 24.39, and the anoestrus of 19.23 days (Table 2). Fig. 2 presents the values of average sexual cycles, anoestrus and oestrus in the female lineages.

Upon investigation of the oestral cycle in paternal groups (Fig. 3), we concluded that the highest average sexual cycle was shown by the mares from the group of El Paso stallion (bay) 1967 (Czort – Ellora), the value being 30.06 days, and the lowest values were shown by the mares from the group of Banat stallion (bay) 1967 (El Azrak – Bandola), where the value amounted to 23.08 days (Table 3).

We investigated the significance of differences of average sexual cycles in both male and female sublineages, on the basis of which we can notice a greater variation and dispersion of that feature for female lineages,  where there are significant and highly significant differences. However, we can also observe differences significant for extreme groups in males (Tables 2 and 3).

We used the coefficient of success (Wp) as an indicator of the use value of purebred Arabian horses  [3,4,5], and the rate was used to evaluate correlations of that feature to other features characteristic for the population of this particular breed of horses. In this case, they included average lengths of the sexual cycle and periods of anoestrus for a group of mares with a multiple oestrus in one breeding season divided into groups according to the values of the coefficient of success (Table 4). We observed significant and highly significant differences in the feature of the length of the sexual cycle for both the mares participating in races in the Polish National Horse Races and those that did not participate in such races. Within the racing group, we noticed an interesting dependency, where starting with the values of Wp = 0.00 and continuing in the third group, the average length of the complete cycle increases, and it decreases for mares with the coefficient of success equal to 3 and above, as shown by Fig. 4.

We conducted calculations of the correlation index between the features of the length of the sexual cycle and the coefficient of success, as well as the periods of anoestrus and the coefficient of success for 147 mares participating in the Polish National Horse Races that were characterized by the multiple oestrus cycle within one breeding season. The correlation amounted to –0.06 and –0.05 and was significant.

It is commonly believed by farmers of other horse breeds that an intensive racing use of horses has an adversary effect on the breeding value of mares [7]. Earlier research conducted [6,8] as well as recent breeding methods prove that in reference to purebred Arabian horses the practices traditionally used by Bedouins still hold true, that is their emphasis on the breeding mare's racing performance and endurance, which are subsequently passed on to the progeny, and related to the mare's suitability as mother. As to disambiguate the problem, we attempted an investigation into the correlations between racing performance and the features of breeding activity. We divided the populations of mares according to the values of success rate, and among those groups we calculated the average lengths of gestation (Table 5). The differences among them are small and insignificant, therefore we cannot attribute any conditioning between the length of gestation and racing performance. As the coefficient of success increases, we notice a slight decrease of the average length of gestation in the first three groups (from 331.43 to 331.31 days), whereas in the group of mares characterized by a good and very good racing performance, the average length of gestation significantly increases to the value of 332.19 days (Fig. 5).

Table 6 presents the most important correlations among the investigated features, from which we can conclude that the correlation of the length of the complete sexual cycle, oestrus and anoestrus and the racing performance of investigated mares and their progeny is low or negative.

CONCLUSIONS

1. Among the populations of purebred Arabian horses present in Poland we can distinguish genetic lineages characterized by highly significant differences in the length of oestrus.

2. We noticed characteristic variations in the average length of oestral cycles, the oestrus itself, and anoestrus in particular ranges of the coefficient of success.

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Accepted for print: 26.09.2008

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