Abnormal reproductive patterns in Przewalski's mares are associated with a loss in gene diversity

The effects of inbreeding on covering success, gestation length and foal sex ratio in Australian thoroughbred horses

Background

Horses produce only one foal from an eleven-month gestation period, making the maintenance of high reproductive rates essential. Genetic bottlenecks and inbreeding can increase the frequency of deleterious variants, resulting in reduced reproductive levels in a population. In this study we examined the influence of inbreeding levels on foaling rate, gestation length and secondary sex ratio in Australian Thoroughbred mares. We also investigated the genetic change in these traits throughout the history of the breed. Phenotypic data were obtained from 27,262 breeding records of Thoroughbred mares provided by three Australian stud farms. Inbreeding was estimated using the pedigree of each individual dating back to the foundation of the breed in the eighteenth century.

Results

While both gestation length and foaling rate were heritable, no measurable effect of inbreeding on either trait was found. However, we did find that the genetic value for both traits had decreased within recent generations. A number of environmental factors also had significant effects on foaling rate and gestation length. Secondary sex ratio had only an extremely small paternal heritable effect and was not susceptible to environmental influences.

Conclusions

In contrast to racing performance, inbreeding had no measurable effect on foaling rate or gestation length in Australian Thoroughbred horses. This could be because the level of inbreeding in the population examined is not high enough to show a discernible effect on reproductive traits. Populations that experience higher levels of inbreeding due to use of artificial reproductive technologies or extremely small population sizes may show a more pronounced reduction in natural foaling rate or gestation length. It is also possible that the intensive management techniques used in the Thoroughbred population masks any negative effects of inbreeding. The decrease in the genetic value of foaling rate is likely to be because horses with unfavourable genetic potential have not yet been selected out of the population. The change in genetic value of gestation length may be due to selective breeding favouring horses with shorter pregnancies. We also found that prioritising the mating of older mares, and avoiding out of season mating could lead to an increased breeding success.

Saving wild ungulate diversity through enhanced management and sperm cryopreservation

Wild ungulates throughout the world face the impending risk of extinction. Small founding population size, lack of interest in exhibiting wild ungulates and declining space in zoos are not sustaining ex situ populations. Animals managed in ex situ collections continue to experience >20% neonate loss globally. To ensure population sustainability there is a critical need to: (1) manage ungulates in large herds, increasing mate choice and reproductive efficiency; (2) improve husbandry and genetic management; and (3) develop consistent assisted reproductive technologies, including sperm cryopreservation and AI. Recently, new models in the management of ungulates have begun to emerge. Animal managers and researchers are also beginning to exploit advances in genomics to improve genetic management of their collections. Furthermore, the past decade has witnessed significant advances particularly in semen collection and cryopreservation in numerous species. Advances in gonadal tissue cryopreservation now offer additional opportunities to preserve male genomes. The new knowledge generated is enabling the creation of genetic (sperm) banks to rescue and enhance reproductive management of wild ungulates. The present paper reviews the threats to ungulate populations, the status and relevance of animal management and biomaterial banking efforts to ensure long-term survival of these charismatic species.

A protocol to correct for intra- and interspecific variation in tail hair growth to align isotope signatures of segmentally cut tail hair to a common time line

RATIONALE

In recent years, segmental stable isotope analysis of hair has been a focus of research in animal dietary ecology and migration. To correctly assign tail hair segments to seasons or even Julian dates, information on tail hair growth rates is a key parameter, but is lacking for most species.

METHODS

We (a) reviewed the literature on tail hair growth rates in mammals; b) made own measurements of three captive equid species; (c) measured δ(2)H, δ(13)C and δ(15)N values in sequentially cut tail hairs of three sympatric, free-ranging equids from the Mongolian Gobi, using isotope ratio mass spectrometry (IRMS); and (d) collected environmental background data on seasonal variation by measuring δ(2)H values in precipitation by IRMS and by compiling pasture productivity measured by remote sensing via the normalized difference vegetation index (NDVI).

RESULTS

Tail hair growth rates showed significant inter- and intra-specific variation making temporal alignment problematic. In the Mongolian Gobi, high seasonal variation of δ(2)H values in precipitation results in winter lows and summer highs of δ(2)H values of available water sources. In water-dependent equids, this seasonality is reflected in the isotope signatures of sequentially cut tails hairs.

CONCLUSIONS

In regions which are subject to strong seasonal patterns we suggest identifying key isotopes which show strong seasonal variation in the environment and can be expected to be reflected in the animal tissue. The known interval between the maxima and minima of these isotope values can then be used to correctly temporally align the segmental stable isotope signature for each individual animal.

Characterization of the estrous cycle of Asinina de Miranda jennies (Equus asinus)

This study aims to characterize the estrous cycle of Asinina de Miranda jennies in the breeding season, on the basis of data collected from serial ultrasonographic examination and serum progesterone determinations in 14 females during a total of 33 cycles. The length of the interovulatory interval was 23.8 ± 0.55 days, the diestrus and estrus lasting 17.9 ± 0.46 days and 6.65 ± 0.30 days, respectively. Age and body condition score (BCS) affected the length of the interovulatory intervals; BCS also influenced the diestrus length and the time in heat after ovulation (P > 0.05). The incidence of single, double, and triple ovulations was 57.58%, 36.36%, and 6.06%, respectively. Multiple ovulations affected neither the length of the interovulatory interval nor the individual cycle stages (P > 0.05) but lengthened the interval from the beginning of estrus to the last ovulation (P = 0.01). When combined with age, higher BCS affected the ovulation rate (P = 0.001). Deviation of the dominant follicle occurred around Day 8.7 (Day 0 = ovulation) when both single and multiple ovulations were considered. The dominant follicle was larger at divergence in single ovulators (19.18 ± 0.97 mm) compared with that in multiple ovulators (18.05 ± 1.16 mm). The overall maximum follicular diameter before ovulation was smaller in multiple ovulatory cycles than that in single ovulatory cycles (37.2 ± 0.83 mm vs. 40.2 ± 1.41 mm, respectively; P = 0.03). The daily growth rate of dominant follicles was independent of the ovulation rate (P > 0.05) for the intervals before and after the estrus onset. The dominant follicle size and the follicle growth rates were independent of BCS (P > 0.05). Data collected in this study revealed resemblances between Mirandese and other Iberian and Brazilian breeds with regard to estrous cycle characteristics.