Theriogenology2020; 157; 18-23; doi: 10.1016/j.theriogenology.2020.07.017

A retrospective study on semen quality parameters from four different Dutch horse breeds with different levels of inbreeding.

Dini, P
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Bartels, T
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Revah, I
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Claes, AN
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Stout, TAE
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Daels, P

Abstract: A high degree of inbreeding has been reported to negatively impact semen quality in Friesian horses and Shetland ponies. Both breeds are characterized by a closed studbook, small population size, and high incidence of inbreeding. The Dutch Warmblood studbook (KWPN: Koninklijk Warmblood Paardenstamboek Nederland) is a much larger studbook with two distinct populations: the KWPN-Riding horses, managed as an 'open' studbook, and the KWPN-Harness horses, representing a much smaller subpopulation within the KWPN breed and managed as an 'almost closed' studbook. It was recently reported that the degree of inbreeding in KWPN-Harness horses has increased in recent decades due to the small gene pool; however, the degree of inbreeding is still lower than that of Friesian horses and Shetland ponies. We hypothesized that a high or rising degree of inbreeding might negatively impact semen quality. In the present study, we retrospectively compared semen quality parameters of stallions from four different breeds or types (Friesian Horses, Shetland Ponies, KWPN-Riding horses, and KWPN-Harness horses), each reported with different degrees of inbreeding. Semen concentration, and percentages of motile, morphologically normal and live spermatozoa, and the total number of morphologically normal, progressive motile spermatozoa per ejaculate (TNM) were analyzed for 2832 semen evaluations performed over a 15-year period. KWPN-Harness horses had a significantly lower sperm concentration, % motile spermatozoa and % live spermatozoa than KWPN-Riding horses but the % motile and % morphologically normal spermatozoa and TNM in both KWPN-Harness and KWPN-Riding horses were significantly higher than in Friesian horses and Shetland ponies. These results suggest a lower semen quality in KWPN-Harness than KWPN-Riding horses, potentially as a result of a higher coefficient of inbreeding. The negative trend observed in the KWPN-Harness horses may be a warning sign, and breeders or stud books should monitor the degree of inbreeding carefully to avoid a further reduction in semen quality, to the levels observed in Friesian horses and Shetland ponies.

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Publication Date: 2020-07-21 PubMed ID: 32768723DOI: 10.1016/j.theriogenology.2020.07.017Google Scholar: Lookup

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The research investigates the effect of high inbreeding levels on semen quality in different Dutch horse breeds. Existing evidence suggests a significant negative impact on semen quality in Friesian horses and Shetland ponies due to inbreeding, and this study extends the research to the Dutch Warmblood horse breed.

Study Background and Hypothesis

The Dutch Warmblood horse breed comprises two primary populations: the KWPN-Riding horses, which constitute an open studbook or breeding register, and the KWPN-Harness horses, an almost closed studbook due to their smaller gene pool.
The research’s hypothesis is based on previous studies indicating a negative impact of inbreeding on semen quality, suggesting that the increased inbreeding levels observed in the KWPN-Harness horses might adversely affect their semen quality.

Research Methodology

The study was retrospective, indicating that it used existing data rather than collecting new data through experimentation or surveys.
It compared semen quality parameters across four different horse breeds (Friesian Horses, Shetland Ponies, KWPN-Riding horses, and KWPN-Harness horses), each with different inbreeding levels.
Several parameters were examined in the analysis, including semen concentration, percentages of motile (capable of movement) sperm cells, and morphologically normal sperm cells (cells with normal shapes and sizes). It also included the total number of morphologically normal, progressively motile sperm cells per ejaculation (TNM) over a 15-year period, with 2832 semen evaluations used in the study.

Key Findings

The study found that KWPN-Harness horses had significantly lower sperm concentration, motility, and viability than KWPN-Riding horses.
However, both KWPN subpopulations showed higher percentages of motile and morphologically normal spermatozoa, as well as a higher TNM, than the Friesian horses and Shetland ponies.
Results suggest that the lower semen quality in KWPN-Harness horses could be a result of higher inbreeding levels.

Implications and Recommendations

The study identified a potential early-warning sign for breeders, suggesting that increased inbreeding levels could potentially reduce semen quality.
Breeders and studbooks were encouraged to carefully monitor inbreeding levels to avoid further degradation of semen quality, as observed in the Friesian and Shetland pony breeds.

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APA

Dini P, Bartels T, Revah I, Claes AN, Stout TAE, Daels P. (2020). A retrospective study on semen quality parameters from four different Dutch horse breeds with different levels of inbreeding. Theriogenology, 157, 18-23. https://doi.org/10.1016/j.theriogenology.2020.07.017