Oral Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

The effect of paternal age on progeny performance in Australian Thoroughbred horses. (#72)

Ceilidh Jenkins 1 2 , Róisín Griffin 1 , Aleona Swegen 1 , Natasha Hamilton 2 , Rose Upton 3 , Zamira Gibb 1
  1. HMRI Infertility and Reproduction Research Program, The University of Newcastle, Newcastle, NSW, Australia
  2. Equine Genetics Research Centre, Racing Australia, Scone, NSW, Australia
  3. Conservation Biology Research Group, The University of Newcastle, Newcastle, NSW, Australia

In human and rodent species, significant research has demonstrated that older fathers have poorer reproductive outcomes. Recent research in northern hemisphere Thoroughbred horses has uncovered that increasing sire age is associated with declining racing speed and performance in offspring. However, differences in breeding objectives and the geographical isolation of Australia has led to the production of Thoroughbreds from a distinct gene pool. The aim of this study is to investigate the effect of sire age on progeny racing performance in the Australian population.

Data on 35 stallions was collated from Arion NZ and restricted to only include retired stallions who actively bred ≥16 years old. Offspring (n=33,538) were assessed for racing performance. Dam age at conception and stallion fertility (seasonal pregnancy rate) were also recorded. Progeny were grouped by sire age conception: ≤8 years;9-13 years;14-18 years; and ≥19 years of age. Data were checked for normality and statistically analysed using appropriate tests in JMP (version 17.2.0).

Assessment of intra-stallion offspring performance revealed that the progeny produced earlier in their breeding careers had a greater likelihood of participating in any race (80.0 ±1.67% ≤8 years vs 62.0±1.90%≥19 years;P≤0.0001); placing in a stakes race (9.8±1.03%≤8 years vs 1.5±1.15%≥19 years;P≤0.0001); winning a stakes race (5.7±0.53%≤8 years vs 0.8±0.59%≥19 years;P≤0.0001).

Moreover, there was an age-associated decline in stallion fertility, with fertility rates at ≥19 years significantly lower than all other age groups (69±1.81%≥19 years vs 87.8±1.62%≤8 years,86.3±1.62% 9-13 years,82.8±1.62% 14-18 years;P≤0.0001).

Our data confirms that the performance of Australian Thoroughbreds significantly declines as sire age increases. It is vital that future investigations are conducted into the effect of ageing on sperm DNA damage in stallions, including identifying regions of the genome that are vulnerable to this damage. This will allow insight into how ageing contributes to decreased offspring performance.