Reproductive efficiency of intensively managed Thoroughbred mares in Newmarket.
Authors: Morris L H A, Allen W R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Reproductive Efficiency in Thoroughbred Mares Morris and Allen's 2002 analysis of 1393 Thoroughbred mares across 22 Newmarket studfarms provides valuable longitudinal insight by directly comparing reproductive outcomes from the 1998 breeding season against equivalent data from 1983, revealing both progress and persistent challenges in mare fertility management. The researchers examined conception rates, pregnancy loss, and live foaling outcomes in relation to mare age and status, stallion factors, breeding timing, and therapeutic interventions, tracking pregnancies from initial conception through to term. Whilst the foaling rate improved substantially from 77% in 1983 to 82.7% in 1998—and initial conception at 15 days post-ovulation reached an impressive 94.8%—this apparent success masks significant pregnancy wastage: the per-cycle pregnancy rate of just 59.9% required mares to be mated an average of 1.88 times before establishing pregnancy, and 12.5% of pregnancies failed between the initial diagnosis and the October pregnancy test. For breeding operations and veterinary practitioners, these figures underscore that despite advances in studfarm management and diagnostic protocols over 15 years, pregnancy loss remains a major source of economic loss in Thoroughbred breeding, warranting continued investigation into the underlying causes of embryonic and early foetal mortality rather than assuming current management practices are optimised.
Read the full abstract on PubMed
Practical Takeaways
- •Nearly 1 in 5 mares fail to produce a live foal despite improvements over 15 years, representing significant economic loss—early pregnancy monitoring and intervention protocols are essential
- •Account for substantial pregnancy loss between day 15 and day 35; implement targeted uterine treatments and management strategies to reduce losses during this critical window
- •Mare age and status are critical factors affecting breeding success—adjust management protocols and breeding decisions based on individual mare characteristics and reproductive history
Key Findings
- •Per cycle pregnancy rate was 59.9% at 15 days post-ovulation, with 94.8% of mated mares pregnant at least once at this timepoint
- •Pregnancy rates declined from 94.8% at day 15 to 89.7% at day 35 and 87.5% at October pregnancy testing, indicating substantial early pregnancy loss
- •82.7% of mares surveyed gave birth to live foals at term, an improvement from 77% in 1983, but overall pregnancy failure rates remain high
- •Mare age and status significantly affected per cycle pregnancy rate and pregnancy loss incidence; mean matings per oestrus was 1.12