Age, body weight, and pregnancy loss

Retrospective analysis of 3000 mare-years in which standardbred mares were examined with ultrasound and weighed three times a week whilst in oestrus until after ovulation and again on Days 14-18, 28-31, and 40-45 of pregnancy. Mares were aged 3 years to 24 years and weighed from 364 kg to 646 kg at first examination, reaching a constant mean weight of about 500 kg by the age of 8 years. Embryo loss was not related to age until over 18 years. Maiden mares gained most weight during the observation period. Mares that failed to conceive lost 3 kg. Barren and lactating mares that remained pregnant until 40-45 days gained 23 kg and 18 kg, respectively. Barren and lactating mares that lost the pregnancy lost 3 kg and 14 kg, respectively. Pregnancy loss was highest in lactating mares, particularly after foal heat conception, twice that of barren mares and 15% higher than in maiden mares. © 2005 Elsevier Inc. All rights reserved.