Effects of season on placental, foetal and neonatal development in horses

Seasonal changes in metabolic rate have been shown in horses and we hypothesized that this leads to the birth of smaller foals early in the year. Mares and their foals were assigned to three groups by day of foaling within the year (e.g. 1 January = day 1): Group 1 (n = 10) day 40–65, group 2 (n = 8) day 67–92, group 3 (n = 9) day 94–121. Groups did not differ with regard to parity. In foals, height at withers and body weight were determined on days 1–5 and weekly until 12 weeks of age. Chest circumference, distances fetlock to carpus, carpus to elbow, poll to nose and crown-rump length were determined on day 5 and weekly until 12 weeks of age. Placental weight (p