True or false: Mares purchased in foal are more likely to have fillies?

Cover image courtesy of Widden

As breeding stock sales approach, we investigated the sex ratio of foals born from mares sold in-utero at prominent sales. The findings may defy common expectations.

Analysing data from the Inglis Chairman’s Sale, Inglis Broodmare Sale, and Magic Millions National Broodmare Sale over the past three years (2021 to 2023), we observed an even distribution of colts and fillies born to mares purchased in foal.

Out of 2274 mares studied, 12 per cent did not return a stud record for various reasons such as miscarriage, foal mortality, or the mare being exported.

Of the nearly 2000 mares that foaled post-sale, the sex distribution was almost perfectly balanced: 49.5 per cent fillies and 50.5 per cent colts.

Table: Sex distribution of foals born from mares sold in-utero

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