Gestation length variation in domesticated horses and its relation to breed and body size diversity

Abstract

The domestication process and selective breeding reportedly alter some life history variables. In horses, it has been claimed that gestation length is particularly variable. Some of the factors influencing gestation length are already known and can be grouped into environmental and genetic factors, but the effects of breed and body size have rarely been evaluated. In this study we tested the influence of breed and body size on gestation length for 25 horse breeds from Central Europe. The mean gestation length for all breeds was 342.3 ± 10.2 days and we found significant differences among breeds with a variation of up to 11 days. Body size did not show a significant correlation with gestation length. Our data suggest that breed affiliation explains part of the large variability of gestation length in horses.

Bone histology provides insights into the life history mechanisms underlying dwarfing in hipparionins

“…Despite the size disparity, different-sized horse breeds have comparable growth patterns 75 . Gestation lengths also show little variation between breeds 76 , and the time of growth plates closure is similar between small and large horses 77 . Considering this, the size difference in domestic horses is not caused by variations in the duration of growth, but by the higher or lower prenatal 76 and postnatal 77 growth rates.…”

“…Gestation lengths also show little variation between breeds 76 , and the time of growth plates closure is similar between small and large horses 77 . Considering this, the size difference in domestic horses is not caused by variations in the duration of growth, but by the higher or lower prenatal 76 and postnatal 77 growth rates. Accordingly, we identified a trend indicating higher growth rates in femora of larger extant equids compared to smaller representatives of Equus .…”

Geographical Origin, Delayed Implantation, and Induced Ovulation Explain Reproductive Seasonality in the Carnivora

“…Mammalian gestation periods show a large degree of variation, even within precocial or altricial species (Clauss et al, 2014). Similar-sized species of similar ecology can vary enormously in their gestation period, such as between hyraxes (e.g., Procavia capensis , 230 days) (Millar, 1971) and hares (e.g., Lepus europaeus , 42 days) (Roellig et al, 2010) or between cattle (280 days), horses (330 days), dromedary camels ( Camelus dromedarius , 390 days), and okapis ( Okapia johnstoni , 450 days) (Clauss et al, 2014), or within domestic species among breeds (Heck et al, 2017, 2018). Within a lineage, a reduction in body size typically does not lead to a proportional reduction in gestation length (e.g., Müller et al, 2011), so that particularly long gestation periods for a given body size have been interpreted as indication for secondary dwarfing (Geist, 1966).…”

Seasonality of reproduction in Asian elephants Elephas maximus and African elephants Loxodonta africana: underlying photoperiodic cueing?

“…), and horses (Heck et al. ) and camelids (Chen et al. ) are long‐day breeders with gestation lengths of around one year.…”

“…Assuming a targeted birthing season in spring (when days are getting longer, dashed rectangle), seasonal breeders with very short gestation lengths such as hamsters Cricetus spp. are long-day breeders with parturition in the same season (Pévet 1988), seasonal ruminants are short-day breeders with rutting in autumn and gestation lengths of less than one year (Zerbe et al 2012), and horses (Heck et al 2017) and camelids (Chen et al 1985) are long-day breeders with gestation lengths of around one year. Assuming an adaptation to seasonality in elephants, they would be expected to be long-day breeders based on their long gestation length.…”