Maternal influences on growth and development of full-sibling foals.

This study used six pairs of full-sibling Quarter Horse foals, created through embryo transfers and immediate re-breeding, to analyze the influence of maternal factors (primarily the difference in parous status) on growth and development. It revealed that full-sibling foals produced by multiparous and nulliparous mares, which are of a similar body type and size, exhibited no noticeable differences in growth by the time they are 4 months old.

Methodology and Parameters Investigated

• The research team created pairs of full-sibling Quarter Horse foals by performing non-surgical embryo transfer and immediate rebreeding of donor mares.
• In each pair, the donor/recipient mares included one multiparous mare (who has given birth more than once) and one nulliparous mare (who has never given birth).
• The mares chosen for the study had similar body types and sizes. This controlled the variable of physical size and type.
• The team gathered data on milk yield shortly after specific time points in early, mid, and late lactation stages postpartum, using the weigh-suckle-weigh method.
• After collecting milk samples, the researchers also weighed and measured the foals following day, recording data for wither height, heart girth, metacarpal length, metatarsal length, carpus height, tarsus height, and hip height.

Key Findings of the Study

• Nulliparous mares had a longer average gestation period than multiparous mares (343 days vs. 333 days).
• During early lactation, daily milk production was higher in multiparous mares compared to nulliparous ones, and it tended to be higher during mid-lactation. However, by late lactation, the milk production of the two groups was similar.
• Milk composition remained consistent between the two groups throughout lactation.
• During early lactation, foals produced by multiparous mares were heavier than those from nulliparous mares. But there were no significant weight differences between foals from multiparous and nulliparous mares in mid- and late-lactation stages.
• The Average Daily Weight Gain (ADG) was comparable between the two foal groups during early and mid-lactation, but ADG slightly increased for foals from nulliparous mares in late lactation.
• The study concludes that by age four months, there were no significant differences in the size and weight of foals produced by nulliparous and multiparous mares of the same breed and similar body type and size.
• This suggests that the parous status of the mare may not significantly affect the growth of the foal by the time they reach four months old.