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

Six pairs of full-sibling Quarter Horse foals were produced by non-surgical embryo transfer and immediate rebreeding of donor mares. Each pair of donor/recipient mares consisted of one multiparous (donor) and one nulliparous (recipient) mare of similar body type and size. Milk yield was determined within 2 d of 8, 15, 22, 29 d (early lactation); 45, 60 d (midlactation); and 90, 120 d (late lactation) postpartum by the weigh-suckle-weigh method. On the following day, milk samples were collected, and foals were weighed and measured for wither height, heart girth, metacarpal length, metatarsal length, carpus height, tarsus height, and hip height. Mean gestation length was longer (P < .05) in nulliparous mares than multiparous mares (343 vs 333 d). Daily milk production was greater (P < .05) during early lactation (12.1 vs 10.8 kg) and tended to be greater (P = .08) during midlactation (11.7 vs 10.4) in multiparous mares but was similar between groups in late lactation. Milk composition was similar between groups throughout lactation. Foals produced by multiparous mares weighed more (P < .03) throughout early lactation (70.4 vs 63.1 kg), but no differences in weights occurred between foals from multiparous and nulliparous mares through mid- and late lactation. Average daily weight gain (ADG) was similar between foal groups through early and midlactation. During late lactation, ADG tended to be greater (P = .07) in foals from nulliparous mares (1.05 vs .92 kg/d). These data suggest that nulliparous and multiparous mares of the same breed and similar body type and size produce foals with no differences in size and weight by 4 mo of age.