Domestic animal endocrinology1996; 13(3); 197-209; doi: 10.1016/0739-7240(96)00014-8

The ontogeny of serum insulin-like growth factor-I concentration in foals: effects of dam parity, diet, and age at weaning.

Cymbaluk, NF
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Laarveld, B

Abstract: The effects of dam parity, age at weaning, and preweaning diet were examined in the ontogeny of serum insulin-like growth factor-I (IGF-I) concentrations in foals. Foals born to 13 primiparous and 19 multiparous draft-cross mares were weighed and bled near birth. About one-half of the foals in each group were weaned early (about 13 wk old); the remaining foals were weaned late (about 16 wk of age). Pooled values for serum IGF-I concentrations between birth and 17 wk of age were higher (P < 0.065) for foals born to multiparous (386 ng/ml) than to primiparous mares (237.5 ng/ml). Colts (378 ng/ml) had higher (P < 0.05) serum IGF-I concentrations than fillies (254.5 ng/ml), regardless of dam parity. Colts (173.5 kg) also tended (P = 0.12) to be heavier than fillies (159.2 kg). Weaning, whether at 13 or 16 wk of age, reduced (P < 0.05) growth rates and serum IGF-I concentrations. Serum IGF-I values recovered to preweaning values within 1-3 wk postweaning concurrent to an improved weight gain. Fifteen 1-d-old foals in a second study were fed milk replacer for 7 wk and were compared with five foals that nursed their mares for 8 wk. During the first 2 wk, replacer-fed foals (0.46 kg/d) did not gain as rapidly (P < 0.03) as mare-nursed foals (1.73 kg/d). The associated serum IGF-I values for replacer foals (139.4 ng/ml) were lower (P < 0.0001) than values for mare-nursed foals (317.4 ng/ml). Despite similarity in gains for both groups there-after, serum IGF-I concentrations of replacer-fed foals were only 36 and 60% of values obtained for mare-nursed foals at 8 (weaning) and 18 wk of age, respectively. The intrinsic differences between mare-nursed and milk-replacer foals in serum IGF-I concentrations persisted to 1 yr of age despite similarities in dietary management and body weight of the foals. At 1 yr of age, the serum IGF-I concentration of mare-nursed foals (1,203 ng/ml) was 48% higher than that of replacer-fed foals (815 ng/ml). These data indicate that dam parity, sex of foal, and preweaning nutrition affect the ontogeny of serum IGF-I concentration in the foal. The chronic, persistent difference in serum IGF-I values created by the early nutritional management of growing animals has implications in the interpretation of longitudinal serum IGF-I studies in all species.

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Publication Date: 1996-05-01 PubMed ID: 8738861DOI: 10.1016/0739-7240(96)00014-8Google Scholar: Lookup

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Summary

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This study investigated how the maternal parity, age of weaning, and diet prior to weaning impacts the development of serum insulin-like growth factor-I (IGF-I) levels in foals. The results suggest that these factors do affect IGF-I levels, with foals nursed by their mothers exhibiting higher concentrations of serum IGF-I than those fed with a milk replacer.

Methodology and Participants

The study’s participants were 32 foals, born from either 13 first-time mothers (primiparous) or 19 experienced mothers (multiparous).
Approximately half of the foals from each group were weaned at 13 weeks, while the other half were weaned later, at around 16 weeks of age.
A second study focused on 15 one-day-old foals which were fed milk replacer for seven weeks and another group of five foals that were nursed by their dams for eight weeks. The two groups of foals were also compared.

Findings

Over the course of the first 17 weeks, foals born to experienced mothers showed higher levels of IGF-I than those born to first-time mothers.
Male foals demonstrated higher serum IGF-I concentrations compared to female foals, irrespective of the mother’s parity.
Weaning, whether at 13 or 16 weeks of age, led to drops in both growth rates and serum IGF-I concentrations.
After weaning, serum IGF-I levels recovered to pre-weaning levels within 1-3 weeks, coinciding with an improved weight gain.
Foals who were fed milk replacer did not gain weight as rapidly as mare-nursed foals in the first two weeks. Their IGF-I levels were also lower. Despite similar weight gain between the two groups afterwards, replacer-fed foals’ serum IGF-I concentrations remained lower.
This difference in serum IGF-I levels between mare-nursed and replacer-fed foals persisted until the foals reached one year old.

Implications

The study demonstrates that factors such as dam parity, sex of the foals, and pre-weaning nutrition contribute to serum IGF-I concentration development in foals.
The persistent difference in serum IGF-I levels caused by early nutritional management of growing animals has implications for interpreting longitudinal serum IGF-I studies across all species.

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APA

Cymbaluk NF, Laarveld B. (1996). The ontogeny of serum insulin-like growth factor-I concentration in foals: effects of dam parity, diet, and age at weaning. Domest Anim Endocrinol, 13(3), 197-209. https://doi.org/10.1016/0739-7240(96)00014-8