Insulin-like growth factor I in growing thoroughbreds.
Authors: Staniar W B, Kronfeld D S, Akers R M, Harris P A
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary: Insulin-like Growth Factor I in Growing Thoroughbreds Staniar and colleagues conducted a 16-month longitudinal investigation into how dietary energy source influences plasma insulin-like growth factor I (IGF-I) concentrations and growth rates in pasture-raised thoroughbred foals, recognising that IGF-I is a key endocrine regulator of skeletal development during the critical growth phase. Monthly measurements of plasma IGF-I and average daily gain (ADG) were collected from foals fed either starch and sugar-rich or fat and fibre-rich concentrates, alongside environmental variables including day length and ambient temperature. The researchers found a moderate positive correlation between circulating IGF-I and ADG (r = 0.32, p < 0.001), with both parameters exhibiting pronounced seasonal variation—peaking in May–June and nadir values in March—patterns that closely tracked day length and temperature fluctuations. Whilst the fat and fibre diet did not consistently elevate IGF-I levels, starch and sugar supplementation did produce significantly higher IGF-I during the rapid spring growth phase of year two, suggesting that dietary energy source exerts a time-dependent effect on growth endocrinology. These findings have considerable practical significance for practitioners designing nutrition and management protocols for young stock, as they indicate that seasonal modulation of energy provision may optimise the metabolic milieu supporting skeletal maturation and reduce developmental orthopaedic disease risk.
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Practical Takeaways
- •Monitor growth velocity and seasonal patterns when designing feeding programmes for young thoroughbreds, as IGF-I and growth are influenced by both diet and natural seasonal cycles
- •During rapid spring growth phases, energy-dense feeds (high sugar/starch) may better support skeletal development through IGF-I pathways than fibre-based alternatives
- •Account for seasonal and environmental variations when evaluating foal growth and considering interventions to manage skeletal development and prevent orthopaedic problems
Key Findings
- •Plasma IGF-I concentration was positively associated with average daily gain (ADG) in growing thoroughbreds (r = 0.32, p < 0.001)
- •Both ADG and plasma IGF-I showed clear seasonal patterns with peaks in May-June and troughs in March, correlating with day length and ambient temperature
- •Sugar and starch-rich feed showed higher plasma IGF-I compared to fat and fibre-rich feed during rapid spring growth phase (p < 0.10), but no significant difference at other times
- •Environmental factors (season, temperature, day length) and dietary energy source influence the relationship between IGF-I and growth rate in young thoroughbreds