Cymbaluk N F, Laarveld B
Department of Animal and Poultry Science, University of Saskatchewan Saskatoon, Canada.
Domest Anim Endocrinol. 1996 May;13(3):197-209. doi: 10.1016/0739-7240(96)00014-8.
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.
在马驹血清胰岛素样生长因子-I（IGF-I）浓度的个体发育过程中，研究了母马胎次、断奶年龄和断奶前饮食的影响。对13匹初产和19匹经产杂交母马所生的马驹在出生时称重并采血。每组约一半的马驹早期断奶（约13周龄）；其余马驹晚期断奶（约16周龄）。经产母马所生马驹（386 ng/ml）出生至17周龄期间血清IGF-I浓度的合并值高于初产母马所生马驹（237.5 ng/ml）（P < 0.065）。无论母马胎次如何，公驹（378 ng/ml）的血清IGF-I浓度均高于母驹（254.5 ng/ml）（P < 0.05）。公驹（173.5 kg）也倾向于比母驹（159.2 kg）更重（P = 0.12）。在13周龄或16周龄断奶均降低了（P < 0.05）生长速率和血清IGF-I浓度。断奶后1 - 3周内，血清IGF-I值恢复到断奶前水平，并伴随着体重增加改善。在第二项研究中，15匹1日龄马驹用代乳品喂养7周，并与5匹由母马哺乳8周的马驹进行比较。在最初2周内，用代乳品喂养的马驹（0.46 kg/d）增重不如由母马哺乳的马驹快（P < 0.03）（1.73 kg/d）。用代乳品喂养的马驹的相关血清IGF-I值（139.4 ng/ml）低于由母马哺乳的马驹（317.4 ng/ml）（P < 0.0001）。尽管两组此后的增重相似，但在8周龄（断奶时）和18周龄时，用代乳品喂养的马驹的血清IGF-I浓度分别仅为由母马哺乳的马驹的36%和60%。尽管马驹的饮食管理和体重相似，但由母马哺乳和用代乳品喂养的马驹血清IGF-I浓度的内在差异一直持续到1岁。1岁时，由母马哺乳的马驹的血清IGF-I浓度（1203 ng/ml）比用代乳品喂养的马驹（815 ng/ml）高48%。这些数据表明，母马胎次、马驹性别和断奶前营养会影响马驹血清IGF-I浓度的个体发育。生长动物早期营养管理所造成的血清IGF-I值的长期、持续差异对所有物种纵向血清IGF-I研究的解释具有重要意义。
