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Serum Concentrations of IGF-I in Postpartum Beef Cows^1,2,

University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Abstract

Four experiments assessed changes in serum IGF-I under various physiologic conditions in postpartum cows. In Exp. 1, anestrous suckled cows (n = 25) were infused for 6 d with either saline or glucose at two different infusion rates. In Exp. 2, anestrous cows (n = 29) received either a saline (weaned and suckled controls) or 3 g/d phlorizin (weaned phlorizin) infusion for 3 d. Calves from the weaned groups were removed from 15 h before and throughout infusions. In Exp. 3, cycling suckled cows (n = 20) received prostaglandin F₂ (PGF₂) when the 5-d saline or phlorizin infusion began. In Exp. 4, suckled cows (n = 20) had ad libitum access to feed or received 50% of control feed consumption from 30 to 40 d postpartum. Increasing glucose availability (Exp. 1) increased (P < .05) serum IGF-I by 30 to 35%. IGF-I remained stable after weaning (Exp. 2) in phlorizin-infused cows (128.8 ± 12.7 ng/ml), but increased (P < .05) by 3 d after calf removal in weaned control cows (152.2 ± 7.5 ng/ml). IGF-I also remained stable in phlorizin-infused cows following PGF₂ injection (Exp. 3), but increased in control cows by 2 d after PGF₂ (156.8 ± 18.3 on d 2 vs 133.7 ± 9.8 ng/ml pre-injection; P < .05) and remained elevated (P < .05) during the periovulatory period. In cows receiving restricted feed intake (Exp. 4), IGF-I decreased by approximately 50% within 4 d of feed restriction (71.3 ± 9.4 vs 137.4 ± 16.6 ng/ml; P < .05). Serum concentrations of IGF-I were related positively to energy availability in postpartum beef cows. Changes in IGF-I were coincident with changes in reproductive endocrine function.

¹ This work was funded by Alberta Agriculture, Farming For The Future.

² The authors gratefully acknowledge the technical assistance of Anita Unruh.

³ Address reprint request to this author. Current address: Alberta Agriculture, Beef Cattle & Sheep Branch, #204, 7000 - 113 Street, Edmonton, Alberta, Canada, T6H 5T6.

⁴ Dept. Vet. Physiol. Sci., Univ. of Saskatchewan.

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