HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Interpretive Summary Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Obese, F. Y. Articles by Anderson, G. A. Search for Related Content PubMed PubMed Citation Articles by Obese, F. Y. Articles by Anderson, G. A.

Variation in Plasma Concentrations of Insulin-Like Growth Factor-I in Pasture-Fed Holstein Cows

F. Y. Obese^*, A. R. Rabiee, K. L. Macmillan^,1, A. R. Egan^*, S. Humphrys and G. A. Anderson

^* School of Agriculture and Food Systems, the University of Melbourne, Victoria 3031, Australia
School of Veterinary Science, the University of Melbourne, Werribee, Victoria 3030, Australia
Primegro Pty. Ltd., Thebarton, SA 5001, Australia

¹ Corresponding author: k.macmillan{at}unimelb.edu.au

The objective of this 5-wk study was to determine dietary effects on plasma concentrations of insulin-like growth factor-I (IGF-I), as well as milk production and milk components in pasture-fed dairy cows. Thirty-two Holstein cows 4 to 5 wk postpartum were randomly assigned to 4 dietary subgroups. Feed was provided twice daily ad libitum at 0900 and 1600 h composed of fresh-cut pasture, meadow hay, and pelleted cereal grain to achieve differing levels of DMI and ME density (LL: 16.6 kg of DMI and 174 MJ of ME; HL: 17.3 kg of DMI and 181.1 MJ of ME; LH: 15.4 kg of DMI and 183.1 MJ of ME; HH: 17.9 kg of DMI and 213.3 MJ of ME, with the first letter indicating DMI and the second ME, and with H indicating high and L indicating low, respectively). The first day cows were placed on their diets was designated d 0. Concentrations of IGF-I were measured in frozen-thawed samples of plasma using a verified ELISA. Dietary treatment had affected plasma concentrations of IGF-I by d 7 with cows on high ME diets having greater IGF-I concentrations at d 14 (83.7 vs. 45.6 ng/mL) than cows on the low ME diets. The level of DMI had less effect on plasma concentrations of IGF-I at d 14 (72.2 vs. 57.1 ng/mL). Dietary treatment effects on these concentrations had stabilized by d 21. Day-to-day variation in mean plasma concentrations of IGF-I within each dietary treatment was low during an intensive period of daily sampling for 14 d (from d 22 to 35). Within-cow day-to-day variation was also low compared with that among cows within the same dietary group and was associated with a high repeatability in the day-to-day concentration of IGF-I in individual cows. Intraclass correlation coefficients for IGF-I ranged from 0.56 (± 0.14) to 0.88 (± 0.06) with a combined (pooled) value for the 4 subgroups of 0.77 (± 0.05). The ME and DMI effects (H vs. L) at d 35 were 79.3 vs. 41.4 and 62.0 vs. 55.7 ng/mL, respectively. Although the ME and DMI differences also affected milk yield and compositional parameters, the effects were not as proportionately great as those measured for IGF-I. Altering the ME or DMI components of the pasture-based diets produced changes in plasma IGF-I concentrations that did not become stabilized for 3 wk, but were then highly repeatable for individual cows within each dietary group. Both observations have relevance to interpreting data related to plasma concentrations of IGF-I in lactating Holstein cows.

Key Words: insulin-like growth factor-I • day-to-day variation • pasture-fed • dairy cow