21. Plasma concentrations of insulin-like growth factor-I (IGF-I) and resumption of cyclicity in pasture-fed dairy cows

Abstract

Low plasma concentrations of IGF-I in early lactation have been associated with extended periods of calving to first ovulation in dairy cows (1). The objectives of this study were to compare plasma concentrations of IGF-I in cycling and anoestrous Holstein-Friesian (HF) cows and to establish any relationship between these concentrations and intervals from calving to first ovulation. Experiments 1 and 2 were conducted in 2001 and 2002. Before the AI program commenced in 2001, 23 of the 72 cows had >1 oestrous cycle, 26 had only 1 cycle, 10 cows ovulated but did not display signs of oestrus and 13 cows remained anovulatory. Year 2 included 30 cows from Year 1 that cycled early (12), late (12) or very late (6). Plasma concentrations of IGF-I were measured at calving, and at 1, 5 and 10 weeks into lactation with an ELISA. Experiment 3 involved 40 cycling and 30 anoestrus HF cows. Plasma concentrations of IGF-I were measured on Days 0 (day of insemination), 6, 12 and 18. In Experiment 1, cycling cows had higher (P<0.01). mean plasma concentrations of IGF-I than anoestrous cows; concentrations ranged from 48.8 ± 5.9 to 68.5 ± 4.4ng/mL for the anoestrous and cycling cows respectively. Cows that were anovulatory had a longer interval from calving to first ovulation than the other three groups (76.5 ± 2.5 v. 39.9 ± 2.9 days, P<0.001). Early cycling cows in Experiment 2, had higher plasma concentrations of IGF-I compared to the very late cycling cows (96.5 ± 10.9 v. 51.4 ± 15.4 ng/mL, P<0.05). In Experiment 3, plasma concentrations of IGF-I in cycling cows were higher compared to anoestrous cows (76.50 ± 3.85 v. 60.30 ± 4.4ng/mL, P<0.01). Cows with low IGF-I concentrations in early lactation are at greater risk of experiencing extended intervals from calving to first ovulation and of not showing signs of oestrus at that ovulation.