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.
On average, 25% of Holstein-Friesian (HF) cows in pasture-fed herds in Victoria experience extended periods of anovulatory anoestrus (AA) (1). Their conception rates to first insemination (1 st AI) are lower than those obtained in spontaneously ovulating (cycling; CYC) herdmates when AA cows have been treated with progesterone (P4) and oestradiol benzoate (ODB) to stimulate oestrus and induce ovulation (30% v. 45%; 1). The aim is to compare plasma P4 concentrations (PPC) and corpus luteum (CL) size in HF cows from 25 to 37 days after 1 st AI associated with a spontaneous ovulation or an induced ovulation involving treatment for AA, and were pregnant to that 1 st AI or had an extended luteal phase and were not pregnant. Blood was sampled from each of 127 HF cows in 3 herds at 25, 30 and 37 days after their 1 st AI (day 0). These cows had not been observed in oestrus after these inseminations. Their pregnancy status was diagnosed by uterine ultrasonography on days 30 and 37 when the dimensions of each CL were also recorded. A standard treatment for AA had been used with 96 of the 127 cows and meant that ovulation had been induced with injected ODB (1 mg). Eighteen of the 96 cows (18.75%) treated for AA had elevated PPC on day 25 but were not diagnosed pregnant on days 30 or 37. The average PPC for all cows increased from 5.6 ng/mL on day 25 to 6.9 ng/ml on day 30 and to 7.4 ng/mL on day 37 (P< 0.001). Cows treated for AA had lower PPC on each of these days (5.4 v. 6.3 ng/mL, P<0.01; 6.5 v. 8.1 ng/mL, P<0.001; 7.0 v. 8.7 ng/mL, P<0.001). Pregnancy status did not affect average PPC in either spontaneously ovulating or AA-treated cows (5.50 vs. 5.63 ng/ml; p> 0.2). The average diameter of the CL on day 30 was 3.12 cm compared to 3.27 cm on day 37 (P>0.1). These averages were not influenced by pregnancy status or whether the animal had either ovulated spontaneously or been treated for AA. The average PPC in cows treated for AA was lower than spontaneously ovulating contemporaries from day 25 to day 37 after 1 st AI. These averages were not affected by pregnancy status and were not associated with differences in CL size. Nonetheless, the lower PPC in these cows may be reflected in their lower conception rates to 1 st AI.
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