Effect of concentrate supplementation during early lactation on plasma IGF-I concentrations and reproductive performance of dairy cows

An experiment was conducted to assess the effects of body condition score (BCS) at calving and level of feed supplementation during early lactation on the Insulin-like growth Factor-I (IGF-I) and reproductive performance in 72 Holstein cows in a pasture-based system following seasonally-synchronized calving. At the start of the seasonal breeding, plasma IGF-I concentrations in cows that had recommenced ovarian activity with detected oestrus were compared with those in anoestrus. The cows (n = 72) were managed over a period of five months to calve in a BCS of 4, 5 or 6 - using a scale from 1 (thin) to 8 (obese). The cows were maintained on pastures and supplemented during early lactation with either 1 or 6 kg grain per day. The BCS at calving did not affect plasma IGF-I concentrations. The plasma IGF-I concentration at week 10 was elevated at the higher level of grain supplementation (87.8 vs. 72.1 ng/mL). Higher conception rate following the first insemination of cows calving with a BCS of 6 (71% vs. 46% and 37% for a BCS of 4 and 5, respectively) was associated with more cows in that group conceiving during the first three weeks of the artificial insemination (AI) programme (75% vs. 46% and 46% for a BCS of 4 and 5, respectively). At weeks 0 and 10, cows that commenced ovarian activity by the start of the intensive AI programme, recorded higher plasma IGF-I concentrations than anoestrous cows. These findings indicate that diet can affect the plasma IGF-I levels, which in turn may be involved in affecting the resumption of cyclic ovarian activity and conception in dairy cows.