Reproductive performance of pasture-fed dairy cows supplemented with monopropylene glycol

AIM: To determine the effects of monopropylene glycol (MPG) on resumption of oestrous cycles and pregnancy rates in mixed-aged cows in commercial herds, when administered for 6 weeks before the planned start of mating (PSM).
METHODS: A trial was conducted using 1,814 pasture-fed predominantly Holstein-Friesian cows on four spring-calving dairy farms in the Waikato region of New Zealand. Each farm contained >500 cows, >60% of which had a body condition score (BCS) ≤4.5 two weeks before the planned start of calving. Within each farm, cows that had calved but not been seen in oestrus were allocated at random to one of three treatment groups, viz Control cows receiving no MPG (n=580), a second group receiving a single dose of 200 ml MPG after the morning milking (n=622; MPGx1), and a third group receiving 200 ml MPG after each morning and afternoon milking (n=612; MPGx2). Administration of MPG commenced 6 weeks prior to the PSM. Observations for oestrous behaviour and removal of tail paint was carried out at least daily. One week prior to the PSM, all cows with no recorded oestrus were examined to determine whether they had ovulated or not, and anovulatory cows were treated to induce oestrus and ovulation. Cows were artificially inseminated ~6 weeks from the PSM, then bulls were introduced for up to 12 weeks. Pregnancy diagnosis was carried out using transrectal ultrasonography at 12 and 16 weeks after the PSM. Milk production was determined from one herd test during the treatment period, and a second 2–3 weeks after the end of the treatment.
RESULTS: There were no effects of treatment with MPG on resumption of oestrous cycles. Pregnancy rates at 12 and 16 weeks after the PSM were greater for cows in the MPGx1 group compared with those in the MPGx2 and Control groups (p<0.05). The yield of milk protein at the fi rst herd test was greater in cows in the MPGx1 and MPGx2 groups than in Control cows (p=0.013).
CONCLUSION: This study showed that MPG given to cows with a low BCS for 6 weeks prior to mating had limited benefits on reproductive outcomes.
KEY WORDS: Dairy cows, monopropylene glycol, reproduction, anoestrous, postpartum