Last year’s ban on oestradiol benzoate (“OB”) meant that we had to rely on programmes that looked good on paper, but were untried in New Zealand.

We had a few sleepless nights wondering how successful they would be, particularly when we found that so many cows did not display “bulling” behaviour. Putting up cows for service with no visible signs of heat was an act of faith which we are glad to say seems to have been justified. This year we can back up our advice with a whopping 2222 cow trial, involving 12 herds (average size 510), comparing 3 options for dealing with non-cyclers 9 days before the start of mating. The results from this trial can be summarised by the following graph which shows the proportion of cows in-calf (1.0 = 100%) as mating progresses, depending on whether the cows were treated with OvSynch (GPG alone), CIDRSynch (CIDR + GPG) or No Treatment.


As would be expected, non-cycling cows that receive no treatment gradually start cycling and get in-calf, so that by day 21, 36% are pregnant. This will vary hugely from herd to herd, depending on a range of factors, most notably cow condition and calving spread. This trial does not include cows calved less than 20 days at the time of examination, and I would not expect too much from these girls! The main benefit in treating non-cyclers appears to be early on, with in-calf rates by day 21 in excess of 57% for the CIDR based programme, and somewhere in between for OvSynch. By 8 weeks (day 56), the lines have pretty much converged, and the message here is that we wouldn’t expect early treatment of non-cyclers to have much effect on your induction rate or empty rate. Treatment should be viewed in terms of giving extra days in milk next season, with 10 extra days per treated cow with OvSynch, and 16 extra days with CIDRSynch. For a $7.00/kgMS payout, this works out at $82.00 per cow net return on treatment with OvSynch, and $135.20 per cow with CIDRSynch, once treatment costs and additional feed costs (for cows calving earlier) have been accounted for. Speak to your vet as soon as possible for further details, timing and costs for these programmes.


Written by Jason Darwen BVSc

Extract from the Dairy Newsletter – October 2008