John Harvey discusses biosecurity and the frequency of twins

Ok it’s still a bit cold but the youngstock are out and we’ve even got our first cut silage done. Mowed on the April 29, it was our earliest first cut ever, and we were actually pleasantly surprised by the quantity we got. And, given how it was sticking to the compactor wheels, hopefully the quality will be good too.

We’re aiming to get all our early cuts in one pit while we try and get to the back of the other one for the first time in several years. Currently the cows are on third cut from ‘23, with first cuts from ’22 and ’21 to come. Hopefully silage matures with time like a fine wine or single malt. The switch in silage has led to slight drop in milk quality (4.5%BF, 3.5%P) but the volumes have lifted a touch to compensate and are now at 39 litres/cow in the tank.

We had a bit of reminder of the importance of biosecurity last month. We do the dairy check test every six months for BVD, testing 10 stirks from each group. As a closed herd this is the most judicious method to monitor our status as it saves on the cost and paperwork associated with tissue testing every calf.

Anyway, when we did the test in mid-March, one of the animals (an A-A X) came back with a weak (waning) positive antibody signal. As she was 13 months this was unlikely to be from residual maternal antibodies, leaving the alternative that she’d been exposed to the virus at some point.

So, as well as the land here at Drum, we also have a small parcel of land nearer Dalbeattie and each summer we send a group of Aberdeen Angus cross calves to graze there bringing them back and housing them with their peer-group black and white calves (which graze during the summer on fields at home) over the winter. It would appear that at some point last summer the positive animal most likely had nose-to-nose contact over a fence with a PI (persistently infected) animal, thereby leading to the immune response that generated the antibodies.

The good thing was that on retesting the positive antibody had gone so clearly there was no on-going exposure, and as I said the rest of the animals had all tested negative originally. However, it does show that while Scotland is pushing to eradicate BVD it is by no means there yet and vigilance is still required. Hopefully the new rules the government has introduced as part of phase six whereby non-negative herds can’t buy-in cattle, will encourage those that haven’t already to get on top of it.

As well as all the actual farming this time of year also brings a lot of that most joyous of things – paperwork! To the usual SAF application and tidying everything up at the end of the tax year, our milk processor has asked that we add pulling together the information for a carbon audit.

While not the most exciting of jobs it does throw up some interesting insights. For example, while I was aware that we had quite a high twinning rate I hadn’t realised quite how high. In 2025, we calved 281 cows and heifers with a total of 319 calves born, which is 38 sets of twins or 13.5%. According to Google, dairy cows will normally give 4-5% twins although it increases with older, higher yielding cows, hence our high rate. On the positive side, although twin calves are more likely to be weaker and suffer dystocia, we only lost 30 calves as stillborn or dying shortly after birth, so still came out at over 103% live calves/calving.

One other thing was around fertility. So, it is often said that cows are at their most fertile 50-90 days post calving and so it is important to try and breed in that window. However, we have pushed our ‘voluntary waiting period’ (VWP) out to 70 days for most cows as otherwise we felt we were having to dry cows off while they were still producing too much milk.

When you look at the conception data though, DIM seems to make very little difference as conception rate is quite flat: 41% at first insemination, 37% at second, and 40% for all subsequent inseminations. Possibly any decrease because of DIM is balanced by the reduced metabolic pressure as the cows come off peak milk production. Obviously, this only works for us as we’re all year round calving and are happy with a calving interval in the 400-410 range.

Anyway, I see another calving on the camera so I’d better go and check and see if it’s twins again!