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28th November, 2022


August is a quiet month for spring calving breeding programmes. Cows bred now will calve next June, which makes no economic sense in grass based milk production systems.

Bulls need to be removed 35 days prior to a herd scan to get a full picture of reproductive performance in your herd. Many farmers tell me that they find the day of the final herd scan a very stressful time.  Many farmers do not sleep well the night before!!

Next year’s spring calving programme will be determined by the results of the herd scan. The following information can be harvested from an accurate scan:


  • Identify empty cows.     


    1. The reality on many farms this year is that upward of 20pc of the current milking herd will be culled on the basis of either being empty, empty but late calving with an ailment, nitrate directives, cash flow or the need to improve BCS in the pregnant cows.
    2. It will also reduce the level of competition and give your pregnant cows a greater opportunity to gain BCS. Some farmers are planning to go to “once a day” milking for the latter part of the current lactation. This will enable cows to gain better BCS, increase milk solids, but increases the risk of high SCC.
    3. Removing empty cows now will help cash flow in a year when cash reserves are poor. More critically, it will help reduce the level of competition for grazed grass, which will become a scarce resource in September and October.
    4. In the current year, many dairy farmers plan to identify empty cows as soon as possible after the end of the breeding season and remove them from the herd. Indeed, cows pregnant, but calving in late April and May next year will be sold if they have one or a combination of ailments such as old age, mastitis, high SCC, old cows carrying twins and poor locomotion scores.
  • Accurate ageing of pregnancies    


    1. The critical key to optimal dry cow and early lactation transition management is that cows enter the final 8 weeks of gestation in optimum condition and maintain same through the subsequent calving event.
    2. If pregnant cows in poor BCS are not going to be supplemented with concentrates at grass, it is essential that they get at least an extra 6 week dry prior to the beginning of the final 8 weeks of gestation.
    3. Please note that up to 10pc of pregnant cows will show heat while pregnant. In the absence of scan data, these pregnant cows end up being culled from the herd. In addition, these “false heats” create inaccurate due dry off dates.
    4. It is important that you establish an accurate due dry off and calving dates for your herd based on the scan data. The ageing of pregnancies using scanning should be accurate to within 5 days between 25 and 80 days of pregnancy, to within 10 days between 80 and 110 days and to within 15 days between 110 and 150 days. Beyond day 150 of pregnancy, there is a greater risk that none of the foetus will be visible to accurately age the pregnancy.
  • Identify cows carrying twins   


    1. Longer dry cow periods, use of rumen boluses which increase dry matter intakes help prevent BCS loss and associated increased risk of metabolic diseases.
    2. Scan data can accurately identify twins up to 110 days of pregnancy. However, it should be noted that up to one third of cows carrying twins will not deliver twins at full term. There is a greater risk of later embryo and foetal death, abortion and cows losing one of the twins.
    3. The incidence of twins at birth ranges between 2 and 10pc in dairy herds. There are greater risks of survival in both the dam and her offspring. Future reproductive performance and risk of metabolic disease is increased among cows carrying twins.
  • Identify the sex of the calf  


  1. The sex of the calf can be accurately identified from a scan between 52 and 110 days of pregnancy. Farmers use this information to cull cows if she is carrying a Friesian bull calf and has an ailment such as mastitis or high SCC. Farmers will also use this information for stock sales.


Dr. Dan Ryan is a bovine reproductive physiologist and can be contacted at

Article written by Dr. Dan Ryan for the Farming Independent 23rd August 2016.