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23rd February, 2019


Breeding programmes for spring calving dairy herds have now begun on all farms. This period literally sows the seeds for both the next generation of replacements and the calving pattern for next spring.  It is essential that a primary focus is placed on accurate heat detection where AI will be used to get cows in calf.

The primary aids to heat detection are tail-paint, scratch cards and teaser bulls with chin-ball markers. With limitations and frequently poor desire of farm labour to spend time with cows at pasture monitoring bulling groups, farmers have resorted to identifying cows for AI at milking time on the basis of either tail-paint removal, colour change of scratch cards or chin-ball marking by teaser bulls.

These heat detection aids will accurately identify heats in approximately 80% of cows. However, you should spend 20 minutes monitoring activity at three hours after the morning and evening milkings.  This will pay dividends.  You will identify cows presenting with milk signs of heat which may not have any markings associated with heat detection aids.

You should confirm that these “silent bullers” are actually in heat by placing a gloved arm into the vagina to check for the presence of a clear “bulling mucus”. This procedure will increase the number of cows accurately presented for AI.  An emphasis needs to be placed on “accuracy” of heat detection.  In an effort to maximise submission rate, cows are presented for AI based on inaccurate signs of heat or indeed mis-identification of cows.

Accurate heat detection has to be your priority when one considers the financial gain of €250 for each additional heat accurately detected at this stage of the breeding season. As herd size increases, the risk of “shy bullers” increases.  Therefore, it becomes more critical to spend time observing the herd to identify the “shy bullers”.

Unfortunately, most dairy herds will not address problematic cows until they are 4 to 6 weeks into the breeding season. This subgroup can account for 15pc of the eligible herd for breeding.  A prebreed scan will identify these cows and provide an opportunity to optimise the financial gain by accurate heat detection early in the breeding season.

The timing of insemination is still an issue on many farms. In our experience, too many cows are inseminated too early in the heat period.  Where once a day Ai service is used, the temptation is to AI cows on the day which have “markings” at the morning milking.  You need to remember that cows will not ovulate for a period ranging from 24 to 36 hours after the onset of standing heat.  Therefore, cows starting bulling at 6AM are being AI’d too early at 8 to 10AM.  A simple approach to avoid this scenario is to identify cows in heat when monitoring activity at 9PM.  The cow identified on the day up to this time enter the AI group on the following day.

It is essential that all stressors are minimised during this critical breeding period. Lameness, mastitis, pneumonia, dietary imbalance and underfeeding are typical examples.  The suggestion that cows can produce 29 litres of milk from grazed grass with 0pc concentrates will lead to an unsustainable calving pattern unless replacement rates of 30% pertain.

Are your vaccination programmes up to date? Many farmers have removed the cost of vaccination as milk price dropped to uneconomic levels last year.  Vaccination against BVD should not pertain if we had a strict policy of removing persistently infected calves from the herd.  In a recent case study, a dairy farmer bought an angus bull to mop up empty heifers among a group of 65 heifers confirmed pregnant having used sexed semen.  It transpired that the stock bull was a PI and infected the pregnant heifers at a critical stage of their development.  Twenty three PI heifer calves were born, which had to be removed from the herd.

Stock bulls are used on many farms as the sole method of getting cows in calf. This works if both the bulls and cows are fit.  Almost 10pc of stock bulls are infertile.  In addition, bulls may have poor libido or an inability to ejaculate.  Injuries to bulls will not alone increase the risk of failure to breed cows in standing heat, but also results in infertility of semen ejaculate 6 weeks after the injury.

Relying on stock bulls “hides” the identification of problem breeders in the herd. It becomes essential to use to use a prebreed scan to identify and manage problem breeders where stock bulls are used.

In conclusion, accurate heat detection, early identification and management of problem breeders are a cornerstone to compact calving on a spring calving breeding season.


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


Article written by Dr. Dan Ryan for the Farming Independent  9th of May 2017.