Heat Detection & Synchronisation

Heat detection is used to identify cows that are about to ovulate. Comprehensive programs based on the technique can have a major impact on overall herd reproductive performance.

Heat detection methods

The best heat detection results are achieved by combining paddock observations and heat detection aids, such as tail paint and heat mount detectors. A twice-daily time commitment outside of milking is required, but it is a very accurate method if a farm team is well-trained, and cows can be easily identified in the paddock.

Automated heat detection systems use electronic sensors to record one or more hormonal, physiological or behavioural changes around the time of heat and ovulation. A computer algorithm analyses the records and based on threshold settings, identifies those cows most likely to be on heat.

Doing pre-mating heat detection gives the option of managing a non-cycling problem early for better results. It is also a great opportunity to train staff in heat detection before mating starts. A practical way to do pre-mating heat detection is to tail paint all the cows with one colour four to five weeks before the mating start date. Apply a second colour once or twice a week to cows that have lost their paint and top up the original colour as required. After three weeks of observation all the cows with the original colour are non-cycling cows and can be treated.

Heat synchronisation

Heat synchronisation involves treatment of cows with reproductive drugs to predictably time when their next heat and/or ovulation will occur. It can offer efficient use of labour, as the work of heat detection and artificial insemination is shortened into planned, intensive periods.

In seasonal and split herds, it can be used to compress three cycles of breeding (nine weeks) into a seven-week mating program, or two cycles (six weeks) into a four-week mating program. Key factors when considering a heat synchronisation program are:

  • It may help increase heat detection rates in large herds, if people do not have the skills or time for detecting heat.
  • Most programs have a limited effect on in-calf rates. Therefore, management benefits should be the biggest consideration when deciding whether to use synchronisation or not.
  • Simple aids such as tail painting or heat mount detectors are essential when detecting heat during a program.
  • Some programs require fixed timed inseminations, meaning that no heat detection is required at all during that period. Some programs allow resynchronisation of returns to service to help achieve increased heat detection rates for returns to service.
  • If considering using heat synchronisation for the first time, consult your ReproRight advisor or a veterinarian who has experience using heat synchrony options.

Non-cycling cows

Cows that do not come on heat at the optimal time for mating can prevent farmers achieving their target of six-week in-calf rates (seasonal and split calving) or 100-day in-calf rate (all-year-round calving).

Good heat detection is essential to reach submission rate targets, but too many non-cycling cows will hold back herds that have good heat detection rates. The proportion of late calving cows that need treatment as non-cyclers should be less than 10 per cent for cows calving in the first four weeks from the planned start of calving date.

Treatment options for cows not detected on heat are being frequently updated as further research results become available. It is recommended that farmers consult their ReproRight advisor or vet about current recommendations for each product.

Assessing heat detection

Heat detection practices should be regularly assessed to see if there is room for improvement. Calculating the submission rate – the proportion of eligible cows detected on heat and inseminated – is a good first step in measuring heat detection performance. A high submission rate needs cows to be cycling and heat detected.

Split and seasonal calving herds should seek help if their three-week submission rate for early-calved, mature cows is less than 85 per cent. Meanwhile, all-year-round calving herds should seek help if their 80-day submission rate is less than 61 per cent. Submission rates can be low for two reasons — cows are showing heat normally but it is not being detected and/or there are lots of ‘non-cyclers’ in the herd not showing signs of heat.

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