Before mating starts it is good to review performance from last year. The Fertility Focus Report provides a quick way of doing this. Check the key performance indicators of six-week in-calf rate and empty rate. If the herd is not achieving targets, assess what areas may be ripe for improvement on your farm. For many herds, poor submission rates limit six-week in-calf rates. The aim is to get more than 90% of cows bred in the first three weeks of the mating programme. If this is not being achieved it could be because of truly non-cycling cows in the herd, or poor heat detection.
Signs of heat include the primary sign of a cow standing to be ridden, and secondary signs such as increased walking, bellowing, sniffing, chin resting, and mounting behaviour. The period during which the cow will stand is shorter than the overall period that she is showing secondary signs. On pasture, a cow will stand for an average of nine hours, during which there will be an average of 11 mounts on her, with the average mount being only about 2½ seconds. However there are big variations between animals in the intensity and duration of oestrus, illustrating the challenge of heat detection.
One way to assess how good heat detection is on your farm is to look at the heat detection indicator on the Fertility Focus Report. You should expect more than 95% of the mature, early-calved cows to be inseminated in the first three weeks.
However figures from across New Zealand show only about 81% of cows bred in the average New Zealand dairy farm in the first three weeks of mating.
So what can we do to improve heat detection?
Decide on a heat detection system for your farm, such as tail paint, heat detection aids, or other method.
Ensure everybody on the farm to understands the system and what their role is
Get heat detection systems in place four to five weeks before the start of mating so that the number of non-cyclers can be assessed before mating starts. If fewer than 65% of cows are in heat before mating starts, consider intervening.
Decide how you will deal with non-cyclers, and plan to do so before the planned start of mating as this the most cost-effective time
Monitor matings and ensure about 5% of the herd are inseminated each day in the first round.
Given the relatively short duration of oestrus, visual detection alone is unlikely to result in a good submission rate. Tail paint works well, but care is needed to ensure that it is applied correctly – apply a 20 x 5cm strip over the base of the tail, ensuring that winter coat is removed before paint application, and touch up weekly. Using heat detection aids such as Kamars or scratchies could improve heat detection in some farms as they might be easier to interpret than tailpaint.
‘The technology looks promising, but more work is required to optimise the system so that the majority of cows truly in oestrus are detected.’
Teaser (vasectomised) bulls have been used by some farmers. There is evidence from the beef industry that bulls will stimulate cows to cycle more quickly after calving, but there’s little evidence of the effect in dairy cows. It appears that if bulls increase submission rates, it’s because of better heat detection, rather than any kind of stimulatory effect of the bulls directly on the cows.
New technology is emerging to aid with heat detection. This technology includes systems that rely on the cow’s mounting behaviour, such as pressure-activated tail sensors, and camera systems that detect rubbing off of tail-mounted cards. It also covers systems that rely on secondary signs of heat such as increased walking activity, measured by accelerometers or pedometers, or changes in body temperature, or systems that track the hormone progesterone to estimate the time of oestrus and ovulation. Some of these systems have been assessed on pasture-based farms, but with variable results. Two NZ studies showed no benefit for pressure-based mechanical recorders of heat or neck-mounted accelerometers, compared with tail paint and-or visual inspection. However, use of image analysis software and tail-mounted cards was linked to an improved six-week in-calf rate on one NZ dairy farm.
The technology looks promising, but more work is required to optimise the system so that the majority of cows truly in oestrus are detected, meaning a high true positive rate of heats, but minimising the number of cows not in oestrus put up for mating. It is likely that the best heat detection system will use a combination of visual detection, tail paint and potentially some of the new technology coming through.
With mating coming up, heat detection is an important thing to consider. Improving heat detection is likely to be cost-effective on many NZ dairy farms.
