During this time of year, farmers are focused on scanning cows and extending the grazing season, but replacement heifers should not be overlooked.
A couple of weeks ago, it was recommended to weigh your replacement heifers and make sure that they were on target before we progress into the winter months.
Research has show that lower survival rates to third lactation and reduced milk yields in subsequent lactations, are just some of the consequences of failing to achieve the target weight for age when rearing replacement heifers.
Identifying any underweight heifers and ensuring they are the correct weight by mating start date is crucial, as it will ultimately lead to heifers calving down at the optimal age of 22-24 months, and in turn will help to maximise farm profitability.
The maintenance sub-index is the main tool to determine the cow’s future mature weight, and the higher the maintenance sub-index, the lighter the cow.
An easy way of looking at it, is that February-born weanling and yearling heifers should be 30% and 70% respectively of their pre-calving body weight on August 1, if they’re to be successfully calved at two-years-of-age.
The target bodyweight guidelines for replacement heifers is as follows:
| Age | Percentage of mature cow body weight |
|---|---|
| Six months | 30% |
| 15 months | 60% |
| 24 months | 90% |
Having these targets in mind is crucial in reaching your target weight and making sure the heifers calve down at two-years-of-age in good condition.
The reality is that only 75% of heifers calve down at 22-26 months of age, which has a significant consequence on the calving pattern, and your production which will have a massive impact on your overall costs.
Acting on underweight replacement heifers
Weighing is the best way of identifying underweight heifers to ensure that all heifers are on course to achieve their desired weight before the start of breeding.
If there are a few heifers that are underweight, supplementation should be added to their diet immediately, as it will be too late to try and correct underweight heifers next April or May.
Heifers should be receiving top quality silage of a dry matter digestibility (DMD) of 75% over the winter period in order to improve their performance and live weight.
Replacement heifers can go backwards in the blink of an eye, so it is important to make sure they have enough feed space when supplemented with meal at grass, and also at housing during the winter.
Heifers that are clearly lighter and are behind target should be grouped together, away from the high performing heifers, so that the lighter heifers can be prioritised with a better flush of grass, better silage and extra supplementation.
Your replacement heifers should be eating at least 2.2% of their target bodyweight by now, which equates to roughly 4kg DM/day for a Friesian-type calf.
In the spring time, getting your heifers out early is key, as higher weight gains come from pasture and if the heifers are not uniform, you should prioritise letting the lighter heifers out first.
However, the priority at this moment in time, is that your heifers are all uniform and on target, and if they are not, now is the time to act and rectify the situation to ensure a healthy heifer getting bulled next May.
