Guide to rearing replacement heifers

Author: Jack Scallan – Ruminant Feed Specialist 


At this time of year, most spring-born calves are out at grass, albeit 2-3 weeks later than normal. Now is a good time to consider what targets should be met over the next 12 to 24 months to achieve the desired weight and size at first calving (approximately 24 months old).

Setting goals is particularly important for replacement heifers as it can cost between €1400 -1600 to raise a replacement heifer from birth to first calving. Any delay in reaching the desired goals will incur extra costs that will have to be paid back at a later stage.


Calf Growth Rates: 

Calves should be able to achieve a growth rate of 750 grams/day on fresh well-managed grass, to reach a target weight of 260 kg on November 1st. Many factors such as a poorly managed or old pasture, bad weather, etc., may result in a requirement for supplementation with concentrates (up to 1.5 kg/head/day of a high energy, high fibre, 16% crude protein nut/ration), to attain this target. Routine vaccination and dosing programmes should be introduced in the first summer at grass as this will boost the immune system and help prevent major disease breakdowns in later life, such as IBR, BVD, etc.  Calves should be weighed at least three times in the first summer; at turnout, mid-summer (when being treated for worms, etc.), and at housing, to ensure that they are gaining the required weight.


Silage Quality: 

Silage quality will determine how much if any, concentrates are given in the first winter, to maintain an average daily gain of 0.5 kg, however, 0.75 kg/day should be the target. This will ensure that the heifers are at 60% of their mature body weight at breeding (320 – 350 kg).  If silage quality is poor, approximately 62% DMD, then up to 2 kg of 16% crude protein concentrate should be fed per day. The housing itself should be airy but not draughty with plenty of space to move around. Clean fresh water should always be available.

Silage being held and check for quality


At breeding time, the heifers should be weighing about 350 kg, as the better-developed heifers at mating will produce more milk in the first lactation. Early turnout to grass in the spring will encourage the heifers to cycle regularly and therefore can be synchronised to be mated in a designated time frame, so that they calve down in a similar time frame, preferably at the beginning of the calving season, so that bullying in the herd is reduced to a low level. Conception rates for heifers should be around 70+%.

Again, routine vaccination and dosing programmes should be carried out during the second summer at grass. A daily liveweight gain of 0.67 kg/day should be easily achievable at grass but this will depend on the prevailing conditions such as grass quantity and quality, etc.



During the second housing period, the heifers will be approaching calving. The aim is that they achieve 90% of their mature bodyweight at calving, approximately 540 kg. The silage/forage should be of good quality, but it is important to not let them get too fat (BCS> 3.25).  It is recommended that the replacement heifer is fed 1-2 kg of concentrates in the last two weeks of pregnancy to help her through the calving event. In fact, the nutrient requirement in the last month of pregnancy is higher for the replacement heifer than it is for the mature cow (8.52ufl, 733g PDI/day for the heifer compared to 8.1ufl, 626g PDI/day for the mature cow).

Calf resting in bed of straw

Post Calving: 

Post calving, the heifer must be managed carefully to help her recover from calving. This involves reducing stress by a gradual introduction to the herd, once a day milking for about 10 days, a gradual increase of concentrate intake as well as looking out for any metabolic disorders and infections that might occur.


Further Information: 

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