Getting heifers to the right weight and stature for 24 month calving requires an average weight gain of 0.8kg/day throughout the rearing period. Achieving this performance at grass can be a challenge, but is entirely possible with the correct feeding and management.
Depending on the age, weight and rearing environment of a heifer, she will require a daily energy intake of approximately 70 KJ in order to achieve a 0.8kg daily liveweight gain (DLWG).
Understanding grass covers will highlight the amount of concentrate or forage required to buffer any shortfall in the energy that grass intakes alone will provide. However, it is important to assess not just the amount of grass available to the youngstock, but also its dry matter (DM) content.
If grass DM is only 15%, a 12-month old heifer would need to eat 60kg (fresh weight) to meet her energy requirements. DM can vary hugely depending on weather and time of year so make sure you know the value of your grass.
The energy that a heifer requires to achieve target growth rates will depend on liveweight. It is therefore important to identify whether dry matter intakes from grass will be sufficient to supply your heifers with the required levels of energy to sustain daily liveweight growth rates at a target rate of 0.8kg/day. Concentrate feed should be used to balance any predicted shortfall in energy requirements and to maintain optimum growth rates.
Grazed grass generally has a high crude protein content (normally 15-20%) so there is no need to supplement with high protein concentrates. Standard protein target for heifer rations is 14-16%. Low protein, high-fibre concentrates are available and have been specifically designed to help complement a heifer's diet whilst at grass.
The impact of inadequate intake of vitamins and minerals is often slow to materialise and doesn't have an immediate effect of heifer performance. However, in the long term, insufficient intakes can have a negative impact on the health, growth rates and fertility. Grazing concentrates often have a higher vitamin and mineral content and can help maintain good levels of supplementation throughout the grazing season, even when fed at low rates.
Regular monitoring of heifer weights can help you keep track of whether growth targets are being met by grazing. It will also alert you as to when you should increase supplementation in order to ensure good growth rates and maintain heifer health.
Try to graze smaller groups of heifers, based on age or size so that grass intakes and concentrate supplementation can be monitored and adjusted as required.
When heifers are turned out to grass, it is vital that their performance is carefully monitored and plans are in place to ensure key growth targets are maintained. You do not want to find yourself in the difficult position of bringing heifers back indoors at the end of the grazing season, and realising that they are well behind and not ready to calve at 24 months.
Failing to achieve growth targets at grass can result in delayed service, resulting in significant additional rearing costs. It is often a far more cost effective option to supplement heifer rations with concentrates during the grazing period to maintain good growth rates and ensure optimum conditions for bulling and first calving.