Dairy producers should be monitoring heifer growth rates at every opportunity as wet weather hinders dry matter intakes and potentially growth rates.
Many heifers will have been at grass for more than 10 weeks, so should have gained well over 50kg in weight (0.8kg a day) with younger heifers gaining a lot of height to achieve good bulling stature, said DairyCo extension officer Chris Coxon.
"However, with most of the start of summer being wet, good intakes of energy from grass alone may have been limited, so it's important to check growth rates now and supplement with dry concentrates to keep them on track."
Mr Coxon stressed a seven-month-old heifer calf would probably struggle to get enough energy from grass at the moment. "A seven-month-old calf needs 15MJ of energy for growth and she has the potential to eat 5kg of DM a day, so a 10ME grass isn't going to be enough to keep her going and gaining 0.85kg a day," he said.
Mr Coxon said a kilogramme of concentrate should help keep heifers on track as well as rotationally grazing. "Providing good quality, preferably rotationally grazed grass will provide much of the energy required with protein requirements being matched by the grass."
Lucy Carling, technical specialist for Kingshay, said producers should also be wary of low protein levels in grass.
"Compared with last year, protein levels are at 13-14% on average; they were 20% last year. This is because many people haven't been able to graze as tightly and a lot of grass has gone to head reducing the quality.
"For heifers gaining 0.85kg a day you need a balance of protein and energy as the protein drives frame and growth but too much energy can lead to fat animals."
Ms Carling recommended the following protein and energy requirements for the size of animal:
- For heifers up to 300kg, the diet crude protein should be 16-18% and the energy density of the ration 11-12MJ/kg.
- For heifer weighing 400-500kg the crude protein should be 14% and energy density 10MJ/kg
- For heifers over 500kg the crude protein should be 15% and the energy density 11MJ/kg.
"It's important producers know what their grass is doing, so taking fresh grass samples for testing is recommended so you can then supplement appropriately."
Ms Carling also stressed the importance of not overestimating intakes. "Young heifers at grass compared to older heifers and cows graze more selectively and for shorter periods of time. So it is also important to know what intakes are."
Low protein in dairy cow rations can also result in reduced milk yields and reduced conception rates, said Ms Carling. "But when considering dietary protein in lactating rations it is important to look at both protein and energy levels together," she said.
Mr Coxon also urged caution with dairy cow rations. "Rations are all over the place at the moment due to the amount of rain we have had. Changing the ration too often from a grazing ration to a winter ration can cause problems, so it's important to keep an eye on what is going on. Failure to do so could result in fertility issues later on," he said.
To make sure heifers reach calving at the recommended 24 months old:
• An optimum growth rate of 0.7-0.8kg a day is required
• Monitoring growth rates important
• Weigh when doing other routine procedures such as worming and TB testing
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