Hitting a target age at first calving of 24 months has the potential to lower feed costs and the carbon footprint of heifer rearing by around 20%, whilst also delivering milk yield benefits.

Modelling work carried out by Mole Valley Farmers showed that calving at 24 months versus 30 months required 13 fewer heifers to be carried on farm per 100 cows. It also reduces the feeding period from three months until calving by 180 days (see table).

Mole Valley Farmers’ sustainability and technical manager, Dr Matt Witt told farmers at Dairy-Tech that using a specific scenario, heifers were fed rations based on grass silage, straw and a heifer rearer concentrate in the winter and grazed in the summer. The feed rates were altered to support growth rates of 0.81kg per day on the 24-month system or 0.65kg per day on the 30 month system.

Dr Witt told a seminar at the event: “Total feed cost per heifer from three months old to calving is slightly lower on the 30 months system. However, because more heifers are required to maintain the herd’s replacement rate of 25% and they’re unproductive for longer, the overall total feed cost is almost 20% higher.”

This had implications for the farm’s carbon footprint (CFP), not just because of higher feed intakes on the 30 months system, but also because of greater predicted enteric methane production. Fertiliser application requirements were also higher due to greater grazing area requirements, whilst manure output and energy use also increased.

Dr Witt added: “Calculations carried out using the Cool Farm Tool show that if you reduce age at first calving from 30 to 24 months in a herd averaging 10,000 litres per cow per year, there’s the potential to lower emissions associated with the heifer unit from 0.23kg CO2e per litre of fat and protein corrected milk to 0.18kg CO2e per litre in this modelled example. That’s about 20%, but the actual amount will vary from farm-to-farm.”

He also explained that there would likely be milk yield benefits from calving heifers at a younger age. “By calving at 24 months old, these heifers have an extra 176 days in milk in their lifetime, compared to those calving at 30 months,” he argued. “If heifers yield 30 litres a day at 36ppl, that generates about an extra £2000 in milk value per heifer.”

TABLE: The impact of reducing age at first calving (AFC) on heifer numbers and feed costs:

AFC 24 months AFC 30 months

Total number of heifers needed on farm per 100 cows

52 65

Feeding period from three months old to calving (days)

630 days 810 days

Total feed cost per heifer from three months to calving (£)

£620 £595

Total feed costs all heifers from three months to calving (£)

£32,200 £39,000

(Culling rate of 25% and mortality rate of 3%. Based on feed prices at time of writing)