MMN March 2025 – Turning Out Heifers, Fed not Forgotten

Highly nutritious spring grass can be an effective tool for promoting growth in youngstock and can support growth rates of up to 1kg/day. Turning heifers out to grass can reduce rearing costs and ease the pressure on forage and straw stocks. Ensuring heifers reach the desired growth rate at grass is dependent on effective grassland management and knowing when to target supplementary feeding to achieve consistently good growth rates for calving down at 24 months.

Daily liveweight gain (DLWG) targets are used as a key assessor of replacement heifer development. Calves need to be averaging a growth rate of 0.75-0.8kg/day to be on target for calving down at 24 months (assuming a 700kg mature body weight). Heifers should reach 55-60% of their expected adult body weight in preparation for their first service at 14-15 months and be around 85-90% of their adult body weight by 22 months.

Monitoring growth performance of heifers at grass is desirable but not always practical. At a minimum youngstock should be weighed pre-turnout, halfway through the grazing season and again at the point of housing to calculate DLWG. Ideally, they would be weighed more regularly (monthly) to identify poorer growth rates and allow for corrections to be made through supplementary nutrition.

Measuring wither height is an alternative option for monitoring growth if weighing is not an option. The target heights and weights for Holstein-Friesian heifers are noted in the table below (these figures will vary depending on mature body weight).

Target weights for age in Holstein-Friesian heifers

Heifer age (months)	Target weight (kg)	Target wither height (cm)
3-4	100-125	85-95
6-8	170-220	100-105
14-15	360-400	115-125
24	585	125-135

Source: CAFRE

Young heifers will see benefits from being fed supplementary concentrates in their first grazing season, in particular shortly after turnout and later in the year as the pasture quality and availability declines. Turning the youngstock out with access to concentrates or their housed ration will help prevent summer scour syndrome (SSC), which is most commonly seen in calves under six months of age but can be an issue up to 12 months of age. SSC is most likely to occur within the first month of turnout and is typically characterised by rapid weight loss and persistent scouring. The likelihood of calves contracting the condition is higher if they are turned out onto pastures which are heavily slurried and fertilised.

In a rotational grazing system heifers should be turned out to pastures with a pre-grazing cover of around 2400-2800kg DM/ha, or a sward height of no more than 4inches/10cm, where the D value will be around 75%. Grass quality will suffer later in the season if the group are unable to graze down to the desired residual of around 1500kg DM/ha or a sward height of 1.5inches/4cm for youngstock (if heifers are under eight months of age, a residual of 1800kg DM/ha is acceptable). If it is found that the heifers are unable to keep up with grass growth, it would be beneficial to close a paddock for silage production or immediately top the pasture after the heifers have been moved to allow for a leafy regrowth to support good growth rates in the next grazing period.

Tips for rearing heifers at grass:

• Monitor growth rates throughout the season to ensure heifers are on track for service and calving at 24 months.
• Maintain grass quality and measure sward height with a plate metre throughout the grazing season.
• Supplement the heifers with their housed ration or concentrates to ease the transition to grass and reduce the risk of SSC.
• Monitor the heifers for signs of a parasite burden which can hinder growth. Consider utilising the Preparing for Sustainable Farming, animal health and welfare intervention funding to investigate if a parasite burden is present and receive veterinary advice on the best treatment options. Preparing for Sustainable Farming - Cattle Interventions | Helping farmers in Scotland | Farm Advisory Service

Consider utilising FAS specialist advice funding to create tailor made heifer rations, including grazing plans. Specialist Advice | Helping farmers in Scotland | Farm Advisory Service.

 

keira.sannachan@sac.co.uk; 01555 704497