16 Nov 2015
James Dixon
Job Title
Average age at first calving is currently 28.8 months, compared to a target average of 24 months.
Managing replacements is a key element of running a dairy herd and one of the biggest costs, with a study putting the average cost of rearing a heifer at £1,819 (Boulton 2015).
This means with average replacement rates of 25.8% (CHAWG, 2014), a typical 150-cow, 8,000 litre dairy herd will be spending £70,000 per year (5.8ppl) generating replacements. The greatest drivers of this cost and, therefore, of how long a heifer must stay in the herd before she becomes profitable, are the heifer wastage rate, and the age at first calving.
Heifer wastage is made up of mortality rate and culling and it is estimated around 22% of heifers fail to reach first lactation, meaning a longer delay to break even in the remaining heifers as they are also having to repay the rearing costs for their fallen herd mates.
Average age at first calving is 28.8 months (NMR, 2015) compared to a target average of 24 months and, with a weaned, empty heifer costing £1.65 per day to rear, this equates to an extra cost of £240 per heifer.
It is clear efficient heifer rearing has the potential to dramatically improve margins on many UK dairy farms and this can be achieved by prioritising youngstock rearing and ensuring replacement heifers receive the best housing, nutrition and care.
The environment calves are kept in is crucial, especially in the early stages of life. Whether it is a calf hutch, an individual pen, or a group pen on an automatic feeder, the principles remain the same – calves need to be dry, warm, well fed and well ventilated.
Some key aspects identified as success factors for calf housing (Nordlund, 2014) are:
This group recognised a well-managed individual hutch is likely to be the best environment for calf health, but that it can be hard on the operator, especially during winter and this may impact on the care given to the calves. When considering hutches, try to place them somewhere sheltered, well lit and near to all the required amenities.
It is worth mentioning a reduction from 28-month to 24-month calving of heifers in a typical herd would mean 14 fewer animals required in the pipeline – a 9% reduction in housing requirement.
In recent years interest has increased in nutrition of the preweaned calf, with many advisors advocating higher concentrations and volumes of milk replacer to take advantage of the young calf’s highly efficient feed conversion ratio; with the added benefit of improved health, reduced rearing times and better yield after calving.
Whatever the feeding system, good management practices are still essential and include:
A sensible target for preweaned calves is to double their birthweight before weaning, meaning the average calf will need to put on between 40kg and 45kg in the first eight weeks of life. This is a daily liveweight gain (DLWG) of between 0.7kg and 0.8kg per day.
With a feed conversion efficiency of around 0.5, these calves will need to consume between 1,400g and 1,500g per day of feed (milk powder plus concentrates) as an average over the birth-weaning period, with most of this coming later on as they begin to eat more concentrate feed.
Some high milk rations (for example, 6L/day at 150g/L) can provide a large proportion of the feed intake from milk alone. It is, therefore, critically important, when feeding higher levels of milk, to ensure calves are taking sufficient concentrates before weaning, otherwise they are likely to experience a check in growth rates while they adjust to life without milk.
A good aim is for calves to be consuming at least 2kg of concentrate per day, along with good quality fibre to encourage rumination. In this instance, a gradual reduction in the amount of milk offered in the two weeks running up to weaning will encourage extra intake of concentrate and smooth the weaning process considerably.
To correct for breed and farm variations, heifer weight gain targets are usually expressed as a proportion of their predicted mature bodyweight, usually defined as the average weight at calving of a selection of animals in their third lactation or higher.
If it is not possible to weigh these older cows, then an average of barren cow weights can be used, so long as any cows sold in particularly high or low body condition are excluded. Using this system, so long as the current weight of the animal is known, it is very straightforward to calculate the required growth to reach any target up to 100% mature weight.
In general, the target is to achieve 55% mature bodyweight at conception and then 85% at first calving, or 330kg and 510kg respectively where adult bodyweight is 600kg.
Assuming a weaning weight of 80kg at 60 days, the target growth from weaning to conception is 250kg and should ideally be attained by 15 months, although the target should be to start breeding at 13.5 months to allow for an average of two breeding cycles before conception across the group.
Using these targets we can see DLWG is likely to vary at different points in the rearing system, with 0.6kg/day the target from weaning to breeding and then 0.7kg/day required thereafter to reach 510kg at 24 months of age.
It is beyond the scope of this article to discuss youngstock disease in detail, but a few key areas can impact dramatically on the growth and ultimate production of dairy heifers.
Occurring predominantly in the first three to four weeks of life, calf diarrhoea is a major issue in some rearing systems, leading to reduced growth rates, increased labour and medicine costs as well as calf mortality. Even when calves are not lost, it is often a precursor to respiratory disease, which can lead to death or permanent lung damage.
Key management principles in preventing scour are:
Where scours do occur, it is crucial to make an accurate diagnosis so the correct preventive measures (and, if necessary, vaccines/treatments) can be applied. Sampling a minimum of five calves from any cohort will give the best chance of a diagnosis.
A multifactorial problem, pneumonia can cause huge losses through mortality, but also through reduced growth rates due to lung damage in surviving heifers. Any incidence of respiratory disease must be thoroughly investigated, covering the following areas:
Having been successfully weaned, we often see disease or reduced growth rates in older calves (three to six months of age) caused by coccidiosis due to the stress of weaning and joining a larger group, or due to build-up of infection in group pens or even pasture.
Coccidiosis is incredibly damaging to the intestines and, in a severe outbreak, surviving calves are often left stunted and will not keep pace with the rest of the group.
Control relies on allowing calves to meet a low-level challenge and build immunity without suffering clinical illness. This can be achieved by:
Improved coccidiosis control can have a dramatic effect on the age at which heifers reach their target breeding weight.
Breeding and rearing replacement heifers is one of the keys to success in dairy farming and regular and accurate weighing is hugely important in identifying weak points within the rearing system.
Once a good and consistent management system is established for youngstock, with minimal disease challenges, they are easily capable of achieving the growth targets listed in this article and the results can be spectacular.
