Successful heifer rearing: focus on the pre-weaning calf

Heifer rearing costs represent the second highest cost on dairy farms after feed, with costs ranging from 13-20 per cent of total milk production costs.

Calving at between 22-24 months reduces rearing costs and also results in greater lifetime performance and reduced metabolic issues at calving compared to calving at a later age. As such, the goal should be to calve a heifer at between 22-24 months of age at 85-90 per cent of the mature bodyweight of the herd.

It is now widely accepted that the period from birth to weaning is a critical phase in a heifer’s development. The target is for calves to double their birth weight by weaning at 8-10 weeks of age. For a typical 45kg calf at birth, this requires a growth rate of 0.80kg per day to reach a weaning weight of 90kg after 8 weeks.

Colostrum – Quality, Quantity, Quickly

Probably the most important part of calf management is getting quality colostrum into calves quickly and in the correct quantity. The neonatal calf is born with very few energy reserves and colostrum is a rich source of carbohydrates, protein, fat and insulin-like growth factor 1 (IGF-1 – a hormone that is important for promoting gut development within the calf), which serve as essential nutrient sources during the early stages of life.

Most importantly, calves are born with an undeveloped immune system and new-born calves depend on the passive transfer of immunity from colostrum (immunoglobulins-IgG) to protect themselves from infection and disease until their immune system can start to develop its own antibodies. Colostrum quality can be tested using a Brix refractometer. It is worth remembering that the IgG level (antibody level) increases in colostrum with increasing maternal age (parity of the dam/mother), and colostrum from first calving heifers should, therefore, be avoided. Surplus good quality colostrum should be frozen and stored to ensure that a stock is built up. Frozen colostrum should be gently thawed using warm water before feeding, to minimise damage to the IgG.

Recommendation: Feed colostrum with more than 50g/litre of IgG at a rate of 10 per cent of the calf’s bodyweight within 4 hours after birth, to achieve a minimum of 10g/litre of IgG in the calf’s plasma by 24hrs after birth. Typical feed rates are 4-5 litres per calf but this will depend on IgG content. Colostrum should be fed as soon as possible after birth as IgG absorption rates reduce by 60 per cent 6 hours post birth. Don’t let calves suckle their mother as there is no way of knowing the quality or quantity of colostrum consumed, and there is a risk of contamination from dirty teats.

If insufficient or poor quality colostrum is provided to the calf, or if calves are delayed in receiving colostrum, then it is possible to get failure of passive transfer of immunity. This increases the calf’s susceptibility to respiratory infection and pathogenic diarrhoea. There is also a correlation with failure of passive transfer of immunity to incidence of diarrhoea and resulting slower growth and poorer lifetime performance. Calves with serum IgG >10g/litre 30-60hrs post birth are healthier and at less risk of succumbing to disease. They also reach required bodyweights for first insemination sooner. Good hygiene should be followed when managing colostrum to avoid pathogenic infection and colostrum should not be left in buckets around dairies or calf sheds for extended periods of time, as this heightens the risk of contamination.

Milk replacer

Current recommendations are to feed 6 litres of milk per calf per day, containing 125g of milk powder/litre. It is important to promote high rates of daily gain with milk replacer early in life but also not to over-feed as it can reduce or delay starter feed intakes, which are vital for rumen development.

A 45kg calf requires approximately 380g of milk replacer (3 litres fed at 125g/litre) for maintenance alone, with any additional milk intake being utilised for growth.

Recommendation: As an easy rule of thumb, provide 1.5 per cent of bodyweight as solids during the first week of life, increasing to 2 per cent of bodyweight from the second week of life until the week before weaning, when one feeding is dropped.

Increasing the milk replacer feed rate during cold periods of weather maybe required as the calf’s energy requirements to stay warm increase during such periods and this can reduce growth rates. It is important to ensure that protein and energy are in balance to deliver efficient growth and you should consult your milk replacer provider for the correct specification for your calves.

Rumen development

At birth the rumen is a sterile environment and the initial bacterial community is transmitted to the rumen of the calf via the skin, saliva and birth canal from the mother, as well as from the environment. Populations of cellulolytic bacteria become established within a few days after birth, however they cannot increase to the numbers necessary for significant forage fermentation until the rumen pH stabilises at or greater than 6.0. Fifteen days after birth the ruminal diversity of the calf is the same as that of a mature cow but population numbers continue to increase throughout the first few weeks of life.

Starter feed intake and chopped forages

It is vital to promote early intake of starter feed to physically and microbially develop the rumen so that the animal can start to digest fibre. Don’t forget the importance of clean, fresh water provision either! Promoting high rates of starter feed intake is essential to produce Volatile Fatty Acids (VFAs), which are the result of rumen fermentation of carbohydrates. These VFAs, and specifically propionic and butyric acid, are vital for the development of the rumen papillae, which are essential for nutrient absorption from the rumen.

Recommendation: Fresh starter feed should be fed daily and target 300g of starter feed intake by 3 weeks of age, of a feed that contains >32 per cent starch, high quality protein (with good levels of UDP) and low digestible fibre. In addition, current recommendations are to feed a source of forage as 4 per cent of total solid feed, chopped to 2.5cm and containing >65 per cent NDF (e.g. chopped hay or straw) as this promotes muscular development of the rumen thereby facilitating higher intakes of starter feed. A source of chopped forage will also aid rumination which will contribute to raising rumen pH above pH 6.0.

The weaning process should start when the calf is approximately 45 days old and should involve gradually reducing the volume of milk fed daily, which should promote increased intake of starter feed. A typical recommendation is to wean Holstein calves once they are consuming 2 kg of starter feed per head per day for three consecutive days.


Including Actisaf Sc47 protected live yeast in the ration provides significant benefits to calves during the pre-weaning stage. Through its mode of action, Actisaf reduces oxygen levels in the rumen and creates an environment where the main cellulolytic bacteria will grow and thrive, thereby improving fibre digestion when it is already challenged by low rumen pH and enhancing the development of the core ruminal microbiome.

Actisaf also eases the transition on to starter feed, as it conditions the rumen microbes for the change in diet by biologically buffering the rumen and promoting a higher rumen pH through the stimulation of lactic acid-utilising bacteria. These bacteria reduce the build up of lactic acid in the calf’s rumen, which reduces the incidence of digestive upsets such as acidosis, which can greatly impact on feed digestion, rumen development and calf growth rates. Trials have also demonstrated that when supplemented during the pre-weaning period, Actisaf increases average daily gain and feed conversion efficiency, which ultimately can reduce the days to weaning by up to 7 days.

Calf health

It is generally recommended that animals are individually housed to minimise the spread of disease and facilitate the control of starter intake. With many farms now feeding calves by automatic milk feeders it is proving increasingly difficult and impractical to house calves individually. Grouping calves in batches of ten or less in this scenario is advisable to minimise stress and reduce disease risk. Ensuring calves are bedded in a clean, dry environment, which is well ventilated and supplied with adequate lighting, is vitally important to minimise stress and reduce the risk of scour and respiratory disease.

Poor calf health during the pre-weaning period has been shown to affect lifetime performance. Figure 1 shows the impact of pre- weaning scour on dairy heifer performance and figure 2 details the impact of persistent calfhood pneumonia on the performance of dairy herd replacements in first and second lactation.


Feeding Safmannan, which is a Mannanoligosaccharide-based (MOS) pre-biotic, can prove beneficial to calf performance, and is particularly pertinent with the increasing focus surrounding antibiotic usage and subsequent resistance in calves.

Safmannan is a premium yeast cell wall, manufactured from unique strains of yeast under extremely consistent manufacturing conditions. Beta glucans and mannans - the functional properties of Safmannan – strongly support the immune system of the calf, thereby strengthening its defence mechanism to challenges. During farm evaluations, which included nasal and respiratory observations, an improvement in Health Scores was observed.

Safmannan also promotes the growth and repair of the intestinal villi, ensuring that nutrient absorption from the lower gut is maximised, while also binding to specific bacterial pathogens that may enter the calf’s gut, thereby reducing the calf’s susceptibility to scours. Supplementation with 1 gram of Safmannan per head per day results in stronger, healthier calves that exhibit greater growth rates.


Figure 1: Impact of pre-weaning scour on dairy heifer performance (Source: AFBI herd data)


No Scour



Live weight (kg)


12 months




18 months




% mortality





Figure 2: Impact of persistent calfhood pneumonia on the performance of dairy herd replacements (Source: AFBI herd data) 


No pneumonia

Multiple episodes of pneumonia


1st lactation yield (kg) Milk












2nd lactation yield (kg)















  • Pre-weaning rearing period has a significant impact on herd profitability 

  • Colostrum protocols critical to health and performance 

  • Adequate starter feed required from young age to drive rumen development 

  • Supplementation with Actisaf live yeast and Safmannan premium yeast fraction can support gut development and performance 

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