In recent times, there has been a renewed focus on the importance of successful calf rearing to profitable dairy production. Dairy heifer rearing uses up a large amount of farm resources, including feed, housing, and labour. Teagasc estimates the total cost of rearing a replacement heifer at €1,545. To offset this, management must be handled in a manner that yields the best-quality heifer, with a high potential to be productive, and at minimal cost to the farm.

Emerging evidence suggests early calf-rearing practices are crucial to these aims and can have a lasting influence on the productivity and longevity of heifers as lactating cows. Achieving optimal calf growth during the expensive pre-weaning period is recognised as the critical criteria to successfully raising dairy calves and has a significant bearing on achieving herd productivity targets. Pre-weaning, a sound calf-nutrition programme is the most important factor for calf growth during the first two months, coupled with the integration of animal husbandry and health management skills of the farmer.

Milk feeding

Milk or milk replacer (MR) is the sole nutrient source for the calf’s growth and maintenance needs for about the first three weeks after birth. The amount of MR offered will depend on the calf body weight, desired growth rate and nutritional composition. For successful calf rearing, the target is to achieve 700g per day growth up to weaning, resulting in 100kg liveweight at 12 weeks. Because of the cost and labour involved, milk-feeding programmes (milk fed at 8% to 10% of BW – 4 litres/day) were traditionally designed to provide nutrients for limited body growth, with the main goal of the pre-weaning period to facilitate early transition from milk to dry feed. These diets failed to meet the nutritional requirement of calves, performance was poor, growth targets were rarely achieved and calf health and morbidity issues have plagued them. To hit the growth target, nutritional requirements indicate that calves need to be fed milk at 12% to 15% of BW. Under most circumstances, the recommendation is that a standard MR is offered at a feeding rate of six litres (125g/l; split between two feeds), equating to 750g of powder per day.

In terms of composition, MR should contain a minimum of 20% protein, (22% to 25% protein if it contains non-milk proteins such as soy protein) and 15% to 20% fat are preferred.

Fat sources in milk replacers such as milk fat, tallow, choice white grease or lard are preferred over vegetable oils, which are utilised poorly by the young calf. In general, MR containing milk products are digested better than those containing vegetable proteins and vegetable oil.

If MR containing non-milk protein sources are going to be fed, it is recommended not to start before three weeks of age. After the third week, calves should be able to better digest formulations with non-milk protein sources.

Conventional v intensified

Intensified feeding of calves for accelerated growth is a hot topic in calf management. With conventional feeding strategies, the argument proposed is that calves are fed to minimum nutrition rather than optimum nutrition.

In the first few weeks of life, conventional feeding rates only provide enough nutrients for maintenance requirements and up to about 150-300g/day growth. Until calf concentrate intakes increase, there will not be enough nutrients consumed to allow calves to begin to grow sufficiently.

Alternatively, intensified feeding allows calves much greater intakes of milk in early life, with feeding rates approximately twice those offered in conventional systems. Compared with conventional systems, the major difference in performance is seen in the first two to four weeks of life. After that, growth rates between enhanced and conventional rearing programmes are similar. The Nutreco LifeStart programme is a good example of an enhanced feeding regime – feed calves 6l/day (15% concentration; equating to 900g powder/per calf/day), split between two or three feeds. Offer milk at this rate for 40 to 42 days and then start to reduce levels gradually to wean at 60 to 70 days. Target growth rate at three months is 115kg to 120kg, with an input of 48kg of milk powder. Also, the MR contain 25% to 28% crude protein to support the potential of young calves for rapid lean growth, and 15% to 20% fat.

Studies have also reported that the enhanced nutrition during the critical window of opportunity at the start of the calves’ life (first two months) can alter future productivity of the cow. With reduction in age at first calving, improvements in health and robustness, enhanced mammary development and greater milk production are some of the reported benefits associated with this feeding strategy. These significant production benefits will more than cover the greater MR feed cost.

Conversely, other reports have failed to show that calves on intensified feeding programmes calved at an earlier age nor did they identify a productivity benefit on milk production later in life, which calls into question the economic payback for the additional investment. Further investigation is needed to paint a clearer picture.

Rumen development

Developing the rumen and in turn changing the calf from a pre-ruminant (depending on liquid diets) to a ruminant animal which can digest concentrates and roughage, is of paramount importance to successful calf rearing and maintaining calf growth targets. Consumption of starch-based concentrates drives rumen development. Once the calf eats concentrates, the rumen begins to supply nutrients produced by fermentation and a population of rumen bacteria begins to grow. Fermentation of the starch component of grain produces volatile fatty acids (VFA), particularly butyrate, which stimulates growth of rumen papillae, essential for the absorption of nutrients in the rumen.

It takes about three to four weeks to develop the rumen papillae from the initial time that concentrate is offered. The earlier starch is digested by the calf, the faster rumen development occurs. From a management viewpoint, rumen development can be assisted by providing high-quality concentrate to the calf in the first few days after birth, along with access to water. Nutritional management plays a crucial role in determining rumen development and ultimately will determine weaning age.

I. Concentrates the key to success: Concentrate and water should be offered to calves within three to four days of birth. Calves should be eating some meal by five to seven days of age and at two weeks of age the calf should be eating approximately half a pound of meal (200g to 300g). Calf starter should be high-quality and coarse in nature to provide the best texture for calves. Avoid finely ground, dusty feeds. Dusty diets may lead to increased incidence of respiratory disease. A good concentrate should contain between 17% and 18% crude protein, the necessary mineral and vitamin supplements and have an energy value of at least 12 MJ/kg (>0.95 UFV/kg). Always try to encourage starter intake. Keep the calf starter as fresh as possible and only feed small quantities. It is important to clean out mouldy or spoiled feed and replace with fresh feed daily, to stimulate appetite. Ensure feed buckets and troughs are the correct height to enable easy access for the calves.

II. Feeding roughage: Calves in general do not need roughage during the pre-weaning period (less than eight weeks old). Roughage such as hay or chopped straw is not required until a time when the calves are consuming about 2kg to 2.5kg of concentrate, which typically doesn’t occur until after weaning. Long forage is beneficial to promote the growth of the rumen muscular layer and maintain the health of rumen epithelium. A general recommendation would be to offer roughage starting at week eight and monitor meal intake to ensure hay is not being overeaten. Including too much roughage would lower the energy content of diets and would not therefore be beneficial. When a calf has unrestricted access to large amounts of roughage, rumen capacity increases. However, excess roughage intake (especially hay) results in a pot belly condition. To limit this, research suggests that a concentrate to roughage (hay) ratio by weight of eight to one is satisfactory.

Successful weaning

Depending on the feeding strategy, calf weaning age can vary from six to 10 weeks. However, age should not be the main criteria. Weaning decisions should be based on the calf’s solid feed intake. Once a calf is consuming 1.3% to 1.5% of its body weight as dry feed, this will provide sufficient nutrients to maintain its weight and growth without liquid feed. For Friesian dairy calves, this equates to weaning when the calf consumes 1kg of calf starter per day for three consecutive days. To stimulate concentrate intake, the general advice is to reduce liquid feed consumption by 50% per day one week prior to desired weaning date. Measuring the calf starter intake is crucial. By monitoring starter intake, farmers can adjust weaning dates for calves that fall behind due to an illness, and wean only those that are healthy and eating well. Importantly, if the rumen is not prepared and functional, the calf will suffer a post-weaning growth check for up to three weeks after weaning and this will occur regardless of calf age or calf weight.

Weaning imposes significant stress on calves due to changes in their diets, housing and environments. Simple management practices can reduce stress. Give calves time to adjust to weaning – wait at least a week after weaning before you move calves to a new house. Ensure housing areas have adequate ventilation and are clean and well bedded. If group housing, keep the group small and try to keep the ration the same as before weaning for the first two to three weeks. Also, avoid management practices that cause stress, such as dehorning and vaccination, around the time of weaning.

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