Key principles for calf-rearing success

Key principles for calf-rearing success

Herd Management
These much-used illustrations from Penn State University show quite clearly the lack of rumen development caused by feeding hay compared with feeding just milk and grain. Photos courtesy of Penn State University

These much-used illustrations from Penn State University show quite clearly the lack of rumen development caused by feeding hay compared with feeding just milk and grain. Photos courtesy of Penn State University

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It is imperative for everyone involved in calf management to have a good understanding of the key principles involved in keeping calves healthy and growing well.

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THE increasing demand by consumers for transparent animal welfare practices makes it imperative for all those involved in calf management to have a good understanding of the key principles involved in keeping calves healthy and growing well.

Even casual staff, such as backpackers, should be given some training in the major concepts involved in raising calves to reach health and growth milestones.

It is important that farms keep at least basic records of calf health and growth rates; setting key performance indicators for calf rearing will help ensure that targets are being met.

This also helps to get everyone on the same page when it comes to what is acceptable in terms of calf weights, body condition scores, mortality and morbidity levels.

Keeping track of mortality and morbidity rates is a relatively simple matter of noting which cow has calved, what sex the calf is, what is the predicted end use of the calf (replacement, beef, slaughter, etc.) and then making sure that details of any illness and treatment suffered by the calf is noted and accounted for in the year's statistics.

If a calf dies it is useful to note the cause and age as well as the date.

Knowing what calves weigh is a powerful management tool and a set of scales is a minor financial outlay compared with the high cost of having heifers culled early due to poor performance.

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Accuracy is important with all record-keeping; fudging the figures will not alter the facts.

There are many ways to rear good calves but there are three outcomes-based measures that will help quantify that success.

  • Calves should double their birthweight by eight weeks at the latest. Early life body condition score is a good indicator of whether calves are on track to achieve this.
  • Mortality should be less than 1 per cent of calves born healthy.
  • Morbidity (calves that need to be treated in some way, either with electrolytes, antibiotics or vet visits) should be no more than 5pc.

I'd like to discuss three calf-rearing topics in the hope that a better understanding will help people rear healthier calves.

Immunity

The first topic is immunity - a topic that is at the forefront of our minds in recent months, thanks to COVID-19.

Immunity is a state of having sufficient biological defences to avoid infection, disease, or other unwanted biological invasions, and is regulated by the functions of the immune system. In simple terms, it is the body's ability to fight off threats from pathogens (or germs) such as bacteria, viruses, fungi and parasites.

Immuno-competency is not a stand-alone state; it is interwoven with the level of contamination in an environment, nutritional status and stress levels. In baby calves, nutrition plays a big part in the calf's ability to respond to an immune challenge.

Calves are not born with full immunity to diseases; they get short-term immunity from colostrum and develop long-term immunity themselves when they are exposed to pathogens or vaccines.

Innate immunity

There are natural barriers to infection, both physical and physiological, which are known collectively as innate immunity. The skin is the largest organ in the body's defence against infection.

The mucous membranes lining the respiratory tract are another barrier against infection. Some of the other organs involved in defending the body against infection are the tonsils, adenoids and spleen. This type of immunity gives a broad, general defence against pathogens or germs.

Adaptive immunity

Apart from innate immunity, there is also something called adaptive immunity, which can be broken down into two types of immunity - passive and active.

The basis of adaptive immunity is that the body "adapts" its functioning in response to exposure to particular pathogens. Pathogens (germs) that have gained entry to the body have components (antigens) that stimulate the body to mount an immune response.

Antibodies are the basis of this immune response; they act by attaching themselves to a foreign antigen and weakening or destroying it. This sort of immunity is pathogen-specific - for example, the antibodies that recognise and disable Salmonella dublin will not recognise Salmonella typhimurium. Once these antibodies are formed, they generate a "memory" and will continue to recognise and destroy that particular pathogen.

Both passive and active immunity can be acquired naturally or artificially.

Passive immunity can occur naturally such as when immunity is conveyed to newborns via colostrum or across the placenta; later in life it can be conveyed artificially by injection e.g. a tetanus anti-toxin. Passive immunity is immediate but short-lived and is normally superseded by active immunity.

Human babies acquire natural passive immunity via the placenta i.e. the antibodies pass, early in pregnancy, from the mother's bloodstream to the baby's.

In calves, the antibodies are too big to pass through the placenta and so calves must receive their early immunity to common diseases from an adequate supply of high-quality colostrum in the first few hours of life, which provides the necessary antibodies for passive immunity.

Calves that receive no colostrum have no immunity (a state known as agammaglobulinaemia); the early life challenges calves face makes it unlikely that an agammaglobulinaemic calf will survive.

Active immunity is developed naturally by the body in response to exposure to pathogens or artificially by exposure to dead or modified disease-causing organisms (germs) in the form of a vaccine. It is generally longer lasting and can give a lifetime's protection against a particular infection by stimulating a memory that is used by the body later when it is exposed to the same germ.

The calves shown in the photo are in poor condition and will never reach their genetic potential for productivity or profitability and would not meet acceptable animal welfare standards.

The calves shown in the photo are in poor condition and will never reach their genetic potential for productivity or profitability and would not meet acceptable animal welfare standards.

Colostrum

Immunity leads on to colostrum. Nature intended calves to run around in green pastures behind their mothers i.e. minimal environmental contamination. Colostrum, as cattle were evolving, was of sufficient quality to give the calf the immunity it needed to survive the few disease challenges to which it was exposed.

Today's calves are often raised in conditions of overcrowding, significant pathogen challenges (too many germs in the environment), high stress levels, lack of continuity of care (multiple carers) and, if left to suckle their dam, to have inadequate immunity. So, not only are they deficient in immunity, they are subjected to far more immune challenges than their immature immune systems can manage.

There has been a lot of emphasis placed on good colostrum management and by now everyone involved in calf rearing would know how important it is to calf health.

Colostrum is the first milking from a freshly calved cow; but something which needs to be emphasised here is that "first milking" does not mean 24 hours after giving birth. The colostrum constituents quoted below are for milk harvested within a couple of hours of birth. Any delay in harvesting colostrum is going to significantly reduce the benefits to the calf.

Colostrum is a complex blend of nutrients, immune proteins, immune cells, hormones and growth factors, which give the calf an immediate source of energy, confer passive immunity and positively influence productive and reproductive capacity later in life.

Colostrum has:

  • nearly twice the solids;
  • 4.5 times the protein;
  • nearly double the fat of milk; and
  • a massive 80 times the immunoglobulins that milk contains.

Colostrum quality declines within six hours of calving to the same level as in second-milking colostrum.

There are three main types of antibodies (or immunoglobulins) in colostrum:

  • IgA, which attaches to the lining of the intestine and prevents pathogens from attaching and causing disease.
  • IgG, which is the smallest and most prolific of the immunoglobulins and can pass from the bloodstream into other parts of the body, identify pathogens and defend the body against them.
  • IgM, which is a large molecule that stays in the blood and protects against septicaemia (blood poisoning).

IgG and IgM need to pass from the gut into the bloodstream. Later in life it is not possible for such large molecules to pass out of the gut but immediately after birth the gut has a special feature that allows this to happen. In a process called pinocytosis, enterocytes absorb the macromolecules, transport them across the cell and deposit them into the lymphatic system.

A simplistic explanation of this is that within the first 24 hours of a calf's life the gut has the ability to allow large molecules to pass through it (think of a soaker hose). The important thing to remember is that the older the calf gets and the more things pass through the gut, the more the passage of molecules is restricted, with the permeability of the gut dropping to 50 per cent by six hours after birth and to zero by 24 hours of age.

Another important factor to consider is that the process of Ig absorption is non-selective; the enterocytes will absorb any large particle that passes through the gut. If calves are born in a dirty environment or if they are fed colostrum that is contaminated, some of the particles absorbed will be pathogens - "bad guys" rather than "good guys".

Several studies have shown that a high percentage of Australian dairy calves do not have adequate passive transfer - in other words they do not get enough immunity to be healthy just by suckling their dam. If colostrum collection is delayed because the calves are left on their dam for more than 12 hours, the quality of the colostrum has declined and the calves' ability to absorb immunoglobulins has also plummeted. Milking the cow 12-18 hours after it has given birth will yield colostrum that has a low Brix score; by 12-18 hours after the calf is born, its ability to absorb immunoglobulins is less than 10 per cent of what it was shortly after birth.

Nutrition

Another contributing factor to calves' level of immunity is their nutritional status. In the first few weeks of life, calves should get most of their nutrients from milk. This gives the immune system the fuel it needs to develop and become more effective.

It also kickstarts the metabolic programming that is responsible for future milk production and reproductive ability. The aim of most calf-rearing programs is to rear calves that can be weaned earlier than they would in their natural state. However, the calves need to be sufficiently nourished to go on to be efficient producers of milk in later life. This will not happen if calves are nutritionally deprived in the first few weeks of life; compensatory growth does not exist for weight that is not put on in early life.

Aiming for high grain consumption early in life is also detrimental to future productivity and is an indicator that calves are not being offered enough milk.

A milk-fed calf, no matter how big, sleek and shiny, cannot be successfully weaned unless it has sufficient rumen development to enable it to function as a ruminant rather than a monogastric. Weaning should be based on grain consumption rather than age or weight; calves will be able to survive without a post-weaning slump if they are consuming one kilogram a day of concentrate.

The development of the rumen is stimulated by the presence of volatile fatty acids (VFAs) produced by the digestion of feeds by microorganisms in the rumen. This development turns the inside of the rumen from a smooth pale surface to a convoluted dark coloured surface, with greatly increased surface area (papillae) and rich blood supply. This increases the ability of the rumen to absorb nutrients.

The much-used illustrations from Penn State University accompanying this article show quite clearly the lack of rumen development caused by feeding hay.

Rumen development is stimulated by encouraging the early consumption of dry feed. Traditionally the feeds used have been pellets and straw/hay (forage), which was thought to contribute the vital "scratch" factor.

Decades ago, research showed that the "scratch" factor is a myth and that forage consumption pre-weaning is actually counterproductive in rumen development. However, the habit of feeding hay to pre-weaned calves lingers within the industry.

Current suggestions are that pre-weaned calves should have 5pc forage by weight included in a muesli-style grain mix. Pellets are acceptable, but generally viewed as a less desirable feedstuff than a muesli mix.

The digestion of grain, whether whole or pelleted, results in the production of the volatile fatty acid (VFA) butyrate, which is the main driver of ruminal mitosis i.e. cell division within the rumen wall, thus enlarging the size of the rumen.

Feeding hay, straw or other forage to young pre-weaned calves will retard rumen development because calves will limit consumption of some of the butyrate-producing grain in favour of low quality, acetate-producing forage.

Calves have a high energy requirement relative to their ability to consume dry feed. If calves consume significant amounts of hay, their intake of grain or pellets will be limited and growth and rumen development will be slowed.

Once calves are completely weaned and are totally dependent on rumen function for survival, they do need high-quality forage to develop the size and musculature of the rumen.

Water

The rumen cannot function without a supply of fresh water. Milk does not help rumen development at all, as it does not enter the rumen.

Calves should have fresh clean water available at all times; this means that troughs must be properly cleaned both regularly and frequently. A 90kg heifer will drink about 12-15 litres on a 25 degree Celsius day. This will increase significantly in hot weather.

Body condition scoring

Body condition scoring is a good way of keeping track of calf development. Healthy, well-fed calves will not lose body condition after birth. Loss of body condition is an indicator that the nutritional or health status of the calf is poor.

The calves shown in the photo are in poor condition and will never reach their genetic potential for productivity or profitability and would not meet acceptable animal welfare standards.

Improving calf raising outcomes to satisfy welfare standards and meet consumer expectations requires changes to how calves are raised. Making these improvements is also financially beneficial to the enterprise, so is a win-win position to be in.

*Jeanette Fisher operates a dairy heifer advisory business, Heifermax, and can be contacted through her website www.heifermax.com.au.

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