HEIFERMAX

During a recent discussion, a dairy farmer made the comment that beef calves get on fine when they are left to suckle their colostrum from the cow. He went on to query the recommendation that dairy farmers routinely administer colostrum to their calves.

His comments highlighted the fact that many dairy farm personnel are confused about colostrum and the role it plays in the life (or death) of a dairy calf.

I hope this article develops a better understanding of the reasons behind this recommendation.

 Immunity

Immunity is a word which farmers use but sometimes can’t clearly define. An understanding of this is necessary to appreciate why colostrum is so important to dairy calves.

Immunity is the body’s ability to defend itself against invasion by bacteria, viruses, parasites etc. The immune system is comprised of skin, intestines, mucous membranes, blood components, lymph system, other organs and tissues. The “workers” in this complex system are millions of specialised cells which have the ability to recognise and disable invading organisms.

 In any mammal, including humans, there are two types of immunity - passive and active.

• 1. Passive is conveyed to neonates via colostrum or across the placenta; later in life it can be conveyed by injection e.g. a tetanus anti-toxin. Passive immunity is immediate but short-lived.
• 2. Active immunity is developed by the body, either in response to exposure to disease or to dead or modified disease causing organisms in the form of a vaccine.

Human babies acquire passive immunity via the placenta i.e. the antibodies pass from the mother’s bloodstream to the baby’s. This means that human babies are born with immunity to the diseases to which the mother has been exposed. Colostrum is not essential for survival.

Newborn calves, however, are essentially born without immunity to disease because in calves the antibodies are too big to pass through the placenta. Nature has designed calves to receive their immunity from colostrum.

 An adequate volume of high quality colostrum is required to provide the necessary antibodies to achieve a high level of passive immunity.

  In calves, passive immunity starts to decline within the first few days of life, while active immunity only starts to ramp up at about two weeks of age. This can mean there is a gap from about 3 days to three weeks when calves are very vulnerable to disease challenges. Various factors influence the time and speed at which this active immunity develops.

 A simplisitic explanation is that until the newborn calf receives colostrum, its immune system is like a rifle without bullets - all there and in working order but without the ability to perform its role. The “bullets” needed for full functionality of the immune system are called antibodies (also known as immunoglobulins or Igs). These cells seek out and neutralise foreign cells such as bacteria and viruses. These foreign cells are known as antigens. Colostrum provides “temporary bullets” (passive immunity) which make the system workable until the calf can start manufacturing its own “bullets” (active immunity). The current recommendations are that calves be given colostrum at the rate of least 10% of birth weight ASAP but certainly  within the first 4 hours life to enable them to receive adequate passive immunity.

 Colostrum

Colostrum is the first milking from a freshly calved cow (or sheep, pig, human, goat etc.). The milkings subsequent to this but which are unsuitable to go into the vat are “transition milk”. Colostrum is a complex blend of nutrients, immune proteins, immune cells, hormones and growth factors needed to provide a nutritional “kick start” in life and to confer immune competence to the newborn calf.

The table below demonstrates clearly the value of colostrum as a concentrated source of nutrition as well as the calf’s only source of immunity. Note colostrum’s very high levels of IgG, total solids and proteins compared to milk. 

 Foley & Otterby, 1978, J of Dairy Science

The values in the table above are based on the first milking being less than one hour after calving (with subsequent milkings being at 12 hourly intervals). If the first milking post calving is delayed by 6 hours (a common situation on Australian dairies) it is estimated that the colostrum contains only 60% of the level of antibodies which were contained directly after parturition. There is likely to be a similar decline in the nutrient levels as well, bringing the qualities of that first milking down to about the levels normally found in the second milking.

 Why is it emphasised that calves get their colostrum very early in life?

There are three types of antibodies (or immunoglobulins) in colostrum:  IgA, IgG & IgM.

These are used by the body in different ways; two of these types of antibodies need to pass from the gut into the bloodstream. It would not normally be possible for such large molecules to pass out of the gut but the intestines of newborn calves have a special function called pinocytosis which allows this to happen. A simplistic explanation of this, is that for about 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 older the calf gets the more the passage of the molecules is restricted; the permeability of the gut has dropped to ≈ 50% 6 hours after birth and has virtually gone by 24 hours of age.

If a calf fails to absorb sufficient immunoglobulins to provide adequate passive immunity, it is described as having “failure of passive transfer” or “FPT”.

 The need for administering colostrum.

Let us return to the dairy farmer’s question about why dairy calves need to be fed colostrum when beef calves get on fine without someone fussing over them.

There are two important differences between grazed beef cattle and dairy cattle:-

1. Production levels of dairy cows; dairy cows produce far more milk than beef cows. This production increase extends to the amount of colostrum yielded in the first milking. Cows deplete their own reserves of antibodies to build up levels in their colostrum. The number of antibodies available remains the same no matter how how great a volume of colostrum she produces. Therefore, in the colostrum of the higher producing dairy cow, the antibody levels are likely to be much lower per litre than that of the beef cow. A calf would have to drink far more litres of dairy cow milk to get the same number of antibodies. A high percentage of dairy calves left to suckle their dams do not consume sufficient volume to give adequate passive transfer.
2. Environment; the second important thing that is different is the environment in which the calves are raised.

Beef cattle are run in more or less the same environment as Nature intended. Calves extensively grazed with their mothers encounter minimal environmental contamination; beef cows have evolved to produce colostrum of sufficient quality to give the calf the immunity it needs to survive the few disease challenges to which it is exposed. In consequence they are mainly healthy and grow well.

Today’s dairy calves are often raised in conditions of overcrowding, massive pathogen challenges (too many germs in the diet and environment) and high stress levels. So, not only are they deficient in immunity, they are subjected to far more challenge to their immune system than beef calves in extensive grazing systems.

 What are the consequences of inadequate colostrum consumption?

The commonly accepted indicator of failure of passive transfer (FPT) is plasma IgG concentrations of less than 10 mg/ml at 24 to 48 hours of age. It is a major contributing factor to gastro-intestinal disease and pneumonia in calves. Calves with FPT have greatly increased morbidity and mortality rates, lower ADGs, higher rearing costs and are more likely to have delayed puberty, delayed conception, difficulty getting back in calf, lower lifetime production and higher cull rates than calves with adequate passive transfer.

 The following table summarises the findings of one particular trial done several years ago which suggests that there are long term benefits of feeding 4 litres of high quality colostrum immediately after birth. There is ample evidence to support the findings of this trial.

 Performance of calves fed either 2 or 4 litres of colostrum immediately after birth.

Source: Faber et al., 2005. Prof. Anim. Sci. 21:420-425.

 It is thought that good colostrum management not only reduces the incidence and severity of health problems in calves, but may improve nutrient digestion and metabolism in the young calf, thus allowing it to grow more efficiently. Better growth rates are thought to positively influence endocrine function related to mammary development. All these factors contribute to improved milk production and increased chances of heifers staying in the herd longer.

 A heifer’s genetic potential for milk production is the maximum production level she is capable of attaining. Her phenotypic ability to reach this genetic potential is governed by several interacting factors. Early life growth rates are a crucial factor in determining whether or not a heifer is able to reach her genetic potential. Colostrum management is a integral factor in achieving high early life growth rates.

 Heifer management is a key driver of profit on modern dairy farms. Across the herd, the economic gain generated by the lifelong benefits of optimal colostrum management and therefore early life growth rates make a mockery of any attempts to save money by cutting calf rearing costs. The comparatively low costs of implementing management protocols to ensure heifers receive sufficient colostrum to ensure adequate passive transfer is more than repaid in reduced costs of veterinary intervention, lower death losses, increased growth rates, optimal reproductive performance and increased lifetime milk yield.

It is important to realise that the inability or unwillingness to manage colostrum and provide adequate passive transfer to calves is responsible for most diseases affecting calves in the first few weeks of life.

Not ensuring that every calf is given colostrum because it is “too hard” will not alter the biology of the calves. If a farm wants to make business like decisions to ensure predictably good heifer rearing results, the calf management system must be adapted to fit the physiology of the calves.