HEIFERMAX

Baby calves have evolved to drink milk. Although they have a digestive system comprised of the same 4 “stomachs” or compartments as an adult ruminant, 3 of these stomachs, the rumen, reticulum and omasum are non-functional at birth.

Calves are born as mono-gastrics, utilising only their abomasums to digest milk.

The abomasum functions much like our stomachs, in that hydrochloric acid and enzymes such as pepsin and chymosin (rennet) are secreted into the stomach. Other enzymes, such as lipase and bile,  secreted by the pancreas and liver, further aid the digestion of milk in the abomasum and in the intestine.

If a calf were to be fed only milk until slaughter there would be no change to the function or development of its other three stomachs but its abomasum would increase in size to accommodate the growing volume of milk needed to support maintenance and growth.

 The differences between the digestive systems of a mono-gastric calf and the adult ruminant it will become, create unique nutritional needs in pre-weaned calves. These unique needs are especially important in replacement heifers, which must be weaned far earlier than nature intended but which must also achieve the growth rates necessary for them to mature into productive dairy cows.

Left to nature, the transition from mono-gastric to ruminant is a process which occurs over a period of almost a year. The space restrictions, the  relatively time  consuming nature of milk feeding and the high costs of labour mean that modern dairy farmers have to reduce this process to a period of 3 to 4 months.

In a baby calf the abomasum comprises ≈ 60% of the calf’s stomach capacity, while the reticulo-rumen contains ≈ 30% and the omasum 10%. In an adult animal the proportions occupied by the abomasum and reticulo-rumen have more or less reversed, while the omasum size has remained about the same.

Rumen development.

The rumen in a neonatal calf is non-functional, with a smooth, relatively avascular lining and no microbial population.

There are two separate aspects in the development of the rumen into a functional organ, capable of digesting sufficient feed to sustain high growth rates.

Firstly the rumen lining must change from a smooth membrane with a small surface area and low absorptive capacity due to restricted vascularisation. It must become a convoluted surface with many fingerlike papillae dramatically increasing the surface area and with an extensive network of capillaries to absorb the nutrients digested in the rumen. These changes are dependent on the establishment of a population of microbes within the rumen. Initially, the microbes enter the rumen from ingested bedding, hair and feed and from dirt ingested from the environment. Once a population is established, its composition changes in response to the types of feeds ingested by the calf. Forages are digested by different microbes than starches.

Secondly, the size and musculature of the rumen must increase, so that it can contain sufficient feed to sustain life and so that the contents can be churned to optimise digestion.

 Both aspects of change are dependent on solid feed entering the rumen but the changes are stimulated by two different factors:-

1.      Changes to the interior of the rumen are stimulated by the presence of volatile fatty acids produced from the digestion of starch.

2.      Changes to the size and musculature of the rumen are stimulated by the volume and texture of the rumen contents. The level of forage in the diet influences the amount of ruminating (cud chewing) that occurs.

Factors influencing feed intake.

There are many interacting factors which influence the consumption of solid feed:-

·         the quantity of milk fed

·         availability and cleanliness of water

·         palatability of the starter

·         particle size of the starter

·         type of grain feeders and space available per calf

·         the design of calf housing

·         calf health

·         stress levels

·         calf management

·         the environment, particularly temperature and humidity.

Palatability and preference are terms that are often interchanged. In fact, they are two separate things. Palatability is the “tastiness” of a product – whether or not the flavour appeals to a calf. Preference, which is a term often used in comparative trials run by companies promoting a particular product, means the product will be chosen by the calf when it has limited choice e.g. pellets versus muesli or aniseed flavoured pellets versus unflavoured. Neither of the choices may be palatable to the calf, but it is likely to consistently choose the less unpleasant of the two choices. Intake is driven by palatability; if calves find the aroma, texture and taste of a starter pleasing, they will eat more of it than of a feed in which one or more of the factors is not as acceptable. 

Internationally, there has been a lot of research into what solid feeds are the best for developing the rumen of the baby calf. Texture has a major impact on consumption. Baby calves do not like fines; any starter which has a large percentage of powdery particles will be less acceptable to calves.  As a generalisation, many commercial and home made calf starters I see on farms in Australia are much too finely ground.

Outflow from the rumen through the pyloric sphincter into the abomasum is determined by particle size. The size of the orifice is directly related to the size of the animal. An adult cow’s sphincter will let whole grains pass, undigested, out of the rumen. The much smaller calf’s sphincter will hold the same size particles back in the rumen. They will then be regurgitated, chewed again and returned to the rumen for further microbial digestion. Therefore, large particle size in calf diets will result in slower digestion of grains, reduced incidence of acidosis and more efficient use of the feed.

Water.

Rumen microbes require water to develop, multiply and to digest feeds. If water is limited, microbe numbers will remain low and digestion will be restricted. Water must be clean, fresh and freely available at all times. Milk and even the water in milk replacers, bypasses the rumen and goes directly into the abomasum. This has no benefit in developing the rumen. 

A textured starter with low fines, will encourage calves to start consuming solid feed. Molasses is often used to increase palatability and to bind fine ingredients such as canola meal. An inclusion rate of ≤5% molasses will increase palatability and make the product smell nice, which entices baby calves to taste the mix (even this relatively low level of inclusion is too high for a bulk mix stored in a silo). Fat/oil can also be used to bind powdery ingredients and as an energy source but should be limited to about 2-3% as at higher levels it will decrease intake.

Starter composition.

The following information has been gained from talking to many erudite scientists, vets and nutritionists.  Amongst these is the heifer advisor to a farm which averages >38.5 litres/cow/day in a 1,200 cow herd which comprises 50% first calvers and which has a death rate of <1% in their pre-weaned calves.

Starters typically have as fed protein levels of 19 – 21%. Those with high protein levels (23 – 25% as fed) encourage lean body growth and skeletal growth, particularly in calves fed high levels of milk.

The best protein sources are:-

·         soybeans – either roasted or as a meal. Either of these heat treated forms is very palatable.

·         the sweet lupins grown in Australia, which are a safe and palatable high protein feed.

·         faba beans are acceptable at low inclusion rates but have various anti-nutritional factors as well as low levels of two essential amino acids. Heat treating will destroy the anti-nutritional factors.

Less acceptable protein sources are:-

·         canola meal, which is a valuable source of protein with a good amino acid balance but which is very unpalatable to baby calves.

·         wheat, which is too fermentable to be a good calf starter ingredient.

·         brewers/distillers grains, which are not easily digested by baby calves.

·         urea, which is hard for calves to process.

Energy can be supplied from corn, oats, barley, molasses and fat. Barley, rolled or steam flaked, should be included at only about half the amount of corn, as the starch it contains is much more available than that in corn, and is therefore more likely to cause acidosis. The ideal energy source is corn (whole, roasted or cracked); whole oats are another acceptable energy source.

Fibre is not an essential component of the diet of pre-weaned calves; in fact, it is undesirable at the levels commonly recommended in Australia. In starter for pre-weaned calves (< 8 weeks) the use of fibre should be limited to maximize gain and efficiency. No fibre is acceptable in a primarily corn/soybean ration. In starters containing more highly fermentable cereal grains, high quality lucerne chaff could be added at ≈ 5%. Straw is totally undesirable and even good quality pasture hay is counter productive. The reason for this is that the size and digestive capacity of the rumen of very young calves is extremely limited; the food going into the rumen needs to be as nutritionally dense as possible to maximise rumen development.

Once calves have been weaned for a week or so, they can be gradually introduced to forage. Their rumen capacity is still limited, so the forage source should be a high quality hay. Even if grain fed calves are not weaned by 12 weeks, forage should be included in their diet.

Conclusion

Care must be taken not to lose sight of the end goal if choosing low cost options when selecting ingredients. Some of the current Australian calf feeding recommendations make it easy to “throw the baby out with the bathwater”. Economising on the costs of calf feed can ultimately be the most expensive option. The aim of feeding calves is to provide a supply of replacement heifers which are sufficiently productive to remain as profitable members of the herd for several lactations. There is no point choosing a cheaper ingredient if it makes the starter less digestible or unattractive to the calves with a resultant reduced intake and subsequent depression in growth rates. This approach is likely to deliver heifers which are culled early for:-

·         failure to meet target mating weights/get in calf

·         calving difficulties

·         low productivity

·         failure to get back in calf.

Calves which are healthy and grow rapidly in the first eight weeks of life will be far more productive and profitable than limit fed heifers which are raised on a budget and which are not given the building blocks to reach their genetic potential for milk production. The cheapest calf feed is the one which produces the highest number of litres of milk over the lifetime of the heifer; calf feeds which result in  heifers being culled for the above reasons are unlikely to be the cheapest options.