Where do nutrients go?

The energy and protein requirements for a range of livestock classes; dry cows, cows in calf, cows with calves at foot, bulls and young growing stock, are well-documented.

The basic principles are to first provide nutrients, mainly as energy and protein, for maintenance of the animal and beyond this nutrients are provided for physiological needs such as lactation, activity, muscle growth and fat deposition.

However, losses and distribution (partitioning) of nutrients can potentially occur throughout the production cycle in beef cattle.

Next time you observe cattle feeding consider where the nutrients might end up or be lost.

Losses and distribution could be categorised as: Physical losses Wastage – pasture trampling, un-grazed manure and urine patches and spillage or spoilage of supplementary feed.

Indigestibility – some parts of diet can be ‘indigestible’, not providing nutrition. Physiological ‘losses’ Maintenance – temperature, chill factors, terrain.

Utilisation – site of digestion (rumen, reticulum, omasum, abomasum, small/large intestine) and nutrient balance.

Immune function/response – to pathogen load, if any, from the environment or vaccination. Tissue partitioning In cows, egg production, foetal growth and milk production Muscle growth and repair Fat deposition In relation to physical losses, a feed wastage study by Dairy Australia showed that hay wastage, when fed to stock at pastures, could range from three to 27 per cent depending on hay type and feeding system.

Cattle will actively avoid ‘indigestible’ parts of a ration.

Physiological ‘losses’ for example, could be the energy needed to traverse paddocks. Another example is excess dietary protein.

0.18 MJ ME is required to process every one per cent of crude protein in excess of needs.

Additional physiological losses could occur if parasites have damaged the digestive system affecting nutrient uptake or, if an animal has an infection requiring a high immune response leading to the utilisation of nutrients away from other requirements.

While information relating to this issue for beef cattle is scarce, other livestock sectors note more than 20 per cent of energy intake may be lost when an animal’s immune system is dealing with infection.

In beef production, consumed nutrients (including protein and energy), after meeting maintenance requirements, should be partitioned to meet production needs.

For young cattle growing at one kg/day, about 40 per cent of the nutrient (energy) intake goes towards growth.

In contrast, in a cow at the point of calving, about 38 per cent of nutrient supports the pregnancy while after calving over 50 per cent of nutrient intake supports lactation.

The ability to convert nutrients from grazed forages and supplementary feeds into production is an important aspect of overall efficiency of cattle production systems.

Feed efficiency in a beef herd is complex and has genetic, management and environmental components.

In summary, nutrients, as resources into a beef production system must have minimal physical losses, provide the minimal amount necessary towards maintenance while additional nutrient should aim to maximise partitioning to tissue needs without unnecessary physiological losses.