July Meeting – Nutrition for Beef Cattle

We discussed the very informative MLA guide which can be located on the website under Cattle Care.  The following is a brief summary of the main points in the publication.

  • Ruminants, such as cattle and sheep, have a complex digestive system with 4 stomachs, each of which has a different job; the first is the Rumen.  The rumen changes as the animal grows and balancing the nutrient requirements of both the rumen micro-organisms and the animal is essential for good animal performance.
  • Between 60-70% of all digestion happens in the rumen; fibre is broken down and much of the protein ingested is converted to microbial protein.
  • Microbial protein (the protein contained in bugs in the rumen) cannot routinely supply all the protein requirements of young calves and breeder cows producing high volumes of milk.
  • At birth a calf’s rumen is small and doesn’t function until the calf is around 8 weeks old when it is able to break down plant protein.
  • The type of feed available will influence rumen activity, for example, mature dry grasses will be low in protein and carbohydrate, thereby limiting microbial growth.

The basic process of protein in digestion and absorption

  • The degradable portion of the feed protein is broken down in the rumen to ammonia and volatile fatty acids.
  • Urea is a form of ammonia supply.
  • Rumen micro-organisms use ammonia to build their own bodies and synthesis of microbial crude protein.
  • Energy is needed to drive the process (here comes the technical bit).  Approximately 12 megajoules of metabolizable energy is required for the growth of 100g of microbial crude protein.  The booklet has a great deal of technical information on feed ratios if you want to know more.
  • The availability of energy and protein need to be in balance.  If energy is deficient the surplus ammonia will be lost in the urine.  Similarly, if protein is deficient the surplus energy will be used inefficiently.
  • There is an upper limit to the rate of microbial protein synthesis, if protein is surplus to the requirement the excess will be lost in the urine.
  • Young animals have a high requirement for protein as a significant proportion of their growth is muscle.
  • Similarly, cows in late pregnancy have to supply protein to the rapidly growing foetus.
  • Protein is a significant and important component of milk.  Therefore, lactating cows have a higher protein requirement to meet the demands of milk production.
  • Often the high protein requirements of fast-growing young animals and cows in late pregnancy cannot be met by the rumen alone and these animals requirement supplementary protein.

Pasture or Grain?

  • While Grain is able to provide high percentages of the nutritional requirements of beef cattle, improved pastures is in fact the most cost effective feed.
  • Pasture growth is seasonal and influenced by fluctuations in water availability, temperature and day length.
  • Many native pastures decline rapidly in quality after flowering, frosting reduces plant quality even further.
  • Soils have different levels of inherent fertility, ensuring high levels of soil organic matter will enhance soil structure, water holding capacity and nutrient cycling.  The key to maintaining high levels of soil organic matter is to only graze a small proportion of pasture (up to 30%) leaving plenty to protect the soil and remain as organic matter.

Four phases of pasture growth and development

  1. When plants are growing rapidly. Pastures are most nutritious here but are susceptible to over grazing.
  2. When grasses begin to grow stem that is lower in quality.  This is the most favourable stage to gaze pasture.
  3. When grasses set seed and quality declines.  Pasture bulk is usually not limiting and little growth will occur after this.
  4. When pasture become dormant.  Quality is low and declines further with frosting.
  • Tropical pastures have more fibre and are less digestible than temperate pastures such as rye grass.
  • Young green shoots of spear grass can have protein contents of up to 18%.
  • Aim for Perennial, Productive and Palatable grasses.  The amount of the 3P grasses is a good indicator of pasture quality.  The amount of leaf left can also be used as leaf is more digestible than stem.
  • If stocking rates are set at a level that utilises only the leaf from pasture over a 12 month period, then you will be stocked to carrying capacity.  Generally utilising no more than 40% of pasture is best for cattle and pastures. (Measure this by weight, not height of the grass.  Utilise 30% of the total plant, not just the tallest leaves)

Choosing a grazing system.

  • Any system that allows cattle to select green leaf, or leaf in winter when there is no green in the pasture, will give the best result for both cattle and pastures.
  • A system of grazing that allows pastures to be spelled in the early growing season every three to four years is good for pasture condition and therefore cattle production in the long-term.
  • Cattle tend to utilise pastures closer to watering points (within 1km) more heavily.  The spacing of watering points will have an influence on the evenness of grazing.
  • Reducing the grazing period for each paddock in a rotation so cattle always have access to green leaf will improve weight gains.

Mineral nutrition of cattle

  • Cattle need 22 different elements in correct proportions to thrive.  The most important are Phosphorus sulphur, copper, sodium and cobalt.
  • Vitamin supply is not usually a problem for grazing animals.
  • Diagnosing mineral deficiencies is complicated and usually required profession assistance.
  • Whatever mineral supplement you use it is important to ensure a constant supply rather than risk an overdose if it has not been freely available for some time.
  • Soil tests can help identify mineral deficiencies in your soil.

There is a great deal of information in addition to this summary and this is by no means all there is to learn.

An additional booklet has been loaded under the Cattle Care tab on our website thanks to Heath.  It is the Meat Standards Australia Beef Information Kit giving guidance on how to improve the meat on the plate.