Unlocking the Secrets of Ruminant Nutrition

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Common mistakes made regarding supplementary feeding are getting the timing wrong, confusing protein and energy and poorly diagnosing mineral deficiencies. Photo: Kondinin Group

Common mistakes made regarding supplementary feeding are getting the timing wrong, confusing protein and energy and poorly diagnosing mineral deficiencies. Photo: Kondinin Group

A recent webinar hosted by the renowned animal nutritionist Dr Terry McCosker, Director of Resource Consulting Services (RCS), has highlighted the need to ensure that any supplementary feeding of livestock is profitable, as you don’t make money out of maintenance feeding. McCosker went on to explain some of the common mistakes producers make when supplementary feeding ruminants, how to predict the nutritional needs of livestock at different times of year and how to ensure your supplementary feeding regime is economically worthwhile.


  • Dividing the year into ‘nutritional seasons’ will help predict times of potential energy and protein deficiencies in the diet of ruminants.
  • Both macro and micro-nutrients can also be deficient in many areas and seasons, but most can be simply tested for and addressed.
  • Introducing a portion of a herd to a new forage type before the main herd will help the rumen bugs more easily adjust, minimising production losses.


For nearly 50 years, Terry McCosker has worked in Australian agricultural research, extension and property management. During this time, his passion for ruminant nutrition has led to him to develop concepts and research to help explain ruminant feed requirements in different seasons and diagnose deficiencies. According to Terry, the most common mistakes he sees producers make regarding supplementary feeding are getting the timing wrong, confusing protein and energy and poorly diagnosing mineral deficiencies. Timing is all about what to feed when, and all too often McCosker sees time and money being wasted by the wrong supplement being fed at a certain time, or the right supplement being fed but at a time when it is not needed by the animals.

FIGURE 1. Nutritional seasons for northern, tropical regions of Australia.


To help determine when ruminants might benefit from supplementary feeding, McCosker developed the concept of ‘nutritional seasons’. These occur each year, around the same time, but can vary in length year-to-year. They are defined by analysing the quality and quantity of paddock feed on offer, to see if they are rising or falling and at what rate. Figure 1 shows the nutritional seasons typically experienced in the northern, tropical regions of Australia, where C4 grass species are dominant. Figure 2 shows the nutritional seasons for the southern, temperate zone of Australia, where C3 grass
species are dominant. The two zones have many similar nutritional seasons, but the timing of these throughout the year is very different between the two zones.

FIGURE 2. Nutritional seasons for southern, temperate regions of Australia

FIGURE 2. Nutritional seasons for southern, temperate regions of Australia.


Energy is by far the largest nutritional requirement of ruminants and drives animal production. In contrast, protein is a much smaller requirement and drives the flow of energy through a ruminant via the rumen. Protein is required to keep the rumen bugs healthy, to enable feed to be processed and turned into energy. If you have a low quantity of pasture but it is high quality feed (highly digestible), it is likely animals will require energy supplementation in the form of hay, silage or grain. This typically happens during nutritional seasons 5, 6 and 7 in southern Australia, when pasture is green but very short during the cold winter. In contrast, during nutritional seasons 4 and 5 in northern Australia, the dry season usually starts with a quantity of pasture of declining quality, requiring a protein supplement to be fed. But it is important to remember that it is degradable protein (such as urea) that is needed to feed the rumen, whereas bypass protein (such as cottonseed meal or copra) feeds the animal itself. Adequate amounts of good quality water must also always be available to livestock to ensure good rumen health and function. Supplementary feeding is used to make up for either a protein deficiency, mineral deficiency or both in the available paddock feed. This form of feeding can be economically viable if you get the timing and choice of supplement right. Substitution feeding is replacing energy, which should be available in paddock feed, by feeding hay, silage, grain or molasses. As energy is the largest feed input which must be supplied to livestock for production, substitution feeding can quickly become uneconomical unless it is done to maintain the body condition score of breeders.


As McCosker pointed out at the beginning of his webinar, poor diagnosis of diet deficiencies is one of the three most common mistakes producers make when analysing ruminant performance. The macro nutrients that are typically found to be deficient in the diet are phosphorus (P), sodium (Na), sulphur (S) and magnesium (Mg). Phosphorus deficiency is often suspected if animals begin chewing bones. It can be comprehensively diagnosed through soil analysis, but more reliably through dung and blood samples from livestock. Sodium, sulphur and magnesium deficiencies can be diagnosed in a similar manner. Imbalances between Mg and calcium (Ca) cause particular problems during winter in southern areas, often resulting in grass tetany and milk fever in breeders. Macro nutrients are usually relatively easy and cheap to feed as a loose lick-type supplement, so this is generally the best approach to correct any deficiencies. A number of micro nutrients including cobalt (Co), selenium (Se), zinc (Zn) and copper (Cu) are often deficient in ruminants, particularly in certain areas of the country. Some deficiencies can be seen in animal behaviour, with zinc-deficient cattle often wanting to stand in water for example, as they develop heat in their feet and lower limbs. Producers often say a rough, light colour coat on cattle indicates a copper deficiency. While a blood test can confirm a deficiency, McCosker suggests conducting a simple on-farm trial if a particular micro-nutrient deficiency is suspected. If slow-release rumen boluses or ‘bullets’ are available for these micro-nutrients, give them to a small sample of individually identified animals in a herd or flock and monitor their weight gains against the rest of the herd, to see if treatment is worthwhile. A diet deficient in protein results in low rumen ammonia levels and energy in feed not being fully accessed and utilised. The most accurate way to confirm a suspected protein deficiency is to look at faecal nitrogen levels in animal dung samples. If nitrogen levels are below 1.3%, animal performance will be improved by protein supplementation.

Cattle forage

Introducing a small proportion of a herd to a new forage type well before the rest of the herd will help the rumen bugs of the cattle adjust more quickly. Photo: Pamela Lawson


One webinar participant asked McCosker about the virtues of shifting livestock from predominantly dry paddock feed throughout the summer to lush, growing cereal crops over the winter, rather than having them on a consistent, albeit lower quality pasture year-round. The producer felt his cattle performance always seemed to go backwards for quite a while when shifted from the dry pasture to green crop. McCosker explained this reduced performance was due to an imbalance in the Carbon:Nitrogen ratio in the diet, probably due to inadequate roughage in the crop paddock. Winter cereals are usually too high in crude protein (about 25%), which is about 10% more than the rumen bugs can handle. The C:N imbalance of a grazing cereal crop can be addressed adding roughage to the diet, in the form of poor quality hay or access to an area of rank grass. Rumen nitrogen levels can also be reduced by feeding animals bentonite, which binds to the N and removes it through the faeces. One useful tactic McCosker mentioned for situations where animals were going to experience a significant change in forage type was to introduce a small portion of the herd to the new diet about two or three weeks before the rest of the herd. This gave the rumen bugs of these animals time to adjust to the new diet, so by the time the rest of the mob was introduced, their rumen
bugs will be quickly cross-inoculated with the rumen bugs of the animals already adjusted. This minimises the period of reduced animal performance due to dietary changes. This tactic can also be used when introducing new cattle to a property. Placing a few of your existing cattle in with the new mob when they arrive will again allow the cross-inoculation of rumen bugs between them and help the new animals adapt to their change of diet and surroundings.

For more information about this webinar and Terry’s home-study program ‘The Farmer’s Guide to Ruminant Nutrition’
which includes step by step instructions and tools for creating a nutritional program specific to your circumstances, go to www.rcsaustralia.com.au.

Dr Terry McCosker, RCS
1800 356 004


Farming Ahead” August 2016, No. 295