Supplementary feeding aims to correct nutrient imbalances present in the available pasture, by increasing intake and/or improving utilisation of available paddock feed. With any livestock enterprise, the entire farm management strategy revolves around great seasonal variations in pasture production which, depending on location and time of year, can be low in both protein and digestibility.
The aim of most beef cattle and sheep producers is to generate the maximum return from available grass. In order to achieve this, supplementation is a necessary key management strategy in Northern Australia.
Provided there is an adequate quantity of grass available, pasture quality determines live-weight gains and productivity. Pasture quality is a function of the digestibility and protein levels of the pasture. Digestibility is measured by that proportion of the diet that is used by the animal and not passed out as faeces.
The higher the digestibility, the faster the feed passes through the animal, the more pasture the animal can eat and as a result, greater live weight gains are achieved. Pasture quality and availability vary throughout the year which is reflected as a variation in live weight gains. As protein and digestibility fall, so does feed intake and consequently stock may fail to gain weight or start to lose weight.
As pasture feed reaches maturity, the available digestible energy and protein levels fall, resulting in slower ruminal digestion with a consequent reduction in feed intake. This leads to reduced livestock performance and productivity.
Digestibility of pasture is largely influenced by the stage of pasture growth. As pasture matures, digestibility declines and energy and crude protein content falls.
To maintain normal body functions, cattle and sheep require certain minimal levels of:
However for productivity gains (e.g. growing out, finishing or breeding) the requirements of the above are even greater, particularly for protein and energy.
Microbes in the rumen break down the fibrous component of feed to produce energy. These ruminal microbes require a constant source of nitrogen for their survival and growth. Nitrogen is obtained from digestible crude protein found in grasses and other feeds, and from supplements of non-protein sources such as urea.
If the barrel on the left represents the nutritional well being of an animal and our aim is to fill the barrel to maximise the animal’s productivity, then it becomes obvious that we need to shore up the nutrient that is lowest. In this case it is protein. Once protein and energy have been supplied then phosphorus may limit production.
The "principal of limiting nutrients" says that there is no point supplementing the animal with phosphorus for example when protein and energy are the limiting factors. There will be no response until the limiting nutrients are satisfied.
Most of the digestion of forage occurs in the rumen by bacteria. In fact the rumen is very efficient at digesting roughage and inefficient at digesting grain.
The aim of feeding cattle and sheep is to ensure the rumen is working at maximum efficiency. As pastures mature this efficiency, along with feed intake declines and therefore supplementation is required to maintain productivity.
The choice of supplements is critical in stimulating maximum efficiency in the rumen and at the same time allowing some of the supplement to bypass the rumen. When pastures decline in protein and digestibility, large increases in feed intake and production response can be achieved by strategic supplementation.
Cattle and sheep absorb protein through the intestines. This can come from two sources:
As crude protein levels fall in pasture, microbial protein becomes the main source of protein for the animal. However, as feed protein levels drop, the rumen microbes are also placed under nutritional stress due to lack of incoming nitrogen. This will result in slower digestion and a reduction in feed intake. Under these conditions, a supply of non-protein nitrogen (NPN) such as urea will maintain the animal’s microbial population, ensuring that sufficient microbial protein is produced for body maintenance.
Cattle require energy for:
The amount required will vary with the productive status of the animal. Without irrigation, supplementary feeding is generally essential during the winter dry season in northern Australia.
Pasture management in northern Australia is important in maintaining high levels of pasture digestibility, including stocking rates and pasture types, to meet the energy requirements of high producing cattle and sheep. However, without irrigation, it is impossible to maintain high levels of digestible feed.
Deficiencies of trace elements, particularly selenium, cobalt and copper will impact on the productivity of cattle and sheep. Supplementation can generally help remedy such deficiencies in a cost-effective manner.
Cattle and sheep have a continuous need for phosphorus for growth, reproduction and lactation. However, the phosphorus content in pasture can vary greatly during the season, with low levels regularly found in dry, mature pasture.
As seen below, the vast majority of northern Australia is phosphorus deficient.
The following livestock may require phosphorous (P) supplementation:
In a normal dry season we are looking at providing breeders with a low input, minimum cost per head supplement that minimizes weight loss by providing the limiting nutrients- protein and energy.
Breeders in the north are limited by lack of protein during the dry season.
Urea is the main supplement ingredient used during the dry season. In technical terms, urea is a concentrated form of non-protein nitrogen for making protein and works well provided there is dry feed available.
A dense form of protein suits northern herds where limited labour and large transport distances are the norm. Some phosphorus is used in mixes when urea is supplemented on low phosphorus soils.
Salt is also required in the north and is added as a carrier and attractant. Sulphur is required when urea is supplemented and protein meals and trace minerals are added as required.
Calf weaning is an often underestimated management tool to maximise the output from your breeding herd.
The process of weaning dramatically reduces a breeder cow’s nutrient requirements. This has flow on benefits to the herd because the combination of body reserves and nutrition has important effects on milk production, weaning weight and conception rates.
Dry season feeding has a crucial role in retaining cow body condition; but have you considered which is a more important strategy for retaining body condition?
Research suggests that weaning earlier improves live weight potential by 0.35 kg/day compared to weaning late. It also has a greater impact than dry season supplementation, which improves live weight potential by only 0.11 kg/day. The good news is that the effect of earlier weaning and dry season supplementation are additive.
It is almost impossible to wean every calf early and early weaning is not a “free lunch”. The lower the weaning weight, the more intensive the management and feeding options required to ensure the calf continues to grow.
Choosing the right type of weaner supplement will vary widely between individual properties. It will be dependent upon the feeding objectives, infrastructure and labour.
1 Dixon RM, Playford C, Coates D (2011) Nutrition of beef breeder cows in the dry tropics. 1. Effect of nitrogen supplementation and weaning on breeder performance. Animal Production Science 51, 515-528.
Weaners (e.g. less than six months of age and less than 150 kg live weight) will not compensate at all, or if they do not nearly to the same extent as older cattle. When good nutrition is available following nutritional restriction these young cattle are likely to grow at much the same rate or only slightly better than if they had not been restricted. These animals are likely never to achieve their full growth potential.