Cost Effective Feeding Decisions

By Andre Nel

Feeding balanced diets is an important factor in improving both performance per cow and production per hectare. Balanced diets maximize milk production per kilogram of feed consumed and encourage higher dry matter intakes.

These benefits ensure that the most cost effective use can be made of available feed ingredients.

On most Victorian Dairy Farms pasture is the most cost effective feed source so most of this workshop is directed towards balancing diets to improve performance from pasture. These will include managing supplements to maximize pasture growth and utilisation per hectare, as well as balancing diets to increase pasture intake per cow and milk production per kilogram of pasture.

Growing And Utilising Pasture:
With the primary objective to increase performance from pasture the first step is to ensure sufficient high quality pasture is available for the cows. Along with agronomic inputs like plant species, water and fertilizer; supplementary feeding can play an important role in facilitating optimum pasture growth. This is achieved by using supplements to allow better management of grazing pressure. By only grazing pasture at the ideal growth stage more tonnes are grown per hectare. Pasture grazed at this stage also has a low Neutral Detergent Fibre (NDF). This allows high dry matter intakes per cow, as well as providing higher energy per kilogram of dry matter. This combination of factors therefore results in the maximum amount of energy being consumed from pasture. Basically, by being on the right rotation for a given time of year, the cow is offered the most feed and of the quality she can consume the most of.

Supplements should be introduced or increased whenever there is a risk of over grazing. By preventing over grazing higher growth rates are maintained. Being prepared to feed a supplement when required also allows a more appropriate grazing regime to be followed. As there is less reliance on having a pasture wedge to cover feed gaps, pasture can always be grazed at the 2.5 – 3 leaf stage. Feed value is highest at this stage due to growth being predominantly leaf with little stalk. Pasture production is also increased as there is less shading and pasture is not wasted through older leaves dying and decaying.

Optimising Feed Intake:  
The next application of supplements should be to ensure that the maximum amount of pasture is utilized per cow and that the optimum milk is produced per kilogram of feed available. To be able to develop a ration that accomplishes these outcomes we need to understand the cow’s nutrient requirements and how these nutrients interact together.

The first major nutrient is energy. Energy is the driver of milk production and a cow will only produce according to the amount of energy available to her. Energy is measured in mega joules (MJ) of metabolisable energy (ME). Energy requirements are calculated by adding together the requirements for maintenance, activity, milk production, growth of the developing calf and weight change. When balancing a diet the form of energy used needs to be taken into consideration. Cows derive the majority of their energy from carbohydrates. These can be either structural carbohydrates that form fibre, or non-structural carbohydrates like starches and sugars. The carbohydrates in fibre are usually the cheapest energy source but due to their slow digestion rate and bulky nature, cows can often not eat enough to meet their nutrient requirements. On the other hand starches and sugars, found mainly in grains and food by-products, are highly digestible and allow for high-energy intake, however they can lead to acidosis when fed at high a rates. Ideally to maintain a good rumen environment a forage to concentrate ratio greater than 60 forage: 40 concentrate is preferred. Other energy sources include fat and protein. Fat has a high energy density but depending on the type of fat can have a depressing effect on intake and rumen function if fed at levels over 3% of the diet. Supplemental fat can however be of benefit at peak milk yield and over the joining period, if at maximum intake the cow is still not meeting her energy requirements. Protein can also provide energy to the cow in some circumstances. Where there is excess true protein in the diet, it can be broken down to release energy and in cases of severe underfeeding, body protein can also be catabolised to supply energy. This is however an inefficient process and should be avoided.

Protein is the next major nutrient that must be balanced to ensure optimal intake and production. Protein is measured both in percent and grams. The percentage measure is used mainly to determine the suitability of a diet for the rumen microbe population which function best between 14% - 18% Crude Protein (CP). The weight of protein in grams reflects the cow’s actual requirements, which are correlated to her physiological condition (stage of lactation, milk production, pregnancy etc.). Protein is supplied in two main forms Rumen Degradable Protein (RDP) and Rumen Undegradable Protein (UDP). RDP can consist of true proteins and non-protein forms of nitrogen (NPN), which rumen microbes can use to manufacture microbial protein. UDP on the other hand is unavailable to the microbes and is digested directly by the cow.

Protein levels are crucial for optimum intake. If crude protein is below ruminal requirements, dry matter intake will fall resulting in reduced overall energy intake and milk production. When CP levels are above requirements, energy is wasted excreting the excess nitrogen as urea and at very high levels cow health is affected and intake is depressed.

Fibre, though not strictly a nutrient is an important element that needs to be balanced in the diet. To maintain optimum rumen function diets should provide at least 28 - 32% neutral detergent fibre (NDF) of which 70% should be forage NDF from feed at least 12.5mm long. The role of fibre is to maintain a rumen raft for effective rumen mixing while also encouraging chewing which is critical in maintaining a stable rumen pH.

Balanced mineral levels in the diet are important not only to maintain health and fertility but also feed conversion efficiency. Feed digestion, energy metabolism and milk production are all controlled by enzymes and hormone systems, which require specific minerals to function effectively.

Minerals are broken down into two groups Macro and Micro minerals. Macro minerals are required in gram quantities per day and usually result in a clinical disease if deficient. These include Calcium, Phosphorus, Magnesium, Sodium, Chloride, Potassium and Sulphur. Micro minerals are only required in milligram quantities and deficiencies are usually associated with a weak immune system and poor reproductive performance. The most important micro minerals are Zinc, Copper, Cobalt, Selenium, Iodine and Iron. Mineral imbalances can be the result of regional soil deficiencies, interactions between minerals or insufficient intake in high yielding cows

Water is a critical nutrient too often ignored when balancing a cows diet.

Water is required to provide an environment suitable for microbial fermentation by facilitating the movement of microbes to food sources and nutrients to the gut wall, excretion of waste products and helping to regulate pH and temperature. To achieve optimum feed intake sufficient good quality water needs to be available to encourage cows to eat to their potential.

Signs of Ration Imbalance:
By observing cow habit and noting changes in milk production or composition we can pick up signs of poor ration balance. All nutrients interact with one another so it is important to take all factors into consideration when determining the cause of any imbalance.

The following are some of the signs to look for:

1. Low rumination (cud chewing) rates are usually a sign of insufficient effective fibre in the diet.
2. Depressed appetite often indicates poor rumen function. Which is most often related to a nutrient imbalance.
3. Very loose dung consistency can be the result of excess protein or acidosis due to excess non structural carbohydrates or insufficient fibre. While very firm dung can indicate protein deficiency.
4. Loss of body condition indicates insufficient energy in the diet, as can rapid declines in milk production.
5. Changing milk compositions; a declining protein test along with a rising fat test often indicate a lack of energy as fat mobilized from body reserves is used to maintain milk production. Low fat tests can indicate insufficient fibre in the diet, or acidosis.
6. Poor hair coat, high incidence of disease and poor reproductive performance are usually associated with poor mineral balance but can also be related to insufficient energy in the diet.

Balancing A Diet:
The first step in balancing a diet is to calculate the cow requirements (see sheet).

Energy should be the first nutrient requirement we attempt to meet. After an initial energy balance, fibre levels need to be checked, as excess fibre will limit intake. If NDF is above the cow’s maximum potential intake, energy balance will need to be repeated using lower NDF feed sources. Once energy is satisfied, protein levels need to be checked and if required the diet rebalanced to meet appropriately protein levels. Once energy, fibre and protein levels meet requirements the total amount of minerals supplied can be calculated and the appropriate additional minerals added if required.

When we have a number of feed ingredients to choose from we should attempt to use the optimum cost combination to achieve a balanced diet. The cheapest feeds per tonne do not necessarily produce the cheapest rations. For example if we have an option between the purchases of two lots of hay, Hay A for $160/t (8MJ/kg DM) or Hay B for $185/t (10MJ/kg DM).  Hay A costs 2c/MJ while the Hay B costs 1.9c/MJ. As production is driven by mega joules not tonnes the cost per litre of milk will be lower with Hay B. This simple cost comparison can only be applied between similar feeds that only vary significantly for one major nutrient.

Conclusion:
As with most things the saying “you only get out what you put in” also holds true for dairy cows. We can only expect milk production proportional to the nutrients we provide to a cow in her diet. Therefore to increase our opportunity to maximise profit we need to provide the cow with a diet that allows her to consume a large amount of nutrients while ensuring the majority of these nutrients are supplied from our cheapest feed source. Ration balance is an important tool in achieving these outcomes.