By: A. Riasi (PhD in Animal Nutrition & Physiology) تغذیه دام در مرتع Animal nutrition on the rangeland (Part 5)

What is the role of energy in animal nutrition?  The nutritional concern for ruminants centers on: Energy Protein Minerals Vitamins Water

What is the role of energy in animal nutrition?  Energy is the single most important dietary component for an animal after water.  Energy is derived from carbohydrates, fats, proteins, and from the animal’s body reserves.  Energy intake maintains body functions and facilitates growth and development.

GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY Heat increment NET ENERGY Maintenance Gain Reproduction Milk Production

Determining Caloric Energy

TDN An energy index based on a carbohydrate Calculated from proximate analysis

Calculating TDN % CP × Digestibility = x % EE × 2.25 × Digestibility = x % CF × Digestibility = x % NFE × Digestibility = x SUM TDN

Example (Chemical composition of a feedstuff): Water12% Crude protein 12.5% Ether Extract 4% Crude Fiber10% Ash 2% NFE 59.5%

Water 12 CP (2% N × 6.25) 12.5 × 0.8 = 10 Ether Extract 4 × 2.25 × 0.75 = 6.75 Crude Fiber 10 × 0.4 = 4 Ash 2 NFE 59.5 × 0.8 = TOTAL (TDN) Example (Chemical composition of a feedstuff):

What is the role of protein in animal nutrition?  Crude Protein is calculated from the nitrogen content of the forage.  The CP of forage is important since: Protein contributes energy Protein provides essential amino acids for rumen microbes as well as the animal itself.  Protein in forages is most correlated with forage maturity, as more mature forages have a lower percentage of crude protein.

Kejeldahal method for CP and N analysis

What is the role of protein in animal nutrition?  Cattle require two types of protein in their diet: Degradable protein in the rumen (RDP) Undegradable protein in the rumen which passes straight to the abomasum or stomach for digestion (RUP)

What is the role of protein in animal nutrition?  The microbial degradation of protein is an energy-dependant process.  Generally more microbial protein is synthesized from green forage diets than from hay or mature forage diets.

Matching nutritional requirements of livestock  Forage supply is not continuous throughout the year.  Cool-season pasture growth begins in the early spring and quickly produces very large amounts of forage.  Given adequate moisture, cool-season pastures will often produce a second surge of growth in the fall before going dormant.

Matching nutritional requirements of livestock  Warm–season pasture begins later in the spring and continues into early autumn when day length shortens and temperatures fall.  A diverse mix of cool- and warm-season pastures benefits livestock managers by overlapping the growth curves of both types, meaning more high-quality pasture than otherwise.

When supplementing protein or energy is necessary?  In temperate regions with lengthy grazing season, supplementation on green, growing, vegetative, well-managed pastures should not be necessary.  Well-managed grass-legume pastures can be highly digestible with protein concentrations approaching 25 percent while vegetative.

 The problem on high-quality pastures often becomes one of inefficient protein use.  Supplementing energy with digestible fiber in these situations can make the animals utilize protein more efficiently. When supplementing protein or energy is necessary?

 When supplementing ruminants on pasture, consider the following questions: Will the added production cover the expense, especially if the feed is shipped from off the farm? Is there an inexpensive local source of protein? Do you raise the feed on the farm? Do you have necessary harvest, storage, and feeding equipment? When supplementing protein or energy is necessary?

 Remember: On high-quality pastures, energy is often the limiting nutrient. Supplementation of protein on low quality forages will increase forage intake, and therefore increase energy intake. Digestible fiber feeds are good for ruminants on high quality forage because they do not reduce intake, and provide energy for protein metabolism. When supplementing protein or energy is necessary?

 If you choose to have your forage analyzed for nutrient content, the key nutrients to consider are: CP TDN NDF ADF Mineral content Forage sampling and production estimates

 Graziers must pay careful attention to the negative health effects that certain plants can cause in livestock: Bloat Grass tetany Prussic acid Nitrates Fescue toxicosis Poisonous plants Plant toxicity and grazing- related disorders

 Poisonous plants contain: Resins Alkaloids, and/or Organic acids that render them unpalatable. Plant toxicity and grazing- related disorders