Supplementation in Grazing Systems

General overview of supplementation strategies, biological responses, and economic considerations in grazing systems based on a lecture transcript.

Why is supplementation necessary in subtropics grazing environments?

There is natural variability in pasture production, with high dry matter production during summer months and a slowing of production during winter and spring, creating a gap between herd requirements and pasture availability.

When managing seasonal forage surplus, what does 'stockpiling' involve?

It is the practice of separating paddocks so they are not grazed during the summer months, allowing that forage to grow and be consumed during the winter or dry season.

What is the cheapest source of nutrition for a herd in a grazing system?

Grazed swards (grass produced on the areas being grazed by the animals) are always the cheapest option per unit of metabolizable energy.

What are the recommended trough requirements per head for mineral supplements versus concentrate supplements?

Mineral supplements typically require $1$ to $3\,cm$ per head, whereas concentrates provided at $0.6\%$ to $1\%$ of body weight require $15$ to $20\,cm$ per head.

How does nitrogen fertilization affect the 'feed gap' between summer and winter pasture production?

Fertilization increases overall productivity but also increases the difference between summer and winter production, making the feed gap larger because winter production remains low despite high nitrogen levels.

What is the minimum threshold of dietary crude protein required for the animal's rumen to function properly?

The rumen requires a minimum of $6\%$ dietary crude protein.

Which areas of Australia are identified as having an acute deficiency of phosphorus in the soil?

Northern Australia has large red-mapped areas where phosphorus deficiency is common, likely requiring supplementation for grazing animals.

What is the primary difference in preservation strategy between hay and silage?

Hay is preserved through dehydration (reducing moisture to restrict microorganisms), while silage is preserved through the fermentation of water-soluble carbohydrates, which reduces the pH to prevent deterioration.

What are the three main categories of supplements discussed?

Conserved forages (hay, silage, stockpile), concentrates (grains, byproducts, pellets, molasses, urea), and minerals (loose licks, blocks, rumen bullets, injections).

What occurs during a 'substitution' response to supplementation?

As supplement intake increases, pasture intake decreases, though the total dry matter intake (pasture plus supplement) of the animal generally increases.

Define the 'complementation' response in grazing animals.

A scenario where providing a supplement, such as phosphorus or urea for low-protein pastures, leads to an increase in the intake of the pasture itself.

How does supplementation affect the relationship between stocking rate and live weight gain per area?

Supplementation allows a producer to maintain individual animal live weight gain at higher stocking rates, thereby increasing the total production (meat produced) per hectare.

What is 'compensatory growth'?

The accelerated growth rate observed in animals during the wet season following a period of nutritional restriction during the dry season.

What are the requirements for compensatory growth to occur?

The animals must have access to both a high quantity and high quality of pasture to allow for maximum dry matter intake.

According to the modeling trial in the Northern Territory, what is the maximum supplement price to maintain a positive gross margin when selling cattle at $3.00$ per kilo?

The maximum price for the supplement would be $600$ per ton; paying more results in a negative gross margin.