Feed value differences between cultivars under good pasture management are small.
Combining good cultivars with good pasture management allows for feed value and production to be maximised in farming systems.
Cultivar comparisons (ME)
Importance of ME
ME is a key driver of animal performance in most NZ pasture-based systems. ME has a double affect, because as the ME value of feed increases so do animal intakes. Feeds with a low ME require extra time in the rumen to degrade. For example the rate of passage of a high fibre straw (ME = 7-8) is 45-55 hours where a good quality grass (ME = 11-12) is 18-24 hours. When a ruminant reaches a 'fullness' level it will stop eating, therefore feeds with a low ME value limit dry matter intake.
Importance of management
Good pasture management is the key to maximising pasture quality and achieving high ME levels. Strategies include:
- Managing pastures through late spring.
- Grazing to the correct pasture residuals.
- Grazing at the right time - when ryegrass has 2.5-3 new leaves per tiller.
- Maximising pasture legume content.
Water soluble carbohydrates (WSC)
WSC are simple sugars present in plant cells and are an important energy source for animals. WSC content is highly correlated with ME, and, in most cases ME gives a better indication of animal performance than WSC.
Animal performance responses, in milksolids or liveweaight gain, to WSC have been much smaller and less consistent than response to ME.
Importance of WSC
The affect of increased WSC on animal performance is varied. ME is a far better indicator. Increased levels of WSC at times have environmental benefits through reducing the amount of nitrogen lost in the urine; this is currently being researched.
Crude protein (CP)
CP is needed by animals to maintain body tissue and produce milk/meat. Ideal CP levels for dairy cow production are 18-25%. NZ pastures are relatively high in CP content and it is generally not limiting to animal production.
Pastures containing high concentrations of CP (26 -30%) usually lead to increased levels of nitrogen in the urine, rather than increasing animal production.