Fibre & Starches for Heat Stress
breakdown of fibre and starch during warmer conditions
With daily dry matter intake (DMI) reduced over summer, the quality and amount of fibre and starches can assist heat stress management.
High quality fibre will maintain rumen stability and increase nutrient density without producing excessive metabolic heat. Low-quality forage (high NDF) gives too much dietary bulk and makes it difficult to reach the daily nutrient intakes needed for milk production.
Higher fibre intakes add safety and help cows return to good health after an excessive heat event has passed.
Mixer wagons that allow feeding fibre with other feeds in a partial mixed ration (PMR) give much more flexibility. It is best to feed the PMR under shade between the morning and afternoon milking and allow cows to graze best-quality pastures overnight.
Ensure all cows get equal access when feeding out quantities of forage fibre to your herd. Heifers and less-dominant cows may be more at risk of acidosis than others.
Starches as a source of glucose
Heat stressed cows have a greater need for glucose. Provide a form of starch that will slowly ferment so the cow has a steady supply of glucose across the whole body. Corn (maize) is the most readily available slow-fermenting starch source of all the grains.
A slowly fermenting starch source will assist feed digestion in two main ways. Firstly, it takes some of the starch fermentation away from the rumen.
This reduces the rumen energy yield and allows for greater glucose formation in the liver.
It also reduces the risk of ruminal acidosis through excessive starch fermentation. A quickly fermenting starch releases energy too fast and rapid fermentation pushes rumen pH down.
The starch that is not digested in the rumen will normally be digested in the small intestine. At this site of digestion, it produces glucose for use by the gut tissue.
Heat stress affects grain digestion, so manure screening is a good indicator of grain digestion efficiency and informing choices around dietary management.