ISSUE FOCUS 36 FEED & ADDITIVE MAGAZINE July 2022 Specific nutritional strategies to reduce the physiologic impact of heat stress, to support milk yield and health status of cows: • Time and frequency of feeding. These two factors can influence feed intake. For appetite stimulation 60-70% of the ration should be fed overnight, when the ambient temperature is lower. Fresh feed portions should be provided after milking. Increased feeding frequency reduces the overall heat produced by the animal after ingestion. Offering smaller portions also reduced the risk of feed spoilage and keeps if fresher. • Forage/concentrate ratio. High production dairy diets normally have a roughage (forage) content of 45-60% of total DMI, providing a significant part of dietary fibre. More heat is produced as a result of the fermentation of more fibrous diets and more acetate is produced, compared to diets with higher levels of grain were starch is fermented to propionic acid. Hence, it seems logical to reduce ruminal production of acetic acid at the expense of propionic acid by reduced proportion of roughages in the diet. However, such transition should be done carefully by maintaining sufficient levels of physical effective fibre and Neutral Detergent Fibre (NDF) and preventing concentrates exceeding 60% of DMI. There is an increased risk of sub-acute ruminal acidosis (SARA) if forages drop too low resulting in impaired rumen function and further depressions in DMI and milk butterfat. Forage and fibrous feeds should be of the highest quality and harvested at the correct maturity stage. Highly digestible roughages stimulate DMI while reducing heat increment and therefore aiding thermoregulation. Brewers grains, cotton seeds and beet pulp are recommended ingredients in situations during heat stress. Their nutrient content favours a more balanced fermentation pattern in the rumen. • Fat level. Increased fat addition in the diets of dairy cows during heat stress is recommended due to the fact that less heat is released during their metabolism compared to carbohydrates and proteins. This contributes to a reduction in heat production and it is beneficial for maintaining normal body temperatures. Supplementing with fats increases energy density of the diet, partially compensating for reduced DM and energy intakes. Total fat content should not exceed 6-7% dietary DM content however. In practical diets fat can be added in the form of oil seeds (sunflower or cotton) or ruminally protected fats. Oil seeds should be provided whole to prevent fast release of free oil which in turn can suppress rumen fermentation.
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