Source: South Dakota State University
Body temperature regulation in dairy cows is constantly challenged by a combination of environmental heat with that produced during rumen fermentation and nutrient metabolism, says Alvaro Garcia, South Dakota State University Extension dairy specialist.
"Heat stress occurs when cows cannot dissipate enough heat to maintain their core temperature below 101.3 °F. Internal heat production increases at higher dry matter intakes which make high producing cows more sensitive to heat stress," Garcia said. "Body temperature increases of just 2.7 °F have been shown to result in intake reductions of almost 13 pounds."
Garcia says that often this intake depression caused by heat stress, prompts nutritionists to reformulate for energy-dense diets by increasing the amount of concentrates and reducing that of forages. This is a sound practice when adequate effective fiber is maintained which necessary to stimulate rumination and maintain adequate rumen pH.
"Heat-stressed cows reduce rumination and tend to select finer feed particles. This combination of more concentrated rations together with a reduced capacity to buffer rumen pH increases the risk of acidosis during hot weather. These changes can be observed in farms by a reduction in milk fat and higher incidence of lameness," Garcia said.
Garcia shares a checklist of feeding strategies that help reduce excessive drops in intake:
• Feed early in the morning (5 - 6 a.m.) or evenings to avoid the highest metabolic heat production (rumen fermentation) coincide with maximum environmental temperatures.
• Avoid feed shortages in the feed bunk. When offering fresh feed there needs to be 0.5 to 5% refusals. Target refusals by pen as follows: Fresh cows 3-5%, high pen 1 - 4%, low pen, 0.5 - 3%. Remove refusals at least once a day to minimize heating of the fresh feed.
• Feeding a TMR is better than supplying feedstuffs individually (component feed).
• High moisture forages (e.g. silages) improve ration acceptability. In addition, as fermented feeds have lower pH they slowdown mold and yeast growth in the ration and reduce heating. Mold and yeast growth oftentimes result in compounds with unpleasant odor and taste for cattle.
• The inclusion of other high-moisture products such as sweet bran, beet pulp or wet distillers grains also helps increase ration acceptability.
• Add water when the DM of the diet exceeds 60% to bring it down to 50%. Water addition conditions the ration, reduces the dust, and increases its acceptability.