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.
• Feeding at least twice a day and mixing the TMR immediately prior to feeding helps reduce the heat build-up of the ration in the feed bunk.
• Push-up feed 8 -10 times a day. Make sure there's feed available along all the feed bunk; cows tend to concentrate and eat close to the area of the fans or water troughs.
• Manage the face of the silo adequately to prevent secondary fermentations and heating. Defacer equipment minimizes air infiltration. Remove at least one foot in depth from all the exposed face. Use all silage removed as soon as possible to minimize secondary fermentations on the removed pile.
• Use feed additives to control mold growth, reduce secondary fermentations, and excessive heating of the ration in the feed bunk; most of these products are organic-acid based (e.g. propionic acid).
• Feed high quality, highly digestible forages. Target minimum effective NDF at 22% of the diet DM. This can be accomplished with cereal straws as needed (e.g. 1 to 1.5 pounds). Forage particle size has to be between 2.5 and 5 cm to minimize sorting.
• Avoid excessive particle breakdown during mixing. Most TMR mixers have 3 to 6 minutes mixing time when they have been turning during loading. Check particle size with the Penn State particle separator. The superior sieve should retain approximately 2 - 8% of the diet (for the three sieve/one tray particle separator).
• Feed additives such as yeasts (Saccharomyces cerevisiae), fungus (Aspergillus oryzae) and/or probiotics (Lactobacillus spp, Propionibacterium spp., Enterococcus spp.) can be included to improve rumen health.
• Increase buffer concentrations in the diet (e.g. sodium bicarbonate) up to1% of the diet; supply sodium bicarbonate free choice (this should not substitute its inclusion in the diet).
• Heat-stressed cows lose lots of minerals. Increase the concentration of sodium, potassium and magnesium to a minimum of 1.5, 0.45 and 0.35% of the diet DM, respectively. White salt (sodium chloride) is a source of sodium however it is important to maintain the concentration of chlorine at 0.35% of the diet DM, and not exceed 0.5% of white salt in the diet.
• Use rumen-protected fat to increase the energy density of the diet, avoid the inclusion of unprotected fats such as vegetable oils or tallow.
• Maintain high concentrations of starch and sugars in the diet (26 and 8%, respectively). Cereal grains that contain starch with slower degradation rates (e.g. corn, milo) are a better option than those with faster degradation rates (e.g. wheat, barley).
• It is very important to have the water troughs in the shade and clean them frequently. Cows prefer to drink water with a temperature between 63 and 82 °F; if the water is not cool enough it further ads to the heat load.
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