With summer heat stress conditions, dairy managers will be challenged to maintain normal milk components. For Holstein cows, milk fat test should range from 3.6 to 3.8 percent and true milk protein test should average 3.0 percent or higher. For Jersey cattle, milk fat test can range from 4.5 to 5.0 percent with 3.6 percent true milk protein. With milk protein valued at nearly $2 a pound and milk fat priced at $1.60 a pound, lower milk components will cost you money and may indicate a feeding and/or health problem.

Strategy One. Heat stress can lower milk yield and components if not managed dropping milk fat percent by 0.2 to 0.3 percentage milk fat point (from 3.6 to 3.4 percent milk fat for Holstein cows for example). Cow cooling factors that can maintain performance include adding shade, wetting down cows, moving air with a fan, provide adequate free stall space, and maintain comfortable cow stalls encouraging cows to lay down.

Strategy Two. Several feeding management approaches can be effective to maintain feed intake, normal rumen function, and milk components.

· Increase sodium bicarbonate (a buffer) to 0.5 pound (Holstein cows) per day improving buffer capacity and providing higher levels of sodium in the ration.

· Calculate DCAD (dietary cation and anion difference) targeting a value over +250 meq per kg (+ 25 meq per 100 grams) of total ration dry matter. Sodium bicarbonate and potassium carbonate are recommended products to raise DCAD levels. Under severe heat stress, DCAD values above +350 meq per kg can improve feed intake and performance. Target 1.20 to 1.40 percent potassium, 0.35 percent magnesium, and 0.35 to 0.45 percent sodium in the total ration dry matter.

· Shift to higher quality forage can reduce heat increment (heat of fermentation and digestion) while providing more nutrients. If legume/grass forage quality is marginal (below RFV of 150), substituting corn gluten feed, soy hulls, or wheat midds can improve energy intake and digestibility.

· Add fat and oil (total of five percent of the ration dry matter) can provide more energy, reduce feed fines, and lower dustiness improving palatability.

· Use a rumen additive such as yeast cultures and direct fed microbial (DFM) can improve the rumen environment and fermentation.

· Maintain feed intake will keep cows milking. Adding molasses (3 to 5 percent of the ration dry matter) can improve palatability while providing a source of dietary sugar. Higher levels of corn silage can improve intake as the lower corn silage pH stabilizes the ration when exposed to heat and dry conditions. Adding water can improve feed palatability, but can cause the feed to undergo a secondary fermentation in the feed bunk. Several commercial organic acid-based feed bunk stabilizers can keep feed fresh and palatable (cost varies from 5 to 8 cents per cow per day).

· Feed more of the total ration at night (after 10 pm) can encourage cows to consume feed during the cooler night time period. Adding another feeding (three times a day instead of twice or once a day) can encourage feed intake and improve feed bunk stability.

· Remove old feed and do not allow mold to build up in the feed bunk surface causing cows to lower feed intake. Plastic bunk liners can increase feed intake.

Strategy Three. Feeding unsaturated fatty acids (from corn distillers grains for example) can lead to the formation of conjugated linoleic acids (CLA). The level of CLA that can reduce fat test by over 0.5 unit (from 3.6 to 3.1 percent milk fat for example) can be less than five grams per cow per day. The oil from distillers grain is not saturated correctly in the rumen leading to the lower milk fat synthesis by the mammary gland. Limit the amount of "free oil" (oil not contained in the seed form such as fuzzy cottonseed or roasted soybeans) to less than 0.5 pound. For example feeding five pounds of distillers grain dry matter containing 10 percent oil would result in 0.5 pound of "free oil". Distillers grains can vary from 8 to 18 percent oil.

Strategy Four. The rumen pH can drop 0.2 pH units due heat stress caused by the shifting of blood flow to the external body surface to reduce core body temperature, slowing the rate of feed passage, and lowering absorption of volatile fatty acids (VFA) produced in the rumen. Lactic acid can also be formed at higher levels which can lower rumen pH (lactic acid is a strong organic acid) while reducing fiber bacteria numbers and fermentation rates.

Strategy Five. Monensin (Rumensin trade name) can lower milk fat if rumen conditions are not favorable and/or unsaturated fatty acids are available in the rumen. Check the level of monensin added (280 to 350 mg per cow per day). A positive reason to add monensin during heat stress is to lower lactic acid formation, improve feed efficiency, and increase propionate production (a rumen VFA) that increases blood glucose levels needed under heat stress.

If your milk fat test has dropped, look for its cause(s) and select the correct strategies to improve cow health and increase your milk price.