Nutritional
Changes Can Reduce Production Losses
JIM LINN
Department of Animal Science
Cows
do best when the air temperature is between 41° F and 77° F. When it gets hotter than
that, cows' efforts to maintain normal body temperatures may result in reduced feed
intake, 10% to 25% lower milk production, decreased milk fat percentage, decreased
fertility, depressed immune system, higher maintenance requirements, and overall less
efficient milk production.
What can you do to minimize these responses? The
most important thing is to provide a cool, comfortable environment. Once you have the
environment as comfortable as possible, you can also look at some diet changes to help
improve hot-weather productivity.
NUTRIENTS
Water. Water is the most
important nutrient for lactating cows, especially heat-stressed cows. Water intakes
increase sharply with air temperature until air temperature reaches the cow's body
temperature. Above that point, water intake decreases because dry matter intake (DMI) and
activity drop.
Provide cows with an unlimited quantity of fresh,
clean water in an easily accessible area close to the feeding area to encourage eating and
drinking. Add fans and sprinklers or at least shade over the area to encourage
consumption. Given a choice, cows will choose to rest in a shaded or cooled area rather
than eat and drink from an uncooled, sunny area.
Should you cool the water? Texas research showed
water cooled to below 59° F helped cool cows, but the small increase in milk production
did not justify the cost of cooling the water. The cows also preferred warm (70° F to
80° F) over cooled water.
Protein. Consider both quantity
and form of protein when feeding heat-stressed cows. Too much or not enough crude protein
(CP) increases body heat production. Responses to increasing high-quality bypass protein
supplements during heat stress have been minimal. Balance bypass (undegradable) and
degradable protein.
Fiber. Excess fiber should not
be fed during the hot summer months, but a minimum amount is needed to maintain DMI, milk
production, and normal rumen function. High-quality forages are the best source of
digestible fiber that is effective and produces minimum heat when fermented in the rumen.
Fat. Research on feeding fat
during heat stress has not consistently shown improved DMI or milk yields. Follow
practical recommendations on feeding fat. Do not feed more than 6% total fat in the
dietary dry matter (DM). Also, avoid feeding more than 4% total fat to fresh cows for the
first three weeks after freshening.
Minerals. The cations sodium
(Na) and potassium (K) are important for the heat-stressed cow. Research has shown an
increase in milk production and DMI during heat stress when K is 1.2% or higher and Na
0.45% or greater in the dietary DM.
The ratio of cations (Na and K) to anions (Cl and
S) may be as important during heat stress as the concentrations of individual minerals. In
Georgia, heat-stressed cows responded to increasing the Dietary Cation-Anion Balance (DCAB
= Na + K - Cl-S) from 0 to 35 milliequivalents/100 g. Using a combination of sodium and
potassium to increase DCAB is recommended. Florida research indicated increasing Cl
concentration in the diet decreased DMI and milk production, resulting in a maximum
recommendation of 0.35% of the DM.
FEED ADDITIVES
Buffers. Buffers can be
beneficial during heat stress for two reasons. First, if fiber content of the diet is
minimized and/or cows are selecting against forages, buffers can help prevent low rumen pH
and rumen acidosis. Second, buffers contain Na (see above).
Fungal or yeast cultures. Arizona researchers have shown that feeding Aspergillus oryzae reduced heat stress in cows
by lowering rectal temperatures. Milk production increased in some cases due to improved
fiber digestion in the rumen.
FEEDING MANAGEMENT STRATEGIES
Some alterations in the feeding program can help
entice cows to eat during heat stress.
- Increase the number of feedings. This has two advantages. First, the feed will be fresher, encouraging consumption. Second,
cows are curious, so if the feeding area is comfortable they will come to the manger more
frequently with increased feedings. The number of feedings to obtain benefits is not
known, but it is probably at least three per day.
- Time feeding right. During hot
weather, cows eat mostly at night and after milkings. Have fresh feed in the mangers after
milking. Feed most of the fresh feed at night. Sunset and about an hour before sunrise are
good times.
- Feed a TMR. A TMR with forages
mixed in helps reduce the cow's tendency to selectively consume concentrates rather than
forages. A well-balanced TMR allows you to optimize fiber in the ration while encouraging
DMI and minimizing rumen fermentation fluctuations and pH declines.
- Add water. Water softens fiber
feeds and reduces dustiness and dryness of the diet, increasing palatability and DMI. A 3%
to 5% addition of water is recommended when ration DM is above 60%.
- Keep mangers/bunks clean. Remove
refused feed every day. Check and clean any moldy and/or heating feed from the corners and
edges of feeding areas at least three times a week, more often if feeding animal protein
and fats. A decaying feed smell may reduce DMI even when fresh feed is offered.
- Increase nutrients. Increase the
concentration of all nutrients in diets as DMI decreases during heat stress. Guidelines
for nutrients that have been shown to influence DMI and milk production during heat stress
are listed below.
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