Dairy cows are quite sensitive to hot weather, and one of the responses to heat stress is to reduce intake. This impacts milk yield and profitability. While the decline in dry matter intake (DMI) cannot be totally avoided in hot weather, there are some things that can help.
Of primary importance is to improve feed quality. Different factors affect DMI when forage is poorly digested, compared to feeding a ration containing more easily digested forage. Feeding poorly digestible forage increases the time necessary for ruminal digestion and fermentation, thus slowing the rate of passage through the digestive tract. This increases the heat produced and complicates the cow’s physiological response to high ambient temperatures. In contrast, feeding forage that is easier to digest permits more rapid passage and lowers the heat produced in the rumen.
While it is always important to provide good quality feed for milking cows, it is even more important during hot weather. Digestible forages include pasture that is lush and growing rapidly.
There are several ways to improve pasture quality.
1) Improve forage varieties.
2) Improve pasture fertility.
3) Manage the grazing of a pasture.
4) Clip pastures to encourage regrowth.
The first item will require some long-range planning unless annuals are planted. There are a number of articles available in our web site: http://www.aragriculture.org/forage_pasture.htm. These can assist in making plans for planting annuals. Examples of these crops are sorghum/sudan, sudangrass, pearl millet, crabgrass and lespedeza. All of these can be used for summer grazing.
The second item also requires some planning, and there are a number of factors involved in the time to fertilize pastures and the type of fertilizer to use. The web site also contains important material on “Nutrient Management in Arkansas,” and that information will help make economic use of fertilizer.
The third item offers several options. It has been a common practice to allow high-producing cows to graze first, then to move those cows to fresh pasture and follow with lower-producing or dry cows. Other rotation plans can be implemented to offer plants a rest period. Some dairy farmers move cows to new pasture every 12 hours, but longer rotation periods fit well on other farms. When you remove the cows, make sure half of the leaf area is left to give the plants time to recover before grazing again.
Finally, clipping pastures will remove the tall stems. As the plants mature and form stems, digestibility decreases. The regrowth will likely not be as digestible as during early spring, but it will offer an improvement. Another completely different way to improve the ration digestibility is to increase the proportion of the grain mixture, thus reducing the forage-to-grain ratio.
While this has worked in past years, it is a very expensive option this year. Likewise, increasing the amount of fat in the grain mixture is likely too expensive, except perhaps for fresh cows. But, don’t automatically dismiss these options, because purchasing feed may be necessary and economical if high-quality forage is unavailable.
It may be tempting to forego the clipping of pasture because diesel fuel is expensive or fertilizing because of the expense involved. However, remember that high-quality feed is also expensive this year. It is much easier to maintain the milk yield of cows than to recover later, because cows do not respond well to improved nutrition during the later phases of lactation.