Drought stress does not automatically mean poor forage quality. How good or how poor the forage is depends on when the lack of moisture hits during the maturation process.
For example, last year the Upper Midwest had some spotty drought conditions, and some producers encountered problems feeding corn silage to their dairy cows. Yeast counts were very high, so it was assumed to be the culprit, recalls Bill Mahanna, general manager of nutritional sciences at Pioneer Hi-Bred International. However, further investigation revealed that often the problem was caused by a higher-than-normal digestibility of the fiber in drought-stressed corn silage. Some nutritionists undervalued the energy in this corn silage, predisposing cows to subclinical acidosis that was further complicated by rapid turnover of rumen mats.
While it"s always important to test forages before you feed them, in an oddball-weather year like this one — drought stress in some areas and excess rain in others — testing forages becomes critical, says Mahanna. You need more information than just the tons of forage on hand; you have to look at what nutrients are in short supply and the availability of those nutrients. For example, when feeding drought-stressed corn silage with high digestibility, you can use some poorer-quality hay to help maintain the rumen mat and stretch your silage supply.
A routine nutrient analysis is just the starting point. Mahanna also recommends that all forages be tested for NDF digestibility and that you get a protein profile. Digestibility and protein content often vary with moisture stress. And, in severe drought-stressed forages — especially in baled hay or sudan grass — a nitrate analysis is advisable.
Randy Asher, consulting dairy nutritionist in Graham, Texas, agrees. To build a balanced ration and avoid the problems that can occur when your forages vary from book values, you must test your forages. Asher recommends two additional tests — a fermentation profile and a mold-and-yeast count with identification of the molds, toxins or yeast present — as critical this year.
Once you have a handle on forage quality, including the availability of nutrients, then you can formulate a plan to feed your cows and heifers for the year. As part of that plan, pay close attention to your cows. They will tell you if the ration isn"t quite right.
Use the following seven signs to monitor your cows and heifers for signs of a ration problem.
1. Dry matter intake.
This is where it starts. Any time the cows consume less feed than normal, it should raise a red flag in your mind, says Asher.
First, rule out any changes in the weather, ration, or the cows" routine. Then, if none of those is implicated and dry matter intake doesn"t return to normal by the second day, you need to investigate.
Paying attention here can help head off a developing problem.
2. Fresh-cow group.
Stressed cows will develop problems sooner than other cows. That"s why cow comfort has become so important in the past few years.
When a cow is stressed due to nutritional stress, injury stress or the impending stress of calving, her immune system may become suppressed, and that opens the door for more health problems.
Pay close attention to cows in the transition and fresh-cow groups. Any increase in fresh-cow problems, such as metritis, ketosis, displaced abomasum and milk fever, can indicate an underlying nutritional problem.
3. Milk components.
These provide another telltale sign for judging the ration, says Mike Hutjens, extension dairy nutritionist at the University of Illinois. Increased fiber digestibility tends to push the fat test higher. If you"re trying to stretch your forage supply and not quite feeding enough forages, the fat test tends to decline. And, protein content will decline when you have a poor rumen environment and rumen microbes can"t do their jobs properly.
Shortly after cow intake drops, loose stools develop. So, if you missed the first sign — a drop in dry matter intake — the cows will give you a second red flag, explains Asher. This can happen with any group of cows, but tends to show up first in the fresh-cow and high-production groups.
Depending on the underlying cause of the problem, you also might see undigested corn and long forage particles in the manure. These, too, are warning signs that the ration needs attention, says Hutjens. (For more on what manure can tell you about your cows, see the article "Read your cows" manure" in the October issue of Dairy Herd Management.)
5. Body condition score.
Body condition score is another tool that you can use to monitor cows" response to a ration. If the ration is up-to-par. then cows should follow normal body condition score pattern, explains Hutjens. Cows should calve at body condition scores of about 3.25 to 3.5, then drop no more than one point into early lactation and start rebuilding body condition by 100 days in milk. Any deviation from that pattern signals a problem. Cows that don"t start regaining body condition by 100 days in milk are not getting enough nutrients.
6. Response to technology.
When the cows" diet doesn"t quite meet all of their needs, they can not fully respond to bovine somatotropin. And in some cases, such as cows in a negative-energy balance, they may not respond at all.
The same is true with 3X milking, says Hutjens. Normally, you get a 7- to 8-pound response to 3X milking. If you switched to 3X and didn"t get that type of response, or switched back to 2X and didn"t see a drop in production, nutrition was limiting your cows" ability to respond.
Of all the animals on your farm, heifers are the most apt to get the short stick when quality forage supplies are tight. "You can"t get heifers off to a good start and keep them growing by feeding them moldy, poor-quality forage," stresses Asher.
The same rules that apply to testing forages and formulating proper rations for cows also apply to heifers.
Mark 1-inch increments on a wall or post to help gauge growth, suggests Mahanna. Look for bright eyes, good body conformation and a good hair coat as signs that the ration meets her needs. Remember, cheating heifers nutritionally now only sets them up for problems down the road.
Watch out for nitrates
Although dairy cattle tend not to be as susceptible to nitrates as beef cattle, problems can still occur, says Jerry Olson, technical services veterinarian with Pharmacia Animal Health. Dairy cows tend to have more grain in the diet, which creates a rumen environment that helps cows get rid of nitrates.
However, nitrates can certainly be a problem among animals in grazing herds and dairy heifers fed a predominantly forage diet.
When dairy animals consume forages with nitrates, the rumen changes it to nitrite and then to ammonia. However, when more nitrites exist than the animal can get rid of, some of those nitrites bind with hemoglobin to form methemoglobin — a condition that prevents red blood cells from carrying oxygen normally. When this happens, several things can occur, depending on the severity of the nitrate toxicity.
Early signs include animals that pant more than normal and exhibit vulva membranes that are brownish in color instead of pink. Other problems can include premature births, still births, and — in extreme cases — death.
Facts about drought-stressed forages
When it comes to feeding drought-stressed forages don"t assume anything, says Bill Mahanna, general manager of nutritional sciences at Pioneer Hi-Bred International. The fiber digestibility and protein content can vary greatly, depending on when moisture stress hits. Always test before you feed.
Here are a few traits of drought-stressed forages that you may not know:
1. Drought-stressed alfalfa is often higher in protein and has reduced fiber content than alfalfa grown in more favorable weather conditions.
2. Drought-stressed corn silage is often higher in fiber digestibility. Analyze for NDF digestibility and starch and use the Schwab-Shaver NE-L equation to get a better indication of the energy in this corn silage.
3. Nitrates in corn silage will be cut in half by ensiling. That means you don"t necessarily have to set the cutter head up a few extra inches to avoid nitrates in the lower portion of the stalk, and you can maximize tonnage.
4. Baled grass hay, sudan grass and grazing situations have the highest risk for nitrates.