Cows fed extra fermentable carbohydrates pre- and post-calving produced 5 pounds more milk per day than herdmates on standard diets in a study at the College of Agricultural and Life Sciences. Your herd”s mileage may vary, but it”s a good idea to make sure your dry cows are getting plenty of fermentable carbohydrates starting two to three weeks before calving. Proper carbohydrate nutrition before and shortly after calving may also help prevent metabolic disorders during lactation, according to dairy science grad student Doug Minor and Ric Grummer, a dairy nutritionist at the University of Wisconsin-Madison.
In this study, standard and high non-forage carbohydrate (NFC) diets were fed as total mixed rations. The cows started on the diets 19 days before calving, and continued through 40 weeks of lactation.
The high-NFC group averaged about 5 lbs/day more milk than the standard group. The high-NFC group also had higher milk protein content (3.18 percent) than the standard group (3.01 percent). Fat percentage decreased slightly with high-NFC diets, but higher milk production offset that decrease and fat yield was not affected.
Prior to calving, the standard NFC diet was primarily alfalfa silage, with straw added to reduce forage quality and bring energy content closer to National Research Council recommendations for dry cows. Forage was reduced in the high-NFC diet, with corn starch and more corn grain added to increase the fermentability of carbohydrate. After calving, the standard NFC diet was 50 percent forage and 50 percent concentrate. To increase NFC after calving, the researchers reduced forage level, added corn starch and fed finely ground corn instead of cracked corn.
While the researchers used corn starch to increase NFC, farmers could also use more corn to get the same effect. Finer grinding can increase the fermentability of corn, and high-moisture corn is more fermentable than dry corn, according to Minor and Grummer. Corn starch could be an option for farmers who have low-quality forage for dry cows and want to increase NFC content of diets, Grummer says. Switching to a different grain can also increase fermentability. For example, the starch in barley is more fermentable than corn starch.
Nutrition for the transition cow is still a bit of a mystery, Grummer says. The National Research Council”s “Nutrient Requirements for Dairy Cattle” recommends a constant diet, very low in energy and high in neutral detergent fiber, for the entire dry period. That ignores the special needs of transition cows, which should be getting more NFC and less NDF in their diets, according to Grummer.
There is a fine line between too little and too much NFC. A high-NFC diet can help adapt rumen microorganisms to the grain diets fed after calving, and high-NFC diets help the rumen to more efficiently absorb the volatile fatty acids needed for milk synthesis, according to Minor and Grummer. However, excessive intake of NFC may cause acidosis and displaced abomasums.
Cows fed the high-NFC diet ate more dry matter during precalving than cows fed the standard diet (1.9 percent versus 1.5 percent of body weight). Cows on standard diets ate a little less than a typical dry cow might. This indicates that diet composition can influence precalving feed intake, according to Grummer and Minor.
Grummer”s previous work has shown that increased precalving feed intake reduced incidence of fatty liver and reduced blood ketone levels. In this study, ketones were much lower at four weeks postcalving with high-NFC diets, at the time the cow is most at risk for ketosis. Non-esterified fatty acids were also lower in cows fed high-NFC diets. High levels of these fatty acids have been linked to a variety of post-calving metabolic disorders. Two other indicators were also positive in cows on high-NFC diets: liver triglycerides were reduced at four weeks post-calving; and liver glycogens (sugars stored in liver) were increased.
“This trial indicated that carbohydrate content of diets fed to transition cows may influence pre-calving feed intake and metabolic status. Further research is needed to determine optimal dietary fiber and NFC for transition dairy cows,” Grummer says. “Until then, we recommend that close-up dry cows be fed a TMR that has carbohydrate and energy specifications that are midway between far-off dry cow diets and early lactation diets. Aim for approximately .70 Mcal NEl/lb, a minimum of 32 percent neutral detergent fiber, and a maximum of 40 percent NFC.”