The author is a retired professor and dairy extension specialist with the University of California, Davis.

Alfalfa hay has long been a premier forage for dairy cattle. Even today, when our knowledge of dairy cattle nutritional requirements has never been more complete, most nutritionists and dairy producers like to see some alfalfa hay in their lactating rations.

The high nutritional plane of alfalfa hay grown and fed today has occurred because growers and dairy producers have focused on better hay quality, even at the expense of yield for growers or higher costs for dairy producers. However, last year was a difficult crop year in many parts of the U.S., including the Midwest, and the result has been higher availability of low-quality alfalfa hay. Could this be an advantage to dairies?

Negating key nutrients

Hits to alfalfa hay quality are due to changes in its nutrient levels, and most of them are negative relative to the overall energy value of the hay. The most obvious change is that of energy level defined by total digestible nutrients (TDN) and relative forage quality (RFQ), which decline as levels of acid detergent fiber (ADF) and neutral detergent fiber (NDF) go up.

NDF captures all of the structural fiber of forage, unlike ADF, which only captures 70% to 85% of it. Since NDF is the slowest digesting portion of hay, a greater level will impede the hay’s TDN and RFQ levels. As well, as the NDF level goes up, its rumen fiber digestibility goes down, which means that on a unit NDF basis there is less energy, but overall there is similar energy from total NDF because there will be more of it in the diet. Still, this is a double negative on TDN and RFQ as there is more structural fiber that is less digestible in lower quality alfalfa hay.

Another negative associated with greater ADF and NDF levels of alfalfa hay is that levels of nonfiber carbohydrates (NFC) diminish. As most NFC are rapidly fermented in the rumen, less NFC equals lower energy in the hay.

Finally, more ADF and NDF in alfalfa hay is linked to a lower crude protein (CP) level. CP is required in relatively high quantities by dairy cows and, if not supplied in hay, it must be purchased in high-cost protein meals such as soybean or canola. It is not just that the CP level falls as ADF and NDF climb, but CP digestibility suffers as well. So, on a unit and total fed CP basis, there is less digestible CP in lower quality hay.

However, the uptick in ADF and NDF levels of the hay will encourage ruminative chewing by cows — as well as linked salivation — which buffers rumen fermentation and prevents low rumen pH and acidosis. In addition, ADF and NDF in alfalfa hay has one of the highest buffering capacities of all structural fibers. This is a good thing since high buffering capacity will hold rumen pH higher, thereby reducing the incidence, and extent, of acidosis. So, overall, higher ADF and NDF levels make alfalfa hay more of a forage and less of a concentrate.

What drives intake?

Intake of dairy cows fed any particular ration is influenced by numerous factors, only some of which can be described mathematically. Two key factors that impact intake of a ration are its level of fiber and its level of NFC, which are mainly starches, sugars, and pectins.

Diet fiber limits intake by increasing ration bulk, thereby requiring cows to spend more time eating and ruminating (cud chewing) per unit of ration consumed. Since there is a limit to how much time cows can do this in a day — roughly 14 hours or 35,000 chews — as the ration ADF and NDF levels go up, potential ration intake is progressively limited.

In contrast, NFC provides little ration bulk but does provide carbohydrates that are rapidly fermented in the rumen. If the amount and rate of fermentation of these carbohydrates create fermentation products faster than bacteria in the rumen can use them, or if they are absorbed from the rumen, then they accumulate to drive down rumen pH.

Low rumen pH is a problem in cows fed rations too high in NFC but, perhaps more importantly, acidosis depresses appetite and total feed intake is limited. Thus, intake of any ration tends to be depressed if the ADF and NDF levels get too high, or if diet NFC level gets too high, or both.

There is an upside

So, how does this impact alfalfa hay use right now? Rations for dairy cows are commonly formulated to meet minimum and maximum levels of ADF, NDF, and NFC. As a result of research and practical experience, nutritionists know that the most effective high-group dairy rations contain between 27% and 32% of dry matter as NDF and 36% and 42% of dry matter as NFC. Rations out of these ranges depress intake and animal performance for the reasons discussed above.

When, as is the current case in some regions, availability of hay with higher levels of ADF and NDF are more prominent than normal, nutritionists often remove high ADF-NDF straws with low buffering capacity from the ration in favor of these lower quality alfalfa hays to attain diets with similar levels of ADF and NDF. This results in lower calculated energy levels, but with higher buffering capacity, more high-NFC feeds, such as grains, can be safely added to the ration in order to bring the calculated energy levels of the diet back to equality with the previous diets that contained high-quality alfalfa hay.

Therefore, current availability of low-quality alfalfa hay offers opportunities to utilize it in dairy high-cow rations by reducing the need for high ADF-NDF straws with low buffering capacity and safely, relative to acidosis, recover the overall energy level of the diet by feeding greater amounts of high-NFC feeds.