Flashback to 20 years ago. It was the best of times; it was the worst of times. The cows ate less but required more feed per pound of milk. There is no doubt today’s cows are exponentially more efficient than even 20 years ago. The dairy industry is making more milk per pound of feed while emitting about 45% fewer greenhouse gasses per pound of milk since 1961.
Today’s cows have evolved quite a bit, particularly in terms of size, dry matter intake (DMI) and milk production. As cows get larger, produce more milk and increase their feed intake, how we think about feed ingredient levels may need to change, depending on many factors. Should you be thinking about your feed ingredients in terms of the quantity delivered to the cow or the concentration in the feed? A great place to start is with the mode of action.
Where does the feed ingredient work?
The gastrointestinal tract is essentially a tube running from the mouth all the way to the back end of the cow. Everything that enters this tube (feed, water, etc.) is still technically outside the cow’s body until it crosses the gut and is absorbed. The moment it is absorbed across the gut, it becomes part of the cow. Where a feed ingredient works, whether in the cow (postabsorptive) or in the rumen contents (preabsorptive), makes a huge difference in how we need to think about the amount fed.
Postabsorptive – if the feed ingredient is utilized by the animal
If the cow herself is utilizing the ingredient postabsorptively (after it crosses the gut and into circulation), it is logical to think about the quantity of whatever feed ingredient we are trying to get into her system. For example, if a cow in 2004 is milking 65 pounds per day, she requires around 1,160 milligrams of dietary zinc per day.
Does a cow in 2023 require more zinc? Yes. However, she is also eating a lot more zinc, so the concentration in the feed doesn’t necessarily change in proportion to her zinc requirement. It is more accurate to pay attention to the quantity of her requirements first, then go back to the math that gives us the dietary concentration to get to the needed quantity.
Preabsorptive – if the feed ingredient is acting on feed or microbes in the rumen
When dosing the feed, it makes sense to think about the ingredient in terms of concentration. Rumen modifiers work in that large black box we call the rumen, and the bigger and fuller the box gets, the more ingredient we may need to have an effect. A great analogy involves a beloved childhood beverage – the nostalgic and refreshing glass of lemonade. It takes about one lemon to make one cup of lemonade. If I need to make 10 cups of lemonade, I would use 10 lemons – not one. The goal isn’t to dose with a particular number of lemons but to have an effectively tasty lemonade with a 1-1 ratio of lemon per cup of water.
Trusted by generations
A great real-world example of a rumen modifier is monensin. Monensin shifts rumen bacterial populations to produce a higher proportion of propionate. This reduces the amount of energy wasted as carbon dioxide and methane, allowing cows to get more energy from the ration.
The label for monensin indicates 11 grams to 22 grams per ton of feed on a 100% dry matter (DM) basis. Let’s go back to the tale of two cows. Back when monensin was first approved for dairy cows in 2004, it was common to feed 300 milligrams per head per day. At 50 pounds DMI (a common average intake in 2004), this equals around 12 grams per ton and falls within the label requirement of 11 grams to 22 grams per ton. Fast-forward to 2023, where 60 pounds DMI is a common average.
If you keep formulating the diet to provide 300 milligrams per head per day, the concentration has now been diluted to 83% of its original value at 10 grams per ton of feed. Monensin is less effective at lower concentrations, and its benefits to milk production efficiency could be underutilized (Figure 1).
The bottom line
There’s significant potential in how nutritionists and producers can rethink quantity versus concentration dosing of feed additives, especially when the mode of action is in the rumen. Keep up to date with your cows. Take advantage of additives that can offer better milk production efficiency. Don’t make bad lemonade. Speak with a nutritionist, an animal health consultant, or an extension representative to assess and optimize your operation’s feed strategies.
References omitted but are available upon request by sending an email to the editor.
The label contains complete use information, including cautions and warnings. Always read, understand and follow the label and use directions.
Monensin (Rumensin)
Caution: Consumption by unapproved species or feeding undiluted may be toxic or fatal. Do not feed to veal calves.
Feeding directions
Dairy cows: For increased milk production efficiency (production of marketable solids-corrected milk per unit of feed intake):
Total mixed rations (TMR or “complete feed”): Feed continuously to dry and lactating dairy cows a TMR containing 11 grams to 22 grams per ton of monensin on a 100% DM basis.
Component feeding systems (including top dress): Feed continuously to dry and lactating cows a Type C medicated feed containing 11 grams to 400 grams per ton of monensin. The Type C medicated feed must be fed in a minimum of 1 pound of feed per cow per day to provide 185 milligrams to 660 milligrams per head per day of monensin to lactating cows or 115 milligrams to 410 milligrams per head per day of monensin to dry cows. This provides cows with similar amounts of monensin they would receive by consuming TMR containing 11 grams to 22 grams per ton of monensin on a 100% DM basis.
