Maximizing rumen efficiency leads to gain
The management principles proposed have the likelihood to increase microbial protein contribution by at least 3% if operating in a normal window
By Benjamin Wenner, PhD, PAS
Several years ago, I was asked to give a few talks on milk pricing and the value of milk components. While how U.S. milk is priced can be a bit nebulous – and is the subject of many recent discussions on reform – the concept of milk component value is much clearer. In most parts of the U.S., both milk protein and fat combine to provide the majority of a producer’s milk check. Unfortunately, far too many producers and consultants continue to talk pounds of milk produced rather than pounds of components.
The problem is that producers and consultants in the dairy industry tend to become complacent when talking about pounds of milk. Numbers in the 90s can feel good but tend to ignore component percentages. When challenged as to what a good goal should be, murmurings in the room range from 5 to 8 lbs of components. But GOALS are meant to be ambitious and to challenge us to be a better version of ourselves – not serve as a benchmark to meet on an annual basis. In the same way, goals on the dairy farm should be the same, and 5.5 pounds of components for most of us barely represents financial stability. If your milk production goals don’t include at least 6.5 pounds of components, you are being left in the dust. The cow’s mere existence represents overhead to your business; you feed her to exist regardless of how much milk she gives you! Many of the opportunities to improve milk components are low hanging fruit and what follows here is mostly not new. After all, very few of the principles to good ruminant nutrition management change.
To set the stage for the following guidelines, the reader must first see the ruminant for what she is: a mammal bred for high energy demands fulfilled in bulk by a massive fermentation vat. A diverse conglomerate of microbes live within her rumen and collaborate or compete for substrate but they ultimately feed at the whim of the cow. As a generalization, microbial fermentation of fiber leads to increased acetate – a precursor for milk fat synthesis – whereas starch fermentation increases our proportional production of propionate for glucose production by the liver. There is a fine balance in feeding cows because we need to provide both rapidly fermentable carbohydrates (as from grains) and slowly fermenting fibers (as from forages) in conjunction with available nitrogen to feed the diverse microbiome in the rumen.
At the time this was written, the marginal gain of a pound of fat (comparing energy cost to produce versus market value) was nearly triple that of protein, and the current protein value in milk continues to fall for the short term. When they are fed properly, microbes not only make energy for the cow but they also grow and die, passing protein downstream to the cow’s benefit. An optimized rumen will synchronize these nutrient categories to capture as much microbial protein for the cow as possible while spiking her total nutrient supply. Thus, the following recommendations will assume a diet is already properly balanced on paper and instead focus on nutritional approaches towards increasing energy to the cow for milk fat and hope that we pull along microbial protein for the ride.
Risk
A lot of the conversation surrounding milk fat production essentially consists of two things: 1) keep the rumen “bugs” happy, 2) avoid milk fat depression. Digestible forage, effective fiber, and pH balance fulfill the first one but the second is a bit more complex. We have studied milk fat depression to great extent and at this point know that the root cause is incomplete biohydrogenation of unsaturated fatty acids in the rumen. Microbes don’t like unsaturated fatty acids and work aggressively to saturate them. However, not all microbes are equally threatened by nor equally committed to removal of unsaturated fatty acids.
I like to use poker as an analogy for risk of rumen dysfunction. Those who play a bit of poker know that winners can’t afford to wait for the perfect hand but must play with the cards we’re dealt or do as Kenny says and know when to fold (i.e., call in a dietary band-aid). As you survey the cards in play, increasingly problematic cards lower your risk of a positive outcome. But the issue is that the rumen doesn’t bluff and neither should you. So, here’s a few key indicators that you have a problem.
Unsaturated fatty acid load is the starting point. Many of us have maximums in our head for how much fat should remain in the diet: 3%, 5%, or even 10% (at least that is what you thought it was on paper), but the right answer is truly situational. Sure, you have lower risk if you have lower fat. But perhaps there is an opportunity to get a buy on some fat that may push your milk fat test a bit. Any time you’re handling a high fat byproduct feed, a feed analysis is probably safer than a book value. The key here is to realize that as fat increases in your diet, your level of caution about other factors should also heighten.
Rumen pH becomes the next focus. As rumen pH declines, many of our biohydrogenating bacteria and fiber digesters suffer first. Thus, conditions that promote a low pH such as overcrowding/slug feeding, high quantities of starch (30+%), or poor rumination from low effective fiber or resting time compound the risk that some fat may be improperly biohydrogenated or microbial protein efficiency hampered. Cows can be pretty resilient to a few changes that lead to temporal low pH, but the continued insult over time is where the risk level rises.
Rapid changes in diet can also influence the level of risk. Remember that the microbes are a living community whose role is to ferment what you provide to the cow, or more realistically what the cow consumes in her ration. Rations can change from ingredient variation, mixing error, delivery or intake shifts (new pen groups, sorting, or overcrowding), or bargain buys. In nutrition, we like to throw out safeguards such as <30% starch or <6% fat in the diet. We know that a cow can be pushed beyond those limits but a safety margin in the diet guards against the highs and lows that may occur due to daily life and mistakes on the farm.
Consistency
Above all else, consistency is key to keeping microbes happy and avoiding risks in the rumen. And happy microbes lead to more fermentation and, N permitting, more growth. Better yet, a happy microbial population is more resilient to the highs and lows inherent with feeding cows. To this end, the Isotrichid protozoa within the rumen are a key example. Beyond being fairly fast swimmers, known for capturing starch and hoarding it away, and for feeding hydrogen to methanogens symbionts, Isotrichids are fairly predictable. In 1989, Dehority and Tirabasso demonstrated a protozoal response to feeding time where they presumably swim towards feeding and then sink away to avoid outflow into the omasum. However, protozoa become accustomed to feeding time and a missed feeding will still prompt this swimming congregation, illustrating that not only does the cow notice poor feeding schedules but so do her constituents.
Similarly, a recent study we performed in sheep (Jermolowicz and Wenner, 2022) highlights the behavioral adaptation of ruminants to management. In this study, sheep were offered water from buckets cleaned every day, twice a week, or one weekly. To the surprise of nobody, the sheep dirtied their water through the week and as the buckets cleaned less frequently became pretty filthy, the sheep consumed an increasing proportion of water from the clean bucket. Once a week, all 3 waterers were cleaned together, however, when offered these three sources of clean water the sheep still avoided the waterer they had historically identified as “dirty”. Like the daughter in the movie Signs, the water was seemingly “contaminated” and sat undrank in the pen where it continued to get dirtier once again. I’d challenge the reader to consider how often you walk a pen and see a dirty waterer? How many days will it go uncleaned and discourage water intake long-term, regardless of what best practices may be implemented a couple times a month?
Management
Feed mixing activity is a another relatively free opportunity to minimize risk through proper management. The constant plague of a good nutritionist is a ration that is a poor match for the diet drawn up on paper. This can be from a bad load cell, limited mixing time, poor mixing orders, or even an inability of the feeder to read the scrawled feeding instructions summarizing the most recent diet change. On several occasions this past year, I’ve watched mixer loads dump in long-stemmed hay or straw at the end of a batch then immediately deliver the ration with clumps of fiber at the end of the bunk. Poor mixing leads to imbalanced intake by the cows in a pen; the diet was balanced for the average cow but now no cow is receiving the average diet.
We also need to think beyond the shrink we can see towards the impact of that shrink on the cow. With sliding IOFCs, producers can be tempted not to sort out molded feedstuffs in an effort to limit shrink values on the inventory. But at what cost are these damaged feedstuffs being fed to the animal? Further, each error in the feeding routine puts a cap on the potential of a diet to maximize milk components. Imagine a ration with a 5% error on loading combined with a 5% loss in ground corn as the wind blows during loading. Your cows are now short up to 10% of the rapidly fermentable starch you intended to add in to feed those microbes who synthesize high quality protein for the cow.
Once the feed gets to the bunk, stocking density becomes the focal point. High stocking density is not forbidden, but it comes at a cost or at bare minimum requires extra attention. Limiting the density in the fresh pen, sorting our first lactation cows out from multiparous, increasing feed push-up times to keep feed available for cows, and paying close attention to sortability of the diet can help limit the negative effects of high stocking densities in the pen. There is a wealth of good literature to help managers quantify the effect of stocking density decisions but the best way to start is by watching three pointers: locomotion (high stall density), fecal inconsistency (sorting or slug feeding), and variability of body condition score (sorting or general feed access restriction).
Microbial Protein
If we follow the suggestions provided about to maximize rumen efficiency, the implied response of microbial growth should come along for the ride. And this gain can be significant. Using CNCPS modeling software, we can predict the contribution of microbes to the total protein balance in a cow and this typically ranges between 45-55%. One could argue that the most efficient balance is nearly 90% protein coming from microbes, at least if you only look at rumen efficiency. That cow does exist somewhere, but she is likely eating cardboard boxes for dinner out of the recycling bin behind the grocery store. And she probably only makes about 8-10 pounds of milk per day. Instead, 50-55% protein from microbial sources is a more realistic goal when you consider maximizing the milk components coming from the cow. And the management principles proposed above have the likelihood to increase microbial protein contribution by at least 3% if you’re operating in a normal window.
What does a 3% increase in microbial protein mean for the nutrition of your cow? Rumen microbes are especially enriched for lysine, but also some of the branched chain amino acids we find limiting in some animal diets. In fact, rumen microbes tend to improve the quality of dietary protein by breaking it down to ammonia and rebuilding it to more essential amino acids. Simple management improvements can increase microbial lysine by 10 grams and methionine by another 3 grams per cow per day. I’ll let the reader do the math in their own economic circumstances, but this gain is both consequential and virtually free to you.
Benjamin Wenner, PhD, PAS, is an Associate Professor - Professional Practice at The Ohio State University
References
Dehority, B., and P. Tirabasso. 1989. Factors affecting the migration and sequestration of rumen protozoa in the family Isotrichidae. J. Gen. Microbiol. 135:539-548.
Jermolowicz, H., and B. A. Wenner. 2022. Effect of waterer color and frequency of cleaning on sheep water intake. J. Dairy Sci. 105 (E. Suppl.):406.
Wenner, B. A. 2018. Feeding the rumen to maximize milk components. Proceedings of the 27th Annual Tri-State Dairy Nutrition Conference, pages 167-185.
