Knowledge of cow biology, feed composition and herd information is vast and ever-expanding. Dairy producers and nutritionists have powerful tools available to balance rations and monitor outcomes for specific groups of animals. The process of getting this balanced ration delivered to and consumed by cows is fraught with risk of mechanical and human error. The feeding process requires skill and attention to detail to deliver a high-quality, uniform ration to all cows within a pen. The following is a partial list of critical control points on which to focus to achieve TMR consistency.
Forage dry matter
Changes in forage dry matter (DM) can have considerable impact on how the consumed ration compares to the one on paper. Let’s say you are mixing a 20,000-pound load of TMR (50% DM) for 180 cows. The corn silage was recently tested to be 38% DM. The load calls for 8,600 pounds of corn silage, which is 3,268 pounds of corn silage DM. However, the corn silage is actually 34% DM, so the mix really contains 2,924 pounds of corn silage DM. That means, on average, each cow is consuming 1.9 pounds less corn silage DM than formulated. Ideally, forage DM should be measured multiple times per week, especially if the forage is stored in bags. On-farm options for determining DM include a Koster tester, food dehydrator, microwave, air fryer or NIR technology.
Mixing faced silage
Nutrient composition across the face of a bunker or drive-over pile can vary considerably due to the nature of silo filling (i.e., multiple fields, DM changes, varieties, etc.). Researchers took 10 equally spaced samples down a windrow of faced alfalfa haylage and found that crude protein percentage (DM basis) ranged from 18.3% to 23.1%. Faced silage for that day’s feeding should be piled and mixed with a loader bucket to decrease nutrient variation from load to load.
Loading location of ingredients
The most common TMR mixers are vertical auger mixers and horizontal reel-auger mixers. For vertical TMR mixers, the feeder should always load in the center of the mixer box to promote distribution of the ingredient throughout the mix. Loading location is less important for horizontal mixers, but loading in the center is still preferred. Use of liquid ingredients – such as water, molasses or whey permeate – makes loading location especially important, as dense liquid feeds can be difficult to distribute if loaded on either end of the vertical mixer. Likewise, design of a spray bar with multiple spouts can improve liquid distribution by spreading the liquid across a wider area.
Levelness of the mixer
Mixers perform best when they are level so they don’t have to fight gravity to distribute ingredients. For example, if the front end of the mixer is tilted downward (due to the slope of the pad or hitch height) and whey permeate is added, the dense, wetter feed may stay in the front of the mixer, leading to poor distribution and ration uniformity.
Overfilling the mixer
Mixer capacity can be confusing to calculate. Manufacturers will typically publish total volume of the mixer box in cubic feet. Maximum load weight is then calculated by multiplying the volume (cubic feet) by the assumed density of the ration (pounds per cubic foot). For example, a 600-cubic-foot mixer loaded with a ration that has a density of 25 pounds per cubic foot would result in a maximum load weight of 15,000 pounds. Ration density can vary depending on the ingredients used, so maximum weight is a moving target in relation to mixer volume. A general guideline for maximum load size in vertical mixers is to keep the feed level no more than 2 feet above the augers. Horizontal mixers should have 4 to 6 inches between the feed and the rails on the reel to allow for the feed to fall at the 12 o’clock position on the reel.
Underfilling the mixer
Mixers can also be underfilled, which typically happens with rations for dry cows or fresh cows, as their pen sizes are much smaller than those of lactating cows. For these loads in vertical mixers, pay special attention to loading location and mixing speed to avoid concentrates and other feeds remaining on the augers. Minimum load size is enough feed to move feed off the augers while achieving an adequate mix.
Mix time and mixer RPM after last ingredient
To achieve acceptable uniformity, it is critical that the TMR receives a final mixing for enough time and with adequate rotations per minute (rpm). This final mix should occur after the last ingredient is added, with the mixer level and preferably stationary. This final mix should last three to five minutes with the mixer in the highest gear. Speed recommendations will vary among manufacturers, but a typical goal is greater than 30 rpm during the final mix. We often see the final mix occur while liquid feed is added (which does not provide enough time after the last ingredient) or with the mixer not achieving adequate auger rpm (which is too slow to achieve desired uniformity).
Equipment wear
TMR mixers are used an incredible number of hours each day, so it is no wonder parts show wear to the point where ration uniformity may be impacted. For vertical mixers, key wear points are the kicker plate, leading edge, knives and mixer walls. One sign of a worn leading edge or kicker plate is leftover feed on the floor of the mixer and poor movement of feed around the perimeter of the augers. Knife condition is important for long-forage processing efficiency and quality. For horizontal mixers, the condition of the auger flighting and reel crossbars can impact ration uniformity. Routine inspection of the mixer, periodic evaluation of TMR uniformity and timely replacement of worn parts are all key in delivering an acceptable TMR to the cows.
People
Protocol drift impacts the feeding operation as well. Bunk calls, increasing or decreasing the amount of feed offered, ingredient order and TMR mixer operation are all tasks that should be standardized so each feeder is operating from the same playbook. Likewise, effective communication among different work groups on the farm can improve the ability of the feeder to determine how much feed to mix that day. While technology helps immensely with communication and should be leveraged, sometimes simple things such as having a whiteboard in each barn for employees to record when cows are low on feed can help the feeder make decisions.
Checking TMR consistency
We recommend checking the TMR particle size variation of the largest and smallest loads by safely obtaining 10 samples equally spaced throughout each load as it is delivered to the bunk. Each of the 10 samples are then processed through the Penn State Particle Separator; the coefficient of variation (standard deviation divided by the mean) for the proportion of particles on the middle sieve and bottom pan among these 10 samples should be less than 5% and ideally less than 3%.
Without a doubt, many “moving parts” are involved in feeding cows the right ration at the right time and in the right amounts. These critical control points for achieving TMR consistency are essential for allowing cows to express their genetic potential, stay healthy and produce profits.
