Recently, I attended the 2016 Western Canadian Dairy Seminar and took in several of the excellent presentations. One of the talks was by Tom Oelberg, who discussed the mixing of the milk cow’s Total Mixed Ration (TMR) as well as some of the improper diets that are often put down in the feed bunk. This lecture made me think we should always implement good mixing and feeding practices to prevent lactating cows from sorting out their diets. Dr. Oelberg is a dairy field technical specialist with Diamond V an Iowa-based animal nutrition and health company.
This is pertinent TMR information, because I find that given the chance, lactating dairy cows can become skilled masters at sorting their rations. For example, I have literally seen cows lay their heads flat against the concrete bunk floor and pick out the more tasty grain/concentrate particles and leave the rest of the diet.
Unfortunately, when they gobble up this part of the diet, it tends to be low in effective fibre and therefore makes them susceptible to subclinical acidosis or SARA. If left unchecked, SARA will eventually compromise their milk performance and health.
From a dairy nutritionist’s standpoint, I believe that if I can reduce the conditions that cause cows to sort their bunk ration; SARA and other related feed problems are not likely to become a significant issue. I find that there are two major reasons, which makes some TMR diets easier to sort than others by dairy cows: (1) a “dry” dairy diet and/or (2) large particle size variation amongst added feedstuffs.
In the first case, an excessively dry TMR has a low physical density. This allows dairy cattle with a shake of their head, to separate the finer grain and protein supplement material from coarser forage fibres. Subsequently, it is much harder for them to separatea well-mixed lactating TMR that is about 50 per cent moisture. In order to achieve this goal, dairy producers can add up to seven kg (15 lbs) of water per lactating head into a TMR diet in order bring moisture content into this optimum range. Again, a dairy diet with various feed particle sizes makes it easy for cows to sort out dairy diets because they can literary “un-mix” their diet. One way to stop them is to add forages with a modest particle length of four to 7.5 cm (1.5 – 3.0 inches). The idea being that cows tend to sort and reject long particles, but are willing to eat medium-sized ones; those often long enough to help meet forage-fibre requirements.
Tips for a mixed TMR
Given these two underlying reasons for sorting, most people either have a general sorting problem in the milking barn or one pops up on occasion (re: hot weather). Therefore, I have five suggestions that helps us mix a proper TMR and is harder for dairy cows to sort:
1. Moisture testing — It is a good idea to test the dry matter content of the major silages (re: corn and/or barley silage) and the other added wet by-products (re: wet distillers grains) added to the TMR and also of the entire bunk ration fed to the cows. If water is added to the diet, the amount should be recorded. Such information is useful when future moisture adjustments are made.
2. Particle testing — Use the Penn State particle separator to determine particle variations within the diet. A sample of the daily mix should be taken, separated out, and fractions calculated. Between six to 10 per cent of the sample weight should lie on the top screen. It should also be something that the cows like to eat; not cobs or woody alfalfa stems. If more than 15 per cent of the ration remains on the top screen, the chances are good that cows will sort this ration.
3. Grind forages — Long-stem hays should be coarse ground (ahead of time) to match the particle size of the other feed components of the TMR. This is most important when more than 2.0 kg of hay per head is fed.
4. Manage the mixer — Many typical TMRs require about three to six minutes of actual mixing time to make a consistent uniform diet. Furthermore, dairy producers should make sure that their mixer wagons are in good working order and consider a checklist for scheduled maintenance (Tom Oelberg, 2016 WCDS).
5. Measure feed refusal — Take a sample of the feed refused by the cows. As part of good bunk management practices, dairy cows should leave about two to three per cent of the original feed put down. Although, it could be picked through, daily feed refusal should be similar in appearance to the fresh TMR. If particle profile of a sample is tested, the amount left on the top screen should not be greater than 10-points compared to the original TMR.
It’s anybody’s guess why many cows sort TMR rations. Maybe it’s part of their natural grazing nature or a modern opportunity to eat the tasty treats in their feed. Regardless, dairy producers should follow these few practical steps when mixing up a dairy TMR, which should be eaten in its entirety by all cows coming up to the feed bunk. †