Crop Comments: Testing Total Mixed Rations is a Good Idea

Of the three main fertilizer nutrients – nitrogen, phosphorus and potassium – P is doing the poorest job of returning to lower pre-pandemic price levels. A number of global factors influences P price (which I’ll evaluate in a later column). P is also the most limiting crop nutrient in Northeast soils, with an unaddressed shortage impacting crop quality and quantity.

Most readers are aware that I seriously advocate testing soils, forages, livestock performance, etc. Not knowing what nutrients are present or lacking in soils is a case where ignorance is seldom bliss.

For instance, a farmer calls me to ask why a meadow is being overrun by horse nettle (aka wild tomato, scientific name Solanum carolinense).

I answer that question with my own question: “What do your soil tests tell you?” That question usually is followed by silence on the part of the non-testing caller.

It turns out wild tomato likes higher pH, low P and poor soil biology. Complete soil tests – including base saturation percentages – would have provided that crop person very useful information. Most of the time, giving the desirable plants the soil nutrient package they need helps chase away undesirable plants.

Testing forages is very important. Intuition only goes so far in tying together crop and feed programs. I take testing one step further, beyond soils and forages, occasionally testing total mixed ration (TMR) blends for dairy folks using this management tool.

TMR programs boast at least four advantages compared to separate ingredient feeding: they can ensure that every mouthful ingested is nutritionally balanced; they enable the cattleman to introduce dietary changes gradually, minimizing offfeed issues; they generally increase total dry matter intake; and TMR analyses provide report cards, grading the ration-balancing skills of the dairy person.

A TMR analysis report arrived in my inbox just before Thanksgiving from a southern Herkimer County organic grass-feeding dairyman named Chester (his middle name). I advise him in both cropping practices and dairy nutrition. That report, from the Dairy One Lab in Ithaca, provided about 30 values expressed on a dry matter basis, costing about $40.

This complete test consisted of two parts – first, TMR NIR analysis (#323), and second, wet chemistry (#329). NIR (near infrared) analysis does not measure added (supplemented) mineral levels in total mixed rations. That’s why we need to use a wet chemistry analysis, which does test for minerals. (Check these options out at dairyone.com.)

On his TMR analysis report were a few values that raised my eyebrows. First, total dry matter (DM) percentage was about 38.9%. Generally, when total diet DM drops below 50%, increasing DM intake (DMI) above current level becomes quite a challenge. In colder weather, soggier TMRs may freeze. Adding at least 3 to 4 lbs. of chopped dry hay perhead- per-day (PHPD) will help dry up the TMR as well as not depress intake of other feeds.

As total DMI pounds increase, generally so does milk production. This particular dairyman’s herd consists of 35 – 40 mostly colored cows, with DMI/ day about 35 – 38 lbs.

The second concerning item was the TMR protein solubility of 47%. Normally, we try to keep that figure closer to 30% (definitely not over 35%). Wetter forages tend to have higher protein solubilities, with a greater proportion of their nitrogenous compounds showing up as non-protein nitrogen (NPN). Thus, more carbohydrates are needed to feed rumen microbes.

Upon receipt of the carbs, these tiny critters couple such energy sources with NPN, synthesizing the more complete – and complex – proteins needed for producing milk, meat, calves, etc. Adding 1 lb. of molasses PHPD (okay for grass-fed organic dairying, if the molasses is organic) provides these microscopic workers the carbs they need to perform this vital task.

My third point of concern (but not a worry) was net energy for lactation testing at 0.67 megacalories/# DMI – against a requirement of 0.60. The molasses that Chester was already feeding no doubt helped ensure that need was met, with a safety margin.

Note: If that dietary protein solubility hits and exceeds 40%, excess NPN in the rumen can result in too much blood ammonia, which actually requires energy to excrete through the kidneys – energy that otherwise could have supported milk production.

Point 4 was a calcium reading of 0.99% (against a requirement of 0.80%), plus a P reading of 0.48% (against a requirement of 0.40%). So these two nutrients looked pretty good.

Point 5 was a magnesium (Mg) score of 0.34% (okay against a requirement of 0.30%). But compared to a K reading of 2.53%, there’s a chance that the K can outbalance the Mg, predisposing these mostly colored dry cows to a hypo-magnesemic milk fever. I recommended Chester feed 0.10 – 0.15 lbs. of Epsom salt (magnesium sulfate) PHPD to dry cows as soon as they start bagging up – and keep feeding it up till freshening.

Point 6 deals with salt, measured by a 0.126% TMR sodium reading. For 38 lbs. daily DMI in the TMR, this means the average cow is consuming about 2.5 oz. of sodium chloride per day. Not bad, but I still recommended Chester topdress a couple ounces of salt with selenium (Se) a couple times per week, just to be safe. (There are some organically approved salt blocks with added Se.)

Let’s remember that grass-fed cow diets tend to run lower in P than regular grain-included rations. This because on a per-pound-of-DM basis, grains bring about twice as much P onto the farm as do forages.

And few folks know this: A little over 1 lb. of actual P accompanies every 1,000 lbs. of milk leaving the farm. This figure is derived from the standard book values for concentrates in my 22nd edition of “Morrison’s Feeds and Feedings” (1959). Raw fluid cow’s milk is listed as a concentrate, showing 0.1% P.

One pound of P exiting the farm with each 1,000 lbs. of milk may not sound like much. But in terms of undermining the cow’s diet, it all adds up – or, perhaps more accurately, subtracts down.

by Paris Reidhead