My classic 1959 copy of “Morrison’s Feeds and Feeding” (22nd edition) comes in quite handy in balancing livestock rations. That hardcover book was a relatively new text when I took basic livestock nutrition at Cornell under Professor Richard Warner in 1966. Dietary energy need was expressed in TDN (total digestible nutrients). There was almost no mention of net energy for lactation (expressed as megacalories per dry matter pound at most modern laboratories).
But mineral and protein measures are expressed about the same way now as they were then. Of the minerals, let’s home in on phosphorus (P), which is the most limiting macronutrient in Northeast soils – and hence, Northeast feeds.
Identifying P deficiencies in crops isn’t too hard. Corn leaves develop reddish-purple leaf tip die-back. Small grasses do the same thing (though not quite as visibly). Heads of small grains don’t fill out completely if P is deficient. Legumes don’t grow very enthusiastically. Certain weeds, however, are encouraged – ones that survive when P is quite limited. Wild tomato and horse nettle (both genus Solanum) seem to enjoy low P. And brome grass is more tolerant of low P than is timothy.
Let’s look at P deficiency in cattle. There are at least five serious major P deficiency symptoms with lactating dairy cattle. If a large (1,400 lb.-plus) dry cow doesn’t get 40 – 50 grams/day of P when she’s starting to bag up, her chances of getting milk fever (parturient paresis) increase significantly. To counter that problem preventively, giving her 2 – 3 oz. of Epsom salt per day is always a good idea (particularly with Jerseys).
The next P deficiency sore thumb is infertility. For some odd reason lactating cows getting less than 0.35% – 0.4% of their dry matter intake as P have trouble settling with calf. It’s like she’s telling you that you’re not giving her the tools to do the task you’ve assigned so she backs off on milk production or doesn’t breed – her way of crying “uncle.”
The third P deficiency symptom may show up when another cow mounts her on an icy floor; she ends up with a broken pelvis, commonly referred to as “splitting.” The most common molecule in any animal’s bones is dicalcium phosphate. Cows milking heavy may mobilize the calcium and P in that molecule to make milk; at some point that weakens bones, making the cow prone to splitting.
The fourth P deficiency symptom would be reduced milk production. My “Feeds and Feeding” shows that fluid cow’s milk is 0.1% P. This means that a cow giving 60 lbs. of milk is voiding 0.06 lb. elemental P every day through the bulk tank. That’s 1 oz. of that element, every day per cow, leaving the farm. It really adds up.
The fifth situation where P is critical is something called the Krebs cycle. According to ScienceDirect.com, “The Krebs cycle, also known as the citric acid cycle, is a metabolic process that produces adenosine triphosphate (ATP). ATP is a molecule that stores energy for the cell to use.” Expressed as simply as possible, if P is deficient at some point, the energy train is setting up for derailment. And these ground rules don’t apply just to cows – they have a lot to do with almost any form of life.
One more technical term in Krebs dialect is “oxidative phosphorylation,” a cellular process that generates energy in the form of ATP. It’s the primary way cells produce ATP, except in some cells like red blood cells.
Let’s move on to soils, because P is the most limiting nutrient in Northeast soils. Native Americans discovered that a solid way to make corn perform its best was to bury fish bones in each corn hill. The rotting bones liberated P into the plants’ root systems. Rotting non-bones also liberated nitrogen and other minerals.
The modern fertilizer industry is dependent on rock phosphate being mined and processed with acids and ammonia to become more available – ultimately becoming mono-ammonium phosphate and diammonium phosphate.
As my title hinted, forages don’t seem to have much to offer in the P department. Most test for P in the 0.2% – 0.25% range. Grains tend to deliver a lot more P. For example, shell corn runs around 0.3% P, and soybean meal (with oil removed) tends to run about 0.7% P. With the idea that cows need their P intake to run in the 0.4% – 0.5% range (depending on milk production), the heavier the level of forage in their diet, the greater their need for P supplementation.
So let’s attack this potential P deficiency at grassroots level. Jim, a Mohawk Valley organic grass-fed dairy farmer, helped me with the next discussion by sharing recent soil test results. He used the Dairy One Lab “803 test,” which includes base saturation values (BSV) – I stress their importance.
Tests showed results quite close to each other. His potassium readings were high to very high (lbs./acre); calcium readings were very high; magnesium readings were very high; pHs were right at 7.0. Soil was Mardin silt loam. Phosphorus levels were very low, and BSV for magnesium was 10.4.
He plans to plant spring barley. Per acre, the lab recommended 60 lbs. nitrogen, 65 lbs. phosphate and 20 lbs. potash. Since he’s organic, I can give him a fertilizer recommendation with Chilean nitrate and bovine bone meal – 25% total phosphate and sulfate of potash.
If he were conventional (non-organic), the recommendation would include urea, diammonium phosphate and sulfate of potash. With magnesium BSV less than 12%, I’d like to throw in about 25 lbs. actual magnesium/acre. With him being organic, the magnesium would have to be in the form of magnesium sulfate. If he were conventional, it would be okay for him to apply magnesium oxide. If pHs weren’t so high, Jim could apply dolomitic limestone to get the magnesium back in balance.
Leave A Comment