An Analysis of a Flawed University Research
Study on Self-Select Mineral Feeding

   In 1977 a study was done at South Dakota State University entitled “Cafeteria Style Free-Choice Mineral Feeder for Lactating Dairy Cows” by L. D. Miller, L. V. Schaffer, L. C. Ham, and M. J. Owens.    1977 J Dairy Sci 60:1574-1582

   The authors stated - “Little evidence was found that dairy cows offered minerals and vitamins free choice consumed to a specific appetite or need under the two nutritional regimes.” 

   “Trial 1 was 16 wk in which two groups of cows in mid-lactation (10 cows / group) were group-fed rations with either corn silage or alfalfa hay as the sole forage, and all supplemental minerals and vitamins were provided free choice.” Comment:This is too small a group and too short a time to really evaluate the nutritional wisdom of animals.
   “Minerals and vitamins were provided in a “cafeteria style” mineral feeder, one feeder per group. The feeder was sheltered and afforded protection from wind and rain. Mineral and vitamin mixes were: calcium (28 to 30% Ca from calcium carbonate), phosphorus (>20% P from monosodium phosphate), potassium (>31% K from potassium chloride), magnesium (21.5% Mg from magnesium oxide and sulfate), sulfur (47.5% S from flours of sulfur), trace mineral, bicarbonate of soda, sodium bentonite, sodium chloride, iodine mix (>.88%I), and vitamins A, D, and E (Vitamin A, 4,400,000 U.S.P. units/kg; Vitamin D, 2,200,000 U.S.P. units/kg; and Vitamin E, 1,100 IU/kg). The remaining portions of the mineral mixes were composed of products such as rice mill by-products, rice hulls, and dehydrated alfalfa. Intake of each individual mineral was determined weekly for each group.”

   The report stated, “Intake of phosphorus, potassium, and vitamins differed between rations. A higher free choice intake of phosphorus by cows fed alfalfa was not expected.” Comment: It should have been expected as it is well known that cattle need to balance their Ca/P ratio. “Cows could possibly have been consuming more P to narrow the wide Ca:P ratio due to high Ca intake from alfalfa.” Of course they ate more P to balance the high Ca in alfalfa. That’s what free choice is all about – giving them the opportunity to self regulate their needs.

   From the report, “Cows fed corn silage consumed more potassium free-choice, but additional intake still was needed to meet requirements.” Comment: Whose requirement are they trying to meet NRC standards or what the cow actually needs? The authors could not explain why this group’s milk production exceeded the alfalfa group even with their assumed K deficiency.

   “Little evidence was found in these two short trials that lactating dairy cows have a specific appetite for individual minerals. Where corn silage and alfalfa, forages that differ in mineral content, were fed as the sole forages to two groups of cows, only in the cases of potassium and vitamins did cows fed corn silage consume large amounts free-choice possibly to compensate for a dietary deficiency.”  Comment: Actually the main mineral ratios were balanced by the cow’s mineral preferences. They balanced the critical Ca/P ration by eating more P to compensate for the high Ca in alfalfa. The cows in the alfalfa group took almost no K while the corn silage group consumed 36 times more K than the alfalfa group.

Given the above perspective, it’s difficult to understand how the
authors concluded that cattle could not balance their own mineral needs.