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.”
Let’s take a closer look at some of the excerpts from that study along with some comments.
“Trial 1 was 16 weeks 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.” This is too small a group and too short a time to really evaluate the nutritional wisdom of animals. A full 12 months would be better as that would encompass the gamut of lactation, dry period, parturition, and back to lactation. Even better would be a multi-year experiment that examines the health and productivity of the calves born to the two research groups, thus evaluating the multi-generational effect.
“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, phosphorus, potassium, magnesium, and sulfur trace mineral, bicarbonate of soda, sodium bentonite, sodium chloride, iodine mix and vitamins A, D, and E. Intake of each individual mineral was determined weekly for each group.”
“Intake of phosphorus, potassium, and vitamins differed between rations. A higher free choice intake of phosphorus by cows fed alfalfa was not expected.” 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.
“Cows fed corn silage consumed more potassium free-choice, but additional intake still was needed to meet requirements.” 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.” Actually the main mineral ratios were balanced by the cow’s mineral preferences. They balanced the critical Ca/P ratio 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.
It pays to “read between the lines” when evaluating research reports. It is also helpful to know who paid for the research, who did the research and where did the researcher worked before and after he did the research. A good dose of common sense is also indicated.
This item was originally posted to a previous issue of Doc Holliday's Blog on November 24, 2018