Dairy nutrition has moved beyond just inorganic versus organic trace minerals.
Hydroxychloride-based, or “hydroxy” trace minerals are technically classified as inorganic, but they tend to behave more like organic trace minerals because of their unique chemical structure.
Dr. José Santos, Professor of Dairy Cattle Nutrition and Reproduction at the University of Florida, shared his insights on hydroxy trace minerals in dairy nutrition on a recent episode of The Dairy Podcast Show. Santos and his team recently completed an extensive lactating-cow study comparing hydroxy trace minerals to more traditional mineral formulations.
“Most trace minerals that we currently supplement beyond the basal diet are in the form of salts,” he explained. “They’re primarily sulfates, which tend to be very soluble in solution, so it is assured that they can easily ionize because they have ionic bonds that are generally weak when they get into aqueous solution.”
But as researchers delve deeper into the intricacies of trace mineral behavior, one important discovery has been that the free metal ions of trace minerals have antibacterial properties. That knowledge led Santos to hypothesize that when trace minerals ionize in the rumen, they actually may kill rumen microbes such as fibrolytic bacteria, thus decreasing total tract NDF digestibility.
They also may have interactions with antagonists within the rumen including copper, sulfur, and molybdenum, leading to poorer absorption and less bioavailability in the small intestine.
Santos said hydroxy trace minerals are not technically “bypass” minerals, but they do remain very stable in the rumen because the covalent bonding among ions make them nonpolar materials, which results in poor solubility in solutions under close to neutral pH conditions such as those of the rumenfluid. “Once they move on to the abomasum, the low pH makes them behave like any other ionized mineral,” he explained.
In the study, the Florida researchers compared 2 types of trace mineral treatments in 141 cows. Half received sulfate sources of zinc, copper, and manganese, and half received the same trace minerals from hydroxy sources. Feeding level of the trace minerals was equal for both groups, at rates just above NASEM recommendations.
Cows were enrolled at 246 days of gestation – about a month before calving – and stayed on their respective rations until 105 days in milk, for about 140 days of treatment. A host of factors were monitored, with the most telling results including:
- Retained fetal membranes incidence was just 3.8% for the hydroxy-supplemented cows, compared to 11.5% for the sulfate group.
- Metritis incidence was 26.4% for the hydroxy group, versus 34.5% for the sulfate group.
- Overall morbidity - factoring a few cases of other illnesses such as mastitis, left displaced abomasum, and lameness – was 34.2% for the hydroxy group, and 52.0% for the sulfate group.
- The hydroxy group showed an advantage in colostrum yield of 2.2 lb. and in Energy Corrected Milk of 3.0 lb./day over the first 105 days of lactation.
“We think the improvement in health set the stage for everything else, which ultimately resulted in higher milk production,” said Santos. “Nevertheless, we cannot discount the benefit of a possible improvement in digestibility of nutrients, as shown by others when hydroxy replaced sulfate trace minerals.”
While hydroxy minerals are slightly more expensive than other trace mineral formulations, Santos said the difference is negligible when looking at the big picture of health and performance.
“You’d be surprised how little the cost per cow is. When you consider milk production and the value of heifers and beef-cross calves today, many of today’s dairy cows are generating $6,000-7,000 per lactation,” he noted. “To supplement the amount of metal that we did from zinc, copper, and manganese, the cost for a typical 340-d lactation is about $3.50 for sulfate sources and $8.00 for hydroxy sources. It’s an easy pay.”
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