THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
Preferential Intake of Hydroxy Sources of Cu, Zn, and Mn by Young Beef Calves
The stressors associated with weaning (cow/calf separation, transportation, commingling, vaccination, changes in feed and housing, etc.) lead to alterations in physiology, immunology and nutrition of calves. In particular, the trace mineral nutrition of calves is impacted due to the liberation of tissue stores of Cu, Zn, and Se for the support of immune function. Our research has sought to improve the trace mineral status of the pre-weaned calf with the central aim of presenting a mineral-adequate calf at the time of weaning, which is prepared to undergo the normal and expected stress-related mineral losses which will occur at weaning. One management scheme, which we have pursued, is the trace mineral fortification of limit-fed creep feeds. In this approach, we have specifically avoided the offering of large amounts of creep feed intake (i.e. unlimited creep feeding), which is associated with decreased feed efficiency and reduced forage utilization. Instead, we have focused our efforts on limit-fed creep-feed supplements (less than 2 lb per day), which have been associated with efficient improvements in pre-weaning ADG and improved concentrate intake in the feedlot. However, our attempts to fortify these supplements with trace minerals have resulted in reduced voluntary intake compared to supplements without trace mineral fortification.
We hypothesized that this reduction in voluntary intake of trace mineral-fortified creep supplements was a result of palatability issues arising from the soluble forms of Cu, Zn, and Mn used in the formulation (Zn and Cu sulfate and Mn oxide). To test this hypothesis, we designed an experiment aimed at measuring the preferential intake of supplements fortified with Cu, Zn, and Mn from, (1) hydroxy, (2) organic, and (3) sulfate-sources. Among these sources, the hydroxy forms are fairly new ingredients available to the feed industry. Hydroxy trace minerals are described as specific crystalline inorganic mineral sources formed by covalent bonds within a crystalline matrix. This covalent bond structure differs from the ionic bonds present in common sulfate-based minerals and is more similar to the covalent bonds present in organic trace mineral sources. Whereas organic trace minerals are covalently bound to a carbon-containing ligand, hydroxy trace minerals are covalently bound to an OH group. Typically, organic trace minerals are presented as single molecules and hydroxy trace minerals are represented by several molecules interconnected to form a crystalline matrix. The distinctive characteristic of hydroxy trace minerals is their lack of solubility at neutral pH ranges. Dissolution of the metal occurs at lower pHs, which are common in the lower gastrointestinal tract. This low solubility appears to also result in improved feed ingredient stability, particularly the oxidative loss of fat soluble vitamins. Additional to these functional characteristics, hydroxy trace minerals are also more concentrated than most organic or inorganic ingredient options, allowing for greater flexibility with formulation space.
Our experiment utilized 4 individual feeding studies involving 8 pens of early-weaned calves (2 calves/pen; average age = 120 d; average body weight 254 lb). Each pen was provided free-choice access to a mixed concentrate ration and ground grass hay. On each study day at 10:00, all feed was withdrawn and calves were offered 3 different mineral fortified supplements, for a 4 h period, provided in three separate feeding containers (Photo Caption 1). Supplements were created using a base mixture containing 52, 46, and 2% cottonseed meal, ground corn, and salt. Supplements were fortified with 2,000 ppm Zn (Exp. 1), 750 ppm Cu (Exp. 2), 3,000 ppm Mn (Exp. 3), and all 3 elements (Exp. 4). Preferential intake was measured over 7- (Exp. 1, 2, and 3) and 14-d (Exp. 4) evaluation periods. In each of the first 3 experiments, when the individual metals were presented, calves preferentially consumed greater amounts of supplement containing the hydroxy forms of Cu, Zn, and Mn with sulfate forms being intermediate and organic forms being the least (Figure 1). In Exp. 4, when all 3 elements were combined within a single supplement, calves almost exclusively selected the supplements containing hydroxy-source elements vs. supplements containing sulfate or organic sources (70.0, 12.5, and 8.0% consumption of supplement offer for hydroxy, sulfate, and organic sources, respectively).
In summary, voluntary consumption of limit-fed creep feeds is reduced when fortified with concentrated amounts of Cu and Zn sulfate and Mn oxide. When provided an opportunity for selection, young beef calves preferentially consume trace mineral-fortified supplements containing hydroxy vs. sulfate or organic sources of Cu, Zn, and Mn. These initial results may have important implications on the formulation of trace mineral-concentrated rations intended for calves. Opportunities to improve voluntary intake of these feedstuffs, particularly in pre-weaned or stressed calves, may result in improved calf health and performance.
Figure 1. Effect of Cu, Zn, and Mn source (750, 2,000, and 3,000 mg/kg, respectively) on preferential supplement intake by young calves. To estimate preferential intake, calves were offered 2 lb of each supplement for a 4 hour period daily. Results are expressed as a % of total supplement take (Figure insets sum to 100%; a,b,c; P < 0.05).
Portions of this article were previously published in Feedstuffs (August 18, 2014 issue). For more information on this topic, please contact John Arthington at firstname.lastname@example.org.