Impact of Trace Minerals on Reproductive Health of Cows

Sustainably Optimizing Mineral Nutrition in Lactating Cows

The literature on animal nutrition has comprehensively addressed the nutrients that cattle must have for healthy growth, reproduction, and lactation. Considerable research has been conducted to determine the amounts of specific nutrients that must be part of any formula for "economically efficient diets" (Weiss, 2010). Both short-term and long-term metrics must be accounted for when developing adequate feeding diets for livestock. This means that the nutrient quantities must not be excessive, but must contribute to the profitability of the livestock raising or dairy operations while simultaneously seeking to minimize the environmental impact of these activities.

Feeding Diet Trace Minerals for Lactating Cows

Trace minerals -- those required in only minute quantities such as milligram or microgram -- needed by lactating cows have been identified through research. Nine trace minerals are thought to be essential for healthy lactating cows. While it is entirely possible that other minerals beyond the nine core trace minerals may be required in the diets of lactating cows: Chromium (Cr), cobalt (Co), copper (Cu), iodine (I), iron (Fe), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn) (Weiss, 2010). Of the nine essential trace minerals, this discussion does not address the role or requirements of iron, molybdenum, and iodine. The following factors help to influence the exclusion of these elements. Iron requirements of cattle are met by basal diets which all contain adequate levels of iron, and iron deficiencies in cattle are not known to be generally observed in cattle (Weiss, 2010). Molybdenum is required co-factor for a number of enzymes, but deficiencies have not been identified as an issue and supplementing molybdenum is not a recommended practice (Weiss, 2010). Iodine is known to be essential for thyroid hormone synthesis, but the dietary recommendation of 0.3 to 0.45 mg of I/kg of dry matter (DM), as measured in parts per million (ppm), has remained stable for roughly 30 years (Weiss, 2010).

Most Impactful Variables in Dietary Needs of Lactating Cows

To clearly understand the trace mineral requirements of lactating cows, researchers have begun by studying the responses of cows to dry matter feeding diets in order to acquire baseline information about the influence of feed quality and consumption. Linden, et al. (2014) studied the effects of diets of chopped warm-season grass hay (5.5% CP, 67% NDF) for ad libitum (at-will feeding) intake and soybean meal (46% CP) at 450 g/d on Angus-cross cows and heifers. The data show that intake patterns are different between cows and heifers regardless of the similarities of dry matter digestibility, passage rates, and plasma glucose and BHBA concentrations in primiparous heifers. Interestingly, the DMI (% of BW) and digestibility showed no substantive difference between pregnant heifers and pregnant mature cows. However, the DMI (% of BW) for lactating heifers was greater than for lactating multiparous cows. Primiparous heifers were not able to consume sufficient warm-season forage for healthy maintenance, growth, and lactation. This is true even though the DMI (% of BW) was greater for lactating heifers than for lactating cows and non-lactating cows and heifers. Lactation resulted in decreased BW over time in heifers, which can result in a longer postpartum interval and difficulties when rebreeding. The Linden, et al. (2014) study indicates that heifers require additional supplementation to maintain growth, lactation, and reproduction and to maintain a 12-month production cycle at age three years.

Overton and Yasui (2014) argue that trace minerals are not generally considered an aspect of traditional approaches for gauging the nutrient requirements for livestock operations. Given the evidence-based research indicating the influence of trace minerals on overall animal health, immunity, oxidative metabolism, productivity, and reproductive performance in dairy cattle, Overton and Yasui (2014) assert that research must focus on the relationships. The emphasis of their research and argument is that trace minerals must be provided in more bioavailable forms when supplementing the diets of lactating cows, particularly during the postpartum transition and early lactation (Overton & Yasui, 2014).

Hackbart, et al. (2010) conducted an experiment to learn if replacing inorganic supplements of zinc, manganese, cobalt, and copper with organic versions of these minerals would result in improved production of milk and reproduction. The researchers used the following as indicators of improved reproduction: Improved embryo quality, increases in circulating concentrations of progesterone, and faster return to postpartum cyclicity. Hackbart, et al. (2010) did find that the organic forms of the trace minerals did increase milk production later in lactation. However, changes in the hoped for reproductive traits were not found by Hackbart, et al. (2010).

Conclusion