Total-tract digestibility and milk productivity of dairy cows as affected by trace mineral sources.

Discipline: minerals; Keywords: rumen fermentation, milk fat yield, hydroxychloride, organic chelate. 

Trace minerals such as Cu, Zn, and Mn are essential to life, and their deficiencies in livestock result in health deterioration. In an effort to prevent such deficiencies, dairy cows are commonly supplemented with Cu, Zn, and Mn. Various sources of trace minerals are used for this purpose, with inorganic sources (oxides, chlorides, sulphates, and carbonates) being the most commonly supplemented to dairy cows. Alternative sources such as organically complexed trace mineral supplements (chelates) are specifically developed to provide greater nutritional bioavailability. This results because their compositions affect mineral solubility in different gut compartments, which in turn affects the nutritional availability of the metal for absorption. Something which is not well studied is the effect of organic trace mineral sources on apparent total digestive tract digestibility, in particular when they are supplied in combination with other sources, which is what usually happens in practice. Thus, Dr J.B. Daniel and colleagues in their study aimed to evaluate the effect of different applied trace mineral strategies on apparent total-tract digestibility and dairy performance, comparing several combinations of Cu, Zn, and Mn sources. The results of their study were published in the Journal of Dairy Science, Volume 103 of 2020, page 9081 to 9089, under the title: Total-tract digestibility and milk productivity of dairy cows as affected by trace mineral sources.

The study was conducted with 52 Holstein cows in a replicated 4 × 4 Latin square design with periods of 21 days. Four treatments differing in their sources of Cu, Zn, and Mn were tested: sulphate form, hydroxychloride form, a mix of sulphate and organic chelate forms (70 and 30%, respectively), and a mix of hydroxychloride and organic chelate forms (70 and 30%, respectively). Treatments were formulated to provide 15, 40 and 20 mg of supplemental Cu, Zn, and Mn, respectively, per kg dry matter (DM). This level of supplementation, together with the basal level present in forages and feed ingredients, resulted in a total average supply of 19, 79 and 84 mg of Cu, Zn and Mn, respectively, per kg DM. Cows were on a total mixed ration, which provided 15.3% crude protein, 21.7% starch, and 35.3% neutral detergent fibre (NDF).

Apparent total tract NDF and crude protein digestibility was reduced (0.8% and 1.0%, respectively) when organic chelate trace minerals were fed, whereas apparent total-tract NDF digestibility was improved (+0.8%) when sulphate trace minerals were replaced by hydroxychloride trace minerals. Cows supplemented with the hydroxychloride source had lower ruminal butyric acid concentration compared with cows fed sulphate trace minerals (13.3 vs. 14.6%). In addition, fat- and protein-corrected milk and milk fat yields were improved (+1.0 kg per day and +51 g per day, respectively) in multi-lactation cows when trace minerals were supplemented as hydroxychloride compared with sulphate. These effects were not observed in first-calf cows. The results confirmed that trace mineral sources alter apparent total-tract digestibility and indicate that milk productivity can also be affected.