Zinc supplementation and somatic cell count in milk of dairy cows

The goal of the study was to test the possibility of raising milk zinc (Zn) concentration by increasing the supplementation of Zn, and to assess the effect on the somatic cell count. The experiment was performed at a farm with Czech Pied cattle, with 500 dairy cows and average milk yield 6,390 1. The experiment included 40 dairy cows, assigned to either an experimental (E, n = 20) or a control group (C, n = 20) based on the principle of balanced pairs (efficiency, lactation stage). The experimental group was supplemented Zn in the chelate form (Bioplex Zn, Alltech Inc., Nicholasville, KY), at the dose of 440 mg Zn per animal per day. Blood and milk samples were taken at the start of the experiment and at the end of months 1, 2 and 3. 1 The average milk Zn concentration during the experiment was 57.36 +/- 10.54 mu mol center dot l(-1), ranging from 38.02 to 86.13 pmol center dot l(-1). A trend towards a positive effect of Zn supplementation on the health of the mammary gland was identified in association with the somatic cell count, which was significantly lower in the experimental group (114.90 +/- 68.7 center dot 10(3)center dot ml(-1) vs. 208.60 +/- 148.1 center dot 10(3)center dot ml(-1); p < 0.05) by the end of month 3. A negative correlation was found between the somatic cell count and Zn concentration in milk (y = -0.0327 x + 61.557; r = -0.441; p < 0.01). Our results indicate that milk Zn concentration is not directly affected by the level of zinc supplementation in the feed ration, but zinc supplementation has a positive effect on the somatic cell count.