1875
Epidemiological study about the effects of chelated minerals on milk, reproductive performance, and locomotion scores of dairy cattle
The objective of this experiment was to evaluate the effects of a partial replacement of chelated trace minerals (CTM) (Mintrex®, Zn, Cu, and Mn; with methionine hydroxy-analogue as a ligand; Novus International, MO) compared with a ration containing only inorganic trace minerals (ITM) on locomotion score, milk production, and reproductive performance of dairy cows in different herds. Twenty-seven herds that were feeding the same TMR were enrolled in a 6-month study. Fifteen herds continued to receive the same TMR (containing ITM), and the remaining 12 herds fed the same TMR with a partial replacement of ITM for CTM. The ITM premix provided 57 ppm of inorganic Zn, 9 ppm of inorganic Cu, and 27 ppm of inorganic Mn; whereas the CTM premix contained 32 ppm of inorganic Zn and 25 ppm of chelated Zn, 3 ppm of inorganic Cu and 6 ppm of chelated Cu, and 17 ppm of inorganic Mn and 10 ppm of chelated Mn. The first month of study was used as a basal line, and then herds were exposed to dietary treatments for 5 mo. Feed composition, feed intake, milk production, lameness score, and reproductive performance were monitored for each herd. All data, except conception rates, were analyzed using a mixed-effects model and conception rates were analyzed with a three-level mixed-effects logistic regression model with herd as experimental unit. There were no differences in feed intake (24.1±0.20 kg/d) and milk production (31.4±0.23 kg/d) between treatments. The overall proportion of cows with a lameness score ≥3 (considered lame cows) was not different between ITM and CTM herds. However, there was an interaction (P < 0.001) between treatment and month of experiment due to a greater incidence of lameness in CTM than in ITM herds during the first 2 mo of study (32.70 vs 29.47%, respectively), and a lesser incidence in the last 3 mo of study (31.30 vs 34.73%, respectively). Conception rate was not affected by treatment, but when cows that were serviced with less than 30 days of exposure to treatments were removed from the dataset, cows in the CTM herds had 2.9 greater (P < 0.05) odds of becoming pregnant than cows in the ITM herds. It is concluded that a partial replacement of inorganic Zn, Cu, and Mn for organic sources decreases lameness scores over time and improves conception rate after a minimum exposure of 30 d.
Keywords: lameness, reproduction, trace minerals