Effects of replacing inorganic salts of trace minerals with organic trace minerals in pre- and postpartum diets on feeding behaviour, rumen fermentation, and performance of dairy cows.

Pregnant cows and heifers (n = 273) were blocked by parity and body condition score and randomly assigned to either STM or OTM diets at 45 ± 3 days before their expected calving date. Both groups received the same diet, except for the source of trace minerals (TM). The STM group was supplemented with Co, Cu, Mn and Zn sulfates and Na selenite, whereas the OTM group was supplemented with Co, Cu, Mn and Zn proteinates and selenized yeast. Treatments continued until 156 days in milk and pre- and post-calving diets were formulated to meet 100% of recommended levels of each TM in both treatments, taking into consideration both basal and supplemental levels. Automatic feed bins were used to assign treatments to individual cows and to measure feed intake and feeding behaviour. Rumination activity was monitored by sensors attached to a collar from week −3 to 3 relative to calving. Blood metabolites were evaluated on day −21, −10, −3, 0, 3, 7, 10, 14, 23, and 65 relative to calving. Ruminal fluid samples were collected using a mouth-ruminal sampling device on day −21, 23, and 65 relative to calving, for measurement of ruminal pH and concentration of volatile fatty acids. The cows were milked twice a day and milk components were measured monthly.

The cows supplemented with OTM tended to have longer daily feeding times (188 vs. 197 minutes per day), and greater dry matter intake (DMI; 12.9 vs. 13.3 kg). They also had a more positive energy balance (3.6 vs. 4.2 Mcal per day) and shorter rumination time per kg of dry matter (DM; 40.1 vs. 37.5 minutes per kg of DM) than the cows supplemented with STM during the pre-calving period. In the post-calving period, OTM increased DMI in multi-lactation cows (24.1 vs. 24.7 kg per day) but not in first lactation cows (19.1 vs. 18.7 kg per day). The difference in DMI of multi-lactation cows was more evident in the first 5 weeks of lactation, when it averaged 1 kg per day. Milk yield was not affected by treatment in multi-lactation cows (44.1 vs. 44.2 kg per day), however, first lactation cows supplemented with OTM had lesser yields than first lactation cows supplemented with STM (31.9 vs. 29.8 kg per day). Furthermore, the cows supplemented with OTM had a greater percentage of protein in milk (3.11 vs. 3.17%), reduced concentration of non-esterified fatty acids in their blood serum (0.45 vs. 0.40 mmol per L), and rumination activity (30.1 vs. 27.8 minutes per kg of DM) than the cows supplemented with STM. At the end of the transition period, the cows supplemented with OTM had a reduced molar proportion of acetate, reduced pH, and tended to have a greater concentration of total volatile fatty acids in their ruminal fluid.

In conclusion, complete replacement of STM by OTM caused modest changes in rumen fermentation, feeding behaviour, energy metabolism and performance of the dairy cows, improving post-lactation DMI in multi-lactation cows and reducing circulating levels of non-esterified fatty acids.