Effects of transient changes in silage dry matter concentration on lactating dairy cows

Transient changes in the dry matter (DM) concentration of silages often occur, which will cause transient changes in the ration. To determine the effects of a transient change in silage DM, 24 Holstein cows (116 d in milk) were used in an 8 replicated 3×3 Latin square design with 21-d periods. Treatments were (1) control, (2) unbalanced (UNBAL), and (3) balanced (BAL). The control diet was designed to have a consistent day-to-day forage:concentrate ratio of 55:45 on a DM basis. The UNBAL and BAL diets were the same as the control diet for most of the period except during two 3-d bouts when water was added to the silage (simulating a rain event) to cause a 10-percentage unit decrease in silage DM concentration. During the bouts, the UNBAL diet was the same as that of the control on an as-fed basis, but on a DM basis, the forage:concentrate ratio decreased to 49:51, which reduced dietary concentrations of DM (63.9 vs. 66.2%) and forage NDF (21.0 vs. 23.6%), and increased starch (30.4 vs. 28.4%). The BAL treatment corrected for the change in silage DM by an increase in the inclusion of wet silage and had the same composition as the control diet on a DM basis, except for ration DM (66.2 vs. 63.9%). Over the 21-d period, treatment did not affect DM intake (DMI; 24.0 kg/d); however, DMI of cows on the UNBAL and BAL treatments tended to decrease during the wet bouts, especially during the second bout. The day following both bouts, DMI of cows fed BAL and UNBAL diets were greater than that of cows fed the control diet, which contributed to the lack of a treatment effect on DMI over the entire period. Milk production was greater for the UNBAL than control cows (39.8 vs. 39.3 kg/d) over the 21-d period. That difference was largely caused by increased milk yield during the first bout by cows on the UNBAL diet. Over the 21-d period, milk yield did not differ between control and BAL cows. Some small differences in milk fat and protein concentrations (≤ 0.1 percentage units) were observed between treatments. Total-tract digestibility of most nutrients was not affected by treatment. Overall, a 10-percentage unit decrease in silage DM over short-term bouts (with or without total mixed ration adjustment) had only minor effects on DMI, milk yield, and composition.