Dr. Bill Weiss, Professor and Extension Dairy Specialist, and Lucien McBeth, former M.S. student, Department of Animal Sciences, The Ohio State University
Silages stored in bunker silos or opened bags can be exposed to rain and snow events which can abruptly, but transiently, change the dry matter (DM) concentration of the silage. We have recorded day to day changes in the DM concentrations of silages (both corn and alfalfa) on commercial dairy farms greater than 10 percentage units. Often, these large changes in DM correlate with a recent rain or snow event. Because diets are formulated on a DM basis but are mixed on a farm using as-fed concentrations, the DM concentration of silage can have a marked effect on diet composition. For example, if a simple diet was 50% silage and 50% concentrate on a DM basis and the silage was 45% DM and concentrate was 90% DM, the mixed ration would be 67% silage and 33% concentrate on an as-fed basis. If the silage suddenly changed to 35% DM because of a heavy rain but the as-fed diet remained 67:33 silage: concentrate, the diet would be 44% silage and 56% concentrate on a DM basis. Because silage was a primary source of fiber in this example, the diet actually being delivered to the cow would have less fiber than the formulated diet, and this could result in rumen acidosis, milk fat depression, and other issues. Changes in DM of silage caused by rain are abrupt but also short term and after a day or two, the DM concentration often returns to its original concentration. We conducted an experiment to determine whether diets should to be adjusted when silage DM abruptly decreased by 10% units for a 3 day period. One treatment was the control diet in which silage DM was constant during the experiment. The other two treatments were identical to the control except during two 3-day bouts (separated by 6 days) water was added to the silage to reduce DM by 10 percentage units. For one of the treatments with the wetted silage, no change in the as-fed diet was made (this means that less forage DM and more concentrate DM were fed than the control diet). For the other treatment with the wetted silage, the as-fed concentrations were adjusted so that on a DM basis, this diet was still identical to the control except the total diet was wetter. The amount of feed offered to the cows was increased when the wet silage was fed since each pound of as-fed diet contained less DM. This was done to prevent the cows from running out of feed.
The major findings from this experiment were:
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Reformulation to account for the transient change in silage DM was not necessary. Average milk production and composition and feed intake were not affected over the 21 day experimental period.
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Dry matter intake by cows on the two treatments that contained wetted silage usually decreased by 2 or 3 lb the first day the wet silage was fed, but by the second day, intake had rebounded and was generally similar to the control (Figure 1). On the first day after cows were changed back from the wetted silage to normal silage, intake by cows that previously had been fed wetted silage was significantly greater than control (by approximately 2 lb of DM). The amount of as-fed diet consumed increased the first day that the wetted silage was fed but did not reach maximum until the second day and remained higher than control for the next 2 days (this included the first day after cows were changed back to the normal diet). Previous studies have shown greater negative responses when silage DM was abruptly changed, but in those experiments, the amount of feed offered to the cows was not increased and the cows ran out of feed.
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Milk yield by cows fed the wetted silages tended to decrease when the wet silage was fed (this was especially pronounced during the second bout of feeding wet silage). However because of the increase in feed intake on the day cows were changed back to normal silage, milk yield was much greater by cows that had been fed the wetted silage. Over the 21 day experimental period, no differences were observed in milk yield (Figure 2).
- When you suspect silage DM has decreased because of a rain or snow event, the amount of feed offered to the cows must be increased and remain increased for several days. If this is not done, cows may run out of feed, which in other experiments has significantly reduced milk yield. Additional feed should be provided for 1 or 2 days after the silage DM has returned to normal because cows compensate for lower intake when wet silage was first fed.
If longer term changes in DM concentration of silage have occurred (for example, a new cutting or different field), diets should be reformulated to account for changes in DM concentrations.
Figure 1. Difference in dry matter intake (DMI) between cows fed control diet (constant during the experiment) and cows fed the same diet except water was added to the silage and diets were either rebalanced (Balanced) or not adjusted for the change in DM (Unbal). The wetted silage was fed for two 3-day period (shaded boxes). * = statistical difference between treatments and control. Note the initial drop in DMI when first fed wetted silage and the high DMI by treatment cows on the days following the feeding of wetted silage.
Figure 2. Difference in milk yield between cows fed control diet (constant during the experiment) and cows fed the same diet except water was added to the silage and diets were either rebalanced (Balanced) or not adjusted for the change in DM (Unbal). The wetted silage was fed for two 3-day period (shaded boxes). * = statistical difference between treatments and control. Note the first episode of feeding wet silage had little effect but the second bout caused milk yield to drop. Also note the increased milk yield by treatment cows on the days following the feeding of wetted silage.