Did you know that overcrowded cows experience rumen acidosis? Recently conducted research at the Institute has shown for the first time that overcrowding the free stalls and feed bunk reduces rumen pH — and this compromised rumen function dramatically influences how the cow responds to her diet. For the dairy cow — being a ruminant — a healthy rumen pH is vital to her well- being and productive efficiency.
Mac Campbell, who is working on his Ph.D. here at Miner Institute, conducted a study that evaluated the interaction between stocking density and diet physically effective NDF (peNDF) for their effect on the behavior, rumen pH, and performance. Overcrowding is a common practice on many U.S. dairy farms: USDA survey data indicate that nearly 60% of free-stall farms overcrowd the feed bunk while over 40% overcrowd the stalls. In the northeastern U.S., research published in 2012 found that feed bunks were overcrowded on 78% of dairy farms assessed.
With this overcrowding challenge in mind, we wondered what effect it might have when we fed cows diets that spanned the usual range in peNDF found on commercial dairy farms. We fed two diets: one based on the usual corn silage/ haycrop silage blend and another with 3.5% chopped wheat straw partially replacing the haycrop silage to boost the dietary peNDF. The "no straw" diet contained about 19% peNDF and 8.5% undigested NDF measured at 240 hours (uNDF240). From a fi ber adequacy standpoint, this diet was on the lower end of what is typically fed. In contrast, the "added straw" diet contained about 22.5% peNDF and 9.7% uNDF240 which are on the upper end of typical dietary fiber content.
We know that in the real world both of these diets are fed under a range of stocking densities, so we fed them to cows at either 100 or 142% stocking density to encompass the range ordinarily encountered on commercial farms. Then we tracked how long rumen pH dipped below 5.8, which is a common benchmark for subacute rumen acidosis (SARA). What happened to rumen pH? At 100% stocking density, addition of chopped straw to the diet reduced the time that rumen pH was below 5.8 by about 17% — important, but not a huge effect. However, at 142% stocking density, the diet with greater peNDF/uNDF enhanced rumen pH by nearly 33%. In fact, rumen pH was below 5.8 – i.e. the cows were experiencing SARA – for over 4 hours per day at 142% stocking density versus only 2.2 hours per day at 100% stocking. Previous research indicates that when pH is less than 5.8 for more than 3.5 hours per day, you will expect to see a significant impact of SARA on rumen fiber digestibility. This study provides the first evidence that diets can be formulated to help alleviate the negative impact of overcrowding.
These changes in rumen pH were associated with reduced lying time in the stalls, less recumbent rumination, and lower milk and milk fat output. In addition, Mac has also been looking at the effect of these treatments on immune function as reflected by serum amyloid A (SAA). His initial data indicate that overcrowding tends to elevate SAA in response to the stress of competing for feed and stalls.
This research drives home the point that the cow's management environment has a tremendous impact on how she responds to a diet. Increasingly, our ration formulation approaches must take into account the feeding environment. Otherwise, we risk rumen health even when feeding well-balanced diets that provide plenty of fiber.