Feed Sorting and Acidosis

Dr. Bill Weiss, Dairy Nutrition Specialist, The Ohio State University (top of page)

On a semi-regular schedule, recent research that is interesting (at least to us) and may have direct application to dairy farms will be reviewed for the Buckeye Dairy News.  The three abstracts discussed below were presented at the joint Dairy/Animal/Poultry Science meetings held this past July (J. Dairy Sci. 90, Suppl. 1).

A study from University of Minnesota (Endres and Espejo, Abstract 341, page 230) evaluated factors that promoted diet sorting.  They collected data from 50 freestall herds in Minnesota.  Sorting was quantified by measuring the particle size of the TMR (Penn State Particle Separator) when it was delivered to the pen, three times during the day, and immediately before new TMR was delivered. 

1.   On average, particle size of the diet increased as time after feeding increased.  In other words, cows had a preference for small particles and left larger particles in the bunk.  Larger particles tend to be forage and since forage usually contains more fiber than concentrate, intake of fiber would have been less than anticipated. Lower fiber diets and diets with inadequate particle size (i.e., insufficient ‘chewable’ pieces’) are associated with acidosis and its related problems, including hoof problems and milk fat depression.  However, in this study at the herd level, there was no statistical relationship between sorting and milk fat percent or between sorting and cud chewing.
2.   Sorting increased as the concentration of hay in the diet increased.  Therefore, replacing a less coarse forage (for example, silage) with hay may reduce intake of fiber and chewable pieces and increase the risk of acidosis. 

3.   Sorting tended to increase as bunk space increased.  If competition for bunk space was less, cows probably had more time to stand in front of the bunk and sort feed.

A study lead by Canadian and Swiss scientists (DeVries et al. and Dohme et al., abstracts 898 and 899, page 653) examined effects of diet and acidosis on sorting and cumulative effects of repeated bouts of acidosis.  In those studies, cows were fed diets with 45 or 60% forage and after 2 weeks were given an ‘acidosis challenge’.  The challenge consisted of restricting TMR intake for 1 day and then offering about 9 lb of a barley/wheat mixture to each cow.  Cows were allowed to recover for 14 days and the challenge repeated two more times.

1. As in the Minnesota study, cows fed either diet selected against long particles, but cows fed the low forage diet also selected against very fine particles (in the pan of the 3-sieve Penn State separator).  Cows apparently prefer to consume medium-sized particles, thus avoid extremes when formulating TMR.

2. After cows were challenged with acidosis, cows on the low forage diet selected for long particles and selected against fines to a greater degree than when not undergoing acidosis. 

3. Severity of acidosis was greater for cows fed the low forage diet than the high forage diet.

4. Severity of acidosis increased as cows were exposed to more acidosis challenges.  This occurred even though cows consumed less of the barley/wheat mixture after each acidosis challenge.  During the first challenge, all cows consumed all of the wheat/barley mixture, but during the third challenge, only 3 of the 8 cows consumed all the grain.  This means that cows become more susceptible to acidosis with repeated exposure, even though they attempt to remedy the situation by consuming less grain.  The effect of repeated exposure to acidosis was greater for cows fed a diet with 45% forage compared with those fed a diet with 60% forage.

Take Home Messages:

1. Do not rely on a single measurement (e.g., sorting, cud chewing, milk fat, etc.) when assessing either the risk for acidosis or the presence of acidosis.

2. Adding hay to a diet can increase sorting and may increase the risk for acidosis.  Avoid extremes in particle size of TMR (both long pieces and fines).

3. Repeated bouts of acidosis, even when separated by two weeks, have cumulative negative effects.