Dairy Corner: Forage fibre the big driver in milk fat production

Put your TMR to the test to determine if it's the proper particle size

dairy cows eating TMR

Maintaining good milk production with adequate milk fat is always the main source of good revenue on most dairy farms. Regardless of the actual feed ingredient formulation, it must work in tandem with the natural body functions of healthy cows. This is something we should keep in mind when reformulating current rations if restrictions are placed upon dietary palm fat to support good milk fat levels.

Effective forage fibre, not palm fat, is the foundation of all good milk fat levels in milk and must be included in all well-balanced lactation diets. Unlike energy and protein, effective forage fibre is not a true nutrient, but there is a requirement for it in milking cows. Its biggest job, which is clearly associated with milk fat yield, is to maintain a healthy population of rumen microbes, which in turn drives optimum fermentation of the dairy diet and essential nutrient metabolism.

Using the checklist

Recently, I visited a 150-lactating free-stall operation (production figures: milk, 37 kg, milk fat, 3.9 per cent, DIM = 173) and it had some underlying issues with inconsistent milk fat production. And this was despite most of the cows chewing their cud in the lactation barn and 400 g per head of palm fat was fed in their TMR. It really gave me an opportunity to use the major points of an “effective-fibre” checklist that I carry around in my head, so I might spot a few troublesome factors, as follows:

  • Look at the cows. It is my understanding from the producer that all the early-lactation cows come into lactation in a BCS of 3.0-3.5, yet many of the cows had a hard time retaining body condition by the end of lactation. A quick look at the close-up cows (21 days before calving), showed me that they would have a hard time achieving good dry matter intake, well into 100-days post-calving.
  • Scoop up a handful of TMR. It was freshly laid down in the bunk, which looked like it had enough effective forage fibre, but using a Penn State Shaker box, which separates TMR particle size, showed me differently. It showed a lot of forage fibre in the top screen (20-22 per cent), 55 per cent in the bottom tray and the remainder (20-25 per cent) in the middle. A lab analysis also revealed that the entire lactation diet provided the standard 28 per cent NDF (neutral detergent fibre) with an adequate 75 per cent of this fibre coming from forage sources. Yet the NFC (non-fibre-carbohydrates) of the ration exceeded a threshold of 40 per cent and starch stood at 24.7 per cent. Moisture of the entire dairy diet stood at 52.3 per cent. (You can learn more about the shaker box in this video.)
  • Investigate bunk management. Each day, the producer makes up only one batch of lactation ration and lays half down in the morning before milking and the other half before the afternoon milking. The feed is pushed up every 2 ½ hours by a robot. Current DMI intake ranged from 50-54 lbs.

After putting all the evidence together, I suspected that this lactation dairy herd suffered from an underlying mild-acidosis condition, despite most of the cows chewing their cud during my initial observations. It was the shaker box that convinced me that a lot of long-stem indigestible fibre from rather coarse first-cut alfalfa haylage (high in indigestible lignin-fibre) and the high level of NFC of the lactation diet both limited optimum rumen function — one of the leading causes of erratic milk fat yield.


So I made the following dietary friendly milk fat recommendations:

  1. Increase the proportion of corn silage (a rich source of hemicellulose; leads to consistent rumen function) and lower the amount of first-cut alfalfa haylage in a final 2/3 to 1/3 ratio.
  2. Limit the amount of barley from 8.5 to 7.0 kg, which reduces excessive NFC.
  3. Switch out 300 grams of palm fat with a 50/50 tallow-palm bypass fat to help recover lost body condition in later lactation cows.
  4. Review the close-up diet and take corrective action to promote dry matter intake before and after calving.

It took about three weeks to see results, which included a slight drop in milk fat, but it largely recovered as soon as the cows adjusted to these major dietary changes. As a footnote — we initially thought of just increasing the bypass palm fat to 500 grams to correct original bouts of milk fat depression, but quickly realized that improving effective forage fibre in the diet was the best way to go.

— Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email.

About the author


Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]



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