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How Do Dairy Cows Chew?

December 5, 2018

Summary by Kai Yuan, PhD, Senior Research and Technical Advisor

In the field, we usually pay attention only to the particle size of feed offered to the cows, NOT the size of the chewed and ingested particles. An interesting study evaluated the relationship between the particle lengths of feeds compared with respective swallowed bolus particles.

PARTICLE SIZE OF INGESTED FEED
Forage Type  NDF, % of DM  Feed Size, mm Bolus Size, mm Chews/g NDF
50-mm rye hay 58.6 42.2 9.9 3.5
8-mm PSPS hay 59.1 25.1 10.8 1.7
Grass Silage 53.1 13.8 11.6 0.4
Corn Silage 48.1 12.0 11.2 0.7
TMR 37.7 13.1 12.5 0.6

Schadt et al. 2012 Journal of Dairy Science 95:4707-4720

Key Points:

1. Regardless of the lengths of feeds offered to the cows, the ingested bolus sizes are around 9 to 11 mm, indicating that cows chew the feeds and reduce the particle sizes to a threshold size before swallowing.

2. Evidence showed that long particles not only promote sorting but also take cows longer time to consume and chew. In overstocked or limited bunk space situations, if the diets are too high in peNDF or contain a lot of large particles, cows have reduced dry matter intake due to longer time to chew and limited time to eat at the bunk.

3. According to Miner Institute recommendation, there should be < 5% of feed on the top screen of the Penn State Shaker Box, > 50% of feed on the top mid screen, 10 to 20% on the bottom mid-screen, and 25 to 30% on the pan.

Feeding QLF Supplements help promote consistent intake of TMR, reduce the sorting of long particle forages, and allows for the feeding of diets with higher peNDF content.

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