Ruminations on Rumination
What is rumination?
Rumination or cud-chewing is the process by which the cow regurgitates previously consumed feed and chews it further. The larger particles in the rumen are sorted by the reticulorumen and reprocessed in the mouth to decrease particle size which in turn increases the surface area of the feed. This physical process improves digestion rate allowing for higher levels of feed intake, thus greater nutrient input. As rumination proceeds, saliva is produced, a lot of saliva. On a daily basis, a typical milking cow can produce 98 to 190 litres of saliva. One important role of saliva is to buffer the pH of the rumen content. In other words, saliva contains bicarbonates that will help minimize the fluctuation of the pH in the rumen. For optimum ruminal fermentation and fibre digestion, the desired rumen bugs require a ruminal pH between 6.0 and 6.4. Rumen pH can fluctuate below this level for short periods. This drop in ruminal pH is a result of the breakdown of dietary carbohydrates such as starch from cereal grains or by-products. This is the reason why small meals of concentrate spread over time are preferred to slug feeding. This is also why a total mixed ration (TMR) helps to maintain optimal rumen function.
The amount of time a cow spends ruminating is diet dependent. Daily intake of forage-NDF is positively related to rumination time while daily intake of starch and sugar negatively affects rumination time. Feeding high levels of concentrates and/or finely ground feeds reduces rumination. It is critical that the ration contains adequate amounts of long fiber to stimulate rumination. Depending on the physical form and composition of forages, a cow will ruminate from 24 to 80 minutes per kilogram of forage consumed.
The ADF and NDF values of a forage sample reported by the lab will be the same regardless of whether the forage is long stemmed, finely ground or chopped for silage. There are, however, differences in how these forages affect rumen function. The finer the chopping, the less effective the forage is to stimulate rumination and saliva production. Chemical composition measures alone, are therefore, not sufficient to define fibre effectiveness. The use of a particle separator to assess effective fibre content can be an invaluable tool to optimise rumination time.
Rumination, comfort and sleep
Yes, cattle do sleep. Cows spend less than 4 hours sleeping per day split between Non-REM sleep (3 hours a day) and REM sleep (45 minutes per day). REM sleep, the "deep sleep" stage is most easily recognized by the rapid and apparently random side-to-side movements of the closed eyes, hence the name (Rapid Eye Movements). Early studies have shown that rumination provides physiological benefits to the animal, similar to those provided by deep sleep. The electroencephalogram (EEG) of a cow shows a brain wave pattern during rumination bouts that is similar to sleep or somnolence state. Rumination activity is closely associated with drowsiness and can even occur when a cow falls asleep into Non-REM phase.
Cows usually spend a third of their typical day ruminating. Cows will eat rapidly with minimal chewing at the feed bunk. Once the meal has been ingested, cows will prefer to ruminate while lying down. Studies have shown that up to 90% of rumination can occur in stalls and a 2% increase in resting increases rumination time by 7%. Availability of comfortable stalls is critical to optimize the rumination process. Management that impairs a cow's lying time also reduces rumination.
Cows have voluntary control over rumination and will stop if disturbed or ill at ease. Rumination is highly sensitive to overall cow well-being. Acute or chronic stress can substantially depress rumination time. Less rumination time means that the long, fibrous particles will stay in the rumen longer causing the rumen to feel fuller. This will reduce the rate of passage and total feed intake which negatively impact milk production.
Using rumination data on-farm from sensors attached to cows is increasingly common. This precision management technology can be an invaluable tool to assess the well being of the herd or individual animals. Since rumination is extremely sensitive to stressors, this assessment may reveal problems even before they become visible, especially if used in combination with activity monitors. For example, a study presented last summer found that a case of displaced abomasum could be detected 3 days before clinical signs begin to show. For ketosis it was a day and a half while metritis and mastitis could be detected almost a day before clinical signs.
The herd manager can rely on rumination sensors to make and validate management decisions. A trial in a commercial herd yielded interesting findings. Over a seven day period, a group of first lactation cows were housed with the mature cows and rumination time per day was recorded. First lactation animals were then moved to a separate pen and rumination monitoring revealed that the average time spent ruminating jumped from 363 to 428 minutes per day, an increase of 18% or about one hour.
Average rumination time for dairy cows is 450 - 550 min per day. The goal is to have minimal variation between cows within the pen, less than 30-50 minutes between pen mates. Any deviation from the baseline is what a manager is after. It is a sign that rumen functions are altered. A graph of rumination time is an excellent way to look at the data for an individual animal as well as the whole group. Rumination monitoring allows for earlier identification of health issues, can validate management strategies such as grouping, stocking density and heat stress abatement amongst others.
Effect on rumination time per day of various environmental and health factors.
This article was originally published in the "Milk Producer Magazine".
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