Supplementing cows on pasture

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By Keith Diedrick

Dairy producers adopt management intensive grazing for many reasons such as reduced cropping, reduced or eliminated crop machinery, lower feed costs and improved lifestyle.

For the early adopters of management intensive grazing for dairy cows there was little research information on the need for and how to supplement cows on pasture.

As the practice of grazing became more widespread, more research was conducted on supplementing cows on pasture.

The column this week highlights the January 2003 Journal of Dairy Science review, Production and Digestion of Supplemental Dairy Cows on Pasture by F. Bargo, L. D. Muller, E. S. Kolver and J.E. Delahay, animal and dairy scientists at Penn State University.

Limiting factors. Lower dry matter intake as compared to conventional TMR feeding (primarily effecting energy intake) has been identified as a major factor limiting milk production by high producing dairy cows.

Pasture dry matter intake in grazing cows is a function of grazing time, biting rate and bite mass. Pasture dry matter intake is also a factor of pasture quality and quantity.

The review reported on six studies that looked at pasture allowance and the effect on dry matter intake of cows on pasture only diets (no supplementation).

Over a range of pasture allowance from 20 to 70 kilograms of dry matter per cow per day saw a pasture dry matter intake increased 0.19 kilograms of increased pasture allowance.

Statistically it was determined that maximum dry matter intake of pasture can be obtained when 110 kilograms of dry matter per cow per day is provided by pasture.

Studies reviewed. Eight studies of supplementing cows on pasture were reviewed.

As you increase concentrate feeding you will decrease pasture dry matter intake.

Concentrate supplementation did not affect biting rate (58 bites/min) or bite mass (.047 grams of dry matter per bite).

Increasing the amount of concentrate supplementation up to 10 kilograms of dry matter intake per day increased the total diet dry matter intake 24 percent, milk production 22 percent and milk protein 4 percent but reduced milk fat 6 percent.

Milk production increases linearly as the amount of concentrate increases from 1.2 to 10 kilograms (2.5 to 22 pounds) dry matter intake per day with an overall milk response of 1 kilogram milk per kilogram of concentrate.

Research has shown that total dry matter intake and milk production will decline when grain feeding exceeds 20-25 pounds per cow per day.

Protein supplement. The paper reviewed eight studies that researched protein supplementations.

It has been suggested that a rumen undegradable protein be fed because of the high degradability of the grazed forage.

In five of seven studies there was no change in pasture dry matter intake when a rumen undegradable protein was fed.

Of the eight studies, two showed an increase in milk production by feeding a rumen undegradable protein.

Schroeder and Gagliosto reported a 6 percent increase when feeding an animal protein blend and reported an 18 percent increase when feeding feather meal.

In the review of protein supplementation there was no report of the crude protein content of the pastures or the total amount of concentrate fed.

Energy balance. Nutritional research has shown that energy is an important nutrient to maximize rumen protein synthesis and there should be a good protein: energy balance.

Many producers do not feel comfortable with pasture being the only forage and supplement with hay or corn silage.

Nine corn silage supplementation studies were reviewed. The response to corn silage supplementation depends on the amount of pasture offered. When the pasture offered was low, corn silage had a positive effect on production.

When pasture allowance was high, the supplementation with 2.3 kilograms of dry matter per day (5 pounds) corn silage reduced pasture dry matter intake and resulted in a similar total dry matter intake and similar milk production.

I still am concerned with feeding over 20 pounds per day of concentrate to grazing dairy cows that are high producers.

They could be susceptible to acidosis therefore feeding concentrate mixed with corn silage is a way of reducing that risk.

Hay. Studies on hay supplementation were conducted using different forms and amounts of hay.

Three studies with early lactation cows reported no response in milk production to hay supplementation, while one found higher milk production when long hay was supplemented, but similar milk production when the hay was chopped and added to the concentrate.

Most of the studies found no effect of hay supplementation on milk fat percent except one that reported lower milk fat content with long hay supplementation.

None of the research showed any affect on milk protein.

Fiber requirements. Hay supplementation to grazing dairy cows raises the question about the fiber requirements of high producing cows on pasture.

Recent recommendations for dairy cows suggested a minimum of 25 percent NDF and 19 percent NDF from forages for the following conditions: forage with adequate particle size, dry corn as the predominant starch source and diets fed as TMR.

When concentrates are fed twice daily and separately from forage, NDF minimums are unknown but probably higher than 25 percent.

There is not enough data to make any specific recommendations for cows grazing and fed concentrates twice daily.

Fat supplementation increased milk production by 6 percent without affecting milk fat and protein content.

However, none of those studies were conducted with cows producing more than 30 kilograms per day.

Many have reported improved body condition score and improved reproduction when fat is supplemented to high producing cows.

As a nutrient. In summary, I guess we can say that energy is the limiting nutrient for high producing dairy cows in a management intensive grazing system.

Concentrate feeding should be limited to a maximum of 20-22 pounds per day.

Feeding rumen undegradable protein in most instances will not improve milk production.

However, protein supplementation may be needed as pasture quality declines.

Feeding fat may increase production and will improve body condition and possible reproductive performance.

(The author is a dairy agent for OSU Extension in Wayne County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)

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