Supplementation Of The Lactating Cow In A Grazing System

Thomas E. Noyes 
Extension Dairy Agent, Wayne Co.

Spring is upon us and it's great to see green grass, although winter was very kind to Ohio this year. Spring management and supplementation of the lactating cow is the most challenging time during the grazing season. At this time forage growth is the most rapid and quality changes quickly make management more intense during the spring flush.

Ideally we would like to keep the grazing height of the forage under 12 inches if you're grazing the tall species (orchard grass and red clover) and under 10 inches if you're predominantly bluegrass and white clover. If you're able to manage your pastures in this manner you will be grazing forage that can be from 24-30 percent crude protein with relatively low fiber with NDF values in the 35 percent range.

The goal of a supplementation program is to feed the cow to capture as much of the protein as possible and to perhaps provide some fiber to slow down the rate of passage. This can be accomplished by continuing to feed a TMR while you begin to turnout on grass, gradually reducing the amount fed over a 7 to 10 day period. Over that period of time your length of grazing has increased from several hours to now all day grazing. If a TMR is not being used follow a similar program of gradually reducing hay and silage feeding as you increase the length of grazing.

Many beginning graziers ask about the continued feeding of a forage throughout the grazing season and on many farms this is practiced. I think there can be continued use of the TMR mixer to feed what I call a PMR (partial mixed ration) while grazing. For the high producing cow this is an ideal way of getting adequate grain intake without "slug" feeding. It slows down the rate of passage capturing more of the degradable protein.

In a grazing system the nutrient most lacking for high production is energy. Therefore, grain feeding should be at a rate consistent with the production goals of the herd but limited to a maximum of 18-22 pounds per day. The content of the grain mix should be primarily a combination of finely ground and coarsely ground corn and perhaps a fibrous carbohydrate like soy hulls along with salt and minerals. By varying the grind of corn and using a fibrous CHO source you vary the rate of fermentation in the rumen thus capturing more of the degradable protein. By incorporating this grain mix with corn silage you've further improved the efficiency of the fermentation process while the cow is grazing.

In the earlier years of adopting management intensive grazing it was thought that due to the high rate of protein degradability of forage being grazed that a rumen undegradable protein source would be needed. However, feeding trials as Purdue University, here at OSU-ATI and recently at Penn State showed there was no increase in milk production by feeding by-pass protein supplements or by increasing the protein percent in the grain mix to 16 percent.

Recent Milk Urea Nitrogen (MUN) studies in New York and in Pennsylvania showed as much variation in MUN levels of grazing herds as with confinement herds and there appears to be no advantage to feeding expensive RUP sources. Excess protein actually utilizes energy for removal therefore avoid overfeeding protein.