Part 1 covered the roles of PMR and pellet in meeting the energy needs of the cow and making the barn flow. Part 2, covers balancing those in specific situations. Most farms will prefer to minimize the amount of pellet and maximize the amount of PMR. That’s simple economics. It is less expensive to meet a cow’s nutrient requirements with forages, like corn silage and alfalfa, than with concentrates like corn, soybean meal, and manufactured pellets. The more uniform the group is, the more closely we can meet their energy needs with the PMR.
There are some thumb rules for formulating PMR in free-flow barns. One is to balance the PMR for 15 pounds less milk than the herd average. Another is 80% of the herd average. That’s a good place to start. Either one means balancing at about 75 pounds of milk for a 90-pound herd.
Variation within groups
Not all 90-pound herds are created equal. There is a difference between a 90-pound herd or group with cows producing between 70 and 140 pounds as compared to a 90-pound herd with cows producing between 40 and 160 lbs. Cows producing 70 pounds are not far from the 75 pounds offered in the bunk. In fact, they are probably eating less PMR than the top producing cows in the pen so they might still crave the energy in the pellet. On the other hand, a 40-pound cow that is eating PMR balanced for 75 pounds is gaining weight and will not come to the robot for extra energy. She will get in the way and slow down the traffic for the whole barn. The robot gives us an opportunity to feed individual cows according to their needs, but we can do a better job meeting those needs if the groups are more uniform. Efficient reproduction, well managed culling, and effective grouping strategies all tools to maintain uniform groups. The green line in the graph can be moved higher if the groups are more uniform.
Variation between lactation groups
Separating first lactation cows from mature cows is another example. Consider the example of a mixed parity pen that averages 90 pounds per cow. Using the 80 percent thumb rule, the bunk should be balanced for 72 pounds of milk. Within that pen, the mature cows might average 100 pounds. Their bunk should be balanced for 80 pounds. If the first lactation cows average 80 pounds, their bunk should be balanced for 64 pounds. Splitting the groups by parity means the PMR can be balanced more closely to each cow’s needs.
8 tons of pellets
To put it another way, the PMR can be balanced for a higher level of production if there are fewer low producing cows in the group. There is less risk of over-feeding low producing cows. At the same time, it’s less expensive to meet the needs of high producing cows with more forage and less pellet. Assume a bunk is balanced for 60 pounds to avoid overfeeding low producing cows, and it takes 1.2 pounds of pellet per 10 pounds of milk to support the higher producing cows. A 180-pound cow at a bunk balanced for 60 pounds would need to eat 14 pounds of pellets. A 200-pound cow would need 17 pounds. The 180-pound cow at a bunk balanced for 80 pounds only needs 12 pounds of pellets. It adds up. 2 pounds of pellets per day for 80 days of peak production for 100 cows is 8 tons of pellets. The blue line on the graph does not have to go as high if the group is more uniform.
The average production for the group dictates the energy level in the PMR. Start with a thumb rule like 80% of the average production for the group. Fine tune the energy level based on rejections and visits. Maintain uniform groups so that the PMR can be balanced closer to the needs of every animal in the group.
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