We give up a lot of control when we stop taking cows out of the pen for milking and expect them to come to the robot on their own initiative. How do we regain control? Some say it is pressure on the udder – but how much pressure? Some say training – but what reinforces the training? Some say cows like pellets – but they like PMR too. The one thing that we can control, and in turn control where cows spend their time, is where cows go to get nutrients. In free-flow barns, that means a cow has to be able to eat PMR until she is full, but be unable to meet her energy requirement from the PMR alone. Then she will save room for a more energy dense feed to fulfill her energy requirement – at the robot.
The chart below shows the relationship. The units on the axes are pounds of milk. There are no numbers in this example because the numbers are different for every farm – and maybe for different groups on the same farm.
Energy Balance Goal
In a perfect world, cows could always be fed exactly what they need – like the red line in the graph. That doesn’t happen in real life. If we gave every cow a spot on the graph, some would be above the red line - gaining weight, and others would be below the red line – losing weight. There are limitations like forage quality, dry matter intake, competition at the bunk, mixing variation and so on. Different combinations of PMR and pellets can be used to keep as much of the herd as close to the red line as possible.
Energy from PMR
With high quality forages, it might be possible to provide everything that every cow needs in the PMR. That’s how it works on most parlor farms. The green line can move higher or lower on the graph depending on forage quality, or grains and other concentrates included in the PMR. As the green line moves higher, more cows are overfed. If the green line moves lower, more pellets will be needed to supplement the PMR. In either case, the PMR should have significantly less energy than the pellet so the cow has a reason to prefer pellet.
Energy from Pellets
Pellets can supplement the PMR but there are limits. A cow that eats a pound a minute and spends 18 minutes per day in the robot cannot eat more than 18 pounds of pellets. Dietary fiber requirements can also limit pellet feeding. Above the maximum amount of pellets, all cows are short of energy. There might be a minimum amount of pellets to keep the cow busy in the robot. The blue line can move higher or lower on the graph, but there are limits. Again, the pellet should have significantly more energy than the PMR so the cow has a reason to prefer pellet.
Part 2 of this series will put the pieces together to determine the balance between the PMR and the pellets for different herds and groups.
*Image concept credit to Jan-hendrik Puckhaber – AMS Academy
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