Knowing with precision how much dry matter intake (DMI) cows are eating is extremely important, especially on high-production herds. These herds have high requirements of nutrients and, at the same time, the rumen has a limited capacity.
This can create difficulties when balancing the diet because we are trying to pack a lot of energy and protein sources in a limited space while keeping good levels of fibre for rumen health, which tend to dilute energy down. This conflict explains maybe 50 percent of the grey hair nutritionists get during their career; the other 50 percent are due to incentive days.
Recently, I did an exercise on a farm I work with as a nutritionist. This is a high-production herd, and the diet is always balanced for a high level of DMI. The concern was that the first-lactation animals would not be able to eat all of that feed and, in fact, the DHI results tended to show some issues in terms of the projected milk for first-lactation animals.
Because the barn allowed doing this, we decided to separate the heifers from the cows, and for about a week the owner measured the DMI of each group. Adult cows were eating 25.2 kilograms of DM, which was expected due to their production. The first-lactation heifers were only eating 21.7 kilograms. This is a big difference.
What does this mean in practical terms? When we formulate diets, we always formulate in terms of density, meaning that we calculate the energy in terms of Mcalories (Mcal) per kilogram of DM, or the percentage of protein per kilogram of DM, as well as the minerals and vitamins. Formulation also takes into consideration the percentage of first lactations and other factors, and this can affect energy and protein density.
If, for example, the herd has a high percentage of heifers, the density increases because it is known that heifers eat less and are still growing.
This normally works well, but these diets tend to be more expensive (normally fat needs to be added to the diet, for example) and, eventually, some cows with high DMI may gain too much condition. Still, it may be difficult to compensate for a difference in DMI like the one mentioned above, even with a higher-concentrated diet.
Let’s explain this with some numbers. Suppose the diet of the above herd was balanced with a density of 1.66 Mcal per kilogram of DM. An adult cow eating 25 kilograms of DM of this TMR will receive 25 kilograms x 1.66 Mcal = 41.5 Mcal per day.
A first-lactation cow eating 21.7 kilograms of the same diet will receive 21.7 kilograms x 1.66 Mcal = 36 Mcal per day. For the adult cow, those 41.5 Mcal allow her to produce roughly 42 to 43 litres of milk.
For the heifer, the 36 Mcal will allow her to produce around 34 litres. Although this is good production for the heifers, we know of many heifers producing more than 40 and 45 litres of milk.
What happens to these heifers is that their reproductive performance may suffer, they may not produce as much as the genetic potential would allow her to produce, or they may not grow as much during the first lactation as they could.
An alternative to alleviate this problem would be to formulate a diet with a higher energy density. This way, even eating a smaller amount of DM, the younger animals will receive more nutrients.
For example, if the diet were balanced for 1.70 Mcal per kilogram DM then, on the same 21.7 kilograms, the heifer would receive 36.9 Mcal and be able to produce around 36 litres.
From a cost point of view, though, to go from a 1.66 Mcal diet to a 1.70 Mcal diet implies an important increase in feed costs and increased levels of concentrate, with the potential problems associated with this. On the other hand, the adult cows may not need such high density of energy because they can compensate simply by eating more feed.
If the farm can separate heifers from the adult cows, a possible way to work around this is to balance the diet for the adult cows, which will allow us to have a cheaper diet per kilogram of DM. The TMR should be prepared for all animals in the barn (adult cows and first-lactation).
We then feed the adult cows, stop the TMR, add some extra “goodies” for the heifers, mix it a bit more and then feed the heifers. These extra “goodies” can be things like fat, extra protein or extra grain.
This is a relatively easy way to provide a diet a bit better balanced for both groups of animals in the barn and, at the same time, take advantage of the higher DMI of the adult cows and feed them a lower-cost diet.
DMI is a very important factor affecting milk production, feed costs and, ultimately, profitability. On average, a 1-kilogram-per-day increase in DMI can support 2 to 2.5 kilograms of additional milk.
Higher DMI generally results in lower feed costs per unit of milk produced because we can use more forage or fewer nutrient-dense feeds as a source of nutrients.
Because of the importance of knowing DMI, there should be good communication between the dairy producer and the feed company. If cows are cleaning the bunk too fast, or leaving too much feed behind, this information should be shared with the nutritionist.
Sometimes it can be just a temporary change in the moistures of the feeds, but other times it’s a more permanent effect due to a different mix of cows in the herd (more heifers, for example) or forages with different digestibility.
Whichever the situation may be, this is very important information to properly adjust the diet. If cows are eating more (even after moisture corrections), maybe we can take out or reduce that expensive fat from the diet. If, on the other hand, cows are eating less, maybe we have to concentrate the diet more; otherwise, we risk loss of body condition.
One of the challenges of DMI is that we rarely know the actual DMI of individual cows in a barn. Eventually, we can have this information in a tiestall barn, but on a TMR-fed herd, the most we can know is the amount of DM consumed in the barn or in a particular pen of cows.
This problem is greater with a greater diversity of cows in a particular barn or pen. This is one of the reasons that at least separating first-lactation from adult cows can have a positive effect.
An important tool that should be used to evaluate nutrition on single-TMR herds or in particular pens of cows is body condition scoring. According to Bill Weiss, from Ohio State University, body condition scoring can be monitored on individual cows and can be used as a proxy to individual DMI.
He explains that the variation of body condition scoring can be used for example to evaluate nutrition and feeding management of early lactation cows in pen situations.
Cows in early lactation are expected to lose some body condition; according to Weiss, a loss of 0.25 is a good average. However, if many cows lose more than 0.5 points, fresh cows are likely not eating enough.
It’s important to manage the barn in a way that DMI is not affected, especially during the fresh period. As we mentioned before, milk production is very closely related to DMI. In addition, cows which peak higher in early lactation produce more milk over the entire lactation. Keeping a consistent, high-quality source of feed in front of the cows is a high priority. PD
References omitted due to space but are available upon request. Click here to email an author.
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Pedro Nogueira
- Nutritionist
- Shur-Gain
- Email Pedro Nogueira
