Are You Monitoring Your Peak Milk and Days in Milk at Peak?
Part B. Days in Milk at Peak

Dr. Allen Young
USU Extension Dairy Specialist

    In the January �99 Dairy Newsletter I made the point that there is a linear relationship between the level of peak milk production and how much milk a cow will produce during that lactation. This month I want to continue by talking about Days in Milk at Peak (DIMPK).

    On average, my rule-of-thumb is that herds should peak at around 55-60 Days in Milk (DIM), recognizing that first lactation animals peak later in lactation. Less than this and production is compromised, but greater than this isn�t necessarily bad because, as some producers with high herd averages have noticed, their DIM at peak are actually much higher, probably because the cows are fed and managed better. The second part of the dairyman�s question from last month was whether higher producing herds peak later in their lactation. The simple answer is yes, but with a great degree of variability (Figure 2).

Figure 2. Days in Milk at Peak (DIMPK) versus Average Pounds of Milk at Peak for Utah dairies on DHIA. (Data obtained on 7/10/98.) Solid line is a regression of the data.

Peak B. Fig. 2

    Figure 2 shows that as DIMPK increased so did the number of pounds of milk at peak. This relationship is not as clear as the plot of peak milk against average production per cow, but it is still positive. In Figure 3 it is a little easier to see the positive relationship between Rolling Herd Average (RHA) and DIMPK. The big question is why? Should we be trying to manage our cows to peak later in lactation and thereby get more milk? The answer, I think, is a qualified NO.

Figure 3. Average Days in Milk (DIM) at Peak versus Rolling Herd Average Milk for Utah dairies on DHIA (data obtained on 7/10/98).

Peak B. Fig. 3

    What I think is happening is that you are seeing the effect, rather than the cause. Cows in higher producing herds keep going up in production longer before they peak and therefore reach peak production at a higher level, further out in lactation. Some of my rationale is shown in Table 2. Table 2 contains average Lactation-to-Date (LTD) milk production for Lactation 3+ cows only, at three different stages of lactation, and three different Herd Average 305-ME Milk levels. LTD is a measure of how many pounds of milk a cow has produced up to a certain point in her lactation. The first three columns show that as herd production increased, the amount of milk produced by a cow at any given point of lactation also increased. The last two columns show how much milk was produced between time points. Again, cows in higher producing herds produced more milk within a given time period than those in lower producing herds. In data not shown it appears that lower producing herds begin to plateau in production while higher producing herds are still increasing. This translates into cows in higher producing herds producing more milk for a longer period of time than those in lower producing herds. This leads to later DIMPK.

    What does this mean for you as a dairy producer? In order to increase peak production and subsequently increase DIMPK, you need to get your cows off and running at optimum speed. Trying to hold a cow back and get her to peak later does not work. The same things I mentioned for evaluating peak milk also apply here, because if peak milk increases, then the other trend also increases. While it is difficult to know how hard to push a fresh cow so that she produces at optimum level without getting sick, my observation is that many dairies with lower average production don�t have adequate nutrition in early lactation and also don�t give her the opportunity to produce to her potential. Loss of milk production in early lactation cannot be gained back later.

    The most underutilized DHIA data in monitoring nutrition and production in early lactation are Peak Milk, DIMPK, and Persistency. Financially it is worth the effort to monitor these values in your herd.

Table 2. Average Lactation-to-Date Milk Production (LTD) by Days in Milk (DIM) for cows with three or more lactations (data from over 3,000 animals from Utah dairies).
Herd Average
305-ME Milk
Days In Milk
b-a1 c-b2
18,999 or less 1317 2666 4940 1349 2274
19 - 23,999 1892 3352 5924 1460 2572
24,000+ 1832 3980 7115 2148 3135
1The difference in LTD milk between the average of 31-60 DIM and 21-30 DIM.
2The difference in LTD milk between the average of 61-90 DIM and 31-60 DIM. ©