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

Dr. Allen Young
USU Extension Dairy Specialist


    Recently I was asked a question by a dairy producer about peak milk and days in milk at peak. I decided to do some analysis of Utah dairies to better answer his question.

    Peak milk, as defined by DHIA, is the highest level of milk a cow produces within the first 90 days of lactation or days in milk (DIM). In a normal lactation curve, milk increases to some peak level, on average at about 56 DIM, then gradually decreases to the end of lactation (the rate of decrease is called persistency). The relationship between peak production and subsequent milk production for a lactation is positive. To illustrate that relationship I have included a graph of peak milk production versus average 305-ME milk production for 240 dairies in Utah (Fig. 1). As the pounds of milk at peak increase, so does the 305-ME milk (correlation is 0.96; 1.0 would be a perfect correlation).

Figure 1. Average Pounds of Milk at Peak vs. Average 305-ME Milk for 240 Utah herds (Data obtained on 7/10/98).

Peak A, Figure 1

    Analysis of this relationship demonstrates that one extra pound of milk at peak is equal to approximately 273 pounds of 305-ME milk or 239 pounds of Actual 305 milk over a lactation. This means that if you could increase the level of peak milk by one pound it would translate into 239 extra pounds of milk per cow over a lactation. At $12/cwt milk that is an additional $2,868 extra for a 100-cow herd.

    I have also included in Table 1 a list of the amount of milk at peak and the resulting 305-ME milk and 305 Actual milk based on the relationships from the 240 Utah dairies. Compare your herd against this chart to see how you are doing. If your numbers are below these averages, evaluate and make changes right now. It is important to monitor peak milk every month and also by lactation number. I analyzed the records of one dairy where peak milk had decreased over a 6 - 8 month period by an average of 12 pounds of milk per cow. Using $12/cwt milk, a 100-cow herd would lose $34,416 in milk sales as a result. I think you can see that this producer was losing a great deal of potential income and didn�t even know it.

    In addition, you should also monitor persistency levels. Analysis of DHIA records by the University of Idaho has found the following average decreases in 30-day FCM: 1st lactation = 1.7 lb, 2nd lactation = 4.4 lb, and 3+ lactation = 5.9 lb. If your decreases are greater than these values, it suggests a problem is occurring; possibly nutrition related.

    If your peak yields are not where you want them, start troubleshooting by evaluating transition and early lactation rations and feeding management strategies (bunk management). In addition, you should Body Condition Score each cow and make sure they don�t lose an excess amount of weight (more than 1 BCS unit) in the first 2 months of lactation; again a function of nutrition. This is a very critical time in determining how well a cow will produce over the whole lactation and the numbers to monitor it are easily obtained from monthly DHIA records. In the next newsletter issue I will continue with the second part of the dairyman�s question regarding Days in Milk at Peak.

Table 1 (all values in pounds)
Milk at Peak 305 ME Milk 305 Actual Milk
50 11,984 10,732
60 14,711 13,119
70 17,437 15,505
80 20,164 17,892
90 22,891 20,278
100 25,617 22,665
110 28,344 25,051
120 31,070 27,438
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