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Evaluating Milk Peak and Persistency Using DHIA Data Part 2

This article discusses the DHIA 202 Herd Summary peak milk and persistency data.

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Updated:

May 6, 2025

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Peak milk and lactation persistence are important management metrics that reflect the management's dedication to the transition program, fresh cow performance, and set the pace for the whole lactation. These two metrics define the lactation curve and how much the herd deviates from the normal lactation curve. The general goal is to reach a high peak milk and for the post-peak lactation curve to decline as slowly as possible. This would ensure considerable benefits to the producer.

Peak milk is a herd management metric that is useful when evaluating a herd's production and is defined as the highest test day milk production that has occurred in a cow's lactation. In the 202 Herd Summary, it is listed for each lactation group as well as for all animals. The potential milk production for a cow's lactation is determined largely by her peak milk yield. If a cow has a peak, she should have a productive lactation. However, milk yield loss occurs if she does not peak as expected, and her entire lactation will be below expected production.

Even though peak milk can occur before 100 days in milk, it is calculated after 100 days in milk from the available test date and is updated until 150 days in milk. Peak Milk is averaged for all lactations and each lactation group of cows. Any days after 305 days in milk is not included in the calculation (DHIA-202, 2016).

Peak milk is not a lagging metric. However, there can be some time lag as the test days are a month apart and the peak milk can occur far from the test day. Also, fresh cows removed from the herd before reaching peak can cause a bias of the peak average. It is a sensitive metric, and any management changes in the nutrition program that affect the production can be evaluated promptly.

Cows usually peak around 45- 70 days (8 - 9 weeks) post-calving and first-calf heifers peak a little later at 50-90 days into milk. It has been estimated that for every pound of milk higher that a cow peaks, she will produce more milk over her entire lactation. In a study by Amaral-Phillips, (2011), they estimated that the increase in milk can be over 300 pounds for first-lactation cows and between 200 and 250 pounds for mature cows (Amaral-Phillips, 2024; Bass, 2011). Generally, first-calf heifers peak at 75 to 80%, and second lactation cows peak around 90% compared to third lactation or greater cows.

Producers find the Peak Milk by lactation groups (1^st, 2^nd, 3^rd+, and all groups) in pounds of milk for each group in the Herd Summary DHI-202 ‘Production and Lactation Summary’ table. To find out how these groups are performing, a producer needs to calculate the peak ratio for the 1^st and 2^nd lactation cows.

For example, in the table below, a DHIA Peak Milk for 1^st Lact Cows is 74 lbs, for 2^nd Lact Cows 96 lbs, and for 3+ Lact Cows is 110 lbs.

Table 1. Production by Lactation Summary, Herd Summary 202

Peak Milk ratio is calculated as follows:

(Peak Milk 1^st Lact Cows / Peak Milk 3+ Lact Cows) * 100 = Peak Milk Ratio

(74 / 110) * 100 = 67% - for 1^st Lact Cows

(96 / 110) * 100 = 87% - for 2^nd Lact Cows

In this example, the first-lactation group peak ratio of 67% would suggest that first-calf heifers perform only 67% of mature cows, way below the expected minimum of 75% or 78 lbs. If this farm improves Peak Milk by ten pounds, each of the cows would potentially produce an additional 2,500 lbs or more of milk over their lactation.

Producers are also recommended to evaluate the number of cows in the lactation group, as a small number of cows would not provide a meaningful value. For example, there are 24 cows in the 1^st Lactation group (Table 1), which is enough for the peak milk to be reliable. If there were only 4 or 5 cows, the peak milk value may not be reliable.

Lower Peak Milk ratio for the first-calf heifers would warrant a review of the heifer raising program and transition management. Are heifers reaching recommended body size and weight, and are they receiving the correct dry matter intake and mineral balance, or are they poorly performing heifers that should be culled?

Higher than expected Peak Milk ratio for the first-calf heifers would indicate that there is a problem with mature cows (3^rd+ Lact Cows). Appropriate body size and weight at calving, feeding management, and transition period diet (dry matter and energy intake) would be areas to examine.

Lower Peak Milk ratio for 2^nd Lact cows would suggest that first-calf heifers were not provided adequate nutrition during mid to late lactation, and they did not regain body condition. Consequently, the 2^nd Lact cows cannot support the energy demand for higher milk production in early lactation. Subclinical metabolic disorders that limit feed intake, like ketosis or metritis, could be the cause of the lower ratio as well.

However, the peak milk information in Table 1 does not provide information about how many days in milk (DIM) the groups achieved their Milk Peak.

Persistency of milk production is another metric that is used to evaluate the performance of the herd. Persistency in lactation is defined as a measure of the rate of change or decline of milk production between test days (DHIA Info Sheet).

Producers can find persistency in the form of 'Test Period Persistency Index' (TPPI) on the Herd Summary 202 Form at the Yearly Production and Mastitis Summary (Table 2).

Each cow's expected percentage change in production from last month to current month is computed as the ratio of each cow's standardized 150 DIM for the last two test days. An average ratio is computed to determine the test period persistency for the herd for the last 12 test periods (DHIA 202). This way, the producer can evaluate any management changes in the herd based on expected production for the last 12 months.

Table 2. DHIA Herd Summary 202, Yearly Production and Mastitis Summary. Only Yearly Production part is depicted.

In the example in Table 2, the herd's TPPI is above 100 for seven months of the year, suggesting that the herd is doing better than expected, increasing milk yield from previous tests. However, there is a period of three months where the Index dropped to the 92-95 level. It would be worth investigating what management changes were implemented at that time that caused the drop in milk yield. Generally, if TPPI is less than 90, it may indicate that there were changes in management practices that caused a negative effect on herd production.

Milk Peak and Persistency characterize, determine, and define the lactation curve shape. For example, if the cows in the herd have a normal peak and drop milk production as expected, so they do not deviate from the normal lactation curve, the Test Period Persistency Index would be 100. However, if the TPPI is below 100, milk production will decline faster than expected.

Cows in the herd can deviate from this scenario in two ways. The cows can have a normal peak but poor or weak persistence, or their peak can be low while persistence is normal. In either scenario, milk production is limited. Ideally, Peak Milk and TPPI should be over 100. If producers are seeing lower Peak Milk or TPPI numbers, looking at other factors affecting these numbers could help the farm make improvements.

Part 3: Evaluating Milk Peak and Persistency Using DHIA Data