Evaluating Milk Peak and Persistency Using DHIA Data Part 1

Milk Peak and Persistency in Review

Peak milk and lactation persistency are metrics that help to evaluate milk production and herd performance and improve the overall management and profitability of the dairy herd. Both peak milk and persistency are of economic importance for the dairy manager because they directly impact several factors. They influence feed costs by increasing the fraction of feed energy provided by roughage compared to more expensive concentrates (Dekkers et al., 1998), as well as health, and fertility (Swalve, 2000).

What is Peak Milk and Persistency?

The description of persistency and/or peak milk has been somewhat inconsistent.

For example, Gengler et al. (1998) defined persistency as the flat curve for the daily milk yield throughout the lactation period, which does not descend immediately after the peak. Grossman (1999) stated that persistency is 'the number of days during which the level of constant yield is maintained'.

Pettersson et al. (2011) defined persistency as the rate of decline in milk yield between days 100 and 300 post-calving. Cobucci (2013) described persistency in lactation as the capacity of a cow to maintain her milk yield after reaching the maximum level of early lactation.

Persistency can also be described as a measure of the rate of change in milk production between tests. Milk yield at one test is expressed as a percentage of milk yield at an earlier test, adjusted to a 30-day interval between tests (DHIA Info, 2014).

In order to model persistency, researchers used persistency as a ratio or rates of yields, measures derived from milk yield tests, and parameter estimates (Grossman, 1999).

VanDoormaal (2017) suggested that lactation persistency is the amount of milk a cow produces at 280 days in milk (DIM) compared to when she was at 60 DIM (Figure 1).

Milk peaks and persistence differ between lactations. A typical first lactation curve has lower daily milk yields; thus, the peak production is also lower, and the decrease of milk yield, stronger persistency, is more gradual. Although lactation curves for second and third lactations are similar, they exhibit higher milk peaks, and persistence is weaker or more rapid decline of milk yield (Figure 1, VanDoormaal, 2017).

Effect of Milk Peak and Persistency on the Dairy Herd

Peak milk and milk production persistency can describe lactation curves either for the whole herd, group of cows, or individual cows. Several reports indicate that the persistency of lactation is affected by various environmental factors such as genetic group, sire effect, herd management, lactation number, feeding, gestation, and season of calving of animals (Koloi et al., 2018).

Herd management, such as milking frequency, nutrition, disease prevention, and photoperiod length, influences peak milk and persistency. For example, temporary increased milking frequency post-partum increases milk yield not only during this period but also after its immediate secession (Bar-Peled et al., 1995) and for the entire lactation (Capuco, 2003). This increased milk yield is caused by enhanced mammary secretory cell activity followed by the proliferation of secretory tissue (Knight et al., 1990).

Pettersson et al. (2011) researched milk production persistency using automated milking systems. It was reported that milking frequency did not differ significantly between cows and heifers in early lactation, but thereafter decreased significantly more in cows than in heifers. Also, high milking frequency was associated with increased peak yield in both cows and heifers but improved lactation persistency in cows only.

Cows with high persistency tend to produce more milk than expected at the end of the lactation and less than expected at the beginning (Koloi et al., 2018). A management strategy to reduce the period of production before the peak and increase the period after the peak was suggested to improve persistency (Lin and Togashi (2002).

Cows' exposure to a long day photoperiod, 16-18 hours per day, also increased milk yield and strengthened persistency (Dahl et al., 2000).

Researchers also pointed out that reproductive measures also influence persistency. Milk production level and lactation persistency are factors determining the optimal calving interval length as the ability of cows to maintain production following peak yield (Wood, 1967).  Other observations from Andersen et al. (2011) and Atashi et al. (2013) noted that cows with shorter calving intervals had low intercepts, steep ascending slopes, and descending slopes, were less persistent, and produced less than 305 days of milk, although their first 120 days of production were the highest.

Delayed open period can lead to increased lactation persistency as well as increased milk yield in the subsequent lactation. Arbel et al. (2001) found that a delay of 60 days to the usual voluntary waiting period has economic advantages of $0.21/day and $0.16/day for primiparous and multiparous cows, respectively, compared to cows bred during the usual voluntary waiting period. Chen et. al. (2024) also reported that cows conceiving later in lactation showed higher persistency.

Several studies also found similar relationships between the lactation curve parameters, such as day of peak yield, persistency, and milk productivity, affected by selection for higher milk yield. Buckley et al. (2003) found that the higher the peak yield is, the higher the total milk yield.

On the other hand other research found that higher persistency and lower peak yield improve cows´ robustness to the stress of lactation and metabolic disorders (Hermiz and Haddad, 2020). This is because of improved energy imbalance, followed by less body reserves mobilization to meet the nutrient demand for lower milk production (Atashi et al., 2013). Similarly, Dekkers at al. (1998) and Prabhakar at al. (2023) noted that higher persistency leads to lower metabolic stress and improves reproductive performance.

Reduction of milk yield in early lactation (Togashi and Lin, 2003) followed by lactation persistency increase after lactation peak could help to maintain the health of dairy cows during lactation without decreasing total milk yield (Yamazaky et al., 2011).

Muir et al. (2004) estimated positive genetic correlations between 305 days yield and peak milk day (0.63 ± 0.06) and persistency (0.21 ± 0.06), indicating that as yield increased, the interval from initiation of lactation to peak yield and persistency increased as well. The estimated genetic correlation between peak day and persistency (0.54 ± 0.07) indicated that prolonging the interval from initiation of lactation to peak yield improved persistency. 

Hermiz and Haddad (2020) found that persistency is repeatable during the life of the animal and selecting cows that have higher estimates would improve the productivity of the herds.

In general, if the persistence of lactation could be increased, considerable benefits would accrue to the dairyman. Flattening the declining portion of the lactation curve promotes more efficient lactation (Capuco, 2003)

Part 2: Peak Milk and Lactation Persistency in DHIA Herd Summary

References

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