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0408 PD: Strategies for shortening the dry period

Ric R. Grummer and Robin R. Rastani Published on 27 February 2008

Shortening the dry period to less than 60 days has been promoted during the past few years.

The major consideration for doing so has been a few studies indicating that losses in milk or fat-corrected milk yield in the subsequent lactation may be minor if the dry period is reduced from approximately 60 to 30 days. However, the decision to implement a short dry period should be more complex than simply examining the extra income from milk by extending the lactation versus the potential loss in income from milk in the following lactation.

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Shortening the dry period may involve alteration of grouping strategies and facilities, modification of diets and dietary ingredients, changes in the incidence of metabolic disorders and disease and effects on reproductive efficiency. All of these factors have economic importance and should also influence the decision of whether to shorten the dry period. Unfortunately, beyond the effects on milk yield, little is known about the consequences of short dry periods.

The following discussion is intended to examine some of the issues that are of importance when deciding to shorten the dry period.

Dry period length
As noted above, most of the data available for determining dry period length is based on milk production data. Most studies are older studies and have been retrospective analysis of farm records (e.g., DHI) in which milk yield has been plotted against days dry. These studies do not involve cows that were purposely managed for short dry periods. Therefore, many of the observations for short dry periods represent cows that carried twins, cows with incorrect predicted calving dates, or cows that aborted or had abnormally short gestations. Most of the data from these studies indicated that a 50- to 60-day dry period was most beneficial.

There have been several studies that were specifically designed to examine the effects of reducing the dry period to approximately 30 days on milk production. Examining six specific studies, measurements reflect performance following the treatment period and do not include any data (e.g., additional milk) from the period prior to calving. The length of time cows were followed after calving varies among studies and ranges from 70 to 305 days.

Of the six studies, two indicated a significant drop in milk yield. The study by Sorensen and Enevoldsen, which indicated a significant drop in milk and fat-corrected milk yield, was conducted on eight commercial dairies in Denmark and included Danish Black and White, Red Danish and Jersey cattle. There was a significant drop in milk yield but not fat-corrected milk yield in the study of Rastani et al. (2003). Several studies reported a numerical drop in milk yield that was not statistically significant.

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This likely reflects inadequate replication (cow numbers) to detect a significant difference. By pooling data from all six studies, it seems reasonable to conclude that one might expect a 5 percent drop in milk yield the following lactation if the dry period is shortened from 50 to 60 days to approximately 30 days.

Because treatments were similar across these trials (60 versus 30 days dry), an important question that has not been answered is: What is the optimum dry period length? Can one go shorter than 30 days? If one shortens the dry period to 35 or 40 days, will they not lose 5 percent in milk yield the next lactation?

In the early seventies, Cornell researchers conducted the only study in which there was a designed titration of days dry. Cows on 65 commercial dairy farms (average size 65 cows) were assigned to 20, 30, 40, 50 or 60 day dry period for 42 months. Cows were dried off regardless of treatment when milk production was less that 9 kilograms per day. Consequently, few cows assigned to the short dry period actually “qualified” for their treatment.

For cows that adhered to their assigned days dry, they observed a net milk yield loss (additional milk from the previous lactation was considered) of about 5 percent when dry period was reduced below 40 days. This data suggests that it may be beneficial to aim for a 40-day dry period.

Most dairy producers in the Midwest that have implemented a short dry period have targeted a 40- to 45-day dry period. Doing so allows a margin of safety for cows that calve earlier than expected.

Grouping strategies
Shortening the dry period to 30 to 45 days eliminates the need to have two diets during the dry period such as a far-off dry group and a prefresh transition group. This creates the potential of having one dry cow group. Successful implementation of one dry cow group necessitates that all cows respond similarly (favorably) to shortened dry periods.

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Unfortunately, we know very little about potential interactions between cows and dry period length. If there are groups of cows that are more likely to be negatively affected by short dry periods, then they must be considered for grouping separately and, therefore, creating the potential need for three dry cow groups (short dry group, long dry group/far-off, long dry group/transition).

Research is inconsistent regarding a parity by dry period length interaction. Several studies have indicated that reducing the length of the dry period to less than 60 days has a more detrimental effect between the first and second lactation than between later lactations. However, other analyses have indicated no interaction between parity and optimal length for the dry period.

Although some have speculated that high-producing cows may have a need for a longer dry period, there is very little research available to determine if this is the case. By comparing second lactation milk yields to first lactation milk yields, it was noticed that the advantage of a longer dry period was greater for low-producing herds than for high- producing herds. They speculated that low-producing herds were fed a lower plane of nutrition and that a longer rest period was needed when cows were underfed.

In contrast, a subsequent study indicated higher producing cows, as measured 100 days prior to expected calving, required a longer dry period to obtain peak milk the subsequent lactation, but the relationship was only evident for cows between their first and second lactation. Additional studies are needed before a conclusion can be made whether there is a level of milk production by dry period length interaction.

A very strong interaction has been documented between calving interval and the dry period length to obtain maximum milk yield the following lactation. Cows with longer calving intervals required fewer days dry, and the relationship was stronger as cows got older. Keep in mind that the data are estimates from statistical analysis and the predictions are less reliable for cows with characteristics at the extreme ends of the spectrum (e.g. oldest cows with longest calving interval). However, if a farm is large enough and flexible enough to create a specialty pen for cows that are good candidates for a short dry period, they should consider selecting older cows with longer calving intervals.

Feeding strategies
Typical feeding management of cows on an eight-week dry period includes a far-off dry cow diet and a prefresh transition diet. The far-off diet is low in energy density and is designed to maintain body condition of the cow during the first five weeks of the dry period, while the prefresh transition diet is fed during the final three weeks of the dry period and is designed to acclimate the cow and rumen microorganisms to the high-energy lactation diet that will be fed following calving.

This traditional strategy involves two grouping changes and two diet changes within a three-week time frame. In some cases, this leads to increased stress from grouping and diet changes, larger-than-desired declines in feed intake and metabolic complications postpartum. Feeding one diet the entire eight-week dry period may help reduce the likelihood of this scenario.

However, feeding a transition-type diet that is moderate in energy for eight weeks may lead to over-conditioned cows and an increased incidence of metabolic disorders. Feeding one high-fiber diet during the entire dry period may be successful. However, questions persist as to whether a dramatic jump from a high-fiber diet to a low-fiber diet at calving is best for the cow or the rumen microbes. If one diet can be fed for a 60-day dry period, then multiple dry period lengths can be employed using a single dry cow pen.

A compromise strategy may be to shorten the dry period and feed one diet with relatively high energy throughout the dry period. The target energy density for this diet would vary depending on the length of the dry period. In other words, as dry period length decreases, the energy density of the diet could increase because there would be less time to accumulate excess body condition.

We designed an experiment with three treatments. Multiparous cows were fed a lactation diet from -90 to -57 days prior to expected calving. Cows were dried off and assigned to treatments at -56 days prepartum. The three treatments were:

1. 56 days dry; cows fed a low energy far-off diet from -56 to -29 days prepartum and a close-up transition diet from -28 days to parturition

2. 28 days dry; cows continued on the lactation diet (minus buffer) throughout the dry period

3. 0 days dry; cows continued on the lactation diet (minus buffer) until calving

After calving, all animals were fed a postpartum lactation ration. Actual days dry for the 56, 28 and 0 days dry treatments were 54, 29 and 5. Some cows on the 0 days dry treatment spontaneously stopped lactating (i.e., dried themselves off). Continuation of milking resulted in higher dry matter intakes prior to calving. However, even cows on the 0 day treatment experienced a decline in feed intake as calving approached. Differences in feed intake between treatments continued, but to a lesser magnitude, after calving.

There was no significant difference in production between 56- and 28-day treatments. Cows on the 28-day treatment produced milk with a higher fat test; consequently there were differences in milk yield between cows on the 56- and 28-day treatments.

Loss of body condition score and bodyweight postpartum increased as days dry increased. This reflected a more favorable energy balance as days dry decreased. As one might expect, shortening the dry period resulted in a reduction in plasma nonesterified fatty acids and liver triglyceride. However, the differences were only significant between cows with 0 and 28 days dry.

There were no differences in calf size due to treatment (42.7, 42.9, and 43.1 kg for 56, 28 and 0 day treatments). Insufficient animal numbers dictated that we refrain from a statistical analysis of this data.

Dry Cow treatment strategies
There is very little data to base dry cow treatment strategies on. Dry cow therapy may be more effective in cows with shortened dry periods, and there may be a reduced rate of new infections in cows with shortened dry periods. Unfortunately, dry cow therapy may result in the carry-over of antibiotic residues into milk post-calving.Current dry cow therapies are targeted for cows with a 45- to 60-day dry period. Antibiotics from dry cow therapy reside in cows much longer than do those of lactating cows. Consequently, if cows receive a dry cow treatment and have a dry period less than 45 days, antibiotic residues may be present in milk post-calving.

Implementation of a short dry period with the use of standard dry cow antibiotic therapies should be accompanied by postpartum testing of milk for residues. A reasonable approach may be to use a lactating cow antibiotic treatment during the final milkings combined with a teat sealant following the final milking.

Reproductive strategies
One of the most dramatic effects in our study described above was on reproduction. Ovarian dynamics were monitored by ultrasound three times per week. Clearly, reducing the dry period resulted in a more rapid resumption of ovarian activity. Although this trial ended at 70 days postpartum, reproductive performance of cows was monitored beyond 70 days.

Cows that were on the 0 days dry treatment had higher first service conception rate, fewer services per conception, and fewer days open. However, because these cows were not on experiment beyond 70 days and limited cow numbers were used, these results must be interpreted with caution. It is not known whether these differences in reproductive performance were a consequence of differences in days dry, energy balance or milk yield.

The results, if verified through additional studies, could impact reproductive management strategies. Higher conception rates could allow one to increase the voluntary waiting period since fewer breedings would be required per pregnancy.

Future strategies for reducing dry period length
Available data indicates that a 30-day dry period may be feasible, but a 0-day dry period results in significant milk yield losses the subsequent lactation (20 to 25 percent loss). Will there be strategies in the future by which the dry period can be reduced beyond 30 days without significant losses in subsequent milk yield?

University of Arizona research indicates that the loss can be avoided in multiparous, but not primiparous cows, if they are continuously treated with bST. However, this was off-label use and a control treatment in which cows with a 60-day dry period were continuously treated with bST were not included. Further studies indicated that prostaglandin E2 or four times per day milking postpartum could not prevent the yield loss associated with continuous milking of primiparous cows.

We are currently examining the effects of milking frequency during continuous milking for the final four weeks of pregnancy on post-calving milk production. Preliminary results indicate that milking four times per day during the final four weeks of pregnancy may eliminate the production loss associated with a 0-day dry period in mature cows, but not for those having their second calf. More basic research is needed to investigate the factors that affect lactation persistency, including mammary cell proliferation and mammary cell death, so future strategies can be developed to shorten or eliminate the dry period. PD

References omitted but are available upon request at

—From 2006 Intermountain Nutrition Conference Proceedings

Ric R. Grummer and Robin R. Rastani, Department of Dairy Science, University of Wisconsin-Madison

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