TAKE HOME MESSAGES

• Clean, comfortable stalls bedded with inorganic materials increase lying time and may affect future performance of dry cows.
• Reduce heat stress and reduce photoperiod in the late dry period to improve production and health of cows as they transition into lactation.
• Management techniques that increase production may pull higher DMI during the transition, and thus decrease metabolic and digestive disorders.
• Dry period length can be reduced in mature cows to increase total production and ease the transition into lactation.

INTRODUCTION

Traditionally, management of dry cows was an overlooked area on most dairy farms. With the exception of long acting antibiotic therapy to eliminate subclinical and prevent infections, cows were milked a final time and then removed from the milking herd to for approximately 45-55 days and largely ignored. Over the past decade a tremendous volume of work has accumulated that addresses the nutritional needs of cows during the dry period, with recommendations of two diets, one for “far-off” and another for “close-up” cows being widely accepted as standard practice. More recently it has become apparent that other management factors may also impact subsequent lactational performance. Examples include stall comfort, lighting and cooling, and reevaluation of the appropriate length of dry period. Consideration of the physiological basis of some of those approaches, and how to implement them, are the subject of this paper.

COW COMFORT CONSIDERATIONS

Cows spend a considerable amount of time lying down relative to other behaviors such as eating and standing (6). However, the relative degree of comfort of a stall can affect the amount of time cows lay vs. stand when all other conditions are equal. Tucker et al. (13) observed activity in cows exposed to either a low comfort tie stall, with minimal straw bedding over a concrete base, or a high comfort freestall with straw bedding on a mattress. The cows in the low comfort stall spent more time standing relative to the cows in high comfort stalls, and this was at the expense of lying down as feeding time did not change. Though this example is likely an extreme situation, it provides evidence that stall comfort can affect lying time. But what is the impact on production? There are postural effects on mammary blood flow, and cows have improved mammary gland perfusion when they are lying down vs. standing. Metcalf et al. (10) used 2 different methods to estimate blood flow to the mammary gland, and found that cows had about 25% greater blood flow to the mammary gland when lying down relative to standing. During lactation it takes about 500 volumes of blood perfusing the mammary gland to produce one volume of milk - thus blood flow is critical to milk production. Late in pregnancy the mammary gland is also highly metabolic, so it is likely that tissue perfusion should be maximized. This suggests that from a management perspective, we want to maximize the amount of time cows spend lying down to optimize milk yield. Because many cows are housed in stalls, esp. freestalls, emphasis should be placed on providing a comfortable, clean spot that cows will want to lie down in.

So what defines a comfortable stall? Economic considerations dictate a need to optimize cleanliness and comfort so that cows lie in the stalls but do not increase their risk of exposure to mastitis causing pathogens - i.e. limit exposure to manure! This means a combination of length and width appropriate to the size of the cow. Because cows must lunge their body to stand, adequate space must be provided to accommodate this movement or they will not lie in the stalls as readily. A brisket board, and neck rail are often used at the head end of the stall to allow for lunging but limit the forward movement of the cow so that manure will not be deposited in the stall but rather in the scrape alley. Across breeds, as cow bodyweight increases a longer stall is required both in front of and behind the brisket board. Larger cows will also require a higher neck rail to have room for lunging forward. It is possible to reduce the room for forward lunging by increasing the width of the stall to allow cows to lunge to the side, however, this may also result in greater amounts of manure being deposited in the stall vs. the alley behind the cow, which may increase exposure to environmental mastitis pathogens.

In addition to stall size, a key feature of comfort to the cow is the choice of bedding for the stall. Examples of organic bedding include straw, wood shavings or sawdust, or dry paper. In all cases the bedding selected should be dry, as one advantage of organic bedding is the ability to retain moisture. Other advantages include availability, usually for a low to moderate cost, and the ease of integration into manure handling systems. That is, no need to separate the bedding from manure before it is applied to fields. The major disadvantage of organic bedding is the contamination with mastitis pathogens and the presence of organic materials that support growth of those pathogens (8 ,9,12). Even daily removal cannot completely overcome the increased risk of pathogen exposure.

In contrast to organic bedding, inorganic bedding such as sand does not support mastitis pathogen growth if managed correctly, i.e. daily maintenance (9). It also provides a high degree of comfort as it conforms more readily to the cow’s body when lying down (6-10 inches deep). Disadvantages include the high wear rate on pumps and other components of the manure handling system, the need for separation of sand from the manure before field application, and the cost in some areas. Despite the handling difficulties, there is a volume of evidence that shows that sand bedding reduces mammary gland infections and thus loss of milk relative to organic bedding.

Another option for bedding is use of a mattress combined with limited organic bedding. This provides a high comfort surface for the cow and the reduction in bedding should limit bacterial growth potential. However, even when managed at a high level there is still an increased risk of pathogen exposure w/ mattresses vs. sand, and they have a very high initial cost.

Even the most comfortable stalls will not be used all of the time, and this has lead to stocking densities of greater than 100% for some groups of cows. This is appropriate at later stages of lactation but can lead to problems in the dry period and early lactation, when cows are still making the transition into lactation. Transition cows may not seek feed as aggressively or compete for stall space because they are recovering from calving and the coincident metabolic and physical challenges. Thus, it is recommended that stocking density be reduced if possible in this group. In any case, it is critical that adequate space at the feedbunk and waterer be provided so that lactating cows do not need to wait to eat or feed. For water, this translates to 2 linear ft/10-20 cows; in moderate environments the upper limit is likely adequate whereas the higher amount of waterer space per cow would be recommended in areas where high temperatures prevail. For feeding, a minimum of 2 linear ft/cow will provide enough space so that all cows can eat at once.

Movement of cows can reduce the amount of time available for stall use, and this may be a particular concern when cows are milked at higher frequencies (6). While this is not often an issue with dry cows, early lactation cows should be housed in locations that limit their requirement to walk extended distances to the parlor. The time spent walking to and from the parlor should be minimized during the design phase of construction of a facility. If possible the walkways should be covered or shaded especially in hot environments. If cows have to walk a long distance the surface should be padded to reduce the impact on the hoof. In addition to walking, time spent in the holding pen should be as short as possible in early lactation, as cows will not have access to feed, water or stalls during that period. The holding pen should be well-ventilated and cooled in warmer climates to maximize the comfort of the cows. Because cows have been removed from water while in the holding pen, some producers have found it beneficial to provide water immediately to cows exiting the parlor. Cows will tend to feed after milking as well, so ready access to feed is recommended at that time.

TEMPERATURE AND PHOTOPERIOD

All animals have a thermoneutral zone, the range of environmental temperature that has no effect on the animal’s performance. For lactating and dry cows this range is from about 40 to 65 degrees F. Lactating cows have a lower temperature at which they can maintain performance vs. dry cows, whereas dry cows can withstand higher temperatures without an obvious loss of performance. Much of this is due to the relative intakes of the cows in each physiologic state - lactating cows consume greater amounts of dry matter and therefore have higher heat production due to fermentative digestion. This relationship works against the lactating cow at higher ambient temperatures, because they must rid their bodies of greater amounts of heat. Outside of the ranges, cows will experience varying degrees of performance depression, but at the upper and lower critical temperatures cows can experience adverse effects on homeostasis, and if these extremes are not moderated through management, death can occur.

All animals, including domestic species such as cows, go through various adaptations with the seasons to adjust to changes in heat input from the environment. One of the most visible is the change in density of the hair covering, or pelage, which thins as warmer seasons approach. Of interest, this change is due to photoperiodic inputs rather than changes in temperature, just another example of adaptation of light shifts to predict other physiological needs (5). Cows, especially those that are in lactation and thus on ad libitum feeding, will reduce intake under heat stress. Because of the massive heat increment associated with fermentative digestion this is one response to reduce the heat load a cow is under. Cows also increase water intake when heat stressed which has convective effects in the consumption of cooler fluid, but also aids in evaporative cooling from the body surface. Cows exhibit shelter seeking behavior, especially under heat stress. This is easily visualized in the movement of pastured animals to areas under trees during the middle of the day, but also in animals in a freestall barn that has variation in sun impact because of poor siting; that is, cows will avoid stalls that are in the direct line of the sun on hot days.

An obvious sign of heat stress is the increase in respiration rate - though much of this is an increase in inspiration that allows for greater heat exchange from the lung through evaporative losses. In addition to the outwardly visible changes in the cow under heat stress, there are other physiological changes that occur to deal with the heat. Hormones that are involved in metabolic processes, including thyroid hormones, glucocorticoids, and growth hormone, all decrease during heat stress. In contrast, prolactin secretion increases in response to high temperatures. Because of the effects of prolactin on electrolyte balance, this change likely reflects the shift in water movement during heat stress. With regard to health, there is a greater incidence of mastitis during warm weather, and this is thought to be due to the impact of ambient temperature on pathogen growth in the environment. However, recent evidence suggests that some of the seasonal change in mastitis may result from a decrease in resistance of the immune system, and the endocrine system ( prolactin and cortisol) may be involved.

Light influences secretion of prolactin in cows at all physiological states in the production cycle, with longer days associated with increases in prolactin relative to short days (5). Temperature has similar impact on prolactin secretion; heat increases prolactin relative to cooler temperatures. Work with photoperiod manipulation has already established a relationship between lower prepartum concentrations of prolactin and higher health and performance in the next lactation. Cooling cows would be expected to have the same effect on PRL as reducing light exposure, thus late dry cows should be cooled whenever heat stress conditions are present. Cooling dry cows would also be expected to maintain DMI to a greater extent than non-cooled environments.

It is important to remember that cows will begin to suffer from heat stress at what might be considered relatively mild temperatures that is, greater than 75 degrees F. There are various approaches available for managing heat stress in cows. These include provision of shade or other shelter that allow animals to avoid direct sun exposure. It is important to point out that overstocked facilities can exacerbate heat stress because of limitations on air movement. Because total DMI decreases under heat stress, cows will often self impose a reduction in total caloric intake, though this may be of more impact in lactating cows vs. dry cows. One approach to manage this is to increase the density of a ration, though this in itself can lead to a depression of intake and must be managed carefully. By far the most common and effective method of managing heat stress is to cool cows that experience high ambient temperatures. This is done by convection (fans) and evaporation (soaking cows and then exposing them to a fan).

Studies at Kansas State University (11) support the concept that evaporative cooling is the most effective method to avoid heat stress. Lactating cows were exposed to ambient temperatures between 88 and 95 degrees F with 75-85% relative humidity, and subjected to various combinations of air movement by fans and soaking frequency over a 95 minute period. Body temperature was highest in the cows that had no cooling (no fans, no minutes soaking frequency) and clearly indicates that they experienced heat stress. In contrast the cows that were soaked every 5 minutes and had fans in place to aid in evaporation of that moisture from the skin had the lowest body temperatures over the experimental period. Fans alone helped to cool the cows, but soaking the cows was more effective than fans. There was an inverse relationship between soaking frequency and body temperature, with more frequent soaking decreasing body temperature. The combination of fans and soaking, across frequencies, caused the greatest reduction in body temperature. Milk yield and dry matter intake differences are also inversely related to body temperature, so cooler cows will produce more milk. These data support the concept that evaporative cooling is the most effective management approach to ameliorate heat stress in lactating cattle.

From a management perspective, it is useful to determine a priority for cooling cows (11). Based on the potential depression of intake and other physiological responses, it is recommended that late dry cows be cooled first, before even fresh cows. The logic is that late dry cows will experience a normal decline in intake around calving, so maintaining intake at this stage is critical to a smooth transition into lactation. The next group to cool should be early lactation cows because of the high rate of intake and milk yield; losses of yield at this stage are less likely to be recovered during that lactation. The final group of lactating cows to be cooled given limited resources would be the mid to late lactation cows, as they appear to be more resilient and are already at a lower milk yield at that stage. Finally, cooling early stage dry cows would be the final priority, as intake is rarely a problem in this group and they are not producing milk.

Because DMI is critical to prevent many of the metabolic and digestive tract problems associated with the transition period, every attempt should be made to improve intake from the onset of lactation. One approach that we and others (1 ,4) have used to increase intake is increasing the frequency of milk removal from the first day of lactation. Cows milked 4 or 6 times daily (4X or 6X) produce more milk and consistently increase rates of DMI relative to those milked a more typical 2 or 3X scheme. In addition there is some evidence that the higher frequency of milk removal decreases SCC and that the milk production and quality effects persist after cows return to 2 or 3X.

DRY PERIOD DURATION

A dry period length of 60 days is the traditional recommendation for dairy cows. However, because cows are still producing at high levels 60 days prior to calving many producers are shifting to dry periods of 30 to 45 days in an effort to extend the productive period. Therefore the 60 days dry recommendation is being reconsidered based on new information on the biology of the mammary gland and results of field experiments with shorter dry periods.

It is best to start with consideration of where the 60 day dry period recommendation evolved from. Most of the information was generated from DHI records, and examination of the optimum time dry required for maximal production in the next lactation. Those analyses showed that dry periods of less than 30 days and more than 70 days were associated with reductions in performance in the next lactation. However, there is likely a bias inherent to those evaluations, in that cows on either end of the spectrum (>70 or <40 days dry) had other factors that influenced their production in the subsequent lactation. There are few controlled studies that directly compare a 60 day dry period to an alternative. Bachman (2) observed no difference in subsequent lactational performance of cows dry for 30 vs. 60 days, though the additional 30 days producing salable milk in the 30 day dry cows would be expected to improve their profitability. A similar absence of negative impact of a shorter dry period has been observed in a number of recent studies (2 ,3,7). Of interest is the observation that by reducing the dry period length to around 30 days, it is possible to eliminate the “far-off” dry diet and dietary shifts are minimized, and DMI depression is reduced (7). Preliminary data from researchers at the University of Arizona suggest that elimination of the dry period entirely can be profitable if cows are supplemented with bST throughout lactation (from calving), and this is particularly apparent in mature cows. Overall, the recent evidence from controlled studies supports the concept that reduction or elimination of the dry period is not a biological limitation to milk yield in the subsequent lactation, and may have benefits to transition cows with regard to DMI and mastitis incidence.

REFERENCES

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