Reducing systemic inflammation during the dry period of dairy cattle

Immune system activation of dairy cows results in an increased glucose utilization by the immune system81, which reduces dry matter intake. This in turn results in a poor transition to lactation, resulting in health problems, poor lactational performance and poor reproduction of a dairy herd.

The mammary gland is known to cause immune system activation, particularly when clinical mastitis occurs after calving, but also during the dry period. Oxidative stress during the dry period of dairy cows can trigger liver damage. The effects of immune system activation during the dry period of dairy cattle can still be present at the start of the subsequent lactation83. The risk of udder infections is high both at the beginning and end of the dry period87 (Figure 1). Hormonal changes and the stress around calving can have a negative impact on the immune system of dairy cows88,89,90. It has been shown that the majority of clinical mastitis cases early in lactation are caused by infections during the dry period91.

Drying off dairy cattle correctly will resolve existing udder infections and prevent new infections and mastitis early in the subsequent lactation. It will also reduce the risk of immune system activation of dairy cows.

If milk production of dairy cows drops below 15 kg, reabsorption of milk after cessation of milking takes less than a week. This results in teat openings sealing earlier93 (Figure 2), and a reduction of the amount of milk leakage94,95,97 (Figure 3). For every 5-kg decrease in milk production at dry-off, the risk of udder infections of dairy cows is reduced by 77%92.

• With dairy cows that are known to have a good persistence of lactation, producers can choose a longer voluntary waiting period before insemination starts, aiming at a calving interval of 415 days20.
• If possible, dairy cattle should be fed a dry cow diet during the last 7-10 days of lactation. This is not always possible or will create extra work. To reduce the impact on labour, farmers can choose to select cows to be dried off every 3 weeks. This will increase the length of the dry period for some animals, but it reduces the amount of stress as a result of re-grouping. The pay-off for the extra work and the slightly longer dry period is a significant reduction of the risk for clinical mastitis during the next lactation.
• An alternative to nutritional strategies for reducing milk production prior to drying off is reducing the frequency of milking 98,99,100.

Properly functioning milking equipment and appropriate training of the milkers should ensure teat scores at drying off are 1 or 2 on a scale of 4. Next step is to ensure that teat seals and dry cow antibiotics are applied correctly.

Dry cow therapy with antibiotics aims to cure existing udder infections and reduce the risk of new ones. With selective dry cow therapy, this can be achieved while reducing the use of antimicrobials. Selective dry cow therapy of dairy cattle is recommended when:

• The bulk tank somatic cell count is below 250,000 cell/ml

• The farm uses teat sealing

• Contagious dairy mastitis pathogens are under control with a low incidence of mastitis caused by Staphylococcus aureus or Streptococcus agalactiae

  In case of selective dry cow therapy, all dairy cattle should be tested regularly and those with a somatic cell count of 200,000 cells/ml or greater should be dried off with antibiotics.

During the dry period, hygiene is crucial, because after dry -off and before calving, teat ends are open. Ensure an optimal climate in the barn, including cow comfort, sufficient space and clean bedding for each cow.

The level of hygiene can be assessed by scoring cow udders, thigh, legs and hooves as shown in Figure 4. Scores can range from 1 to 4, with score 1 being very clean, score 2 clean, score 3 dirty, and score 4 very dirty. Hygiene during the dry cow period is considered sufficient if less than 10% of udders have score 3 or 4, with less than 15% of thighs score 3 or 4 and less than 20% of legs and hooves score 3 or 4.

Body Condition Score of a dairy cow at dry-off should be between 3 and 3.5. Feed restriction during the last days of lactation will reduce milk production but cows should always get enough feed to maintain their body condition score. Every dry cow should therefore have a place at the feed bunk, and ideally at least 85 cm of space rather than the 75 cm recommended for lactating cows. Severe feed restriction is undesirable from an animal welfare point of view but will also result in suppression of the immune system at a moment when the risk of udder infections is significantly increased.

Maximum comfort and space may also reduce the risk of udder oedema. High levels of Na+ and K+ in the dry cow ration can cause retention of fluid, which will increase the risk of udder oedema, although this can be partially mitigated by exercise. An increased intake of these ions will also increase the risk of hypocalcaemia. Pasture based forages can be particularly high in Na+ and K+.

To reduce the impact of systemic inflammation, feed supplements that reduce immune system activation should be considered101.