Dry cow environment management and mastitis control in dairy herds

In the last 20 years, studies in UK dairy herds have shown the importance of intramammary infections acquired during the dry period and the subsequent impact of these infections on mastitis control in the next lactation (Bradley and Green, 2000, 2001). The veterinary surgeon asked to review clinical mastitis control must have knowledge of the current pattern of new (first) cases to allow preventive measures to be put in place and to avoid the need to treat in future. Research has shown that clinical mastitis events reported in the first 30 days after calving are likely to be caused by infection acquired during the dry period (Bradley and Green, 2006; Green et al, 2002, 2007b). In addition, individual cow somatic cell counts >200 000 cells/ml at the first milk recording post-calving are also likely to reflect dry period infection rather than a true ‘failure’ to cure pre-existing infection (Bradley and Green, 2004).

Research under-pinning the Agriculture and Horticulture Development Board Dairy Mastitis Control Plan has shown the impact of interventions targeted at improving dry cow environment management and husbandry, for example bedding dry cow cubicles daily, aseptic infusion of dry cow therapy and ensuring dry cow groups at pasture are moved to different grazing and lying areas at least every 2 weeks (Green et al, 2007a). Further work done using the DairyCo Mastitis Control Plan dataset between 2009 and 2012 showed several of these specific interventions during the dry period were cost-beneficial in most situations, including selective use of antibiotic dry cow therapy, the use of individual calving pens and items relating to the management of bedding in loose yards (Down et al, 2016).

For veterinary surgeons working with dairy clients, knowing when to focus on dry cow environmental management can be difficult, as this requires an element of data analysis and understanding of the mastitis pattern on farm. This is crucial in order that other areas that may be classically reviewed, such as parlour hygiene and lactating cow cubicle bed management, are not incorrectly prioritised in those herds that would instead benefit from a focus on the dry period.

A new national scheme (QuarterPRO) has been launched in the UK to provide an accessible route to mastitis control on farm. This incorporates rapid analysis of data with provision of research-led resource material that is freely available (Green et al, 2018). The first step in the QuarterPRO process involves the use of a herd mastitis pattern analysis tool (https://ahdb.org.uk/mastitis-pattern-analysis-tool) that highlights the predominant pattern of mastitis on farm, i.e. one of contagious mastitis infection, environmental lactating period origin infection or one of environmental dry period origin infection. This pattern tool has been validated and demonstrated to have agreement in 90% of herds looked at (Hyde et al, 2018). Recently published research using machine learning has taken this tool and further refined the methodology to achieve an accuracy of 78% in the diagnosis of environmental dry period origin infection patterns compared with environmental lactating period origin infection patterns, and a 98% accuracy in the diagnosis of contagious mastitis infection patterns compared with environmental mastitis infection patterns (Hyde et al, 2020). Having highlighted a dry period origin pattern for example, the veterinary surgeon is then directed to those resources that are linked to the prevention of infection during the dry period (https://ahdb.org.uk/knowledge-library/dry-cow-management-a-practical-guide-to-effective-mastitis-control). This article discusses some of these interventions and considers them under the headings of spring calving, autumn calving and all year round calving herds.

Managing the dry cow environment in spring calving herds

For many veterinary surgeons and advisors, a herd health approach can be difficult for those clients that run spring calving systems, particularly as mastitis control is often perceived to be very good because of the combination of lower milk yields and cows being out at grass. There may also be an issue with a lack of milk recording and health data in spring calving herds, making in-depth assessment and monitoring a challenge. However, advising on dry period management is essential in these herds as poor performance in this area has knock-on effects for the whole of the subsequent lactation — there is no ‘quick fix’ for an increased bulk milk somatic cell count in May and June where the underlying issue can be traced to one-third of the herd calving down infected in February and March. There is also the argument that spring calving herds can always ‘dry themselves out of trouble’ in December, and take advantage of the increased chance of cure across the dry period — but this only works if the environment during the dry period is managed very well.

Therefore, for spring calving herds the importance of focussing on the dry period to optimise cure rate and reduce re-infection risk is essential, and even more so as these herds become so efficient with fertility management such that large numbers of cows are calving in the first 6 weeks of the season (Figure 1). Some spring calving herds are moving to PWAB contracts (‘producing without antibiotics’) and removing antibiotic dry cow therapy, relying on spontaneous cure of major pathogen infection during the dry period. While this may be achievable in low prevalence herds, this approach relies on excellent milk recording data to measure the apparent cure rate in the absence of antibiotic dry cow therapy and excellent management of the dry cow environment to virtually eliminate the risk of reinfection from the environment and allow the cure rate to be as high as possible. A gold standard milking routine is also important to minimize risk of cow-to-cow spread of infection, given that Gram-positive pathogens are likely to predominate in the absence of antibiotic dry cow therapy.

The solutions for dry cow environment management in spring calving herds will depend on the availability of cubicle and loose yards, particularly attempting to ‘ring-fence’ the latter for calving cows only. For those spring calving cows that out winter dry cows, the management of dry cows at pasture is considered under the autumn calving herd section. Veterinary surgeons will be actively involved in prescribing dry cow therapy, therefore it is worth following up the prescription with a visit towards the end of the calendar year to review administration of dry cow therapy as these herds begin drying-off before Christmas. This not only offers the chance to ensure aseptic administration of dry cow therapy (see https://youtu.be/gJHv177D1xc) but then challenges both veterinary surgeon and client to walk through where these freshly dried off cows will be housed and how they will be managed.

Cubicle housing is often available but may be poorly managed, with infrequent bedding and scraping routines, or may suffer from poor ventilation and/or a lack of loafing space. As more cows are dried off and cubicle housing becomes full, the calving yards are used, resulting in build-up of environmental infection as cows are moved into the yards with 2–3 weeks to go before the start of calving. Considering that a 6000-litre herd requires 7.5 m² of bedded lying area per dry cow at 1.25 m² per 1000 litres herd average (Green et al, 2007a), loose yards can and will be heavily over-stocked. Spring calving herds that successfully control infection during the dry period are often those that maintain excellent cubicle housing conditions, with daily bedding or the use of deep sand and good ventilation (Figure 2), and manage the numbers of cows in a loose yard by providing as much space as possible off the beds.

An example of spring calving herd performance is shown in Box 1.

Box 1.Herd E, Leicestershire

• 500 cows, calving February and March, herd average 6500 litres
• On farm database (UNIFORM Agri)
• Milk recording 4–6 times per year (Quality Milk Management Services Ltd.), targeted at the end of the year and at the beginning of the calving season
• All cows dried off with internal teat sealant, cows with one or more cell counts >200 000 cells/ml in September, October or November are prescribed antibiotic dry cow therapy
• Early dry period cows managed in kennel-style cubicles bedded with deep sand; new clean sand added twice weekly
• Calving cows managed in a loose yard bedded with straw at a stocking rate of 6 m² per cow; new clean straw added daily, yard completely cleaned out every 2 weeks; additional loafing space made available using adjacent empty silage pit
• Cell count average in March and April 2020 was 87 000 cells/ml
• For 156 cows and heifers milk recorded on 25 March 2020 that were within 30 days of calving, 12 of these were >200 000 cells/ml (7.7%, target <10%)
• Dry period cure rate 18 from 22 eligible cows (82%, target >85%)
• Dry period new infection rate (cows only) 4 from 99 eligible cows (4%, target <10%)
• Dry period new infection rate (heifers only) 4 from 35 eligible heifers (11%, target 10%)
• Clinical mastitis rate averages 14 cases per 100 cows/year, with 0.15 cows affected with clinical mastitis for every 12 cows in the first 30 days of lactation — well below the target of <1 in 12.

Managing the dry cow environment in autumn calving herds

Herds with an autumn calving pattern have a number of challenges related to the dry cow environment as the veterinary surgeon needs to consider the risk of new infections at pasture as well as from a housed environment. Many autumn calving herds manage early dry period cows at pasture and still ‘set stock’ dry cows in paddocks through the summer, despite evidence that shows moving groups of dry cows every 2 weeks will reduce the risk of new infections (Green et al, 2007a). A review of the drying-off process conducted with the farm team at the end of the season should ask questions around where freshly dried off cows will be managed, and stocking rate at pasture discussed in terms of group size, paddock size and expected number of weeks against a target of less than 100 cows per acre-day (Green et al, 2007b). For example, a group of 60 early dry period cows managed in an eight-acre paddock for 21 days exceeds this target as the stocking rate is 60/8*21 = 157 cow acre-days. These considerations become particularly important close to calving, and especially if calving outside in a common ‘calving paddock’ where build-up of environmental infection can be very rapid. Interventions such as dividing paddocks up using electric fencing, moving mobs of dry cows and alternating calving areas can be extremely rewarding but are labour intensive. This is where conversations around the cost-benefit of saving two or three new cases often helps focus efforts in these areas.

Many autumn calving herds may manage early dry period cows at pasture but prefer to house cows which are close to calving in yards before calving, and manage calving cows inside. Again, careful consideration of space allowances for loose yards, particularly for high yielding autumn calving herds, is important (Figure 3). This is hard to do considering these herds may be achieving 9000 litres or more, meaning at least 10.5 or 11 m² of bedded area per cow, and therefore some lateral thinking is required to find space for dry cows and manage the flow of cows into the loose yards at calving. It may be possible to use existing lactating cow cubicle housing for dry cows, although it must be pointed out that bedding and scraping routines need to be as good as those for lactating cows given that the risk of new infection is so high in transition.

An example of autumn calving herd performance is shown in Box 2.

Box 2.Herd W, Nottinghamshire

• 250 cows, calving July to January, herd average 9000 litres
• On farm database (UNIFORM Agri)
• Milk recording monthly (National Milk Records)
• All cows dried off with internal teat sealant, cows with one or more cell counts >200 000 cells/ml in the last three milk recordings are prescribed antibiotic dry cow therapy
• Early dry period cows managed at pasture and moved every 2 weeks
• Late dry period cows moved into empty lactating cow cubicle accommodation, bedded daily with sawdust and moved across to calving yard within 24–48 hours of expected calving date
• Calving cows managed in a loose yard bedded with straw at a stocking rate of 12 m² per cow to a maximum of 25 cows allowed on the yard at any one time
• New clean straw added daily, yard completely cleaned out every 2 weeks
• Additional loafing space made available using outside yard
• Cell count average for 12 months to May 2020 was 134 000 cells/ml
• Dry period new infection rate (cows and heifers) averages 7% to May 2020 (target <10%)
• Clinical mastitis rate averages 16 cases per 100 cows/year, with 0.35 cows affected for every 12 cows at risk in the first 30 days of lactation (target less than 1 in 12 cows affected).

Managing the dry cow environment in all year round calving herds

Herds with all year round calving patterns are likely to have combinations of all the issues that spring and autumn calving herds face, having periods where dry cow accommodation may be overstocked, periods where dry cow stocking at grass is compromised, issues with having to house heifers alongside dry cows during the winter and so on. Careful monitoring of both cell count new infections across the dry period and the rate of new clinical cases in fresh calvers is required to monitor the impact of environment management, whether dry cows are managed in cubicles bedded on deep sand, on loose yards (Figure 4) or at pasture.

Particularly important is to remove the distorting effect of heifers, as these may disguise an underlying issue with dry cow environment management and/or dry cow therapy infusion technique, especially if heifers are managed away from the main unit. Again, the impact of additional space and discussions around investment are important for dry cows as lactating cows are often prioritised and dry cow housing is left ‘running to catch up’ in the oldest buildings or with inadequate space given increases in herd production. Herd F in the example in Box 3 is an interesting one to consider and one where pressure on herd cell count was clearly driven by dry period environmental infection patterns when data were examined as part of routine monitoring. This was costing points under the Tesco Sustainable Dairy Group QVIS scoring system, and discussions were had around extending dry cow accommodation to cope with variations in numbers and the influx of heifers during winter. Since the yard was extended at the end of 2019 the dry period new infection rate (i.e. proportion of cows dried off <200 000 cells/ml that are reported greater than or at 200 000 cells/ml at the first milk recording postcalving) has dropped sharply from more than 35% to less than 10% (Figure 5), resulting in improved control of herd average cell count.

Box 3.Herd F, Somerset

• 240 cows, herd average 9300 litres milk sold
• On farm database (SUM-IT DairyMate)
• Aligned contract (Tesco Sustainable Dairy Group)
• Milk recording monthly (Quality Milk Management Services Ltd.)
• All cows dried off with internal teat sealant, cows with one or more cell counts >200 000 cells/ml in last three recordings are prescribed antibiotic dry cow therapy
• Dry cows managed as one group and fed single ration including 5 kg chopped straw
• Dry cows housed in large loose yard bedded with wood chip, bedded daily and cleaned out every 3 weeks
• Cell count average for 12 months to December 2019 was 219 000 cells/ml, cell count average for 3 months to April 2020 is 171 000 cells/ml
• Dry period new infection rate (cows and heifers) averaged 23% for 12 months to December 2019, dry period new infection rate averages 8.8% for 3 months to April 2020 (target <10%)
• Clinical mastitis rate averages 24 cases per 100 cows/year, with 0.92 cows affected for every 12 cows at risk in the first 30 days of lactation (target less than 1 in 12 cows affected).

Conclusions

Dry period environment management is important to consider and offer advice on for all dairy herds, but particularly those where analysis of cell count and mastitis data highlight the need for improvement. Interventions are often considered obvious, and yet have either not been discussed or have been discussed but with little or no follow up, and are discarded in favour of focus in other areas. Often, solutions to constraints to dry period performance are found by considering more space allowance, particularly bedded areas on loose yard systems, but this may have to be achieved through over-stocking in late lactation, more frequent bedding up/cleaning out and/or discovering additional outside loafing areas until serious discussion can be had around medium-term investment in additional housing or alterations to existing sheds. The importance of monitoring the key metrics discussed in this article such as dry period cure rate and dry period new infection rate as measured by cell count cannot be over-emphasised if we are to understand the dynamics of infection in herds and expose those herds that require advice on dry cow environment management.

KEY POINTS

• Assessing the impact of dry period environmental infections is important to monitor in dairy herds at least every 3 months in all year round calving herds and before drying-off in spring and autumn calving herds to allow an opportunity to modify dry cow management.
• For block calving herds recording less often than monthly, encourage recordings towards the end of the season and in very early lactation to allow dry period performance to be monitored.
• Dry period new infection rate as measured by cell count both in cows and in heifers should be evaluated for those herds with individual cow cell count data — no more than 10% of cows or heifers should be >200 000 cells/ml at the first recording in lactation.
• Ensure that clinical mastitis data are captured and the rate of first cases in cows less than 30 days calved does not exceed 1 in 12 cows affected.
• For many herds, a focus on reducing stocking density, both for housed dry cows and for dry cows at pasture is important to reduce new infections.