Reducing Mastitis in Commercial Sheep Flocks - Final Report

Farming Connect funded project: January to December 2024

Introduction

Mastitis is common on many sheep farms and leads to poor milk yield, poor growth rate in lambs, higher culling rates and higher ewe and lamb mortality.  Page et al (2021) describes the clinical and sub-clinical condition and the impact on flock performance. The study of Grant et al (2016) showed 2.1 to 3% of ewes in 10 flocks had acute mastitis and this ranged from 0 to 37% of ewes. Clinical mastitis is an important reason for culling ewes in the UK.  In the study of Smith et al (2015) 37 species of bacteria were isolated from 14 udders with Staphylococcus aureus being the most dominant species. Vasileoiu et al (2019) also described the role of staphylococci bacteria in sheep mastitis. Cooper et al (2016) looked at the risk factors for mastitis through a survey of 329 flocks concluding that udder conformation, litter size, nutrition and the lambing environment were key indicators.  

The underlying causes of mastitis are not well understood but housing conditions and hygiene at lambing no doubt play a large part.  

Since pre-lambing nutrition plays a key role in establishing a successful lactation and trace elements like selenium have a role in the development of immunity, then there could well be a direct relationship between nutrition and susceptibility to infection. In fact, Grant et al (2016) concluded that nutrition is an important cause of mastitis in suckling ewes. They found that ewes under fed protein during pregnancy have approximately four times greater odds of suffering from acute mastitis. Hungry lambs at 3 weeks of age are very capable of inflicting significant physical damage to the udder which could be one contributory factor when milk yield is inadequate to sustain the lambs at optimal growth rates. Providing the ewe with adequate amounts of energy (and hence having her in good body condition) and protein could be key to success and from experience in the field it would appear that many ewes are not fed optimal diets before lambing. Young ewes and in particular yearlings are likely to have higher rates of mastitis – given they are still growing and feeding one or more lambs.  Specific management strategies may need to be developed for young ewes.

The main aim of the project was to gain a better understanding of the factors that affect the incidence of mastitis in commercial flocks and to reduce the rate of culling. The overall aim was to improve flock productivity, sheep health and welfare and reduce carbon emissions per kg of lamb produced.

The Project

The project was initiated after discussions within the Montgomeryshire Sheep Discussion Group with members suggesting mastitis as an area of concern.  Eleven members of the group signed up to take part and a wider invitation was sent out across other discussion groups and seven additional farmers committed to the project.  Farms were spread across Wales, eleven in the Montgomeryshire area (SY10, 15, 16, 20,21,22 post codes), and others on Anglesey (LL60, LL65), in Abergavenny (NP7), Denbigh (LL16), Aberystwyth (SY23) and Holywell (CH8).  
Group members were asked to recall details of all mastitis cases in 2023 to set a baseline for more detailed monitoring for the 2024 production year. Questions were also answered about, general flock management, feeding, hygiene at lambing, and treatments for mastitis.

All the farmers took part in a zoom call in January 2024 to discuss the project and for the project manager to provide details of the recording sheets and the sampling procedure.  Dr Liz Nabb from APHA described how to take hygienic samples from infected ewes.  All farmers were given 15 Universal 30ml sample tubes, 15 sets of disposable gloves, paper (and electronic copies) of recording sheets and plastic envelopes for sending samples to APHA, either at a group meeting or sent by post.

In 2024 participants recorded ewe mastitis cases individually by breed, age, body condition score, litter size, rearing rate, diet and date of mastitis case and any treatment given (recording sheet at Appendix 1).  They were also asked to take milk samples from a proportion of infected udders for bacterial culture and antibiotic sensitivity. Up to 10 samples were allowed per farm. Samples were collected as hygienically as possible following APHA guidelines (see Appendix 2), then frozen until sufficient samples had been collected to justify posting to APHA.  Each farmer then discussed sample submission with the project manager so that a dispatch note and a postage paid label could be generated through the APHA Animal Disease Testing Service (ADTS) for posting samples to APHA in Penrith. Farmers were advised to post samples early in the week to avoid samples sitting in the postal system over a weekend.  In addition, farmers recorded total mastitis cases and ewes found with lumpy udders post weaning and pre-tupping.  

Results of testing were sent to all farmers by email and the findings discussed on the telephone.

APHA

Fortuitously this project coincided with a similar project initiated by the APHA Small Ruminant Expert Group on ‘Suckler ewe mastitis’ for samples taken between December 2023 and August 2024.  This service offered free testing of three mastitis milk samples per lambing cohort from ewes or ewe lambs per farm. This project’s aims were:

1.    Improve surveillance of the bacteria causing mastitis in suckler ewes
2.    Provide antimicrobial resistance data
3.    Identify any Mycoplasma organisms that may play a role in suckler ewe mastitis
4.    Provide important surveillance for Contagious Agalactiae (CA)

The 70 samples from this FC project contributed significantly to the total number submitted to APHA (120).  

Results

2023 results
All 18 farmers submitted the initial spreadsheet, either electronically or on paper, giving details on flock management and estimates of the number of mastitis cases.   

Table 1 – 2023 lambing 

Figure 1: When were mastitis cases happening in 2023 

Mastitis cases occurred at lambing and in all weeks up to pre-tupping with the peak of cases at 0 to 3 weeks.  Lambing hygiene routines were not consistent across farms, but the majority of those lambing inside used lime and bedded up group pens regularly with straw, cleaned and disinfected individual pens between ewes, often used lime before bedding, used AI gloves to assist difficult births, checked all teats (9/18), checked some teats (5/18) or did not check any teats at lambing (those lambing outside). Only 2/18 farmers used gloves to strip milk when checking teats.

2024 results

Twelve out of the eighteen farmers submitted milk samples for analysis and 15 provided final numbers of mastitis (clinical and sub-clinical) cases for 2024.  A total of 70 milk samples were collected and details of 117 clinical mastitis cases were recorded (approximately 10 per farm but with a range of 2 to 20).  Not all details were recorded for every case reported, for example not all body condition scores were recorded. 

Table 2: 2024 mastitis cases

For these 15 farms mastitis appeared to be worse in 2024 than in 2023, increasing from 3.6% to 5.9% of ewes mated.  One farm had a particularly difficult spring with 30 ewes lambing down with full udders but with no milk letdown at all.  

The management data for 2024 revealed the following:

• 86% of the ewes recorded lambed inside

• 62% were on upland farms and 26% on lowland, 12% on a mix of lowland and upland

• On average ewes were housed for 6.6 weeks (0 to 10 weeks)

• All housed ewes were bedded on straw and straw was used in all small pens

• 80% of ewes recorded were fed silage and concentrates (includes TMR) and 20% of ewes were fed hay and concentrates pre-lambing (some ewes at grass)

• 78% of the ewes with mastitis had twins

• 10% of the ewes with mastitis died and 90% survived but were culled 

• About 50% of lambs were creep fed

• 81% of udders were normal, 71% of teats were undamaged 

• 97% of udders had no sign of orf

Mastitis cases occurred from lambing right through to 16 weeks post lambing with sub-clinical cases picked up after weaning as lumps in the udder. See figure 2.  The majority of clinical cases occurred between lambing and 6 weeks post lambing (61%) with the remaining cases identified between 7 and 16 weeks. 

Clinical mastitis cases were identified in ewes of all ages from 1 to 8 years with the majority in the 2-to-5-year age span.  See figure 3. 

Weather conditions were recorded when each case of mastitis was identified with the majority of cases happening when it was cold and wet. See figure 4.

Body condition score was recorded for 60 ewes, ranging from score 1 to 4. 35% of ewes were less than BCS 3 and 65% were score 3 or above.  BCS did not seem to have an effect on prevalence of mastitis in this study. 

Sixteen breeds and crosses of ewe were recorded with clinical mastitis.  The most commonly reported breeds included Texel genetics (Aberfield, Abertex, Texel and Texel crosses).  This may simply be related to the sheer number of Texel rams used in the industry and the number of first cross Texel ewes retained as replacements on the project farms, but the breed society has invested in research to investigate breeding for resistance to mastitis (Connington et al (2008) and McLaren et al (2018).
 

Figure 2: Mastitis cases – weeks after lambing 2024

Figure 3: Mastitis cases by ewe age in 2024

Figure 4: Mastitis cases by weather conditions in 2024

Treatment of mastitis cases

Farmers used a range of antibiotics and anti-inflammatories to treat clinical cases. The types of antibiotics are shown in figure 5.

Figure 5: Antibiotics used to treat mastitis

●    70% of cases were treated with a macrolide (Draxin, Tullavis, Zactran, Tuloxxin)
●    27% of cases were treated with penicillin
●    83% of ewes were given an anti-inflammatory/pain killer (meloxicam or flunixin)
●    70% of cases were treated with antibiotics once and 30% were treated at least once more.  

Microbiology

Fourteen bacteria were isolated from the 53 samples.  The laboratory failed to culture any bacteria from 17 of the samples. Some samples had a mixed infection with two or more bacteria. The different bacteria are shown in figure 5.

Figure 6: Bacteria isolated from milk samples

The results were in agreement with previous studies with Staphylococcus aureus and Mannheimia haemolytica being the main causes of infection. Streptococcus dysgalactiae was also found in 4 samples, which for three of the samples coincided with a high number of joint ill cases in lambs.

The APHA laboratory also tested the bacteria isolated for antibiotic sensitivity.  The majority were sensitive to first line antibiotics (penicillin) with only 7% of Staph aureus samples resistant to tetracycline and tylosin and 25% of the Mannheimia haemolytica samples resistant to tetracycline.  All four isolates of Streptococcus dysgalactiae were resistant to tetracycline.

Limitations of this study

Although 18 farmers initially signed up to take part in the study only 15 supplied details of flock management and total cases for 2023 and 2024. The 2023 data was ‘recalled’ so may not have been accurate. Farmers were reminded regularly through a dedicated WhatsApp group and were telephoned or left messages to remind them to submit data and samples. Ultimately only 12 managed to take and submit samples with the others apologising for the lack of samples and stating that limited time, poor weather and difficulties sampling ewes out in the field were the main reasons. On average the 12 who managed to collect milk from infected ewes managed to submit 6 samples for testing – ranging from 1 to 13. Full details of each case were not always given with perhaps BCS, age or weeks after lambing not supplied. Although farmers were asked about the diet offered to the flock, detailed calculations were not carried out to compare what was offered compared to ewe requirements (AFRC, 1993).

Discussion

The results of this project are largely in agreement with other studies identifying the main causes of mastitis in meat producing ewes as the bacteria Staphylococcus aureus and Mannheimia haemolytica. The additional finding that these bacteria are largely sensitive to first line antibiotics is reassuring but some resistance is present in Staph aureus (tetracycline and tylosin), M. haemolytica (tetracycline) and Streptococcus dysgalactiae (tetracycline).  This has served to raise awareness of antibiotic resistance amongst farmers and to emphasise the judicious use of antibiotics in sheep farming.  
Those who provided data for clinical cases treated and sub-clinical cases identified as lumpy udders pre-tupping found 3% of the ewes mated that presented with mastitis were identified at lambing or in lactation and 2.7% were identified post weaning or pre-tupping. This emphasises the impact of sub-clinical and post-lactation infections on culling rate and the need for perhaps more regular checking of ewes post-weaning. Watkins et al (1991) reported a prevalence of sub-clinical mastitis of 5.5 to 7%. Weaning is a milestone in the sheep year when management can generally relax and other important work on forage conservation and general maintenance can take place. There is perhaps a need for additional checks to identify these ewes earlier and treat them appropriately. Sub-clinical cases could be detected by weighing lambs regularly with those lambs growing slowly, perhaps suckling ewes with infections that cannot be identified by visual inspection. However, this could only be achieved in flocks with detailed performance recording. The California Milk Test (CMT) is used as an indicator of somatic cell count (McLaren et al, 2018) and could also be employed to check the udders of poorer performing lambs to detect sub-clinical mastitis. 
It would be interesting to investigate the relationship between joint ill and mastitis caused by Strep dysgalactiae to perhaps gain a better understanding of the connection between the two infections.

Conclusions

The main findings of this project include:

• Staphylococcus aureus (43% of cases) and Mannheimia haemolytica (17% of cases) were found to be the main causes of clinical mastitis

• Staph. aureus and M. haemolytica showed some resistance to antibiotics, although most cases were sensitive to first line antibiotics

• Strep dysgalactiae, found in only four samples submitted that there was resistance to tetracycline in all cases. 

• Mastitis was more prevalent in 2024 than in 2023 and it is assumed that the main factor was the very wet and cold spring and the ongoing wet summer, with poor ground conditions almost throughout the year. 

• Most of the ewes with clinical mastitis were aged between 2 and 5 years and were scanned as twins and were rearing twins. 

• 83% of cases were treated with an anti-inflammatory as well as an antibiotic

• 70% of cases were treated with a macrolide antibiotic, 27% were treated with penicillin. 

• The results have highlighted the need to use antibiotics judiciously and to use anti-inflammatories to relieve pain and suffering.  

• Mastitis cases did not appear to be related to udder conformation with the majority of ewes judged to have normal shaped udders and undamaged teats. 

• It has not been possible to devise management strategies to help avoid mastitis from this study but the results are in agreement with findings of several other studies where hygiene in lambing sheds, ewe nutrition and BCS and weather are likely to have a major influence.  

• 10% of ewes with clinical mastitis died and 90% were culled, emphasising the significant cost of mastitis to the industry, both in higher replacement rate but also reduced lamb growth. 

• For farmers considering vaccination it is important to identify the bacterial cause of infection before embarking on a programme of vaccination since the predominant bacteria varies by farm.  

References

Connington, J. Cao, G., Stott, A. & Bunger, L. (2008). Breeding for resistance to mastitis in United Kingdom sheep, a review and economic appraisal. Vet Record 162 (12) 369-376. https:/doi.org/10.1136/vr.162.12.369.

Cooper, S., Huntley, S.J. and Green L.E. (2016) A cross-sectional study of 329 farms in England to identify risk factors to ovine clinical mastitis. Prev. Vet Med 2016;125; 89-98. https//doi.org/10.1016/j.prevvetmed. 2016.01.012. 

Grant C., Smith E.M, Green L.E. (2016). A longitudinal study of factors associated with acute and chronic mastitis and their impact on lamb growth rate in 10 suckler sheep flocks in Great Britain. Prev Vet Med. 122:27–36.

Page, P., Evans, M., Phythian, C., Vasileiou, N., and Crilly, J.P. (2021). Mastitis in meat sheep. Livestock, Volume 26, No.5.

Ridler, A.L., Rout-Brown, G., Flay, K.J.,Velathanthiri, N.  & Grinberg, A. (2021): Defects and bacterial pathogens in udders of non-dairy breed ewes from New Zealand, New Zealand Journal of Agricultural Research, DOI: 10.1080/00288233.2021.1905005 To link to this article: https://doi.org/10.1080/00288233.2021.190500

McLaren, A., Kaseja, K., Yates, J., Mucha, S., Lambe, N.R. and Conington, J.  (2018).  Animal (2018), 12:12, pp 2470–2479. New mastitis phenotypes suitable for genomic selection in meat sheep and their genetic relationships with udder conformation and lamb live weights. Accepted 8 February 2018; First published online 26 March 2018. https://doi.org/10.1017/S1751731118000393

Smith, E.M., Willis, Z.N.,  M Blakeley, M., Lovattt, F.  Purdy, K.J. & Green, L.E. (2015). Bacterial species and their associations with acute and chronic mastitis in suckler ewes. Journal of Dairy Science, 98 (2015), pp. 7025-7033

Vasileiou N.G.C., Chatzopoulos D.C., Sarrou S., Fragkou I.A., Katsafadou A.I., Mavrogianni V.S., Petinaki E. and Fthenakis G.C. (2019). Role of staphylococci in mastitis in sheep. Journal of Dairy Research 86, 254–266. https://doi.org/10.1017/S0022029919000591 Received: 16 December 2018 Revised: 1 July 2019 Accepted: 5 July 2019 First published online: 19 August 2019