Furthering our understanding of intramammary infections (mastitis) in meat ewes – the role of chronic infection and udder conformation

Project number:                    73104

Lead contractor:                   University of Warwick

Start & end date:                   01 July 2011 – 31 December 2014

 

The Problem:

Sheep producers report 0% – 5% of ewes with clinical mastitis per year. Affected ewes often die from mastitis or are culled because they lose an udder half. Some ewes continue in the flock (potentially still infected) for a subsequent lactation. Anecdotal reports from farmers indicate that typically 20 – 30% of ewes culled from the flock at weaning have chronic mastitis with palpable lumps in their udder.  From studies of dairy sheep we know that intramammary infections (clinical and subclinical mastitis) are the most common cause of involuntary culling of milk ewes.  This also causes decreased milk production, which in suckling ewes is associated with reduced growth rate in lambs and lighter lambs at weaning, even when the only indication is a raised somatic cell count.

 

Project Aims:

  • Investigate lumpy udders of cull ewes to develop a score for udder damage and establish the types of bacteria associated with chronic infection.
  • Understand the impact of nutrition on the occurrence of mastitis
  • Develop a scoring system to evaluate the physical appearance of the udder (texture (including detection of internal lumps), size, shape, teat size and suspension of udder).
  • Monitor ewes over time and score both the udder damage and conformation
  • Test the associations between udder damage and udder conformation.
  • Investigate the impact of retaining ewes with lumpy udders (udder damage) into the next lactation (i.e. is there an increased risk of clinical mastitis or reduced lamb growth rate?)
  • Investigate the costs and benefits of scoring udder shape and teat position and size as part of the selection criteria for replacement ewes.

 

Deliverables:

An understanding of the health and costs of retaining ewes with lumpy udders in a flock that can be used in a BRP campaign.  A clearly explained protocol for selection of ewes as replacements based on udder health and conformation, which can be used as part of a selection campaign.  An estimate of the cost / benefits of adopting selection for good udder and teat conformation as part of replacement programmes, plus the value of good nutritional planning, will be calculated.

 

Approach:

Abattoir samples were collected for pilot work to look at bacterial communities within the udder and the anatomy of lumps.

Ewes on up to 20 flocks (commercial and pedigree) will be monitored to see how their udder conformation and health changes with time.  Nutrition and production data will be collected.  In pedigree flocks, the heritability of udder traits can be calculated.

 

Results:

There have been no studies of the bacterial species associated with chronic mastitis (intramammary abscesses) in ewes. We examined 24 milk samples and 33 abscesses from 16 udders and isolated 35 bacterial species in total. These did not vary by disease state, though Staphylococcus aureus was the most common species, and closely-related strains of S. aureus were present across all clinical presentations. Our results suggest that the udders of ewes with chronic mastitis could be reservoirs of S. aureus.

Twenty-four percent of the acute mastitis cases in the population were attributable to ewes underfed protein in pregnancy, while 25% of the IMM in lactation were attributable to ewes underfed energy in lactation.

Six and four percent of acute mastitis cases in the population were attributable to ewes with teat position 1 and teat angle < 4 respectively. Teat position 1 was observed in 0.8% of Charollais ewes, 1.5% of Texel ewes, 0.8% of Crossbred ewes and 0.6% of Lleyn ewes in year 1 while teat angle < 4 was found in 0.4% of Charollais ewes, 1.2% of Texel ewes, 9.5% of Crossbred ewes and 3.3% of Lleyn ewes in year 1.

Eleven percent of IMM in lactation and 19% of the acute mastitis cases in the population in year 2 were attributable to ewes with an IMM in lactation the previous year; 22.67% of Charollais ewes, 11.52% of Texel ewes, 8.41% of Crossbred ewes and 4.90% of Lleyn ewes were detected with IMM in lactation in year 1.

There are significant benefits to reducing the risk of acute and chronic mastitis by feeding ewes appropriately in pregnancy and lactation. In addition, ewes with IMM contribute a large risk to future acute mastitis. A target should be to reduce the percentage of ewes with IMM in a flock. Where IMM is common then this might be best initiated by separating affected and unaffected ewes into two separate flocks, one for ewes with IMM and the other for ewes without, to reduce the infection to ewes without IMM and slowly reduce the prevalence of IMM over time.

There are minimal benefits to selecting for good udder conformation. This is because the udder conformation of the vast majority of ewes in our study was appropriate for ewes suckling lambs and for maintaining udder health, preventing teat lesions, udder lumps and mastitis. Poor udder conformation tended to be in older ewes, so this could help inform on decisions to cull older ewes. Given that the vast majority of ewes had good udder conformation we do not think genetic selection for the traits we measured would be cost effective and that the best advice is to cull or not select offspring from ewes with extreme udder and teat conformation as necessary.