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Hypogammaglobulinaemia and other causes of death in neonatal lambs

Abstract

This focus article has been prepared by Amanda Carson, veterinary lead of the APHA’s Small Ruminant Expert Group

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Analysis of the Veterinary Investigation Diagnosis and Analysis (VIDA) data collected from the APHA, SRUC Veterinary Services and APHA partner postmortem providers, for the most common causes of neonatal death in lambs (one to seven days of age) for the years 2014 to 2018 and excluding causes of abortion/fetopathy, is shown in Fig A.

Fig A: VIDA diagnoses for neonatal lambs 2014 to 2018 (2018 data are incomplete)

Hypogammaglobulinaemia is the second most common VIDA diagnosis, and is a predisposing factor for many of the infectious causes of neonatal death, including colisepticaemia and watery mouth. The VIDA criteria for diagnosis of hypogammaglobulinaemia are based on blood zinc sulphate turbidity (ZST) values (<15 units relative failure; <4 absolute failure).

Watery mouth is an endotoxaemia caused by multiplication of Escherichia coli within the gastrointestinal tract with the release of endotoxins from the cell walls of dead bacteria. There is often no evidence of diarrhoea and frequently it is secondary to hypogammaglobulinaemia.

The VIDA diagnostic criteria for watery mouth require supportive postmortem evidence, which may include dehydration; excessive salivation; distended abomasum and small intestine without inflammation; and retained meconium. Watery mouth usually affects lambs within 72 hours of birth.

Colisepticaemia is defined as a systemic E coli infection in which lambs less than seven days old have a terminal bacteraemia, again often predisposed to by hypogammaglobulinaemia. Confirmation is by positive pure culture of E coli from blood or tissues.

The incidents of colisepticaemia in sheep as a percentage of diagnosable submissions in the VIDA database are shown in Fig B.

Fig B: Incidents of colisepticaemia as a percentage of diagnosable submissions in sheep, 2014 – 2018 (VIDA; 2018 data incomplete)

The value of a full postmortem examination is clearly demonstrated in the following case report.

A lowland farm of 1000 ewes experienced a disease outbreak in a group of 475 two- to three-day-old neonatal lambs. About 75 per cent of newborn lambs were affected and described as being born alive and well but then developing signs of bloat and salivation, with many deaths. All the lambs had received spectinomycin oral solution and oxytetracycline navel spray as soon as possible after birth. The affected lambs were treated with a trimethoprim/sulfadiazine injection.

Three dead lambs were submitted for postmortem examination, which revealed dry subcutaneous tissues (indicating dehydration) in all three, with evidence of enteritis in two lambs (one of which also had a secondary intussusception and torsion) and severe acute pneumonia in the third. A blood sample obtained from this lamb revealed a gamma globulin level of 18.9 ZST units (reference interval >20).

A heavy pure growth of E coli was isolated from the intestinal contents and/or the livers of the lambs. Antimicrobial sensitivity testing showed resistance to spectinomycin, trimethoprim/sulfamethoxazole, ampicillin and tetracycline.

This case highlights the importance of having an accurate diagnosis, which can inform appropriate management practices, including attention to colostrum ingestion, and demonstrates that over-reliance on prophylactic antimicrobials could increase selection for resistance in bacteria.

Reducing use of antimicrobials

The Responsible Use of Medicines in Agriculture Alliance (RUMA) aims to produce a coordinated and integrated approach to best practice in animal medicines use with a particular focus on the responsible use of antimicrobials in livestock production.

A report summarising the progress against antibiotic use targets identified by the UK livestock industry’s Targets Task Force in October 2017 has been published at www.ruma.org.uk/wp-content/uploads/2018/11/RUMA-TTF-1-year-on-Full-Report-FINAL.pdf. One of the targets for the sheep industry was the reduction of the use of oral antibiotics in neonatal lambs, with the aim of decreasing sales by 10 per cent each year over the next five years.

In 2017 RUMA coordinated a cross-sector ‘Colostrum Is Gold’ initiative highlighting how the ‘liquid gold’ properties of colostrum can play a key role in reducing the need for antibiotics in farm animals and improving their lifetime performance. It promoted best practice, mainly based around achieving the three Qs – ‘quality, quantity and quickness’ – of colostrum delivery, and used social media to help deliver the messages through the website www.colostrumisgold.org.uk and the #ColostrumIsGold tag.

Contacting the APHA

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