Quantitative estimation of the impact of caprine arthritis encephalitis virus infection on milk production by dairy goats
Introduction
Caprine arthritis encephalitis virus (CAEV) and maedi–visna virus (MVV) are small ruminant lentiviruses (SRLVs) with a tropism for the monocyte–macrophage cell lineage of sheep and goats. Infection stimulates a chronic, intense, inflammatory response affecting the brain, lungs, joints and mammary gland which is ineffective in eliminating the virus (Narayan and Cork, 1985). These lentiviruses replicate slowly and animals may be latently infected for many years before developing clinical signs. Infection may occur after birth with the ingestion of virus-contaminated colostrum and milk, and throughout life by exposure to the lung secretions of infected animals (Blacklaws et al., 2004). Most infected animals develop specific circulating antibodies shortly following infection, which are detectable using recombinant ELISAs (de Andrés et al., 2005).
Evaluating production losses due to SRLV infections is complex as this is influenced by virus strain, host and management factors that may differ widely between studies (Peterhans et al., 2004). The negative impact of these infections is greatest in immunologically naïve and intensively raised stock (Blacklaws et al., 2004, Benavides et al., 2006, Leginagoikoa et al., 2006a, Leginagoikoa et al., 2006b). Quantitative data relating to the financial impact of SRLV infection are limited. Peterhans et al. (2004) estimated milk production losses to be approximately 10%.
Seropositivity to CAEV is associated with reduced lactation length, milk fat and protein yield, as well with an increased incidence of other diseases and reduced birth-weight (Smith and Cutlip, 1988; Greenwood et al., 1995). In contrast, Leitner et al. (2010) reported similar milk yields in CAEV seropositive and seronegative does in their second or further lactations and found that milk yield was greater in seronegative, first lactation animals. Other studies examining primiparous goats found no relationship between CAEV seropositivity and milk production (Nord and Adnøy, 1997, Turin et al., 2005). Such conflicting results highlight the need to further clarify the impact of CAEV infection in dairy goats (Peterhans et al., 2004).
The Murciano-Granadina (MG) goat breed originates from Spain and has been selected and used in milk production in many countries (Gonzalo et al., 2002). Given that CAEV infection occurs in this breed (Contreras et al., 1998), we established a study to assess its impact on milk production in selected MG herds.
Section snippets
Herd selection
This retrospective study used total lactation and test-day milk production data from one lactation of 4543/5073 (90%) MG does from all 22 herds belonging to the Asociación de Ganaderos de Caprino de Raza Murciano-Granadina de la Comunidad Valenciana. The goats had given birth between September 2005 and January 2008, and 530 animals were excluded that were either seropositive >6 months after, or seronegative ⩽6 months before, kidding. This was to minimise the misclassification of animals by
Animal and herd seroprevalence
The percentage of seropositive, seronegative and inconclusive ELISA results were 17.8% (807/4543), 82.0% (3726/4543) and 0.2% (10/4543), respectively. Excluding inconclusive results, the seroprevalence was 18% (807/4533): 0% in five herds (0/620 animals); 1–2% in six herds (12/997 animals); 7–9% in two herds (76/898 animals); 19–35% in six herds (436/1541 animals), and 52% (68/131 animals), 60% (200/331 animals), and 100% (15/15 animals) in three herds (P < 0.05), respectively. In herds with a
Discussion
The findings of this study indicate that lactation duration, milk yield and milk fat, dry extract and lactose content are significantly reduced in goats seropositive to CAEV compared to seronegative animals and that this reduction in yield increases with lactation number. It is likely that many goats first become infected early in life and are subsequently repeatedly exposed to the virus. Given the typically slow spread of CAEV and the affinity of this virus for the mammary gland (
Conclusions
The findings of this study provide strong evidence that CAEV-infection can be a major cause of reduction in the milk yield of dairy goats and justify its control as part of herd health schemes. Control measures should include the culling of less productive, older, seropositive animals.
Conflict of interest statement
None of the authors of this paper has a financial or personal relationship with other people or organisations that could inappropriately influence or bias the content of the paper.
Acknowledgements
This research was carried out with the financial support of the Conselleria de Agricultura, Pesca y Alimentación of the Autonomous Government of Valencia (Grant 2007TAHVAL00014). We are grateful to the technicians of the Unidad de Análisis de Sanidad Animal for taking and analysing the milk samples, and to Dr. Ramón Juste for his critical appraisal of the manuscript.
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