Abstract
Somatic cell count (SCC) in monitoring udder health has been described in numerous studies as a useful method for the diagnosis of intramammary infection (IMI), and it is considered in standards of quality and hygiene of cow’s milk in many countries. However, several authors have questioned the validity of SCC as a reliable IMI diagnosis tool in dairy goats. This review attempts to reflect the importance of different infectious and non-infectious factors that can modify SCC values in goat milk, and must, therefore, be taken into account when using the SCC as a tool in the improvement of udder health and the quality of milk in this species. In dairy goats, some investigations have shown that mammary bacterial infections are a major cause of increased SCC and loss of production. In goats however, the relationship between bacterial infections and SCC values is not as simple as in dairy cattle, since non-infectious factors also have a big impact on SCC. Intrinsic factors are those that depend directly on the animal: time and number of lactation (higher SCC late in lactation and in aged goats), prolificity (higher SCC in multiple births), milking time (higher SCC in evening compared to morning milking) and number of milkings per day, among others. Extrinsic factors include: milking routine (lower SCC in machine than in manual milking), seasonality and food. In addition, milk secretion in goats is mostly apocrine and therefore characterized by the presence of epithelial debris or cytoplasmic particles, which makes the use of DNA specific counters mandatory. All this information is of interest in order to correctly interpret the SCC in goat milk and to establish differential SCC standards.
Highlights
Mastitis is an inflammation of the mammary gland and is the most serious and costly disease in dairy goats, representing the most frequent cause of culling for sanitary reasons (Bergonier et al, 2003; Leitner et al, 2008; Marogna et al, 2010)
Adequate sanitary control of herds is the best guarantee to prevent the occurrence of pathogens and to ensure the imperative requirement of food safety of dairy products from small ruminants
Different testing equipment and procedures are of variable reliability and applicability to goat milk, unless appropriate correction factors and calibration are used for this species
Summary
Mastitis is an inflammation of the mammary gland and is the most serious and costly disease in dairy goats, representing the most frequent cause of culling for sanitary reasons (Bergonier et al, 2003; Leitner et al, 2008; Marogna et al, 2010). When mycoplasmas are isolated from subclinical mastitis the SCC cause a moderate elevation, since the value obtained from glands infected by these pathogens is about double that found in uninfected glands (Martinez et al, 1999; Sánchez et al, 1999) In this case, on farms with no clinical symptoms of mycoplasma, the SCC in bulk milk fails to differ depending on whether or not this organism is isolated (Corrales et al, 2004). Fedele et al (1996) studied the effect of different types of rations on the SCC, noting that when the goat diets are only based on grazing, the SCC values are slightly lower than when these are supplemented with a concentrated energy (barley); whereas higher counts are obtained when supplemented with a protein concentrate. Several authors (i.e. Poutrel et al, 1997; Sánchez et al, 2007) conclude that systematic antibiotic treatment of goats at dryingoff is an efficient method for the reduction of subclinical mastitis. Poutrel et al (1997) recommend systematic treatment when SCC in bulk milk is high (> 1,000 · 103 cells mL–1), and when CNS are involved in IMI
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