The udder health/subclinical mastitis in cattle is one the major reasons for low yield and poor quality milk production and ranks first among the diseases that cause substantial loss to farmers of tropics and subtropics. This silent problem causes higher economic losses in the globe.
Radostits et al., (2000) defines mastitis as “inflammation of parenchyma of mammary glands which is characterized by physical, chemical and usually bacteriological changes in milk and pathological changes in glandular tissues”. Consumer preference for better quality milk and milk products has increased due to their enhanced knowledge for health concerns of mastitic milk. They, however, do not compromise with quality standards of the milk and milk products. Researchers continued to study methods to convince dairy entrepreneurs to adapt improved practices against SCM control
(Valeeva et al., 2007; Singh et al., 2020a; Singh et al., 2020b; Singh et al., 2020c; Singh et al., 2020d).
The authors of this article carried out present work in ICAR-NDRI, ERS and Kalyani (WB) during 2017 to 2020 through a project. The article’s aim is to highlight the important advancements in udder health maintenance to ameliorate SCM for higher quantity and quality milk production from dairy cattle.
Impact of SCM/ udder health
Subclinical mastitis has arisen as a global threat to dairy producers as it imparts negative effects (Fig 2) on different performances of animals in almost every country of tropical and subtropical climatic conditions. Developed countries also suffer high financial losses which ultimately leads to culling, poor milk production, compromised udder health status and reduced reproductive performances of farm animals
(Laxmi, 2016). Besides leading to heavy losses in milk production, the SCM animals may remain potent source of infection to other animals in the herd
(Swami et al., 2017; Singh et al., 2020e; Garai et al., 2021, Singh et al., 2021a) and causing poor udder health maintenance throughout lactation.
Causative agents responsible for SCM
Different investigations have shown that SCM cases ranged from 19 to 83% in cows
(Bhakat et al., 2016). Potential sources for sub-clinical mastitis in dairy animals have been presented in the Fig 1. For many years,
Streptococcus agalactiae and
Staphylococcus aureus were seen as the major causal micro-organisms for SCM in dairy animals. This information formed the basis for understanding mastitis in a better way. Different etiological factors associated with SCM cases in dairy cattle have been suggested (Fig 3) to be important in case of SCM
(Sharma and Maiti, 2012). Though numerous bacteria are identified as causative agents for IMI. SCM cases are reported to be more predominant by 15-20 times than clinical mastitis cases in tropics and subtropics. The streptococci were identified as most prevalent bacteria, staphylococci (most likely
Staph.
aureus) were responsible for more than one-fifth of such cases. The occurrence of large numbers of bacteria in milk was an obvious public health issue. In a report of a researcher
(Varshney and Naresh, 2004),
Streptococcus dysgalactiae was major organism observed from SCM cases in cows followed by
Staphylococcus aureus and others. Scientist
(Kumar et al., 2009) remarked that while more than twenty types of infections can lead to mastitis; at least 99% are of
Str.
agalactiae origin and others include streptococci, staphylococci and bacillary mastitis (including coliform, pseudomonas
etc.). The majority of cases were caused by only a few common bacterial pathogens, including different species of
Staphylococcus,
Streptococcus, Coliforms and
Actinomyces pyogenes (Makovec and Ruegg, 2003). During year 1994 to 2001,
Strep.
agalactiae and
Staph.
aureus isolated from different samples of milk given to Wisconsin Veterinary Diagnostic Laboratory showed a dramatic decline
(Makovec and Ruegg, 2003) and gram-negative pathogens were observed in overall results of milk samples from cows showing clinical symptoms
(Oliveira et al., 2013).
Diagnosis of SCM
Potential battery tests for diagnosis of SCM and management strategies for its melioration is presented in Fig 4. As per the recommendations of International Dairy Federation (IDF), microbiological status of separate udder quarters and somatic cell counts were found as common and reliable tests to detect alterations in milk constituents as a result of an inflammatory process
(Sudhan and Sharma, 2010). Researchers
(Kumari et al., 2018) executed different tests for diagnosis of SCM in tropical Indian conditions
viz. modified California mastitis test (MCMT), modified white side test (MWST), surf field mastitis test (SFMT), electrical conductivity (EC), pH test and laboratory test for milk quality
viz. methylene blue reduction test (MBRT). Although thresholds used for defining mastitis were highly variable (reaching 3,000,000 cells/ml), an early comparative study noted that most of milk samples from apparently healthy udder contained <100,000 cells/ml and identified approximately 200,000 to 250,000 cells/ml as a reasonable threshold for discriminating healthy and abnormal milk samples. For many years, the threshold of 500,000 cells/ml combined with isolation of >200 CFU/ml of pathogenic bacteria was commonly used to define subclinical mastitis
(Kuipers et al., 2016). The development of faster and more automated methods to somatic cells count (SCC) in milk was an area of intense research. With progress in methods for measuring SCC, different regulatory authorities started setting threshold limits for bulk tank SCC. The recent era of managing udder health using monthly SCC testing of individual cows was initiated and SCC values came into routine use as a mastitis management tool
(Reneau, 1986).
Dry cow SCM /udder health
Scientists
(Bhakat et al., 2019) stated that IMI in dry cow causing SCM is one of the major constraints for dairy operations at tropical regions. Researchers
(Neave et al., 2017) suggested for after dry period disinfection of teats prior to milking, wiping with separate towels, use of sanitized milking gloves and teat cups. They advocated use of antibiotic therapy at dry cow to further reduce infections. Scientists
(Bhakat et al., 2016) reported that significantly (P<0.01) higher SCC in IMI cows than in non-IMI Jersey crossbred dry cows. National Mastitis Council (NMC) recommended “5-Point Plan” for mastitis (subclinical and clinical) control program (Fig 5) which should be started from dry cow itself. Dairy cattle may be susceptible to IMI during dry period. Management of dry cow /therapy (DCT) has been proposed as an effective way to control mastitis. However, usage of antibiotics for dry cows has been reported to cause adverse effects on both human and animal health. Nevertheless, researchers
(Kumari et al., 2019a) reported that intra-mammary therapy of dry cow with suitable herbal preparations along with internal and external teat sealant may be another management practice to prevent post-calving mastitis cases. In addition to it, they remarked that herbal measures for fly control was effective (p<0.01) for lower SCM cases. Maintenance of proper body condition score (BCS) from drying off to lactation period, through proper energy provision in the diet by changing concentrate amount has been reported to control SCM cases
(Singh et al., 2020d; Singh et al., 2020g). Such farmer friendly management strategies can be considered as an alternative and novel approach for controlling mastitis and maintenance of udder health in dairy cows. Research finding on fly control measures in hot humid tropical region and dry period duration were effectively arrest the transmission of pathogens causing SCM and maintaining good udder health throughout lactation
(Bhakat et al., 2020a and
2021).
Lactating cow SCM / udder health
The first emphasis was on treatment of IMI caused by
Strep.
agalactiae and
Staph.
aureus. Though the use of antibiotics to treat mastitis was common, the limitations of therapy were well known. Researchers
(Trinidad et al., 1990) reviewed for different factors that contribute to therapeutic success of, cow, pathogen and treatment of animals infected with
Staph.
aureus again emphasized that only specific animals responds to therapy utilising antibiotics. As coliform caused mastitis was identified as an emerging problem, researchers began to evaluate unique challenges in treating these infections. Though it was identified that many cases were not severe, defining effective treatment of per-acute and acute cases was a high priority and almost no controlled studies were available to guide treatment decisions. Until 1990s, few trials were performed to validate recommendations for the treatment of coliform mastitis but initial experiments indicated that antimicrobial therapy did not improve outcomes of mastitis caused by
Escherichia coli (Barkema et al., 2006) and challenged prevailing concepts of how mastitis should be treated. The important role of host immune response in clearance of coliform infections (rather than antibiotic therapy) has been highlighted by researchers
(Burvenich et al., 2007). Furthermore, scientist
(Ruegg, 2017) indicated that with the increasing pressure to reduce antibiotic usage on dairy farms, additional research is needed to develop evidence-based line of alternate treatment with herbal applications which limit the use of antibiotics for maintaining good udder health throughout lactation of dry cow.
Control of SCM for better udder health maintenance
SCM control and udder health maintenance in both manual and automatic milking settings remain a questionable task. Role of competent attendant in managing udder health remains necessary today as it was in earlier decades
(Hovinen and Pyorala, 2011).
Scientific management practices of milking operation to curb SCM cases
Researchers
(Bharti et al., 2017) observed more SCM cases in hind quarter than fore quarter of udder parts and remarked from their study that udder structure and it’s type may significantly (p<0.01) cause IMI development and SCM in crossbred cows. A management strategy which reduces bacterial load over teat ends may be one of the measure for SCM control and maintaining good udder health. Pre-milking sanitation is always recommended by washing udders and teats with water or disinfectants, but studies conducted by researchers
(Galton, 1988) indicated that pre-milking teat sanitizations dramatically lowered IMI cases by
Streptococcus uberis. Researchers
(Bhakat et al., 2015) recommended adoption of hygienic milking procedures at each milking. Milk processors prefer the milk with low bacterial contamination, sediments, or residues which in turn is seen to encourage the adoption of pre milking teat preparations.
Automatic milking procedure to control SCM
Researchers
(Bharti et al., 2015a; Bharti et al., 2015b) suggested that suitable machine milking may alter IMI and SCM cases along with considerable changes in milk constituents. Researchers found that working of different parts of milking machines should be uniformed to lower the chances of new IMI
(Baxter et al., 1992). Researches lead down the roadmaps to understand the concept of milking machines which influences the physiology and milk let down along with the occurrence phenomenon of sub clinical mastitis cases. Scientists
(Bhakat et al., 2017a) reported that IMI in dairy animals can be significantly controlled by machine milking as compared to that in the case of hand milking when proper hygiene measures adopted. Researchers
(Thompson, 1981) suggested for judicious follow ups of data generated through various sensors over milking machines. With the progression of time, use of automatic milking systems increased in many regions however, data so obtained from these machines need to be utilized in justified and effective ways
(Jacobs and Siegford, 2012). While, researchers
(Spencer, 1998) found that machine milking may lead to new IMI cases by becoming contagious media for other herd mates and also, it may lead to unwanted changes in teat morphology. However, very promising ill effects of machines for milking were not reported
(Paul and Bhakat, 2018) this might be due to proper hygienic methods followed during complete milking operations. Scientists
(Bhakat and Dutta, 2014; Mandal et al., 2021; Singh, 2021; Singh et al., 2020i) reported that defective floor type of dairy cow shed with automatic milking provision can also affect udder health adversely in tropical climate and ridge ventilation can help to increase milk production with better udder health at lower Gangetic tropical climate.
BCS, genetic selection and animal behaviour to control SCM
Researchers
(Paul et al., 2019) reported that elevated levels SCC in milk of jersey crossbred cows having under or over BCS. Scientists
(Paul et al., 2020) utilized BCS technique though USG (ultra-sonography) for crossbred cows and suggested that consideration of BCS at calving can be recommended as a reliable criterion for selecting cows as a higher milk producing animal having improved udder health. Researchers
(Shook and Schutz, 1994) remarked that genetic susceptibilities towards SCM may cause IMI in different animals belonging to same families. Selections for mastitis resistance properties in animals gradually progressed in US farms
(Vukasinovic et al., 2017). Scientists
(Bharti and Bhakat, 2019) investigated that increasing post milking standing period more than 35 minutes through management interventions such as allocation of freshly chopped fodders just after milking may reduce SCM cases and maintain good udder health throughout lactation.
Hygiene and nutritional strategies to control SCM
Researchers
(Paul et al., 2018; Langer et al., 2014 and
Bhakat et al., 2017b) remarked that higher SCC was very critical as higher SCC in milk disrupts mammary epithelial and reduces milk quality ultimately leading to poor returns. Scientists
(Garai et al., 2017) found that small scale dairy farmers with 2-3 animals had higher SCM cases due to poor hygiene in tropical villages of West Bengal and in these villages most of the small category farmers maintained 1-3 dairy cows. Researchers
(Smith et al., 1985) suggested that high density concentrate based feeding may also lead to SCM cases but associations of nutrition were not observed until scholars
(Weiss et al., 1990) investigated in their study that Vit E and Selenium deficiency in dairy animals were the cause and prolongation for clinical mastitis. Scientists
(Kumari et al., 2019b) investigated that oral supplementation of sodium tri citrate may reduce SCM in hot humid regions. Studies conducted by different researchers revealed the importance of such vital nutrient in the working of neutrophils in dairy animals
(Hogan et al., 1993; Singh et al., 2020f). Researchers
(Wathore and Bhakat, 2016; Singh and Bhakat 2019;
Singh et al., 2020h) observed that dietary supplementation of Vitamin E to cow may potentially reduce SCM in tropical climate and helps for maintaining better udder health status during lactation period.
