Introduction

Mastitis is the most important and expensive disease of dairy industry. It results in severe economic losses from reduced milk production, treatment cost, increased labour, milk withheld following treatment and premature culling (Miller et al., 1993). Mastitis is a global problem as it adversely affects animal health, quality of milk and economics of milk production and every country including developed ones suffer huge financial losses (Sharma et al., 2007). Inflammation of mammary gland is directly accompanied by an increase of somatic cell count (SCC) in milk (Rodriguez et al., 2000). Therefore, many reports have considered SCC as a significant marker for sub – clinical mastitis (Dürr et al., 2008).Somatic cells are indicators of both resistance and susceptibility of cows to mastitis and can be used to monitor the level or occurrence of sub – clinical mastitis in herds or individual cows. Somatic cell count is a useful predictor of intra-mammary infection (IMI), and therefore, an important component of milk in assessment of aspects of quality, hygiene and mastitis control (Sharma et al., 2011). The most important factor affecting the somatic cell count of the milk from an individual quarter depends upon the infection status of the quarter (Dohoo and Meek, 1982).

Somatic cells are always present in milk and they increase due to mammary gland infections. When udders are healthy, the SCC in milk is between 50,000 and 100,000 cells/ml (Skrzypek et al., 2004). If the SCC is greater than 200,000 cells / ml, it is assumed to be a threshold distinguishing a healthy udder from a diseased udder (Skrzypek et al., 2004; Harmon, 2001).This study was conducted to compare the SCC in the milk of lactating dairy cows using TANUCHEK SCC Test and California Mastitis Test and to assess the health of udder based on the SCC at field level.

Materials and Methods

Selection of Animals

Twenty four lactating cross – bred dairy cows from three farms at Vedapatty, Onnipalayam and Kaalipalayam villages of Coimbatore district were selected and the two tests – TANUCHEK SCC Test and CMT were performed simultaneously in the milk samples collected from all the animals.

Somatic Cell Count Determination

The TANUCHEK SCC Test was done using TANUCHEK SCC kit developed by Tamil Nadu Veterinary and Animal Sciences University, Chennai. The teats were washed properly and first two streams of milk were discarded. Milk sample was collected from all the quarters of lactating dairy cow in a separate clean container. From the container a drop of milk sample was taken using a Pasteur pipette and added in a SCC tube provided in the kit. Immediately, 3 drops of the enhancer was added and mixed well and kept at room temperature for 30 minutes. The blue colour developed is compared with the TANUCHEK SCC colour card. The value obtained by matching the colour card was multiplied by 1000 (100×1000 cells, 300×1000 cells, 500×1000 cells, 700×1000 cells, 900×1000 cells ) to evaluate the SCC per ml of milk (Yasothai, 2017) .The California Mastitis Test was performed simultaneously and interpretation of SCC was made based on the scores as described by Nithya et al., 2017.

Results and Discussion

In the present study, 24 lactating dairy cows from three farms of Coimbatore district were selected and the two tests – TANUCHEK SCC Test and CMT were performed simultaneously and the results are presented in Table 1 and 2.

Table 1: Comparison of TANUCHEK SCC Test and CMT for the Somatic Cell Counts in the Milk of Dairy Cows in Coimbatore District

Out of 96 quarters examined each with TANUCHEK SCC Test 24 (25.00%) and with CMT, 21 (21.87%) quarters showed increase in SCC. Comparison between the two methods showed a weak positive correlation (r=0.163) between the two tests when all the test values were taken into consideration (70% agreement between the two methods). Similar positive correlation between CMT and SCC was also observed in dairy cows in Turkey (Kasikci et al., 2012) and India (Sharma et al., 2010). The coefficient of determination r²=0.027 which indicates 2.7% of the variation between the two tests can be explained based on the linear relationship that exists between the two methods.

Table 2: Quarter – wise Comparison of TANUCHEK SCC Test and CMT for the Detection of Sub -clinical Mastitis in the Milk of Dairy Cows

The benefit of low cost, easy availability and adoptability of both tests were equal except the time taken to analyses the sample was high in TANUCHEK SCC Test (30-40 minutes) than CMT (10 seconds) as suggested by Yasothai (2017) but the TANUCHEK SCC Test is very sensitive and specific. Out of 96 quarters examined, the total number of quarters showed positive for sub – clinical mastitis in TANUCHEK SCC Test is 21 (21.88%) and in CMT, 14 (14.58%). The TANUCHEK SCC Test detects increase in SCC precisely and the colour developed compared with the TANUCHEK SCC colour card (Fig. A-D) and this is in agreement with SCC tests of Sharma et al. (2010) and Hoque (2013).

Fig. A: TANUCHEK SCC TEST – Colour developed compared with the score card	Fig. B: TANUCHEK SCC TEST- Interpretation of results with score card

Fig. C: Collection of milk sample in the CMT paddle.	Fig. D: Visible gel formation after adding CMT reagent in the milk sample

Tanwar et al. (2001) also reported that SCC has 96% sensitivity. The low cost for CMT and easiness of its application by the farmers make CMT advantageous over SCC for its wide use in small holding dairy farms for the detection of sub – clinical mastitis as described by Hoque (2013).

The determination of milk SCC is widely used to monitor the udder health and the milk quality. SCC is positively correlated with the udder inflammatory condition. The elevated SCC consists primarily of leucocytes which include macrophages, lymphocytes and neutrophils. During inflammation, major increase in SCC is because of the influx of neutrophils into milk and at this time over 90% of the cells may be PMN leukocytes. Jones (2006) reported that the higher the SCC, the greater is the risk of raw milk contamination with pathogens and antibiotic residues. Yasothai (2017) suggested that TANUCHEK SCC Test and CMT could be used as regular mastitis screening test in field condition, even by less trained dairymen. The TANUCHEK SCC test was easy to interpret and specific since the specific substrate in TANUCHEK SCC test changes to blue colour by the membrane bound enzymes from the cells and the cost of TANUCHEK SCC Test was Rs.2.50 per test.

Conclusion

The udder health status can easily be diagnosed by evaluating SCC by both the methods in field conditions. The present study revealed that comparison between the two methods, TANUCHEK SCC Test and CMT showed a weak positive correlation (r=0.163) between the two tests when all the test values are taken into consideration (70% agreement between the two methods). Although CMT is a cow – side test, TANUCHEK SCC Test is very sensitive and specific and detects increase in somatic cell count precisely and can be used in field conditions to detect sub- clinical mastitis in dairy cows.

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