Mastitis is the most prevalent production disease in dairy herds world-wide and is responsible for several production effects (Henri et al., 2003). On account of its causing serious wastage and undesirable milk quality, is emerging as a major challenge among the others in dairy development of tropics. Subclinical mastitis was found more important in India varying from 10–50% in cows and 5–20% in buffaloes than clinical mastitis 1–10% (Joshi and  Gokhle 2006) and may leads to  80 per cent milk loss in herd (Buragohain and Dutta 1994) without identifiable lesions, causing a staggering loss of Rs 6,053.21 crore. These losses are on account of reduced milk production, treatment cost, discarded milk following treatment, loss of udder and death loss or early culling. If this condition can be diagnosed and treated at an early stage, it may have multifactorial effects on animal production and economic aspect.

With this object a preliminary study was planned to investigate the prevalence, isolation and antibiotic sensitivity pattern of organism involved in sub-clinical mastitis in crossbred cows in organized farms of Mehsana milk shed area. 

A total of 389 midstream milk samples collected from 98 lactating crossbred cows of private organized farms of Mehsana milk shed area were included in present study. Comparison of efficacy of different diagnostic techniques for subclinical mastitis, such as modified California mastitis test (MCMT), bromo thymol blue (BTB), modified whiteside test, trypsin inhibition test, milk pH, and electric conductivity indicated MCMT to be most sensitive (95.16%) and specific (98.02%) test (Joshi and  Gokhle 2006). Thus MCMT was carried out on the spot on all milking cows to detect SCM. Milk samples of CMT positive quarters were collected aseptically for further laboratory studies. Bacteria from affected milk samples were isolated by using MHA broth, MHA agar and nutrient agar following standard procedures. The isolates were tested for antibiotic sensitivity test by using agar disc diffusion method (Matsen and Barry, 1974) against various antimicrobial agents. 

Out of 98 cows tested against SCM, 44 (44.89 %) cows showed positive for SCM in one or more quarter. Our results were in agreement with Dangore et al., (2000). Out of total 389 milk samples from 98 cows, 120 samples (30.84 %) were found positive on CMT. In the present study individual quarters wise prevalence to MCMT was found to be highest in  RH 35 (29.16%)followed by LH 33(27.50%), LF 27 (22.50%) and  RF 25 (20.83%). Study showed hind quarters (56.67%)were more susceptible to SCM than front quarters (43.33%). The present findings lent support of Dangore et. al., (2000) and Joshi and  Gokhle (2006). On the basis of gel formation, the MCMT classified in +1, +2, 3+, and +4 grade. On that basis, in present study, 38 (31.66 %) quarters revealed  +1 followed by 31 (25.83 %) quarters having 4+, 27 (22.50 %) quarters having 2+ and 24 (20.00 %) quarters having 3+ grade.

The animal wise prevalence rate of SCM by cultural examination was 35 (79.54%). However, quarter wise bacteriological examination of milk revealed 92 positive quarters (76.67%). Out of total 92 isolates 35 (35.71%) belong to Staphylococcus Spp. Causing SCM followed by Streptococcus Spp. 15  (16.30 %), gram positive bacilli Spp. 4 (4.34 %), mixed infection 20 (21.73 %)and other gram negative type of organism 18 (19.56%) in the present study. This is in accordance to the findings of Bhalerao et al., (2000).

In vitro drug sensitivity showed that all the isolates were highly sensitive to enrofloxacin (26.95%) which followed by ceftriaxone (19.13%), ciprofloxacine (15.65%), amoxy-cloxacilline (13.91%) and oxytetracycline (11.30%). Our results were in agreement with Datta and Rangnekar (2001). Majority of isolates were found least sensitive to gentamicine, streptomycine, penicilline, doxycycline, and cotrimazine during the study. This variation in sensitivity may be attributed to indiscriminate use of these drugs, which contributed to the increased resistance of different bacterial isolates in the present study.   

On the accomplishment of the present study, I would like to take this opportunity to extend my deepest sense of gratitude, words of appreciation and sincere thanks towards Dr. P. K. Pradhan, PPD, GRISERV, BAIF, Dr. S.M. Desai, CPC, GRISERV, BAIF, Dr. N.T. Prajapati for providing all facilities and invaluable counsel throughout the pursuit of this study. 

Bhalerao, D.P., Jagadish, S., Keskar, D.V., Dangore, A.D. and Sharma, L.K. (2000). Antibiogram and treatment of bovine subclinical mastitis. Indian Veterinary Journal, 71( 3): 244-246.

Buragohain, J. and Dutta, G.N (1994). A note on the efficacy of treatment during lactation for the control of bovine mastitis, Indian Veterinary Journal. 71( 5): 504-505.

Dangore, A.D., Bhalerao, D.P, Jagadish, S., Keskar, D.V. and Sharma, L.K. (2000). Evaluation of some byre-side tests in bovine subclinical mastitis. Indian Veterinary Journal, 77:380-381.

Datta, S. and Rangnekar, A. (2001). Sub clinical mastitis in a jersey herd. Indian Veterinary Journal, 77:380-381.

Henri Seegers, Christine Fourichon and François Beaudeau (2003). Production effects related to mastitis and mastitis economics in dairy cattle herds. Veterinary. Research, 34: 475-491  

Joshi, S and  Gokhle, S. (2006). Status of mastitis as an emerging disease in improved and periurban dairy farms in India. Annals of the New York Academy of Sciences, 1081: 74-83.

Matsen, J.M. and  Barry, A.L. (1974): Manual of Clinical Microbiology. 2nd edition. American Society for Microbiology, Washington, DC. pp 418-427.