Study on risk factors and their association with subclinical mastitis in lactating dairy cows in Trinidad

A cross-sectional study was conducted on dairy farms in eight milking centr es in Trinidad to determine the prevalence of risk factors for mastitis and to assess their relationship to occurrence of subclinical mastitis. The Ca lifornia mastitis test (CMT) was used to determine the prevalence of subcli nical mastitis by estimating the somatic cell counts in bulk and composite milk. Of a total of 177 dairy farms studied, 121 (68.4%), 39 (22.0%) and 17 (9.6%) practised semi-intensive, extensive and intensive management system s, respectively. A total of 129 (72.9 %, 37 (20.9 %) and 11 (6.2 %) farms m ilked cows in parlours, stanchions and pasture/out-on-field, respectively. Based on sanitary practices, 40 (22.6 %, 123 (69.5 %), and 14 (7.9 %) farms were classified as good, fair, and poor, respectively, while 76 (42.9 %) a nd 60 (33.9 %) farms reported to rarely experience and frequently experienc e water shortages, respectively. Amongst the 177 farms, only seven (4.0%) u sed machine-milking primarily, 152 (85.9%) screened for mastitis as a routi ne, 18 (10.2 %) teat dipped, and 49 (27.7 %) practised dry cow therapy. To detect mastitis, of 152 farms involved, 20 (13.2%) used the strip cup while only two (1.3% employed the CMT. Pipe-borne water delivered directly from the hose was the only source of water to 91 (51.4%) farms while seven (4.0% ) and eight (4.5%) farms used only well and surface water (ponds and rivers ), respectively. Based on bulk milk samples, the farm prevalence of subclin ical mastitis was 60.5 % (107 of 177) with a range from 33.3 % (centre 5H) to 100.0 % (centre 2B). The difference was statistically significant (P < 0 .01; chi(2)) However, using composite milk, the farm prevalence of subclini cal mastitis was 52.5 % (93 of 177) with a range from 21.2% (centre 5H) to 92.9 % (centre 2B) and again, the difference in prevalence was statisticall y significant (P < 0.001;chi(2)). Subclinical mastitis was detected in 150 (45.0%) of 333 lactating cows screened and the range of prevalence was from 17.9 % (centre 5H) to 56.3% (centre 1C). The difference was statistically significant (P ( 0.001; chi(2)). Of a total Of 14 risk factors for mastitis studied which were related to animal husbandry, personnel mastitis control and water, only two, the herd size and practice of dry cow therapy were si gnificantly (P < 0.05; chi(2)) associated with subclinical mastitis. It was concluded that the high prevalence of subclinical mastitis in Trinidad dai ry herds could significantly reduce milk production with associated economi c loss. Although a majority of the risk factors studied were not found to b e significantly associated with the occurrence of subclinical mastitis poss ibly due to confounding factors, the need to eliminate or reduce these risk factors cannot be over-emphasized.