Estimation of milk production losses due to sub-clinical mastitis in dairy cattle in Costa Rica.

Five dairy farms, situated on the slopes of the volcano Poas in the pre-mountain cloud forest ecological zone, Alajuela and Heredia Provinces, Costa Pica, provided data for estimation of the production losses due to sub-clinical mastitis. Within the same farm, cows with proven sub-clinical mastitis were marched with cows without signs of sub-clinical mastitis, according to breed, lactation number and days in lactation. A total of 529 cows were detected with sub-clinical mastitis, of which only 200 could be paired with control cows free of mastitis; each pair was used only once. Crude milk production losses per cow with sub-clinical mastitis were estimated at 1.56 kg day-1 for daily milk yield. Milk production loss per affected quarter due to sub-clinical mastitis was estimated to be 17.6% on average. The decrease in milk production in heifers with sub-clinical mastitis did not differ significantly from the decrease in production in older cows. No significant difference in milk production loss was detected when the data were stratified on parity or the number of quarters affected.