Longitudinal study of subclinical mastitis and milk production on crossbred Holstein x Zebu cattle, housed in a semi-intensive system

ABSTRACT

A herd of dairy cattle with different crossbreeding Holstein x Zebu (HZ), housed in a semi-intensive production system, was monitored for 15 months. We aimed to evaluate the longitudinal behavior of somatic cell count (SCC) and the influence of subclinical mastitis (SM) on the milk yield and on the peak yield of crossbred HZ dairy cows. Initially, individual milk samples were collected for microbiological analysis for identification of mastitis pathogens. The SCC was performed monthly to monitor subclinical mastitis. Additionally, milk production was evaluated weekly. To evaluate the effects of SCC on milk production, the cows were identified as falling into two groups: <200.000 and ≥200.000 cells/mL. The isolated pathogens were environmental streptococci (34%), yeasts cells (29%), coagulase-negative staphylococci (31%) and Staphylococcus aureus (6%). The SCC associated to each type of pathogen was 1100.000, 845.000, 275.000 and 620.000, respectively. The average SCC varied from 255.000 to 975.000 cells/mL and the prevalence of SM was 42%. Primiparous cows with SM presented a decrease in total milk yield when compared to primiparous cows without SM (P<0.05). In contrast, the total milk yield of multiparous cows did not change. Differences in SCC, total yield and peak yield between the crossbreeding Holstein x Zebu (HZ) levels were not observed (P>0.05). SCC differed (P<0.01) between drying off and immediate postpartum. Maintaining high environmental risk conditions in a dairy herd, housed in semi-intensive system, can reduce the variations in the occurrence of SM in summer and winter periods. This can also decrease the variations in SM occurrence between cows of different crossbreeding HZ levels. In a herd characterized primarily by the presence of environmental mastitis, milk yield of primiparous cows with SCC above 200.000 cells/mL is reduced when compared to cows with SCC below 200.000 cells/mL. This finding was not observed for multiparous cows.

somatic cell count; environmental mastitis; girolando; dairy cattle