Associations between Milk Coagulation Properties and Microbiological Quality in Sheep Bulk Tank Milk

This study conducted a seasonal analysis of bulk tank milk from 77 sheep farms to establish relationships between the concentration of major microbial groups and milk coagulation properties. The investigated milk traits included composition (pH, fat, casein, lactose), coagulation properties (curd firmness: A₆₀-, rennet clotting time: RCT-, curd firming time: k₂₀-, curd yield: CY-), and somatic cell score (SCS). The main microbial groups analyzed were total mesophilic bacteria (SPC), thermodurics (THERMO), psychrotrophs (PSYCHRO), Pseudomonas spp. (PSEUDO), lactic acid bacteria (LAB), catalase-negative gram-positive cocci (GPCNC), Escherichia coli (ECOLI), coliforms other than Escherichia coli (COLI), coagulase-positive staphylococci (CPS), coagulase-negative staphylococci (CNS), and spores of lactate-fermenting Clostridium (BAB). Mixed linear models were used to explore associations between coagulation properties and the aforementioned variables. Results demonstrated that incorporating microbial loads into the models improves their fit and the relative quality of the outcomes. An important seasonality is demonstrated by an increase in CY and A₆₀, along with a decrease in RCT and k₂₀ during autumn and winter, contrasting with spring and summer. BAB concentration resulted in a reduction of A₆₀ and an increase in RCT, whereas SPC concentration led to an enhancement of A₆₀ and a reduction in RCT. An increase in GPCNC concentration was associated with an increase in k₂₀ and a decrease in CY.