Abstract
Simple SummaryRecently, high-throughput instruments have been used to analyze milk differential somatic cell count, represented by the combined proportion of polymorphonuclear leukocytes and lymphocytes, providing indirect information on the udder inflammation status of dairy cows. No information is available about the relationship between differential somatic cell count and milk quality, so the aim of this study was to investigate the effect of differential somatic cell count on the composition of a large number of individual milk samples. Results showed that milk quality worsened when differential somatic cell count was high. In particular, it was evidenced lower milk fat, protein, casein contents and casein index, and augmented milk fatty acids could be found with an increasing differential somatic cell count level. These findings confirmed that differential somatic cell count could be a new informative tool for dairy farmers to monitor the quality of milk.Recent available instruments allow to record the number of differential somatic cell count (DSCC), representing the combined proportion of polymorphonuclear leukocytes and lymphocytes, on a large number of milk samples. Milk DSCC provides indirect information on the udder health status of dairy cows. However, literature is limited regarding the effect of DSCC on milk composition at the individual cow level, as well as its relation to the somatic cell score (SCS). Hence, the aims of this study were to (i) investigate the effect of different levels of DSCC on milk composition (fat, protein, casein, casein index, and lactose) and (ii) explore the combined effect of DSCC and SCS on these traits. Statistical models included the fixed effects of days in milk, parity, SCS, DSCC and the interaction between SCS × DSCC, and the random effects of herd, animal within parity, and repeated measurements within cow. Results evidenced a decrease of milk fat and an increase in milk fatty acids at increasing DSCC levels, while protein, casein and their proportion showed their lowest values at the highest DSCC. A positive association was found between DSCC and lactose. The interaction between SCS and DSCC was important for lactose and casein index, as they varied differently upon high and low SCS and according to DSCC levels.
Highlights
Somatic cell count (SCC) is used worldwide as an indicator of udder health in dairy animals and to indirectly monitor the quality of milk [1]
SCC is a valid quantitative trait for the identification of the inflammation status of the mammary gland, it does not provide information on the distribution of each cell population. This information, could be extracted by the variation of polymorphonuclear leukocytes (PMN), lymphocytes, and macrophages, which reflects the extent of the inflammatory response of the animal [10]
Herds were selected in order to be representative in terms of size and management with respect to the farms located in the Lombardy region, and characteristics of sampled farms have been previously reported in Zecconi et al [17]
Summary
Somatic cell count (SCC) is used worldwide as an indicator of udder health in dairy animals and to indirectly monitor the quality of milk [1]. SCC is a valid quantitative trait for the identification of the inflammation status of the mammary gland, it does not provide information on the distribution of each cell population. This information, could be extracted by the variation of polymorphonuclear leukocytes (PMN), lymphocytes, and macrophages, which reflects the extent of the inflammatory response of the animal [10]. There is evidence that different proportions of these cell populations, within specific SCC levels, could modify the final characteristic of dairy products [13,14], as well as different categories of environmental microorganisms (i.e., Clostridia) that, nonpathogenic, have a strong unfavorable dairy activity [15]
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