Mastitis, an inflammatory reaction of the mammary gland that is usually caused by a microbial infection, is recognized as the most costly disease in dairy cattle. Decreased milk production accounts for approximately 70% of the total cost of mastitis. Mammary tissue damage reduces the number and activity of epithelial cells and consequently contributes to decreased milk production. Mammary tissue damage has been shown to be induced by either apoptosis or necrosis. These 2 distinct types of cell death can be distinguished by morphological, biochemical, and molecular changes in dying cells. Both bacterial factors and host immune reactions contribute to epithelial tissue damage. During infection of the mammary glands, the tissue damage can initially be caused by bacteria and their products. Certain bacteria produce toxins that destroy cell membranes and damage milk-producing tissue, whereas other bacteria are able to invade and multiply within the bovine mammary epithelial cells before causing cell death. In addition, mastitis is characterized by an influx of somatic cells, primarily polymorphonuclear neutrophils, into the mammary gland. With more immune cells migrating into the mammary gland and the breakdown of the blood-milk barrier, damage to the mammary epithelium worsens. It is well known that breakdown of the extracellular matrix can lead to death of the epithelial cells. Meanwhile, polymorphonuclear neutrophils can harm the mammary tissue by releasing reactive oxygen intermediates and proteolytic enzymes. In vitro and in vivo studies suggest that the use of antioxidants and other protective compounds in mastitis control programs is worth investigating, because they may aid in alleviating damage to secretory cells and thus reduce subsequent milk loss.

Mammary tissue damage during bovine mastitis: causes and control.

Mammary gland function during involution.

The effects of somatic cell count and stage of lactation on the yield and quality of Cheddar cheese were investigated. Cheese was manufactured in a pilot scale factory using milk of low bulk milk cell count (BMCC) from herds in early (LE) and late (LL) lactation, and milk of high BMCC from herds in early (HE) and late (HL) lactation. The deleterious effect of an elevated BMCC on product yield and quality in late lactation was clear. Cheese made from LL milk was significantly superior to that made from HL milk for most yield and quality characteristics measured. Stage of lactation also affected cheese yield and quality, as evidenced by the lower recovery of fat and poorer flavour score for cheese from LL milk compared with that manufactured from LE milk. The observed differences could be explained largely by differences in raw milk composition. We conclude that the effect of stage of lactation was magnified by an elevated BMCC, and that many of the problems encountered when processing late season milk could be overcome by containing mastitis at this time.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022029900031769

Effects of somatic cell count and stage of lactation on raw milk composition and the yield and quality of Cheddar cheese

Electrical conductivity of milk: measurement, modifiers, and meta analysis of mastitis detection performance.

The consequences of mastitis on the technological properties of milk and on the quality of milk products are widely reported in the literature. Besides, recent advances have shed light on the mechanisms involved in the udder response and subsequent milk changes in mastitis cases. This review gives an update on the literature regarding the impact of mastitis on milk composition and processing properties and collates recent data regarding the mechanisms involved in mastitis effects. It is an attempt to link field observations and experimental studies in order to better understand how mastites affect so dramatically the technological properties of milk. Both bovine and small ruminant milks are considered and a special emphasis is given on the role of staphylococci, streptococci, and Escherichia coli, the most common causative agents of mastitis.

/pdf/mastitis-impact-on-technological-properties-of-milk-and-3028vjp47w.pdf

B.J. Kitchen

Papers

Mastitis diagnostic tests to estimate mammary gland epithelial cell damage