By Robert J. Van Saun
Mastitis is the single most important disease of dairy cows impacting milk production and farm profitability. Tremendous amounts of research and extension publications have been generated relative to understanding mastitis as a disease process and its impact on the cow and her performance. Costs associated with a case of mastitis are most often related to milk loss, drug treatments, additional labor, and withdrawal time for milk residue clearance. But what about the cost to the cow's nutritional status and its impact?
In a previous article , prepartum dietary factors in preventing mastitis were addressed, which would be the most desirable approach. In this article, the cost of supporting the immune response was discussed. This is the topic of focus in this article relative to its impact on lactating cow performance. A current area of interest in transition cow metabolism is the role of inflammation during the transition period (i.e., 6-8 weeks centered around calving) and its impact on cow metabolism and risk for postpartum disease. When the body's immune response to an infectious process is considered, this is a positive response helping the body to eliminate the invading pathogen. However, like any other metabolic or physiologic function of the body it takes nutritional support to maintain.
Nearly all essential nutrients are necessary to support an activated immune response, but let's focus on energy and protein metabolism as these are critical nutrients relative to supporting early lactation. The immune response is controlled and mediated through activity of white blood cells, namely lymphocytes and polymorphonuclear granulocytes (PMN). These specialized cells require glucose as their energy fuel and use amino acids in support of protein synthesis of antibodies, enzymes, and signaling molecules (i.e., cytokines). Additionally, the liver, in the face of an inflammatory response, will divert amino acids from selected protein synthesis into pro-inflammatory proteins termed acute phase proteins. These metabolic consequences are recognized in finding low blood concentrations of albumin (e.g., primary blood protein), vitamin A, and iron resulting from reduced liver production of the protein itself or transport proteins for the other nutrients. These proteins that are reduced in production are termed "negative acute phase proteins."
So, what is the impact here? Studies evaluating the nutritional impact of an activated immune response have evaluated the increase in energy expended, mostly from utilization of glucose, the primary substrate for milk lactose, and protein metabolism. The increase in metabolic rate ranges from 10 to over 50% depending upon the type of immune response. What this means is the cow's "thermostat" is increased by burning more fuel. This energy cost is adding to maintenance requirements and taking away available dietary energy from supporting productive functions like growth or milk synthesis. Since the white blood cells exclusively require glucose as an energy source this requires the cow to free up more glucose from other functions to support the immune response. To replace the missing glucose the cow will increase fat mobilization to meet the missing energy needs. It has been recognized that body fat mobilization, measured as elevated blood nonesterified fatty acid (NEFA) concentration, is associated with increased risk of transition cow metabolic diseases.
In evaluating changes in protein metabolism in the face of activated inflammation, research has shown marked increases in both protein breakdown to provide amino acids and protein synthesis for pro-inflammatory proteins. The net result is a loss of body protein in conjunction with reduced animal performance such as body weight gain or milk production. Coupled with this increased protein utilization is a contradictory reduction in feed intake, mediated by pro-inflammatory cytokines, further exacerbating underlying energy balance issues. Again, transition cows are critically dependent upon good feed intake after calving to minimize the severity of negative energy and protein balance that predisposes to common postpartum disease events.
Dairy producers are well aware of negative impacts due to clinical mastitis on that cow's performance and potential for continued milk production and reproductive success. In a retrospective study we looked at cow performance in the 5-weeks prior to and following calving in cows that had no disease events versus those who experienced various disease conditions. Cows diagnosed with subclinical to mild clinical mastitis had a greater decline in dry matter intake over the 3-weeks prior to calving, but more importantly, these mastitic cows ate 225 lb dry matter intake less than healthy cows over the first 5 weeks of lactation. Imagine the potential loss for a cow with severe clinical mastitis!
If this energy loss is accounted for, the observed reduced intake would result in nearly a 0.5 body condition score (1-5 scale) loss in this period. From an energy basis, this lost dry matter intake would account for a loss of 460 lb of 4% milk in this 5-week period or nearly 11 lb milk/day. These affected cows did not have mastitis for this entire period of time indicating the longer-term negative impacts of disease, or inflammatory reactions, on metabolism and production. Research is now focused on use of anti-inflammatory therapies to help reduce this negative impact. Remember stressors experienced by the cow will aggravate any inflammatory response. Producers should consider methods described for minimizing mastitis in dairy herds to allow cows to efficiently use nutrients supplied through feed. Feed costs account for 45-55% of production costs. Feed for milk rather than feeding the inflammatory response!Source : psu.edu