fluids then the amount of nutrients transferred to the cells (for metabolism etc.) is greatly reduced. Therefore, managing the water content in the rumen is important for maintaining both normal rumen fluid volume as well as other body fluid reserves. Beware that not all situations of dehydration in cattle are easy to recognize. The rumen acts as a fluid reservoir by which body fluid balance can be maintained for a short period of time. This will cause “shrink” of the animal’s normal body weight and, if not corrected, will lead into clinical dehydration as identified below. Identifying levels of dehydration Severely challenged cattle can dehydrate in excess of 10 percent of their body weight. This degree of dehydration is potentially life-threatening and clinical signs include the following: • Eyes sunken into orbits • Skin remains tented indefinitely • Mucus membranes are dry • Depressed attitude is evident Cattle with dehydration of 5 - 10 percent of their body weight will exhibit • Partial sunken eyes into the orbit • Skin tenting that is 4 to 8 seconds in duration • Tacky mucus membranes • Reduced dry matter intake • Decreased productivity It should be noted that university studies indicate cattle with 7 - 8 percent dehydration levels show impaired immune response. Cattle with 2 to 4 percent dehydration or less will have minimal observable clinical signs but physiological and performance efficiency can be reduced. Water loss during heat stress can be quite evident by observing the cows body condition. But even in periods when heat stress is not a factor maintaining proper hydration is important as cows continually lose water via:
• Milk production (25-35% of total water intake)
• Freshening (fluid loss equal in weight to the calf )
• Fecal (30-35% of total water intake)
• Urine (15-21% of total water intake)
• Vapor loss from the lungs
• Digestion
• Disease, diarrhea, malabsorbtion
Rehydration Rehydration and hydration maintenance for dairy cattle can be accomplished in three ways: 1. Parental through IV or subcutaneous administration 2. Oral rumen drenching/pumping with large volumes 3. Combination of parental and oral volume of fluid or supplementation of electrolytes.
Electrolytes can be added to the ration on an as-needed basis to improve fluid efficiency due to their role in helping promote nutrient flow and balance. When calculating replacement fluids it’s important to consider maintenance requirements, production needs, and fluid losses due to heat stress, sweat, sickness or other challenges. To maintain normal cellular functions, a 1,000 pound cow requires 12 gallons (96 pounds) of water on a daily basis. Some of this water comes from their feed ration (10-30%) and the balance from daily water volume intake (usually 8 to 9 percent of their total body weight. For a lactating cow, each 10 pounds of milk produced requires an additional gallon of water over maintenance requirements.
2. Circulatory and Nutrient Disruptions During heat stress, a dairy cow uses convective cooling where blood flow, normally used for digestion, is directed to the surface layers of the body to cool. As a result, blood normally utilized for digestive functions, is now redistributed to the skin and puts the digestive system at risk of becoming hypoxic (low in oxygen). Consequently, intestinal toxins can enter circulation and cause inflammation and poor health. In addition, the flow of nutrients and energy away from the digestive system means they are not making it to the cells and tissues where needed… like the mammary gland for milk production. However, these cells and tissues require more potassium, energy, and adequate fluids to maintain health and prevent production losses during heat stress. Convective cooling involves sweating which greatly increases the secretion of potassium and is one of the major reasons that supplemental potassium is required during heat stress. Without supplementation, this cooling mechanism ultimately puts the cow at risk of an energy imbalance and other metabolic challenges and can have a negative impact on the reproductive system. Cows do not have the built-in mechanism to manage potassium levels in their blood stream and therefore rely on dietary input along with urine and fecal output to regulate. Potassium is the primary electrolyte responsible for intracellular energy mobilization and utilization. Responsible for proper fluid balance within cells, potassium is a requirement for proper body function. The combination of low feed intake, sweating, and dehydration from heat stress, leave the cow deficient and therefore potassium supplementation is required to ensure proper cell functioning. Other nutrient disruptions as a result of heat stress include:
• Elevated insulin levels (hypersensitivity)
• Depressed glucose levels are especially present with restricted feed intake during heat stress. Muscle and other tissues are requiring more glucose, limiting glucose avail-
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