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| Summertime and heat stress is back! |
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| El Lechero Dairy Basics - Herd Health | |||
| Written by Fabian Bernal | |||
| Wednesday, 13 July 2011 14:00 | |||
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Hot weather during the summer season is a predictable issue that must be dealt with on most dairy farms. Sunny, hot summer days with high temperatures between 75ºF and 115ºF are not the best conditions for lactating dairy cows.  As mentioned in past issues, lactating cattle produce large amounts of heat due to digestion and metabolic processes, and this heat must be exchanged with the environment to maintain normal body temperature. Managing dairy cows and their environment in ways that will prevent heat stress in dairy cows during hot, humid weather is the name of the game. We want to maintain near-optimum temperature for production and health; we would like to remove pathogens, noxious gases and dust as fast as possible from barns and, at the same time, control excess moisture and increase available fresh air. Heat stress can be understood to indicate all high temperature-related forces that induce adjustments occurring from the sub-cellular to the whole animal level to help the cow avoid physiological dysfunction and better fit its environment. It is important to understand the specific signs of thermal stress. Signs of heat stress • Restlessness • Panting (open-mouthed breathing) • Crowding under shade or around water tanks • Increased salivation • Increased respiration rate (gasping): - 80 to 120 breaths per minute – moderate heat stress - 121 to 160 breaths per minute – strong heat stress - Over 161 breaths per minute – severe heat stress • Decreased activity • Reduced feed intake and rates of ruminal motility Under continuous heat stress lactating cows begin to decline feed intake at 75ºF to 80ºF with a marked decline above 86ºF (RCI heat stress in dairy cattle). Production is affected as metabolisms are compromise. Steps to reduce heat stress There are four main management practices that have been proposed to decrease the effects of heat stress: - Shades – Blocks solar radiation. - Conduction – Transfers body heat to cooler bedding such as sand. - Convection – Blows cool air over the animal to remove body heat. - Evaporation – Wets animal’s back with pressure-controlled water then uses fans to evaporate the water, which removes body heat. Natural shade Trees are an excellent natural source of shade on the pasture. Trees are not effective blockers of solar radiation, but the evaporation of moisture from leaf surface cools the air. Some of the problems associated with this technique are overcrowding in specific areas and damage to the ground, possibly affecting the trees’ vitality. Artificial shade Solar radiation is the main factor in heat stress. Blocking its effects through the use of properly constructed shade structures alone increases milk production remarkably. Two options are available: permanent shade structures and portable shade structures. Portable shade cloth or light structures may be used on temporary shades, allowing for pasture and grounds management. Ventilated barns and sprinklers systems Evaporation is the most effective method for cooling but must be used with caution. It requires 5 to 7 mph air flow from well-positioned fans mounted over both the eating and resting areas. Activated sprinklers systems have been effective at reducing heat stress. Getting cows’ backs wet and evaporating water from the surface of cattle with fans as they stand on feeding alleys represents the most efficient method to remove heat from cattle. However, design flaws have resulted in facilities that do not effectively modify the environment, only deliver enough water to wet the cow’s back. The amount of time and water use depends on the water pressure and systems; keep in mind that your facilities have to handle the extra water. Avoid water dripping around the cow’s body and especially onto the udder. Tunnel or cross-ventilated barns are very effective methods of cooling, but require more energy. Fans are best used in conjunction with sprinkles as discussed above. One critical area is the holding pen. Heat stress can occur here at relatively low environmental temperatures due to crowding. It is reported that well-ventilated\cool holding pens can increase production by 1.5 to 4 pounds of milk per cow per day. Increased water intake Water and mineral needs are increased so cows can be efficient at thermoregulation, maintaining a stable internal body temperature regardless of external influence; metabolically, alterations during heat stress are commonly described in multiple studies. Milk is about 82 to 87 percent water and contains large concentrations of the electrolytes. Therefore, lactating dairy cows have large turnover of water and electrolytes. Management of the dietary electrolyte balance is based on adding essential minerals, salts and electrolytes to the drinking water (if possible) and feed. Proper electrolyte balance promotes homeostasis, assists the osmoregulation of body fluids, stimulates appetite, ensures normal metabolisms, etc. Cows should have access to fresh water at the parlor exit even if water is available in the pens. Metabolic responses Under heat stress, metabolism is reduced, which is associated with reduced thyroid hormone secretion and gut motility. Plasma growth hormone concentration and secretion rate declines with hot temperature. Ruminal pH is characteristically lower in heat stressed cattle. With an increase in body temperature, the muscles used in panting and abdominal respiration require about 30 percent more calories than animals with normal body temperature. Electrolyte needs change with more metabolic need for potassium, magnesium and sodium. The loss of buffer from drooling must be restored as well. Ration energy density should be adjusted and yeast may be used to aid in rumen stability. The metabolic effects of heat stress may be summarized as: • Increase of clinical and sub-clinical mastitis • Udder edema • Loss in body weight • Acidosis • Drinking water intake increases • Lower fertility – conception rate falls, embryo mortality increases • High incidence of milk fever and metritis • Uterine prolapse is common • Laminitis is more frequent • Calves are often premature and small • Growing animals are affected as well with low conversion rates Water Satisfy the cow’s thirst. Temperature is among the most important environmental factors affecting water intake in lactating dairy cows. Water is the single most important nutrient and often the most underestimated on dairy diets. Maintain clean/cool water available for your cows, especially in summer months. Milk cows drink 30 to 60 gallons of water per day (they may consume 30 to 50 percent of their daily water intake within one hour after milking). During the summer, those needs increase by 20 to 30 percent. One thing all water troughs have in common is the need to be cleaned regularly. They need to be big enough for cows to drink freely (three feet available water area for every 10 to 15 cows). Supplemental water is a good idea and will become a great tool when managing feed intake and heat stress.
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