Cattle have a large digestive tract, holding many gallons of feed and fluid. The body weight of an individual may vary, depending on whether the tract is full or empty. This will depend on time of day, how much the animal has eaten or exercised, or how far it has been hauled. Morning weights, when cattle are relatively empty because they’ve been resting during the night instead of eating, are generally less than mid-day or evening weights when the gut is full, unless the cattle were held off feed before weighing.
Mature cattle carry nearly 30 percent of their weight in the gut (and bladder), and may lose a lot of weight quickly if held off feed and water for 24 hours or if they pass a lot of manure and urine in a short time, as when exercising or excited. You can figure a loss of 8 to 10 pounds per defecation or urination; a gallon of fluid weighs about 8 pounds. Shrink losses of up to 10 percent of body weight are not uncommon in cattle held off feed and water for 24 hours, and in some circumstances shrinks of up to 18 percent can occur. Part of this loss is not just fluid from the digestive tract and bladder; some loss is from body tissues – due to physiologic factors triggered by stress.
Dr. A.L. Schaefer (Lacombe Research Centre, Lacombe, Alberta) has worked on several studies addressing problems associated with shrink. “I am a physiologist. Meat scientists at our Research Centre told me they were seeing muscle shrink and dark cutters (meat being dark, firm and dry). Transport and handling creates a novel environment for cattle and they are adversely affected by this stress,” he said.
Cattle are prey animals and their main survival tactics are to fight or flee from predators (short-term stress events). They are not programmed to handle long-term stress like being gathered and sorted, weighed, held overnight in pens without feed, loading or long truck transport. The “fear stress” experienced by cattle in novel situations can be as detrimental as physical stress. Cattle sent to slaughter may experience several hours of transport, after which they are held in pens overnight – and typically lose 6 percent or more of their live weight and carcass weight. They often show degradation in meat quality parameters such as pH, color and marbling score.
“So we started to measure stressors. At that time, part of the attitude in the beef industry was that shrink is just a loss of fluid from the gut. Many people actually thought shrink was good, to get it out of there so the buyer doesn’t have to pay for useless water,” said Schaefer.
“This perception is far from the truth. Over the years we have done studies to look at the composition of fluid loss. We dissected slaughtered animals, comparing the ones with greater shrink with those of lesser shrink. We found that half the weight loss was from the GI tract and half was actually from muscle tissue. There can be loss of muscle in finished animals, resulting in a reduction in carcass yield and quality,” he said.
“Then we looked at the various kinds of physiological insults. Animals lose their muscle sugar (glycogen) and become hypoglycemic (low blood sugar and low muscle sugar). They become dehydrated and lose interstitial water (fluid outside the muscle cells). When animals lost this fluid from the tissues their meat became tougher. The shear forces (pressure needed to cut a steak) and taste (as determined by food tasting panels) changed dramatically,” he explained
“It’s similar to grapes versus raisins. When grapes lose water they become raisins (smaller, thicker, and chewier). The muscle tissue lost a lot of the positive ions, particularly sodium and potassium. These cattle break down muscle because the body is trying to free up the carbon on amino acids, so the carbon can be used to make more glucose – to counteract the loss.” These are survival mechanisms to help the animal survive in times of stress and feed or water deprivation.
Some buyers still prefer to buy “shrunk” cattle, not realizing how adversely this can affect their health, particularly young cattle. “The energy and water that’s been lost is very important. Fluid and material in the stomachs is what gives them energy to counteract stress. If pigs are fed a lot before transport they become motion sick, but cattle do better if they have some gut fill,” Schaefer said.
There are many factors involved in how much a certain animal will shrink, and one of the biggest factors is stress. “If the stress mechanism is triggered, cortisol is produced. This breaks down muscle and fat, for provision of glucose,” Schaefer said.
“If the stressful environment is not part of their history (if they are taken out of their familiar pen, social structure, etc. to be sorted and weighed), this triggers cortisol release. If they are put onto a transport, this triggers it again because they don’t know what to expect. During the ride they are continually stressed, and their bodies are in a protein-breakdown mode.” If this continues for very long they lose not only fluid but body tissue as well.
“With finished cattle, this is why feedlots try to have same-day slaughter, so they can stop this weight loss as soon as possible. With young calves, when they are weaned and shipped and go into feedlots, cortisol has a damaging impact on their immune system, as well,” he said. This creates more risk for illness.
Preconditioning calves can help reduce this risk. During this period they are usually handled more and can become accustomed to gentle handling and are not just scared and wild. “If you acclimate calves to handling and a new environment, they will be more at ease and shrink less at sale time,” he said.
Video sales may have an advantage because there’s less transport and handling involved. The cattle are going directly from the farm or ranch to their destination rather than being trucked to a saleyard, waiting there, and trucked again to a feedlot.
“Solutions to these situations involve many factors. One approach here at Lacombe is to provide calves with more energy before they are shipped, and making sure they have the necessary positive ions in their systems,” Schaefer said.
“We’ve found that some of the amino acids are very effective at reducing protein breakdown. One amino acid called tryptophan is used by the nervous system in cattle and helps calm them so they don’t perceive stressors to be as threatening as they might otherwise. We’ve found this amino acid to be helpful in reducing shrink. How we’d supply this depends on the calves – whether they are unweaned or freshly weaned, or finished animals accustomed to being on feed. You can provide a ‘cow Gatorade’ product that contains some of these necessary nutrients,” Schaefer said.
“We did some work with several thousand animals that demonstrated better retention of weight (less shrink). These animals had a percent or two less weight loss. The cattle treated with nutritional therapy also showed a three- to four-fold reduction in incidence of DFD (dark-firm-dry) meat. Using economic values for beef at the time of the study, the economic impact of using nutritional therapy for cattle held in pens before slaughter was about $22 per head for 800-900 pound carcasses.”
When sending calves to market, there might be times that nutritional therapy would also be beneficial. “Sometimes you can provide this product in feed if calves are used to eating a creep feed or mineral mix. We’ve also tried putting some of these things into the water for calves when they arrive in pens from a pasture. If a calf has never seen a waterer and has only drunk from a pond or stream, it may not work,” Schaefer explained. This is the advantage of preconditioning, so calves can become accustomed to new ways to access feed and water.
“The industry needs to work together, to understand and address these challenges. We still have buyers who want raw, shrunk-out calves. They need to realize this is not a healthy situation for these animals, and that it would be helpful to pay producers more for preconditioned cattle,” Schaefer said. F