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The Complication of Shrink

Shrink is much more than loss of gut contents.

Cattle have a large digestive tract. Body weight varies, depending on whether the digestive tract is full or empty. This depends on 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 instead of eating, are generally less than mid-day or evening weights when the gut is full.

Mature cattle carry nearly 30% of their weight in the gut and bladder. They lose a lot of weight quickly if held off feed and water for 24 hours, or pass a lot of manure and urine in a short time when exercising or excited. They lose 8-10 pounds (lb.) per defecation/urination; a gallon of fluid weighs about 8 lb. Shrink losses up to 10% of body weight are not uncommon in cattle held off feed and water for 24 hours. In some circumstances, shrinks up to 18% can occur. Part of this loss is from body tissues due to physiologic factors triggered by stress.

Al Schaefer, researcher at Lacombe Research Centre, Lacombe, Alta., Canada, worked on several studies addressing problems associated with shrink.

“Transport and handling creates a novel environment for cattle,” he says.

As prey animals, survival tactics are fight or flee, which are short-term stress events. They don’t cope very well with long-term stress like being gathered, sorted, weighed, held overnight in pens without feed, loading or truck transport. The “fear stress” in novel situations can be as detrimental as physical stress, according to Schaefer. Cattle sent to slaughter and held in pens overnight typically lose 6% or more of live weight and carcass weight. They often show degradation in meat-quality parameters such as pH, color and marbling score.

“We started to measure stressors. At that time, many people in the beef industry thought shrink is just fluid loss from the gut, and wanted to get it out of there so the buyer doesn’t pay for useless water,” says Schaefer.

“We did studies looking at composition of fluid loss. We dissected slaughtered animals, comparing those with greater shrink with those of lesser shrink. We found half the weight loss was from the GI (gastrointestinal) tract and half from muscle tissue. Loss of muscle in finished animals reduces carcass yield and quality,” he says.

“Animals lose muscle sugar (glycogen) and become hypoglycemic (low blood sugar/low muscle sugar). They become dehydrated and lose interstitial water (fluid outside the muscle cells). When animals lost fluid from body tissues, their meat became tougher. Shear forces (pressure needed to cut a steak) and taste changed dramatically,” he says.

Schaefer gives an example, “It’s similar to grapes vs. raisins. When grapes lose water they become smaller, thicker, chewier. Muscle tissue loses positive ions, particularly sodium and potassium. Cattle break down muscle because the body is trying to free up carbon on amino acids so the carbon can be used to make more glucose — to counteract the loss.” These survival mechanisms help the animal survive in times of stress and feed/water deprivation.

Many buyers still prefer “shrunk” cattle, not realizing how adversely this affects health, particularly young cattle.

“The energy and water that’s been lost is important. Fluid and material in the stomach gives them energy to counteract stress. Cattle do better if they have some gut fill during transport,” Schaefer says.

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, breaking down muscle and fat for provision of glucose,” says Schaefer.

“If cattle are taken out of their familiar pen, social structure, etc., to be sorted and weighed, this triggers cortisol release. Hauling 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. This is why feedlots try to have same-day slaughter for finished cattle, so they can stop this weight loss as soon as possible. With young calves being weaned and shipped to feedlots, cortisol has a damaging impact on their immune system, as well as creating more risk for illness.”

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Editor’s Note: Heather Smith Thomas is a freelancer and cattlewoman from Salmon, Idaho.



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