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Late pregnancy, winter weather increase livestock energy demands

by Wyoming Livestock Roundup

January exited with a blast of arctic cold. About this time, many gestating ewes and cows entered the third trimester, marking the last phase of pregnancy in which the bulk of fetal growth occurs.

The energy demands of cold temperatures and pregnancy increase the nutritional requirements of ewes and cows, and this is especially true for yearling ewes or first-calf heifers which are still making gains toward their mature body size. 

Nutritional requirements 

The 2022 University of Wyoming (UW) Extension bulletin “Supplementation Considerations for Ewes Managed on Dormant Winter Pastures and Rangelands” contains an excellent overview of nutritional requirements of sheep during this period with critical environmental and physiological burdens. 

On the beef cattle side, there is the 2015 University of Nebraska-Lincoln Extension bulletin “Supplementation Needs for Gestating and Lactating Beef Cows and Comparing the Prices of Supplement Sources.” 

These publications can be found online at and, respectively.

Supplementing with alfalfa, distillers’ grains or range cake supplies rumen degradable protein (RDP) – formerly known as degradable intake protein (DIP) – and can be an excellent source of nutrition during critical environmental and physiological burdens. 

This protein boosts rumen microbes which break down low-quality forages and helps the animal access energy which would otherwise be locked up in cellulose. 

Energy needs and disease

When forage is low in quality, as it often is during winter and after drought, it can become physically impossible for animals to consume enough to meet their energy or protein needs – they simply run out of space in their digestive systems. The growing fetus and expanding uterus further restrict the rumen and capacity for feed intake. 

Without proper management, the animal can go into a negative energy balance and begin to metabolize stored energy in the form of body fat reserves. This puts the body into a state of ketosis. 

If sustained for long periods, ketosis can develop into the metabolic disease commonly known as pregnancy toxemia. This is not the result of a calcium deficiency, as in milk fever, or a deficiency of magnesium, as in tetany, although these diseases should be ruled out when consulting with a veterinarian. 

Pregnancy toxemia is most likely to present late in gestation in sheep and goats carrying multiple offspring or in obese individuals, due to the spatial restrictions imposed on the rumen. 

Less frequently observed in cattle, pregnancy toxemia is most likely at or near peak lactation in high milking capacity individuals fed poor-quality diets which similarly enter a negative energy balance.

Common symptoms of pregnancy toxemia include an animal going off feed and showing lethargic behaviors, progressing to recumbency and death in severe cases. 

Neurological signs such as head pressing or circling may also occur as a result of ketone buildup in the blood. 

Routine observations and treatment 

As ranchers make their daily animal checks, they should look closely for any individuals appearing depressed and “out of it.”

Are they tracking movement? Are their ears up and eyes bright? Are they keeping their heads up as the rancher approaches? Are they up and eating at feeding time? 

These are routine livestock husbandry observations, but catching any problem animals early can lead to the best outcomes.

If pregnancy toxemia is suspected, work with a veterinarian to develop a treatment plan. Since the cause is a deficit in available energy, supplementation with rapidly available glucose is often the simplest and least invasive therapy. 

Many over-the-counter oral drenches are available to counter the effects of ketosis, but be sure the product is labeled for use in the correct species. Something labeled for use in cattle may not be labeled for use in sheep and vice versa. 

In extreme cases, a veterinarian can administer an intravenous glucose infusion. Watch affected animals closely for secondary infection during recovery from pregnancy toxemia.

While treatments are available, it is best to prevent pregnancy toxemia and/or ketosis from occurring in the first place. Ensure animals consume a high-quality, balanced diet and have access to clean water from late gestation to peak lactation. 

Use body condition scoring (BCS) to maintain breeding females in moderate flesh – BCS three to four for sheep and BCS five to six for cattle – avoiding both the thin and obese extremes of the scale. 

Utilize grain or concentrate supplements as appropriate, especially to provide sufficient protein when grazing dormant winter range, as animals enter the third trimester of gestation – 100 to 150 days of gestation for sheep and seven to nine months for cattle – or to counter the effects of severe winter weather events. 

For the rancher, nutritional management is one of the most powerful tools to prevent disease and enhance productivity. Producers can work with their local UW Extension educator to answer questions about winter livestock rations. 

Micah Most is the agriculture and natural resources educator with University of Wyoming Johnson County Extension. He can be reached at, 307-684-7522 or on Facebook and Instagram @UWExtensionJohnsonCounty.

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