Health and Production Implications of Poor Winter Nutrition and How to Correctly Sample a Large Round Bale for Forage Analysis


Utilizing low quality forages can be a cost effective feeding strategy but an understanding of how these forages should be fed is essential. It is important to remember that feeding a beef cow is essentially feeding the rumen where bacterial fermentation is occurring. Rumen bacteria provide the enzymes necessary to break down plant fiber and release the stored plant protein and energy. As the feed moves through the digestive tract, bacteria are continually carried with it and ultimately digested, releasing additional protein and energy to the cow. When feeding low quality forages (for example straw) there may be inadequate rumen protein and energy available to sustain bacterial growth leading to poor digestibility of the forage. Impaction may result in cold weather as the cow attempts to eat more to get the needed energy but the rate of digestion has slowed due to inadequate bacterial activity. This is the principle behind protein and energy supplementation when feeding low quality forages. The additional protein and energy provides the substrate needed to sustain adequate bacterial growth so that the low quality forage can be broken down.

Potential problems with poor nutrition in a pregnant beef cow can be divided into short-term (few weeks), mid-term (several months) and long-term (future generation) consequences. Consideration of short-term negative effects should include the potential for acute or chronic nitrate poisoning and polio. Nitrates are normally picked up by the plant root and transported to the leaves where they are converted into plant protein. If the leaves are damaged due to drought or hail, conversion to protein is interrupted but the plant will continue to accumulate nitrates. If the plant recovers, nitrates will gradually decrease over 10 – 14 days but if the plant has been killed or cut, the nitrates will remain high. When consumed, nitrates (NO3) are converted to the toxic nitrite form (NO2) which interferes with the oxygen carrying capacity of the blood. Exposure to high levels may lead to death while chronic exposure at lower levels can lead to diarrhea, poor grow, reduced milk production and abortion. Canola based forages tend to be high in sulfur and if fed at high levels or in combination with a water source high in sulfur can lead to impaired trace mineral absorption and polio – a nervous disease of cattle. Cattle with polio may be found dead or down and seizuring. Blindness may be observed in the early stages.

Midterm effects of poor nutrition are related to body condition and the subsequent impact on fertility as well as potential negative effects on newborn calf health. Pre-calving nutrition is more important than post-calving nutrition in determining the length of time it takes a cow to begin cycling – in essence poor nutrition through the winter cannot be compensated for after calving.

Seventy percent of the energy requirement of a beef cow is for maintenance requirements and this requirement is a function of both body weight and body condition. Energy requirements of beef cows of similar weight will be different depending on body condition which is why body condition scoring (BCS) is important to use in conjunction with weight when estimating energy requirements of late gestation and early lactation beef cows. The main result of a negative energy balance is interference with the normal hormonal effects on the ovary leading to anestrus or failure to cycle. Early weaning, particularly in 1st and 2nd parity cows, is one strategy that can improve energy status and subsequent production efficiency through improved conception rates and can improve weaning weight of the subsequent calf crop by 15 – 20 lbs.

The importance of adequate protein and energy during gestation goes beyond maintaining cow body condition. A recent U.S. study showed that heifers born to cows that received protein supplementa-tion while grazing dormant winter pastures had significantly better 1st calf conception than heifers born to cows that were not supplemented. This “fetal programming” effect emphasizes the importance of gestational nutrition on subsequent generation productivity. Adequate protein is also essential for colostrum production and the well documented disease protection colostrum derived immunoglobulins and other immune factors provide to the new born calf. In addition to disease protection for the newborn calf, adequate intake of high quality colostrum has been shown to reduce respiratory disease at weaning and improve feedlot performance.

In summary, the goal of a wintering feeding program should be a least cost ration that meets the protein and energy requirements of the gestating cow. Feed analysis and body condition scoring are essential starting points to developing a balanced ration. Insuring adequate consumption of a balanced mineral mix is also important in post calving fertility and calf health.



Video on Taking a Forage Sample from a Large Round Bale with Dr. Keith Johnson (Perdue University)