Much of Oklahoma and the Southern Plains should have wheat pasture to utilize as winter feed for stocker cattle, replacement heifers, and in some cases for adult cows. At, and after calving time next January, February, and March “grass tetany” could occur in a few situations. Planning ahead now could reduce the risk of grass tetany during the spring calving season.
Grass tetany, caused by magnesium deficiency does not seem to be a major problem in Oklahoma although occasional cases are reported. It typically occurs in beef cows during early lactation and is more prevalent in older cows. The reason older cows are thought to be vulnerable is due to the fact that they are less able to mobilize magnesium reserves from the bones than are younger cows. Grass tetany most frequently occurs when cattle are grazing lush immature grasses or small grains pastures and tends to be more prevalent during periods of cloudy weather. Symptoms include incoordination, salivation, excitability (aggressive behavior towards humans) and, in final stages, tetany, convulsions and death.
It is known that factors other than simply the magnesium content of the forage can increase the probability of grass tetany. High levels of potassium in forages can decrease absorption of magnesium and most lush, immature forages are high in potassium. High levels of nitrogen fertilization have also been shown to increase the incidence of tetany although feeding protein supplements has not. Other factors such as the presence of certain organic acids in tetany-causing forages have been linked with tetany. It is likely that a combination of factors, all related to characteristics of lush forage are involved.
When conditions for occurrence of tetany are suspected, cows should be provided mineral mixes containing 12 to 15 percent magnesium and be consumed at 3 to 4 ounces per day. It is best for the supplements to be started a couple of months ahead of the period of tetany danger so that proper intake can be established. Because tetany can also occur when calcium is low, calcium supplementation should also be included. Symptoms of tetany from deficiencies of both minerals are indistinguishable without blood tests and the treatment consists of intravenous injections of calcium and magnesium gluconate, which supplies both minerals.
Cows grazing lush small grain pastures should be fed mineral mixes containing both calcium and magnesium. Learn more about mineral nutrition of grazing cattle by downloading and reading the Oklahoma State University Extension Circular E-861 Vitamin and Mineral Nutrition of Grazing Cattle.
Body condition at calving is still a key to reproductive success
We can sub-title this article: “Back to the basics”. Very often in this newsletter or other beef cow related communications, the term “body condition score” is used. It may be time for a brief refresher about this important management tool. Body condition scoring is a manner of evaluating the fatness and therefore the nutritional status of beef cows. Most small to medium sized ranching operations do not have scales to routinely weigh cattle and determine weight and body condition changes. However, everyone has the capability to visually observe cows from the pickup window or on horseback. Body condition is categorized by a scoring system based on “1” being very emaciated and “9” is extremely obese. Most commercial range cows will be in the middle three scores of 4, 5, and 6.
One of the major constraints in the improvement of reproductive efficiency of beef cows is the duration of the post-calving anestrus period. The “anestrus period” is defined as the days between calving and the return to normal heat cycles. If cows are to maintain a calving interval of 1 year they must conceive within 80 to 85 days after calving. Body condition at calving time determines to a great extent the re-breeding performance of beef cows in the subsequent breeding season. Body condition at calving tends to determine the number of days before the cow returns to heat cycles. Based on research of mature and young cows from several studies, cows that maintained body weight and therefore ample energy reserves before parturition exhibited heat cycles sooner than cows that lost considerable body weight and consequently had poor energy reserves. Therefore cows that returned to heat cycles earlier, had more opportunities for heat cycles and ovaluations during the breeding season and consequently have higher conception rates.
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