Beef cows that have been underfed during gestation and lactation will be less productive than cows fed adequate diets.
“For adequate production, a beef cow’s daily ration must meet nutritional requirements,” says Karl Hoppe, a livestock systems specialist. “Cows will lose body weight when consuming less energy than needed for maintaining body functions and production demands.”
Extreme cold temperatures or wind chills will increase the cow’s energy needs substantially. If the cow doesn’t receive additional energy through her diet, she will take nutrients from her body to meet her energy demands.
Production problems will occur when the cow loses too much weight. However, a heavier cow will be able to lose more weight than a thin cow before serious production problems occur.
Close-up cow generic
A visual method for determining weight loss or gain in beef cows is body condition scoring (BCS). Beef cows that carry more condition (or fat) will rate a higher body condition score (maximum of BCS 9) than thin cows (minimum of BCS 1). A body condition score of 4 is borderline for maintaining adequate production in beef cows.
After calving, thin cows will require more days to reach first estrus (heat) and more days to become pregnant. Researchers report that cows with a borderline or lower BCS need an average of 12 more days to reach first estrus. For example, they found that cows with a BCS of 4 or less needed 61 days while cows with a BCS of 5 or greater needed 49 days to reach first estrus.
In addition, beef cows in this study with a BCS of 4 or less took six more days to become pregnant when compared with a cow with a BCS of 5 or greater (90 vs. 84 days). The researchers also found that 84 percent of cows with a BCS of 4 or less were pregnant within 60 days after calving, compared with 91 percent of cows with a BCS of 5 or greater.
For thin cows, increasing the level of energy in the diet after calving will increase the number of pregnant cows at 60 days after giving birth. Cows with a BCS of 4 or less will have comparable pregnancy rates to cows with BCS of 5 or greater when fed a diet that allows for maintaining or gaining weight after calving through rebreeding.
In this study, the amount of energy fed daily was 15.6, 12.6 and 8.9 pounds of total digestible nutrients (TDN) per head daily for high-, moderate- and low-feed energy diets, respectively. The amount of energy fed daily during flushing was 21.8 pounds of TDN.
Beef cows that are underfed during gestation and lactation may have additional areas of poor production:
• Underfeeding during gestation will reduce birth weights but may increase the number of difficult births, or dystocia.
• Undernourished or thin cows may have reduced quantity and quality of colostrum. Colostrum is a form of milk that mammals produce in late pregnancy. It contains energy, protein, fat and vitamins, plus antibodies to protect newborns against disease until their own immune system is totally functional. Lower-quality colostrum may result in calves with more illnesses (scours) during early lactation. Reduced immunity also may lead to poorer calf survival rates.
“A ration should be balanced for energy, crude protein, minerals and vitamins,” Hoppe says. “Nutrients are needed by the cow in constant proportions every day.”
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