Energy and protein requirements of the cow increase by 15% to 20% from mid to late gestation to support fetal growth and prepare the cow for lactation. Requirements increase again by 20% to 30% during peak lactation (about eight weeks post-calving).
“Failing to meet nutrient requirements prior to and after calving can have major impacts on reproductive performance, particularly for young cows,” said Janna Block, the Extension livestock systems specialist based at North Dakota State University’s Hettinger Research Extension Center. “Reproductive failure is the most common reason for culling cows from the herd, and open cows are a financial drain on an operation due to lost revenue potential and high replacement costs.”
Body condition scores (BCS) at calving are a useful indicator of the cows’ energy reserves and the overall success of the nutrition program. It is a more reliable indicator than weight alone because weight is affected by factors such as gut fill, age, frame size, stage of gestation and milk production, according to Block.
The BCS scale, which goes from 1 to 9, is an indicator of the percentage of body fat. Body condition scores are assessed visually or by touching the ribs, spine, tail head, and hooks and pins.
BCS can be used to determine performance and whether changes should be made to nutritional management several key times of the year, including 90 days prior to calving, and at calving, weaning and breeding. Research has established that a certain amount of body fat is required for the reproductive system to function appropriately.
A strong relationship exists between BCS at calving and the number of days for cows to return to estrus. Ideally, BCS at calving should be 5 for mature cows and 6 for first-calf heifers, with condition maintained through breeding.
Block recommends including BCS of the cow with calving records. This will allow producers to assess the herd’s nutritional status on a large scale and will be useful when evaluating overall pregnancy rates after the next breeding season.
Consequences of calving in low body condition include smaller or weak calves, lower quality and quantity of colostrum, decreased milk production and reduced weaning weights. 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.
In addition, calving in BCS 4 or lower results in more cows being bred later in the breeding season and a reduction in overall pregnancy rates by up to 30%.
“Resuming estrous cycles and initiation of pregnancy are low on the biological priority list for nutrient use; therefore, these functions are likely to be compromised when energy stores are inadequate at calving,” Block says.
In late gestation, cows need to gain at least 100 pounds to support fetal growth and uterine development. If a cow simply is maintaining her weight during late gestation, she actually is losing body condition. Late-gestation diets should be designed so cows gain at least 1 pound per day to maintain condition, and more if an increase in condition is desired.
One body condition score represents about 80 to 100 pounds of live weight. If a 1,200-pound cow has a BCS of 4 at the beginning of the third trimester, she would need to gain at least 80 pounds to gain a condition score and at least another 100 pounds to support fetal development. Therefore, she should weigh 1,380 pounds at calving.
In this example, the cow would have to gain about 2 pounds per day, which may not be possible, depending on weather and access to high-quality feedstuffs. The ideal situation is to increase weight when requirements are lowest at weaning, but attempting to increase condition late is better than not doing it at all.
In situations where cows have calved in less than ideal body condition, weight gain must be increased rapidly following calving to achieve acceptable pregnancy rates.
“This is extremely challenging because large amounts of dietary energy are already required during early lactation just to maintain body tissues and support milk production,” Block notes. “Cows usually utilize a portion of their own energy (fat) stores for the first several months after calving to help overcome deficiencies, which can lead to weight and condition losses.”
Some research indicates mature cows that calve in slightly lower condition (BCS 4) still may have acceptable reproductive performance if they are fed to reach BCS 5 by breeding. However, producers still run a risk of increasing the calving interval.
First-calf heifers are less likely to respond to supplementation due to increased requirements, and negative impacts on reproduction are likely. In one study, heifers that calved with BCS of less than 5 had subsequent pregnancy rates of 67%, despite the fact that they were fed to gain nearly 2 pounds per day from calving to breeding.
“Producers should evaluate body condition at calving and act immediately if they want to salvage the breeding season for thin cows,” Block advises. “It will require enhanced management, access to extremely nutrient-dense feedstuffs and potentially the use of strategies such as early weaning calves to reduce requirements and induce estrus.”
Producers should contact their county’s NDSU Extension agent or an Extension specialist for more information about body condition scoring and ration evaluation. Go to https://www.ag.ndsu.edu/extension/directory/counties to locate an agent in your area.
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