Thanks to South Dakota State Extension for this article!
Nutritional management of the cow herd is more important during the periods of late pregnancy and early lactation than any other time in the annual production cycle.
“Nutrition has a huge impact on the performance of both the cow and the newborn calf,” said Ken Olson, Professor & SDSU Extension Beef Specialist. “Nutrition for the cow is important during this period because of its effect on subsequent reproductive performance.”
Olson explained that the nutritional status of the cow at the time she calves until initiation of the breeding season will determine if and when she returns to estrus (cycles). It will also determine her level of fertility.
“Basically, nutrition plays a large role in determining whether or not the cow will become pregnant,” he said. “Money invested in improving cow nutritional status now will pay for itself in terms of improved cow pregnancy rates and calf weaning weights this coming fall.”
To make the situation more complex, Olson said a cow’s nutrient requirements increase throughout the periods of late-pregnancy through early lactation.
Late Pregnancy Nutritional Requirements
“During late pregnancy, the fetus grows exponentially in the cow’s uterus, causing a directly proportional increase in nutrient requirements,” Olson said.
He explained that 70 percent of fetal growth occurs in the last three months of pregnancy. At the same time, the growing fetus is filling an ever-increasing portion of the cow’s body cavity, thus displacing rumen capacity.
“This often requires the need to provide higher quality feed in late pregnancy to overcome lost capacity for forage intake,” he said.
Calving nutritional requirements
After the calf is born, nutrient requirements rise dramatically to meet the demand of milk production.
“The amount of increase is directly proportional to the genetic potential to produce milk, so the breed and bloodlines of the cow will influence her requirements for nutrients to produce milk,” Olson said.
Nutrient evaluation tools
Olson recognized that all the changing variables make it challenging for cattle producers to manage the nutrient intake and match the nutrient demand. He encouraged producers to utilize tools available to help with this process.
Feed tests are the first tool Olson recommends cattle producers utilize when estimating a feed’s nutritional value.
“These tests are relatively straight forward with harvested feeds,” he said, of the test where representative samples are collected and sent to a feed testing lab.
Once nutrient levels are known, ration-balancing programs can be used to balance diets to meet nutrient requirements.
“Based on results, cattle producers can also consider alternative feeds or supplements to meet requirements, Olson said.
Knowing the nutrient content of grazed forage is much more difficult. “The character of the forage changes as time passes. Also, because grazing animals are selective, what they actually consume is better in quality than the average of everything available,” Olson said.
If sampling a pasture, attempt to grab samples similar to what the cows are eating, rather than clipping to ground level, as clipping does not represent what the cows will actually consume. However, any sample can still be useful in providing a starting point to estimate nutritional value.
Body Condition Scoring:
Body Condition Scoring (BCS) can help producers’ determine if a cow’s nutritional needs are being met. The most common BCS system is to numerically score the cows from 1 (thinnest) to 9 (fattest), with a moderate score of 5 being the most desirable at calving. Based on a great deal of research, Olson said cows with a BCS of 5 will have a high likelihood of returning to estrus by initiation of breeding.
“Managing BCS from calving until breeding is also important,” he said. “Research indicates that feeding management should be adjusted so that cows that are not at a BCS of 5 at calving move toward a score of 5 by initiation of breeding. In other words, thin cows should gain BCS and fat cows should lose BCS.”
Again, Olson added that research suggests movement in nutritional status (BCS) toward a moderate level (BCS=5) will increase fertility so more cows become pregnant.
Most beef cow nutritionists will recommend determining cows’ BCS at calving.
“We suggest taking this very literal,” Olson said. “If a producer is tagging and weighing calves as they are born, take a look at the cow and write down her BCS along with the calf data.”
As calving season progresses, keep track of the running average of the BCS of the cows. “If the running average is 5 or 6, the cows are in great shape and it will be a simple matter of feeding them adequate nutrition to maintain BCS,” he said.
The opposite is true, Olson said if the running average is less than 5. “Then, the feeding program should be changed to give the cows an opportunity to gain BCS before breeding begins,” he said.
Analysis: The second important aspect of recording cow BCS between calving and breeding is whether it is increasing or decreasing over time.
If the running average of BCS at calving is decreasing as calving season progresses, Olson said this is an indication that the cows are in a negative energy balance and pulling fat off their bodies (losing BCS).
He explained by sharing this example. “Let’s say the running average after the first week of calving is 5.2, but at the end of the second week it is 5.1 and by the end of the third week it is 4.9. In this example, there is evidence that BCS is slipping.”
Olson added that although an average BCS of 4.9 seems close enough to 5 to consider the herd to be at the status a cattle producer would want, there is a problem with this. “The BCS needs to remain at 4.9 until breeding and the fact that the running average is declining, suggests that it will not,” Olson said.
Olson added that a decreasing BCS is another indicator that the feeding program should be adjusted to provide the nutrients to gain body weight and condition.
Cow nutrition impacts calf performance
Nutrition of the cow during late gestation and early lactation is also very important to calf performance.
“Adequate nutrition to the pregnant cow will improve the nutritional status of the growing fetus inside the cow. This will lead to a strong calf that will have good vigor so that it stands quickly and suckles colostrum soon after birth,” Olson said. “All of this is important to the early development of the immune system in the calf and will influence its health and performance throughout its life.”
Olson added that under-nourishment of the cow will NOT reduce the birth weight of the calf to increase calving ease.
“It is a myth that under-nourishment of a cow results in a smaller calf and easier calving,” Olson said. “This practice actually backfires. Undernourished cows are weak and cannot labor as vigorously and undernourished newborn calves are weak, slow to rise, slow to suckle colostrum and as a result, will suffer increased risk of sickness and death.”
Cow nutrition after calving will also affect the amount and quality of milk produced, further influencing calf health and performance.