Steve Boyles, OSU Beef Extension Specialist
Feeding a balanced diet to beef females in the last trimester of pregnancy through the breeding season is critical. Nutritional demands increase from early gestation to lactation. Reproduction has low priority among partitioning of nutrients for the subsequent pregnancy. Consequently, thin cows at calving typically remain thin because excess energy in the diet is directed to milk production first.
The common theme is, at least for spring-calving cows, body condition score at calving is related to postpartum interval and rebreeding performance. Plane of nutrition the last 50 to 60 days before calving affects postpartum interval. It is a challenge to increase body condition after calving or elicit a reproductive response to high energy intake in postpartum beef females.
Excessive protein and energy in the diet of beef females can result in reduced conception rates and increased feed costs. Excessive dietary nutrients during the last trimester of pregnancy may negatively influence calf birth weights and dystocia.
Rule of Thumb: When the crude protein (CP) concentration of the diet drops below 8% on a dry matter basis, the microbes in the rumen will not have enough nitrogen to optimize fiber digestion and dry matter intake.
Rule of Thumb: When corn is used as an energy source in a high forage diet, it should not exceed 0.3% of body weight on a dry matter (DM) basis because higher levels can have a negative effect on fiber digestion by lowering rumen pH.
Pelleted Soybean Hulls (SBH) can expand six to eight times in size when they come in contact with the rumen liquid and can cause bloat when fed at high levels. Rule of Thumb: They should be fed at levels not to exceed 1% of body weight on a DM basis (optimum may be. To prevent the possibility of digestive upsets, cattle should be adapted to wheat midds by slowly introducing them into the ration. Rule of Thumb: Wheat midds should not exceed about 0.5% of body weight (DM basis) in forage-based diets. Rule of Thumb: Slightly more corn gluten feed than corn distiller’s grains plus solubles can be added to the diet with a suggested upper inclusion level of 0.6% of body weight on a DM basis. The recommendation for brewer’s grains (wet or dry) is similar to that for corn gluten feed since brewer’s grains contain about the same level of protein as Corn distiller’s grains plus solubles, but typically have less energy, fat, sulfur, and phosphorus than corn gluten feed.
Excess: Overfeeding crude protein to dairy heifers during the breeding season and early gestation, particularly if the rumen receives an inadequate supply of energy, may be associated with decreased fertility. This decrease in fertility may result from decreased uterine pH during the luteal phase of the estrous cycle in cattle fed high levels of degradable crude protein. The combination of high levels of degradable crude protein and energy concentrations in early-season grasses may contribute to lower fertility rates in females grazing lush pastures near the time of breeding in the spring. Negative effects of excess rumen degradable protein intake on reproduction are documented in dairy literature (Ferguson, 2001).
Effect of DIP and UIP on Reproduction: The CP of a feed is fractioned into 2 components, Degradable Intake Protein (DIP) and Rumen Undegradable Intake Protein (UIP). Degradable Intake Protein is used by the rumen microbes to produce bacterial CP. Excess DIP is absorbed through the rumen wall into the blood supply, transported to the liver, and converted to urea, resulting in increased blood urea nitrogen (BUN) or plasma urea nitrogen, and finally exits the animal via urine. The effect of high BUN or plasma urea nitrogen and the negative effect on fertility is more established in dairy females. DIP intake increases BUN and uterine pH. The working hypothesis is that high BUN or plasma urea nitrogen resulting in high uterine pH causes reduced pregnancy rate in beef females. If there are, research suggests the culprit is not urea. There are limited data on the effect of high DIP intake on reproductive performance in beef females.
[Some articles use the terms Rumen Degradable Protein (RDP) and Rumen Undegradable Protein (RUP)]
Undegradable Intake Protein bypasses rumen degradation and enters the small intestine for breakdown and where amino acids (AA) are absorbed. Excess AA are catabolized in the liver producing urea. Some of the urea can be recycled and can return to the rumen as DIP.
Data from an ongoing research theme suggest feeding a ration to beef females high in UIP may positively affects ovarian characteristics. However, until results at the ovarian level can be translated to reproductive performance such as pregnancy rates, postpartum interval, and calving distribution, feeding DIP or UIP at supplementation amounts should be an economical decision.
Perhaps one of the most practical applications of the this system is the calculation of the animal’s DIP requirement to ensure optimal rumen function. The requirement for DIP is thought to be closely associated with the amount of fermentable energy in the diet. Specifically, the DIP requirement can be calculated as 10% to 13% of daily total digestible nutrients (TDN) intake. Lower values in this range are used when the cattle are receiving a low quality diet, such as dry winter forage or low quality hay, whereas higher values in the range are used when the cattle are receiving high quality forage or a ration including at least 50 percent concentrate. The UIP value of the feed can also be calculated by subtracting the DIP value from one. Rule of Thumb: The amount of DIP required to maximize forage use appears to be about 10 to 11% of the digestible organic matter (which is roughly the same as TDN content).
An example of DIP requirement and supply is to assume a cow is consuming 25 pounds of hay dry matter that contains 50% TDN. The cow therefore consumes a total of 12.5 pounds of TDN per day. Therefore, the DIP requirement is 12.5 pounds x 10%, or 1.25 pounds of DIP per day. If the hay contains 6% CP (dry matter basis), of which 65% is DIP, this cow would consume 0.98 pound of DIP each day (6% x 65% x 25 pounds). The requirement for supplemental DIP would be 0.27 pound (0.98 pound to 1.25 pounds).
Literature Citied
Cow-Calf Production In The U.S. Corn Belt. 2011. Midwest Plan Service. MWPS-66
Nutrient Requirements of Beef Cattle E-974. Oklahoma State University.
Rasby, R. and R. Funston. 2016, Invited Review: Nutrition and management of cows: Supplementation and feed additives. The Professional Animal Scientist 32 (2016):135–144.
OSU Beef Team. Library. https://u.osu.edu/beefteam/resource-library/