Even though individual aspects of management conditions and forage quality from one beef producer to another make definitive research regarding the benefits of fat supplementation in beef cattle reproduction an elusive goal, knowledge in some areas has dramatically improved in recent years. Research data shows that supplementing fat for prepartum first-calf heifers probably results in the greatest benefit. Reproductive traits tend to be low in heritability in beef cattle, so providing a supportive environment is critical to reproductive success.
Beef researcher, Rick Funston, at the University of Nebraska's West Central Research and Extension Center, says supplementation as an energy density enhancer to maintain body condition is the primary way lipids are used in today's beef industry.
"Lipids aren't going to cure any specific problem," Funston says. "Good management and feeding a balanced diet will go further in dealing with reproductive issues than adding lipids. Producers will be able to manage reproduction better if they have a good understanding of the role lipids play in that process."
One of the most important roles of lipids in beef reproduction is that of serving as a primary source of nutrition-based energy. In research studies, unsaturated fats seemed to provide an advantage in terms of pure energy. Oils derived from plants appear to have the greatest effect on reproduction, including sunflower, safflower, cottonseed, rice hulls and soybeans.
"Unsaturated fatty acids demonstrated the most consistent effects on reproduction in the research we've reviewed," Funston says. "Saturated fats, such as tallow and calcium salts of fatty acids that are derived from animals, escape rumen biohydrogenation to a greater degree. One exception is the polyunsaturated fatty acids in fishmeal. They also bypass the rumen but have been reported to affect the reproductive process anyway."
Funston notes that lipids high in linoleic acid have been shown to negatively affect reproduction postpartum. A 2003 study demonstrated that high-linoleate safflower oil increased prostaglandin (PGF)-metabolite between 25 and 80 days postpartum. It also tended to decrease first-service conception rates.
"Because it's so hard to duplicate research, our studies on the benefits of fat supplementation on reproduction have mostly been inconclusive," he says. "Most studies show a lack of consistent effect on pregnancy rates."
One of the research exceptions Funston points to is a 1997 study in which late-gestation heifers received safflower seeds from day 230 until calving. The supplement consisted of 0.68 kg per day, which was approximately 4.7% of the fat in the diet. The result was a subsequent increased pregnancy rate of 19% compared to control diets with similar energy and protein content.
A 2001 study provided first-calf heifers either a safflower, soybean or sunflower seed supplement (4.7%, 3.8% and 5.1% fat in the diet respectively) for the last 65 days prior to calving. The subsequent pregnancy rates were 94%, 90% and 91% respectively compared to the control's 79% on an equivalent energy diet that included 2.4% fat.
"Even with duplicated studies like this, hidden exceptions can sometimes emerge," Funston says. "In a third experiment with a sunflower supplement (6.5% fat) the last 68 days before calving, the subsequent pregnancy rate was not improved in comparison to the control diet that was 2.2% fat.”
In analyzing the third study, Funston says researchers determined that forage availability and quality were key factors responsible for the conflicting results. The higher volume and quality of forage available to cattle in the second study allowed them to attain the high rate of reproduction response.
"Even though our research has shown that particular fatty acids can affect specific reproductive processes, producers can't rely on the fact that the supplements will enhance pregnancy rates.
"Our studies show that several hormones important for reproduction are affected by lipid supplementation," he says. "In spite of this, there's a lack of consistent effects on pregnancy rates in the study data. We cannot conclusively determine that improvements in reproduction that were observed in the studies were the direct result of added energy or the effect of specific fatty acids."
As a result, Funston advises producers to consider supplemental fat sources only if the cost of adding them to the ration would be low cost.
"A better approach to reproductive management is a sound herd health program that provides appropriate supplementation to support immune system function, proper overall nutrition and proactive measures to control diseases and disorders that could otherwise negatively affect calf production," he says. "Maintaining the appropriate body condition score is correlated with several reproductive events, including postpartum interval, services per conception, calving interval, milk production, weaning weight, calving difficulty and calf survival."
Funston notes that the appropriate body condition is the single most important factor controlling when a beef heifer will cycle after calving.
"Heifers should have an optimum body condition of 5 to 6 from calving through breeding to assure optimal reproduction performance," Funson says. "Nutritional demands increase greatly in late gestation and are even greater in early lactation. Studies confirm that oilseed supplements in prepartum heifer diets increases conception rates and tend to increase calf weaning weights. Research data confirms that heifers on diets deficient in energy or protein during the last trimester experience more calving difficulty and will breed back later in the breeding season. Their calves also experience increased sickness, death and lower weaning weights."
During the past two decades, Funston and other U.S. researchers have dedicated significant efforts to exploring how, what and when fats influence beef cattle reproduction. Understanding all the roles lipids play in the reproduction process still requires more research.
"The complexity of the reproductive system and makeup of fat supplements are often confounded by management conditions and forage quality, both in research and commercial feeding situations," Funston says. "This has contributed to inconsistencies in research findings. When producers are planning feeding programs, reproduction often has low priority in that plan. The last 50 to 60 days before calving have a profound effect on postpartum interval. So cows in thin body condition often don't rebreed."
Nutritional tips for optimizing reproductive efficiency
• A sound herd health program is essential for reproductive efficiency.
• Keep heifers on a balanced ration the last trimester of pregnancy through the breeding season.
• According to research findings, if there is a reproductive benefit to supplementing fat, it is probably prepartum, targeting those animals most in need, such as young, growing, first-calf heifers.
• Keep heifers in optimum body condition (5-6) at calving and through the breeding season.
Is an Associate Professor in the Department of Animal Science where he Conducts research addressing cow/calf reproductive problem’s that are unique to West Central Nebraska and to other beef producers within the state for the University of Nebraska Lincoln, where he also provides leadership and subject matter expertise for educational programs in cow/calf production management for the West Central District and statewide expertise in beef reproductive management programs. Mr. Funston received his Ph.D. from the University of Wyoming in 1993 and his Post Doc from Colorado State University in 1995. From1998 to 2002 Mr. Funston was the Extension Beef Specialist with Animal/Range Sciences at Montana State University. He assumed his current position as Reproductive Physiologist in the Animal Science Department at the University of Nebraska Lincoln in 2002. His areas of expertise include beef cattle reproductive management research and extension appointment, and Optimizing reproductive efficiency in beef cattle operations to reduce production costs and increase net returns in cow/calf operations.