Fetal Programming Update

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Producers are aware of the complexities of beef cattle production as they attempt to efficiently manage their cow herds throughout adverse environmental conditions. From breeding to end product, managerial decisions impact the herd’s overall performance and profitability. With feed costs being the largest expense in the cow-calf sector, it’s no surprise that producers spend much of their time evaluating nutritional management decisions. These decisions are influenced by a variety of factors, including available forage quality/quantity, current cow condition, production goals, cost and labor availability.

The decision to graze dormant pastures is often made out of economic feasibility, as it can significantly minimize production costs, but it can also impact cow condition and calf performance. While continuous supplementation has been shown to be expensive, with little to no return on investment, it has been proposed that targeting supplementation to critical physiological periods may reduce production costs while positively affecting developmental programming.

Fetal or developmental programming is the concept that stressors encountered during critical windows of fetal growth (such as inadequate nutrient availability or prolonged stress) can alter development and have lasting consequences in offspring. Transgenerational impacts have also been noted, further increasing the idea’s complexity.

The concept of fetal programming is not necessarily new. It originated from human epidemiological data in which stressors in utero, like poor maternal nutrition during famine, altered long-term development, growth and health in children. This theory resulted in subsequent animal studies focusing on understanding how fetal programming could be used to impact animal production, performance, profitability and health.

With their relatively long gestation period, compared to other livestock species, cows are more prone to experience periods of environmental stress or nutrient restriction (either protein and/or energy deficiency) throughout gestation. In the western United States for example, rangeland forage is often dormant during periods of significant energy demands for cows. As a result, their nutrient requirements are not being met. These forage-based production systems are also subject to seasonal variation, which can further increase challenges to producers. For this reason, research has been conducted to understand how different environments and systems impact the production system as a whole, from conception to harvest.

Studies in beef cattle production have mainly been focused on mid to late gestation for two main reasons. During early gestation, producers are often more concerned about the calf at side rather than the gestating fetus, and fetal requirements are minimal in the first trimester of gestation. However, there is critical development occurring at each stage of gestation. Early gestation includes placental development as well as skeletal muscle and adipose (fat) tissue development. Recent studies have found that poor maternal nutrition in early to mid-gestation results in fewer muscle fibers at birth. While muscle cells can grow after birth, they cannot increase in number; therefore, the degree of muscling in an animal depends on both genetic potential as well as nutrition in utero.

Deposition of fat tissue in skeletal muscle also appears to be influenced by maternal nutrition during gestation. Fat cell development occurs in mid to late gestation, and it’s believed that a greater number of fat cells within muscle increases the marbling potential of an animal. This would suggest that if maternal nutrition was compromised, offspring would have decreased marbling potential, thus lowering carcass quality grades.

Past studies have been inconsistent in determining the effects of protein supplementation during late gestation on steer growth and feedlot performance. However, recent research at South Dakota State University found that progeny of energy-restricted cows tended to have an increased ratio of marbling to backfat, resulting in improved yield grades. This result suggests maternal restriction favorably shifted the distribution of fat within the body. There were also no differences seen in other carcass composition or meat characteristics, suggesting it is possible for offspring to overcome gestational restrictions.

Unfortunately, the negative effects that maternal energy restriction had on feedlot receiving weights and potential health in the feedlot need to be further considered, despite favorable carcass outcomes. A decrease in calf health has been noted in numerous studies, including those referenced, as a result of undernutrition in gestating cows.

A recent study from the University of Nebraska evaluated the effect of forage type (sub-irrigated meadow or upland range) and supplementation level on progeny growth and reproductive performance in heifers. Contrary to previous studies, it was found that dam supplementation had no effect on body weight of calves from birth to completion of development. However, sex-specific differences were noted. Heifer-calf 205-day adjusted weaning weight was increased by both supplementation and meadow grazing. Furthermore, pregnancy rate of the heifers as primiparous cows was increased by maternal meadow grazing and heifer progeny’s first calf body weight and rate of dystocia was increased by dam supplementation.

Additional studies have found maternal nutrition may influence the lifetime productivity of heifer progeny. While previous studies did not note significant differences for body weight or reproductive performance of heifer progeny born from protein-supplemented and non-supplemented dams, long-term, retrospective studies have uncovered new findings. Heifer progeny that were exposed to drought conditions in utero had increased lifetime productivity and retention in arid rangelands, possibly due to their ability to adapt to environmental stressors. This suggests that supplementation during key gestation periods may actually imprint progeny to have higher nutrient requirements for reproductive performance in more arid environments.

Continued research is needed to fully understand the application of fetal programming in a production setting. From both current and previous research, it is clear that timing and severity of maternal nutrient restriction can impact calf performance from both a production standpoint as well as carcass and meat quality.

Transgenerational effects of fetal programing are apparent throughout the research but are poorly understood due to influencing factors. Further understanding the mechanisms involved in altering progeny performance as a result of maternal nutrient status is imperative to developing management strategies that will allow maternal dietary management to be used as a tool to positively influence calf performance.

Written by: Emily Stribling, Contributing Writer
Source: Nebraska Cattleman October Issue

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