BY JOHN PATERSON, PhD (Executive Director of Producer Education, NCBA)
What are several production factors to consider when trying to increase a herd’s profit margin?: Four factors to consider are: 1). percent calf crop based on the number of females exposed to the bull, 2). pounds of weaned calf per female exposed, 3). percent calf death loss and 4). average calf weight per day of age as a measure of your bull power. Feed consumed by the cowherd is a major cost of beef cattle production and has been estimated to be between 65 and 75% of total yearly cash costs. Much of this cost is for harvested or purchased feeds which are used to supplement pasture/rangeland during periods of low forage quality and or quantity. We have long understood how the cow’s requirements for dietary protein and energy change throughout the year and these changes can be graphically demonstrated in the following figure. The highest nutrient requirements are during early lactation and the lowest are during mid gestation. With regard to a pregnant cow, we have always assumed that we may not have to put as much effort into nutrition during mid-gestation compared to late gestation when the fetus is rapidly growing. What if we were wrong? Work by USDA scientists at Ft. Keogh in Miles City has raised the question “During early to mid gestation, are we feeding the fetus or are we feeding the placenta”? For example, testicle and ovary development occurs much earlier (first trimester) than rapid fetal growth during the last trimester.
While there is an abundance of research aimed at understanding the influence of nutrition on heifer development and reproductive performance, one limitation has been understanding the long term consequences of nutritional restriction of the pregnant cow on subsequent productivity of her heifer calf. The concept of “fetal programming” has been investigated to determine the long-term consequences of under-nutrition. For example, early work by Barker and his colleagues studied human birth records in the United Kingdom and Europe found that under-nutrition in the first half of gestation followed by adequate nutrition from mid-gestation to parturition resulted in infants of normal birth weight but were longer and thinner than normal. What was interesting from this research was that early fetal under-nutrition resulted in an increased incidence of health problems experienced as adults including obesity, diabetes and cardiovascular disease. With a focus on cattle, Rick Funston and his students at the University of Nebraska conducted a couple in interesting studies aimed at how maternal under-nutrition influenced heifer performance.
Their studies suggested that under-nutrition (no supplement) during pregnancy caused a reduction in heifer weaning weights and subsequent pregnancy percentages. Some other studies have reported instances of compromised maternal nutrition during gestation resulted in increased neonatal mortality, intestinal and respiratory dysfunction, decreased postnatal growth rates and surprisingly reduced meat quality.
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