by: Stephen B. Blezinger

Part 2

Genetic potential. In the cattle industry we talk about this in some manner all the time. Any observable or measurable trait or performance parameter that is ultimately controlled by the animal's genetics is of concern to the producer. In most cases this is especially true of those traits which directly affect profitability.

Genetic traits such as hair coat color, whether the animal is polled or horned, temperament (although this is also affected by management and handling), age at puberty, heat tolerance, stress resistance, external parasite resistance, etc. are controlled by selection but not by feeding or management. But the list of traits that ARE initially predestined by the animal's genetic make-up and subsequently affected by how the animal is fed and managed is extensive and in many cases may be interactive (i.e., the expression of one genetic trait may be linked to another). Some of these include:

1)      Reproductive efficiency

2)      Milking ability

3)      Calf weight/size at birth

4)      Mature frame score

5)      Average daily gain

6)      Weaning weight

7)      Yearling weight

8)      Feed efficiency

9)      Residual feed intake

10)      Carcass characteristics and quality

11)      Immunity

12)      Longevity

This list is not exhaustive but illustrates the many parameters that the cattle producer does in fact have a certain amount of control over through his management efforts. This control and how the producer manages these animals has a significant effect on how these various genetic parameters are expressed as well as how efficiently they are expressed. Interestingly enough, when we regularly discuss the various management and nutrition techniques that research and practice have shown us should be used, this is in relation to how well the animal's genetics respond to these applications and thus are expressed.

A Little Basic Genetic Lesson

In the first part of this series we discussed the starting point of this process: conception. But it actually goes back before that. This truly starts with the selection of the animals that the producer chooses to use in his herd. Each animal has a basic genetic profile that it passes on to its offspring. As such, this genetic profile and how the individual DNA structure sets the blueprint for the new animal at conception. But something to consider is that this parental DNA was affected by THAT animals predecessors and subsequently by how it was fed and managed, etc. because over time, the parent animal's DNA may be affected in some manner by its environment, stress level, plane of nutrition and so on. So you see that the expression of genetic potential is not limited to the immediate generation. This has a very real, multi-generational effect so that in a breeding operation how the producer manages a given group of individuals that may be used for breeding purposes (bulls and heifers) could affect generations to come. As an aside, with this in mind we see that the affect we have on bulls through feeding and management subsequently has a larger overall effect on the herd since the bull has input each year into a larger number of animals born on the ranch.

But let's review the basics of how the genetic material is established in each animal. Remember from middle school biology that the blueprint for all life is deoxyribonucleic acid or DNA. DNA is essentially the instruction manual for everything happening in the animal anatomically and physiologically and includes how cells and tissues divide, multiply and accumulate. It also dictates, as affected by a large number of environmental factors, how the fetus and later the animal grows and develops, establishes the immune system, the ability to grow at a certain rate, and so on.

As mentioned previously the DNA for a given individual is established at the point of conception and is a combination of that DNA delivered from the sire in the sperm and from the dam in the ova. This begins the actual mechanics of the selections breeders make when mating specific males and females. Careful consideration should be given to EPD's (in purebred operations) which provide an indicator of what an animal's genetic potential is for traits like birth weight, weaning weight, milk production and so on. These EPD values have a physiological base in the genetic material that is the platform for this performance. But additionally, consideration must be given to the actual performance of that animal or its parents.

As discussed in the previous part of this series, DNA begins its role almost immediately after conception, instructing the fertilized egg cell to begin dividing and transitioning into an embryo and then a fetus. The DNA blueprint then goes on to set the protocol for how the tissues and various physiological systems develop in the rapidly growing and developing body. During these early stages (only a few days after conception) the cells of the new embryo undergo exponential reproduction and growth, generally the most rapid cellular division of its entire life. If conditions are not optimal (i.e. nutrient availability is lacking or in the wrong proportions), opportunity exists for problems or errors to occur in the genetic codes or instructions. At the very least the embryo/fetus may not grow and develop as it should.

This is where a RNA or Ribonucleic Acid comes into the picture. While DNA is the instruction manual that resides in the nucleus of the cells, RNA leaves the nucleus and the cells and is essentially the individual pages of the instruction manual. It provides specific instructions on how the countless actions and reactions in the cells, tissues and entire body are to occur. It provides instruction as to which cells, tissues and organs are to develop in what sequence.

At this point there is significant opportunity for problems to develop. While DNA is very stable, and has methods to detect errors and mechanisms to repair these errors, RNA does not this same capability. Both DNA and RNA are capable of making copies of themselves. DNA copies are generally very good. This is not always the case with RNA as it can make flawed copies of itself and does not really have a way to repair these flaws. Additionally, RNA replicates itself about 10 times faster than DNA so the necessary building blocks must be in place constantly to support this copying process.

We tend to focus on this process during the embryonic and fetal stage but the process is continuous throughout life and may be seen as the body heals, turns over various cellular “pools” deals with stress, weight gain and loss and gain again and so on. This overall process becomes less effective and efficient as the animal ages. As its ability to recreate new cellular material (per DNA and RNA instruction) declines, the result is the aging process and eventual death of the animal, assuming it dies of old age, of natural causes. This not an overly common occurrence in the cattle business.

Optimization of Genetic Expression

It is doubtful that expression of the genetic base established in a given animal can truly be optimized. This is largely due to the fact that the animal exists constantly subject to environmental. While we can control a great many management components, we can't control heat and humidity, cold and wet, drought, etc. Let's take a moment and talk about what we CAN control.


In the article written here for over 15 years, nutritional management has been a constantly recurring theme. Providing the right nutrients at the right time in the right amounts has been discussed at nauseum. In general this has been in the context of improving performance and profitability. However, the underlying message has always been the provision of proper nutrients at various stages of production in order to optimize the genetics the animal begins with. Note that in this case we are discussing OPTIMIZING genetic expression, not MAXIMIZING. These are two different goals. Although we can never really identify where the animal's maximum genetic potential may be (let's say for average daily gain), research has shown that in many situations, in order to reach that maximum, we would: 1) have to feed and manage all the animal individually since, unless they are clones, these have different genetic makeups and 2) push the animal beyond what might be economically feasible. In this situation, since we generally manage and feed animals in a group we have to target the appropriate ration for that group, in the environmental conditions they are in and the most cost effective feed formulation and feeding rate. So in many cases we are providing feeding and management that may not result in the most genetic expression but the best expression that will be the most profitable for the producer. So in this situation we may not be providing nutrients to maximize average daily gains but rather the goal is to optimize feed efficiency so that the cattle are gaining the most at the lowest level of feed intake and at the best possible cost.

In general, proper nutrition to optimize the genetic base that has been established entails an understanding of what the animal needs (nutritionally) at what stage in its life. For cow/calf operations, the vast majority of the time, this is based on the forage conditions upon which the animal is living. As any producer can tell you that grazes cattle and produces forages for later feeding, this is wildly variable. In a pasture operation, as we have discussed here so many times, the nutrient availability (protein, energy as can be extracted from fiber digestion, minerals, vitamins) fluctuates throughout the year. During those periods when nutrient availability is less than what the animal requires, supplementation of nutrients may be required in order to maintain the availability and “flow.” However, in some case the nutrient availability may be in excess. For instance in cattle grazing early spring winter annuals that have been heavily fertilized, the protein levels may actually be in excess of what the animal requires. This has been shown by research to actually cause problems in many situations and can have negative effects on breeding and even average daily gains.

Minimizing Factors Which Might Create a Drain on Nutrient Intake

Maintaining a constant, properly balanced level of nutrient intake is critical to optimizing expression of genetics in mature and growing cattle. While the producer works constantly to manage forage variability and providing the right and most cost effective supplementation, there are factors that reduce to detract from the nutrient delivery. Some of these factors may also reduce the utilization of nutrients for productive means.

These are commonly known and can be controlled in some situations but not in others. Some examples include:

Internal parasites – it is well documented that the various stomach worms, liver flukes and other internal parasites will consume nutrients that are targeted for the cow. Heavy parasite infestations can significantly reduce animal performance if not controlled. A well-managed, aggressive internal parasite control program is critical to maintaining a productive nutritional plane in the animal.

External Parasites – flies, lice, grubs all create a nutrient drain on the animal by sucking blood and simply the constant irritation they cause. Again, controlling these pests is essential to maintaining the nutrient flow to the animal and reducing stress.

Environmental Stress – in addition to the stress created by parasites, other forms of stress also cause a drain on nutrient supply and availability. During periods of stress the animal much direct certain levels of nutrients (energy for instance) to the parts of the body affected. In cases of heat or cold stress, this may be the entire body as the animal uses increased levels of energy to stay cool or warm. In other cases, such as handling stress can also drain critical nutrients for the animal's body


A focus on maximizing genetic expression is the core of all cattle operations. Every management and nutritional component we utilize has a direct effect on how well the genetic choices the producer makes is exhibited.

Copyright 2014 – Dr. Stephen B. Blezinger. Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at or at (903) 352-3475. For more information please visit us on at www.facebook/reveillelivestockconcepts.

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