Cattle Today

Cattle Today



by: Stephen B. Blezinger

In working with various cattle producing clients the one fact that I work hardest to impress upon the owner or operator is that there is no replacement for good genetics, sound management and proper nutrition. With calving season well into swing, producers should be focusing on what it will take to get these females rebred after the calf is on the ground. Our focus today is once again the nutritional part of this equation and more specifically on concepts that are emerging from years of research. Specifically we are going to take a look at some nutritional effects on reproduction and factors which may come into play when a producer is attempting to get these cows bred. Research and practice has shown us that there are a number of nutritional components that have positive and negative effects on reproduction. We are going to examine some of these concepts and discuss issues concerning the relationships between nutrition and reproduction.

The Basics

Before we go a lot further let's take a brief look at reproductive function and the effect that nutrition in general plays. To begin the first thing we have to recognize is that nutrients taken into the cow are prioritized. In other words, in general nutrients such as protein, energy, minerals and vitamins will be used first by the animal's systems and physiological processes in order of most to least importance. From the perspective of the cow's survival, reproduction is pretty far down the priority list. Generally, it's considered to be dead last. If a cow's nutrient intake is substandard, less than what she needs to perform at 100%, the repro system will be the first to be shut down or at least inhibited. This will result in delayed return to normal cycling after delivery, failure to settle, etc. In some cases it can mean a failure to retain a pregnancy. In studying normal reproductive processes we know that it is a highly complex system. Being that I am a nutritionist and not a reproductive physiologist I won't attempt to go into details only to embarrass myself. We do know that production of hormones such as estrogen and progesterone are required for normal cycling activity and maintenance of the pregnancy. In order for these hormones to be produced at appropriate levels they must have the necessary "raw materials" or building blocks. Research has shown that certain fats and fatty acids are vital to the production of these hormones.

Additionally, we know that other nutrients such as protein, energy, vitamins and minerals are required for tissue generation and regeneration as a normal cycle ensues. A depression in the intake of any of these components can result in any number of complications in normal cycling. It can also result in a delay in placental loss (cleanouts) after calving which can result in infections of the tract. This can obviously have wider ranging implications to the cow's general health.

What Makes Nutrients Different?

When we look at the various nutrients we are concerned with and their role in an organism we see that different nutrients have different functions. We also see that in the process that takes the various nutrients from the plant material or grain that the cow eats to it's ultimate use in the animal's body that a break-down and reconstruction process occurs. The animal takes the feed or forage material in, mechanically breaks down the material through chewing and the microbial fermentation process in the rumen. This results in a disassembly of the plant material to much of the basic components - proteins, carbohydrates, fats, fibers, minerals and vitamins. Many of these nutrients end up ingested by the microbes themselves which in turn are digested by the cow. Through the rumination process and further processing in the other stomach compartments, the nutrients are reduced in size to that which is appropriate for absorption in the small intestine. From there it is taken to the liver and on to the animal's tissues and individual cells for reconstruction into protein, bone, fat or other vital tissues.

Protein is a building-block nutrient. Once consumed it is broken down into smaller protein fragments and into amino acids, the basic component of proteins. What makes these amino acids "special" is that they contain nitrogen. It also contains carbon, hydrogen and oxygen (a couple contain sulfur). This makes amino acids unique in that no other nutrient includes nitrogen. When the amino acids are broken down in the liver, the nitrogen is removed in the form of ammonia or similar compounds and then reassembled into other amino acids for use somewhere in the body. In general proteins or more specifically, amino acids are used in structural functions - muscle and base bone matrix (which is later filled in with minerals to form the bone material we are familiar with). They are also used as components of hormones and enzymes which catalyze many of the processes in the body. In ruminants, proteins are broken down in the rumen. Generally the nitrogen portion is broken off in the form of ammonia. If more protein is available than is utilizable by the microorganisms much of the ammonia is absorbed through the ruminal wall into the bloodstream and then carried to the liver where it is converted to urea. The urea then returns to the bloodstream and much of the excess is concentrated in the kidneys and excreted in the urine.

Carbohydrates are the overall category for fibers (plant material) and starches or sugars (grain material). Carbohydrates are largely used as an initial and readily available energy source and are fairly complex molecules made up predominantly of carbon, oxygen and hydrogen. In general fiber or starch is very similar in it's basic molecular assembly. Only a very few connecting points in the molecule make it different but that makes all the difference in the world. Because of these differences, starches and sugars are much easier and more extensively broken down. When we look for a readily available energy source we typically look to the grains. Fiber material is also a source of energy but is more difficult to break down and cannot be broken down as extensively. Subsequently, we can't get as much energy out of fiber and more tends to pass on through the digestive tract. This is a good thing since in many cases it helps maintain rumen and digestive tract health.

Fats, like carbohydrates, are made up of carbon, hydrogen and oxygen but in a different configuration. Fats are generals composed of chains of carbon of varying length. We've found that fat in general is made up of smaller components called fatty acids and that different fatty acids play different roles in the body. In general fat is also an energy source but generally only after it has been processed through the body and has been deposited somewhere. In a cow that's typically under the skin, between muscle fibers and between muscle groups, in and around the reproductive tract and so on. In a nutritionist it's typically in the gut or on his behind. This fat can be accessed by the body later as an energy source if insufficient energy from carbohydrates is not needed or if they are needed for other purposes, i.e. precursors of hormones, etc.

Minerals and Vitamins are generally found complexed with proteins and carbohydrates in plant material and once broken out and absorbed by the body are used in countless processes. Minerals such as Calcium and Phosphorus are vital to bone growth and development and maintenance of these tissues. Phosphorus is required in metabolism of energy in the body. Potassium and Chlorine are needed to maintain appropriate levels of water in the cells and tissues as well as aid in the transmission of nerve impulses. Iron is required in the manufacture of hemoglobin for the transportation of oxygen in the blood. Copper is required in the cells in the energy generating structures known as mitochondria. Vitamin A plays a vital role in the chemical cycles involved in the vision process. Niacin is required in the energy metabolism processes. These are only a very small number of examples where minerals and vitamins are required.

Nutrient Effects on Reproductive Function

One thing we have learned is that as we look at the various nutrients and more specifically the components that make up these nutrients, we find that the presence, either excess or insufficiency of individual components can have a significant effect on physiological processes such as reproduction, growth and heath. These effects can be positive or negative. Lets look at a couple of examples:

I. Negative Effectors on Reproduction. When we discuss supplemental feeding of a cow herd, in virtually every instance protein supplementation is brought up. In general, the average cattleman thinks of the protein requirements of the cow and unfortunately not a lot else in many cases. Sometimes this is justified. Other times it is not. In many cases during certain times of the year and while cattle are consuming certain forage sources, protein does tend to be lacking. Some interesting research over recent years has provided a different insight into protein levels fed to cattle and how this affects reproduction. We know that insufficient protein can directly influence reproductive activity either directly or indirectly. On the other side of the coin, however, research has found that excessive protein feeding has a negative effect on reproductive function primarily due to the increase in nitrogen levels (remember the discussion above?) in the blood. This nitrogen is, as we discussed, in the form of urea and can be measured as blood urea nitrogen (BUN). Research has shown repeatedly that an increase in BUN, which is a result from over consumption of protein has resulted in reduced conception rates in heifers and mature cows. Several theories have been proposed as to why this occurs. One, it is thought that the excess nitrogen negatively effects the uterine environment. Cows receiving excess protein may be conceiving but because of potential abnormal uterine changes brought about by the high BUN levels, the embryos are not surviving. A second theory suggests that because extra energy is required to detoxify the additional ammonia in the blood, this extra energy is taken away from normal ovarian activity which slows it down. Regardless of which theory is correct (and it may be neither) we know that conception rates decrease when cows receive high protein levels.

Why could this be a problem? It is common for many herds to calve in the spring of the year. In many cases, calving may occur from late January through April. Subsequently we want these cows to breed back within 90 days to keep them in cycle. This puts them breeding back during Feb, March, April, May and June. In the earlier months it is quite common for cows to be grazing winter pasture of some sort either planted or volunteer. Depending on weather conditions - temperature and rainfall, this early spring grazing may be quite lush. Often this grass is very high in protein, especially if it has been fertilized. Fertilized, growing ryegrass can reach 32 to 35 percent protein in many cases. Other early spring forages can also exhibit high protein levels. This can often be coupled with the fact that after the winter months, cows have often lost body condition and the producer sees the need to supplement these cattle. As discussed earlier, in most cases, when a cow man thinks about supplementation he thinks about protein so it's quite common to see cows in the early spring, on decent pasture, receiving a protein supplement as well. In these cases, a situation develops as described above where the excess protein can lead to high blood nitrogen levels which can delay conception. It's not uncommon to hear someone say "I've got them on excellent pasture plus I'm cubing them, I don't understand why they are not breeding better." This shows us a need to monitor our forage conditions and supplement accordingly. During periods when lush grass abounds little or no supplemental protein is necessary, a better supplement would be a grain-based energy supplement that would provide the starch necessary to help the cow utilize the higher levels of protein more extensively. By supplementing with a starch or grain source, the rumen bacteria have more energy and carbon chains to work with to utilize this elevated nitrogen concentration in the blood. The added energy in the diet plus the reduction in BUN can have a marked effect on conception rates. If a protein supplement is provided, the best responses have been from proteins higher in by-pass protein (that which is not as easily broken down by the rumen. This can be found in the form of distiller's grains, corn gluten feed, fishmeal, heat processed or roasted soybeans and a number of others.

II. Positive Effectors on Reproduction. The effects of feeding fat sources to cattle, as a source of increasing energy status in cattle is well documented. Recent research into the effects of fat inclusion in the diet on reproduction have shown positive results. In the mid 1980's work was done comparing the reproductive status and return to cycling of cows in optimal condition and cows in poor condition receiving supplementation with whole cottonseed (which will run 18 to 22 percent fat on a dry matter basis). The reproductive performance receiving the whole seed supplementation was similar to that of the cows in better body condition. More recent studies have compared various fat types from different plant and animal sources as well as investigated the actual physiological changes that take place when fat is used as an energy supplement.

Various studies have shown the positive response noted. Several hypotheses currently exist for why this response is seen.

1) The feeding of the additional energy in the form of fat improves the cow's overall energy status so that she returns to estrus sooner after calving and therefore conceives earlier.

2) Cows fed fat secrete more progesterone, a hormone necessary for implantation and nutrition of the newly formed embryo. One of the effects seen from the feeding of fat is an increase in the size of follicles produced on the ovaries. A review of a series of studies investigating this concept showed that follicle size increased an average of 27.13 percent. The increase in follicle size also resulted in an increase in corpus luteum (CL) size. The CL is the structure which produces progesterone.

3) Specific individual fatty acids (components of fats) inhibit the production of PGF2 by the uterus. This prevents the regression of the (CL) on the ovary so that the newly formed embryo survives. In other words, the CL has a longer lifespan which increased the length of the estrus cycle. This means that a cow has a longer period of time in which to be bred when she is in heat. Certain fat types have been shown to be especially effective in creating this result. Fats higher in linoleic acid (a specific long-chain fatty acid) have been shown to be especially useful in this area

4) Higher dietary fat levels may increase the concentration of cholesterol in the blood stream which acts as precursors or building blocks for reproductive hormones such as progesterone.

Regardless of the exact mechanism, the use of fat in supplementation of brood cows has proven very effective in improving reproductive performance. More research is needed to identify specific feeds or grains that possess the necessary fatty acid profile to produce an optimal response (or at least the best improvement. Cows should receive supplements higher in fats just prior to calving and in the early postpartum period to enhance this effect. Feeding a higher fat supplement which results in the cow receiving 3 to 5 percent fat in her overall daily diet should improve reproductive rates in most cases. Be sure not to exceed 6.5 to 7 percent fat in the daily diet as this can result in reduced fiber digestion in the rumen.


As weve seen here, a better understanding of specific nutritional factors can help the producer improve reproductive performance in his herd. Also as noted there is not one easy answer and there is certainly no silver bullet for the old management gun. The best advice a producer can follow is to search out the best sources of information he can find on these issues and read and study all he can.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at 903-885-7992 or by e-mail at [email protected] For more information please visit


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