Cattle Today

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MANY FACTORS EFFECT HERD'S REPRODUCTIVE PERFORMANCE

by: Stephen B. Blezinger
Ph.D., PAS

Hardly a day goes by when you can't turn on the television, radio or surf the web and not find new and exciting ways to enhance your love life. Be it the latest miracle drug that is taking the world by storm or a unique combination of herbs and other compounds that can make us all bedroom supermen or superwomen, our country is enraptured by the thought.

We tend to take a bit of the same view of the whole concept when we consider our cow herds although for cattle it's more practical and less recreational. Each year producers spend countless dollars on various products and practices they have been led to believe will enhance the reproductive performance of their herd. In some cases these efforts have paid off but in many they do not. As has been stated here before there are no “Silver Bullets” or magical formulas which will replace good management, sound nutrition and plain old common sense.

Since this is the Herd Bull and A. I. edition of this periodical let's take some time and review the basic concepts that make for a good reproductive program.

The Bulls

Remember that your bull is 1/2 of each calf produced. Although the liberal media would probably like you to believe that the male involvement in this process is actually significantly less than this, biology is biology and it takes one bull plus one cow to make one calf. In fact in a given herd your overall calf crop is affected more significantly by your bulls simply because of the normal ration of one bull per 20 to 40 cows. This being the case your bulls have to be in prime working condition in order to complete the task at hand, i.e., getting the group of cows bred that he is placed with. In some cases where this can be quite intensive if the herd is on a limited breeding season or if the group of females has been synchronized.

The basics of reproductive management of herd bulls include six very important factors. These include:

1) Structural soundness - ability to cover the necessary ground and service the cows in the herd. General health and structural soundness are important aspects of fertility. Poor health can affect libido, mating ability, and semen production and quality. Structural soundness, including functional feet, legs and associated joints, is critical for the bull to effectively travel the breeding pasture and service females in heat. Any disease condition which impairs the mobility of the bull will hinder reproductive performance.

2) Soundness and capability of the reproductive organs - everything functions as it should. The reproductive system is complex. Sperm is produced continuously by the testes and stored in the epididymis. The prostate gland, seminal vesicles and cowper's glands secrete the fluid component of the semen. During mating, the penis is extruded from the sheath by the straightening of the S-shaped sigmoid flexure; sperm are transported up the vas deferens to the urethra and exit via the penis.

3) Quality of semen - semen, or more specifically sperm, is viable and motile. The criteria commonly used to evaluate semen quality include sperm morphology (structure) and motility (rate and percent of progressive forward movement). Semen volume and concentration can also be used

4) Scrotal Circumference - Measurement of the scrotal circumference of young bulls is an accurate, repeatable method to assess current and future sperm - producing ability. The measurement gives an estimate of the weight of the testes, which is directly related to the level of sperm production. Scrotal measurement is also positively correlated with semen volume and quality.

5) Level of libido - desire to get out and do the job. Libido (sex drive) is a critical component of fertility. It is independent of scrotal circumference, semen quality, body weight, growth rate or masculinity.

6) Plane of nutrition - nutrition components are in place to support all of the above. Proper nutrition is necessary for good reproductive performance. Balanced amounts of protein and energy are required for sperm production and the physical activity associated with breeding. Adequate amounts of vitamins and minerals are also important in reproduction.

All of the factors are integral and a deficiency in any category will have a negative impact on fertility. The first four factors are related primarily to the animal himself with the cattleman having limited control of these factors past initial selection and properly managing the animal so that these factors are maintained as optimally as possible. Genetic factors play a large role in the first four on this list. Since we have a greater amount of control of the management of the animal's nutritional program let's examine some specific factors that have a direct effect on the bull's reproductive performance.

1) Protein and Energy levels. The need for protein and energy is well documented for all members of the cow herd. Assuming that the bull has been developed properly during youth while he grows, appropriate protein and energy levels are required to maintain normal physiological function in every part of his system. Protein is the building block of muscle and it's components are involved in every system in the body. Energy or the calories the bull consumes act like gas in your car and provide the fuel on which these systems run. Inadequate amounts of protein reduce the body's ability to regenerate the tissue degeneration that occurs naturally. It also impairs sperm production. Inadequate energy intake reduces body condition and the animal's overall energy levels necessary for normal activity. As with the female component of the herd an adequate body condition is necessary especially as the herd enters the breeding season. It is normal for a bull to lose some body condition as the breeding season progresses. His feed and forage intake is typically lower and his activity level is higher during this period.

2) Minerals and Vitamins. Minerals and vitamins are the components which stitch all physiological processes together. The macro minerals such as Calcium, Phosphorus, and Magnesium play significant roles in structural growth and maintenance. These same minerals as well as Potassium and Chlorine are involved in nerve impulse transmission and maintenance of appropriate water and gas pressures in the cells. Trace minerals and vitamins are involved in every reaction that takes place in the body, many times in very small quantities but nonetheless vitally important. Minerals such as Zinc are directly involved in spermatogenesis or the production of sperm cells in the body. A zinc deficiency has been shown to reduce sperm production and subsequent fertility. Use of tools such as chelated minerals have been shown to increase mineral absorption and can enhance reproductive performance both before and during the breeding season.

For all these reasons and many, many others a sound nutritional program is vital to the performance of your herd bulls. They will not function optimally without it.

The Cows

As with the bulls, reproductive performance of the female component of the cow herd is based on a number of factors. Structural soundness as well as integrity of the reproductive tract are of the same importance in both male and female animals. Of significant importance in the cow is body condition which is obviously related to nutrition.

Body Condition Scoring (BCS) is probably one of the most important tools a cattleman can use to manage reproductive efficiency. By insuring that the condition of the animal is appropriate at critical times in the cow's annual production cycle, we improve our chances that she will cycle normally. Research has shown repeatedly that a BCS of 5 will optimize her reproductive performance. At a BCS of 5 at the time of breeding (30 to 60 days post-calving), the cow has the necessary body stores of fat which are required for normal hormonal production for cycling activity. Additionally, utilizing BCS year-round to monitor cow condition helps the producer make sure that the cow will be in the correct condition at targeted breeding times. If a cow approaches calving and she is thinner than we desire (BCS lower than 4 to 5) it will be necessary to increase her energy intake to improve fat covering prior to calving and subsequent rebreeding. The fat in a cows body is used to a large degree as building blocks for reproductive hormones and are essential for normal functioning. If the fat is not there and not in the diet the synthesis (construction) of these hormones is reduced and subsequently we see effects such as delayed cycling, increased services per conception, delayed conception, etc. Improving body condition is not an overnight process either. Once we have determined that BCS is lower than normal (perhaps a 3 instead of 4 or 5) we will need to increase the energy intake by feeding more grain, whole cottonseed, etc. for several weeks to get her up to the next level. In the average 1000 lb. cow, one BCS score is equal to about 100 lbs. of body weight. This is why it is important to monitor BCS year round along with monitoring energy intake so that we don't wake up one day (the middle of calving season) and find that half the herd is in a lower than desirable BCS. Keeping close tabs on BCS and energy intake will reduce this problem and greatly improve reproductive efficiency along with saving a lot of money.

Directly linked to body condition is nutrition. Protein and energy are two of the most essential nutrients in the cow's diet. Requirements for both fluctuate throughout the production year depending on what stage she may be in along with a host of other factors including environment, stress, etc. Protein is required to build and maintain muscle as well as provide numerous precursors for numerous bodily processes, one of the most important being reproductive function. As we've mentioned before, intake and utilization of various nutrients, including protein and energy is prioritized in the animal. In other words, the amounts provided by the diet are utilized in a specific order from most important to least important as related to animal survival and maintenance. Unfortunately, reproduction is on the bottom of this list and if the nutrients are not available, reproductive function will be one of the first to shut down since it is not vital to the animal's survival. This fact helps illustrate why appropriate nutrient intake is so important.

Energy intake is the primary factor affecting body condition. Energy is consumed by the cow in several forms, including carbohydrates from forages (structural), carbohydrates from grains (non-structural) and fat. Feeding of some forms of fat, especially those which are high in conjugated linoleic acid (CLA's) have been shown to enhance reproductive due to the net increase in reproductive hormone production observed during feeding. This can allow a cow to cycle and breed in situations where her body condition is lower than normally required. Fats of this nature are found in products which include soybean oil and cottonseed to name a few.

As in the bulls, mineral supplementation for the cow herd typically provides sources of macro minerals (calcium, phosphorus, magnesium, potassium, sodium, sulfur and chlorine), micro or trace minerals (cobalt, copper, iron, manganese, selenium, zinc) and fat soluble vitamins (Vit A, D and E) as well as other additives. As discussed above minerals and vitamins are necessary in the body as components of various physiologic processes, in many cases as part of enzyme systems required to drive specific reactions. An example of this is phosphorus. A lot of research has been performed on the role phosphorus plays in reproductive activity. One of the main effects phosphorus has is on energy metabolism that relates directly to the activities we discussed above. Phosphorus is a component of several compounds in the reactions that transfer energy through out the tissues. If this phosphorus is not available, this energy transfer becomes less efficient therefore slowing down or inhibiting normal functioning. This therefore reduces reproductive activity in the animal. This basic understanding has led to a lot of over supplementation on phosphorus, especially in the dairy industry, but also in the beef industry as well. It goes back to the old adage that if a little is good, a lot has to be better. If phosphorus levels in the diet are adequate to maintain normal bodily functions, feeding more will not promote greater performance, it will simply be excreted in urine or feces. Therefore a lot of wasted phosphorus ends up on the ground (now considered pollution) which is another potential discussion altogether.

Other vital minerals such as the trace elements are also involved in the energy metabolism process as well as in the reactions required to produce the necessary reproductive hormones. As with phosphorus, if these nutrients are inadequate, it slows down the production of these various compounds and therefore slows reproductive activity. Mineral supplementation is important year round but is accentuated prior to calving and on through rebreeding. I normally recommend that cattlemen use “breeder” mineral about 30 to 45 days prior to calving and up to 90 days post calving to increase the intake of certain minerals and improve absorption. This normally incorporates an organic trace mineral source which has improved bioavailability and improved absorption. This simply helps insure that the necessary minerals and vitamins are available when the demand is the greatest.

Conclusions

A productive and profitable herd is built on it's reproduction program. As we have seen reproductive function and efficiency requires many components to be in order to function properly. This involves time, management and planning by the producer for successful implementation. The right efforts can make a difference between success and failure.

Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, Texas. He can be reached at P. O. Box 653 Sulphur Springs, TX, by phone at (903) 885-7992 or by e-mail at sblez@peoplescom.net.

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