Improving Fertility of the Cow Herd
Although we hear a lot more about growth rate and beef quality and consistency these days, reproductive efficiency is easily the most important factor determining profitability of cow-calf operations. Improving reproductive efficiency is not an easy task, but I cannot imagine any other area where financial rewards are greater. There is an old saying that goes something like, "A dead calf has a very poor growth rate." I think that we can extend this concept to an "un"-conceived or unborn calf. It is impossible to profit from an animal that isn't. With this in mind, let's consider reproductive management "challenges." Furthermore, let's examine how to avoid pitfalls as we address these challenges.
Breeding Yearling Heifers
Yearling heifer management is one of the most trying aspects of cow-calf production. Reasons for breeding failure among yearling heifers usually fall into two categories: 1) the heifer is simply not old enough at breeding time or 2) the heifer is not big enough at breeding time. The age at which heifers reach puberty varies by breed. Typically, smaller breeds reach puberty earlier than larger breeds. Furthermore, breeds from Europe (Bos taurus) generally reach puberty at younger ages than Bos indicus breeds such as the Brahman. As a rule of thumb, heifers should be at least 12 months old at the beginning of the breeding season. Keep in mind this is a minimum not an average.
Average age should be 13-14 months. Heifers also need to reach a specific target weight before they reach puberty. We use a fairly simple rule to establish this target. Heifers should weigh at least two-thirds of their weight at maturity at the onset of breeding. For example, if your mature cows weigh 1200 pounds, heifers should weigh 800 pounds at the onset of breeding. Achieving adequate body weight at breeding requires careful planning. When heifers are selected at weaning, managers should conduct the following exercise.
Nutritional Management of the Cow Herd
Inadequate nutrition is also the most common cause of delayed breeding among mature cows. A reproductively efficient cow should calve every 12 months. But in order for her to accomplish this feat, she must breed back within 80 days of calving. Think about it, she will be pregnant for 285 days of the year, so there are only 80 left to recover from calving and to breed again (365 - 285 = 80). This doesn't leave much room for error. Any nutritional stress from late gestation until breeding can lengthen the postpartum interval. Cows should be in good flesh at calving and maintain this condition through the breeding season. Cows that are thin at the time of calving and those that lose body condition from calving to the onset of breeding will either breed late or end up open at the end of the season.
Breeding Soundness of Bulls
The incidence of infertility among bulls of breeding age has been estimated to be as high as 20%. In other words, one of five bulls is either sub-fertile or sterile! Most reproductive problems of bulls can be diagnosed by a standard breeding soundness exam (BSE) conducted by a veterinarian or qualified technician. Every breeding bull should be tested annually. As I mentioned, most problems can be detected with a BSE, but not all. Recently a new test has become available that can be used along with the BSE to help diagnose an additional problem. Reprotest WB is a procedure that is used to test for the presence or absence of a specific protein attached to sperm cells. The protein, also known as the fertility associated antigen (FAA) appears to affect the ability of individual sperm cells to bind to the egg immediately before conception.
In research trials directed by Dr. Roy Ax at the University of Arizona, bulls that passed traditional BSE were evaluated for the presence or absence of FAA. Bulls that possessed the protein (FAA positive) produced 18% more pregnancies than bulls that lacked the protein (FAA negative). Researchers surveyed bulls in the US, New Zealand, Australia, Mexico and Holland and discovered that 12% of bulls were FAA negative. The test is now commercially available from ReproTech, Inc. in Tucson, Arizona (580-888-0401). Cost per bull is approximately $35 plus the cost of collection and shipping containers. One cautionary note: this is not a substitute for traditional breeding soundness exams. The test should be used along with BSE to better assess the reproductive potential of the bull.
Prevention of Reproductive Diseases
There are numerous diseases that affect reproduction. Fortunately, all of these can be prevented by vaccination and/or management practices. Reproductive diseases cause fetal death or abortion. The list of diseases is lengthy and includes diseases such as infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), leptospirosis (Lepto), vibriosis (Vibrio), trichomoniasis (Trich), and brucellosis (Bangs). Some reproductive diseases are very "dynamic", genetically changing over time. Our highly mobile industry has also created opportunities for disease organisms to move into clean areas with relative ease. Producers should consult a local veterinarian annually and follow his or her advice religiously. If you do not adopt a preventative strategy, you are gambling with the future financial viability of your herd.
Improvement of Genetic Potential
Genetic potential also plays a pivotal role in the reproductive process. Vast differences exist in reproductive potentials among cattle. However, improvement of potential for reproduction is not as straight forward as most other traits because animals do not express reproductive deficiencies until later in life. Researchers, however, have developed techniques to improve fertility indirectly. Let me give you a few examples. First, genetic differences exist within breeds for age at puberty. This trait is very difficult to measure in females (you have to watch them for months to determine when they first cycle). However, in the male, it is easy to establish the relative time he reaches sexual maturity. This can be established by simply measuring the circumference of his scrotum. In most breeds, puberty occurs when scrotal circumference exceeds about 32 cm.
When cow-calf producers select yearling bulls with large scrotal circumference (> 32 cm), daughters tend to reach puberty earlier. Furthermore, daughters of bulls with large scrotal circumferences tend to be more reproductively efficient throughout their productive lives. Another method for enhancing reproductive performance potential is to simply breed heifers as yearlings in a short breeding season (45 days). In other words, if you make it difficult for heifers to breed the first time, only the most fertile will enter the herd. Of course, it is always a good practice to cull non-pregnant cows at the end of the breeding season. However, this has only a minor effect on genetic potential. Cows have often produced daughters that are kept as replacements before being culled.
In general, we need to address reproductive potential early in life. Some new approaches are currently under investigation at various locations including the Noble Research Institute.
Finally, remember cows are very much like a factory. Raw materials that enter the factory include grass, supplements and water. The product of the "cow factory" is a calf at weaning time. As with any factory, efficiency is measured as outputs relative to inputs. Our "cow factory" is extremely inefficient when she fails to breed.