The Cow-Calf Manager
Livestock Update, December 2004
John B. Hall, Extension Animal Scientist, Beef, VA Tech
Beef Cow Reproductive Problems in 2004?
Part 1: Fall calving herds
What a great fall! Mild temperatures and ample moisture resulted in some of the best fall grazing in recent years. However during the fall, multiple sources indicated that some producers were experiencing reproductive and calf survival problems in their herds. Overall these reports appear to be scattered, but they may represent a trend that is being picked-up by better managers. In addition, these problems are of great concern and impact on the affected operations.
What types of problems are being seen? In fall calving herds, the reports indicate premature calves, dead or weak calves, and cows with little or no milk. In spring calving herds, the reports indicate greater numbers of open cows. Since not all producers pregnancy check cows, producers with spring calving herds may not realize a problem exists until next spring.
How pervasive is the problem? Again reports appear to be scattered, and there does not appear to be a huge reduction in the calf crop in Virginia. However, for the individual herd, the effects may be great. For example, a producer has a herd of 30 cows. If one calf is delivered prematurely, and two others starve from lack of milk, then there is a 10% decrease in calf crop. For that producer, calf losses are significant.
What is causing it? The tendency as humans is to want to find a simple answer, one cause, a quick fix. Unfortunately, decreases in reproductive rate rarely have a single cause. Too often producers, veterinarians, nutritionists, and extension professionals are quick to put blame on a single cause. We've seen a lot of guessing this fall. If it's the right one, that's great but too often it is more complex than a single problem. Only after proper testing, analysis and examination of the data can a cause sometimes be identified.
So what is a producer to do? The most productive use of time is to review the possible causes against your reproductive management strategies. Let's go through this list for fall calving herds. Next month Part 2 will focus on spring calving herds.
Fall Calving Problems - Cows with No Milk
Of the problems reported this fall, cows with little or no milk production is the most straightforward, but it is also strange. Possible causes: 1) fescue toxicity, 2) genetics
Fescue Toxicity: Years of research clearly indicate that endophyte-infected fescue reduces milk production in cows. The toxins produced by the endophyte reduce prolactin, the hormone responsible for mammary development and milk production. Cows grazing nearly pure stands of fescue that have been well (over?) fertilized appear to be most often affected. The extended drought of a few years ago may have favored survival of endophyte-infected plants over non-infected fescue and other species. The strange aspect to this problem is not all cows in a herd are affected. In addition, cows that were fine last year, grazing the same pasture are having problems.
My opinion and that of other Extension specialists is that endophyte-infected fescue is the primary cause of the low milk problem. Its effects may start during the last trimester of gestation during mammary development. Overall possibility = Extremely high. Reproductive solution: Move cows to pastures or feed sources that contain 50% or less endophyte-infected fescue during late gestation and early lactation. Cows can be moved back to fescue pastures after calves are 2 to 4 weeks old.
Genetics: There appears to be individual animal sensitivity to the endophyte toxins. However, limited research has been conducted in this area. Recent examples of cows being fine one year and extremely affected the next are confusing. More information is needed on the effects of endophyte toxins on mammary development.
As a manager, I would not agonize over the genetics of my herd contributing greatly to this problem, but I would keep it in mind. Overall possibility = Moderately low. Reproductive solution: Continue to seek replacement genetics that have been raised on fescue pastures.
Fall Calving Problem - Premature, dead, or weak calves
This problem is extremely complex and most likely has more than one cause.
Possible causes: 1) Endophyte infected fescue, 2) Nutrition, 3) Lepto
Endophyte infected fescue: It is easy to jump to the conclusion that fescue is the problem. In fact some individuals try to profit from this idea. Reports that cows with stillborn or weak calves have high levels of metabolites of endophyte toxins in their urine are correct. However, cows with normal calves also have high levels of metabolites of endophyte toxins in their urine because they are grazing the same pasture. Over 30 years of research and practical experience with cows on endophyte-infected fescue demonstrates that the toxins produced are not responsible for late-term fetal death, thickened placentas, or weak calves.
Mares grazing fescue do have problems with weak foals, thickened placentas, and complete lactational failure. However, we need to remember that cows are NOT horses, and to draw conclusions across two very different species is dangerous and unscientific.
Managers should not consider endophyte-infected fescue as a major cause of abortions or weak calves, and they should beware of persons who try to make this connection without controlled research. Overall possibility = Remote. Reproductive solution: Focus your management time on other aspects.
General Nutrition: Protein and energy deficiencies can contribute to weak calves. However these deficiencies are rare in fall calving cows because of good pasture conditions in late gestation, and stockpiled fescue availability during early lactation. More likely nutrition problems may include nitrate poisoning, acorn poisoning, and selenium deficiency.
High levels of nitrogen fertilization (> 60 - 80 units of N/acre) during stockpiling may result in high nitrate levels. Nitrate turns to nitrite in the animal which changes hemoglobin to methemoglobin. Methemoglobin prevents the proper binding of oxygen to red blood cells. Since the fetus is more sensitive to methemoglobin, levels of nitrate which will not kill cows may kill the fetal calf resulting in abortion. Toxins from acorn or produced in response to kidney damage from acorn poisoning may also have deleterious effects on the unborn calf.
Selenium deficiency results in calves that are weak at birth or die suddenly from cardiac failure 2 to 4 weeks after birth. Death is usually sudden, but calves may become stiff and have trouble nursing. With the stiff form of the disease calves can starve to death.
As a manager, I would not rule out the possibility of a nutritional cause to late term abortions. Overall possibility = Moderate. Reproductive solution: Double check fertilization rates of fall pastures and access of cattle to oak trees. Have high selenium containing mineral available for all times for your herd. Give calves supplementary selenium injections at birth. Keep your mind open to other nutritional imbalances.
Leptospirosis (Lepto) and other reproductive diseases: The principal reproductive diseases of cattle in Virginia are Leptospirosis, IBR and BVD. Abortions and decreased pregnancy rates can be a result of these diseases, but often the causes are hard to pinpoint without extensive testing. Samples from aborted fetuses, cow blood samples, and sometimes DNA samples need to be provided to the diagnostic laboratory. Producers are disappointed if inconclusive results are returned from the laboratory, but this should not prevent producers and their veterinarian from using this diagnostic tool.
Leptospirosis is the most common reproductive disease and is prevalent throughout Virginia. It causes abortions in the middle and last trimesters of gestation. The disease can be water borne, and it is spread by the urine of infected animals (cows, deer, dogs, raccoons) contaminating water or feed. In addition, the immunity provided by vaccination is not long lived, so cows need to be revaccinated every 6 months. Recently, a new serovar called Lepto hardjo-bovis appears to be causing problems in some dairy and beef herds.
In addition to abortions, IBR and BVD can produce weak calves or calves that die soon after birth. Vaccinations against these viruses are ideally given as modified live virus vaccines to open (recently calved) cows before the breeding season.
Managers should not ignore these preventable diseases as possible causes for abortions. However, you should not jump to the conclusion as these are the cause. Overall possibility = Moderately high in unvaccinated herds. Reproductive solution: Review your herd vaccination program with your veterinarian. Call your veterinarian after appearance of the second aborted calf.
Determining the cause of reproductive problems is difficult. Producers that believe that their herd is having problems need to consult their veterinarian, Extension agent, and nutritionist. Multiple perspectives are often needed to identify areas for improved management.