Ensuring Reproductive Success of Beef Cattle

December 2000
Dr. Allen Williams - Extension Beef Specialist

Reproductive Measures

To truly evaluate reproductive efficiency in your herd, you must keep accurate records. Data is everything! Remember this phrase, "You can't manage what you don't measure". The most important measures of reproductive efficiency are:

  • Calving Interval (CI): This is calculated as the number of days between the last and the second-to-last calving. CI is one measure of a cow's reproductive performance. Cow's that have a consistently long CI may eventually fail to rebreed during a controlled, defined breeding season. Cows with long calving intervals should be targeted for culling. Ideally, calving interval should be every 365 days or less. Calving Interval = Age (in days) at first calving - Age at last calving = 365/No. Of calvings.
  • Percent Pregnant (PP): Pregnancy percentage is a measure of the success of the breeding season, and should be calculated based on the number of cows exposed to breeding. To produce a marketable product, each individual cow must conceive and give birth each year. Percent Pregnant = (No. Palpated pregnant/No. Cows exposed) × 100.
  • Calving Percent (CP): This is a measure of the cumulative results of the breeding and calving seasons. Cows must not conceive, but must also give birth to a live, healthy calf. If cows are losing calves between breeding and calving, then a definite problem would be indicated. You could be experiencing problems with reproductive disease. Calving Percent = (No. Live calves/No. Cows exposed to breeding) × 100.
  • Weaning Percent (WP): This measures the cumulative results of breeding, calving, and preweaning. It is strongly related to reproductive efficiency of the cow herd. Weaning percent is also called, "percent calf crop weaned", and is recognized as the most single descriptive measure of reproductive performance of a cow herd. Weaning Percent = (No. Live calves weaned/No. Cows exposed to breeding) × 100.

Selection

Reproductive traits are generally thought to be of low heritability , and therefore, hard to influence through selection. However, if you cull all open cows, offering no excuses for an individual female, then reproductive performance in your herd will improve. This includes culling cows that consistently rebreed at the tail end of your breeding season.

Replacement heifers should be retained only from those cows that calve every 365 days, and rebreed in the first half of the breeding season.

By doing this, you will inadvertently be selecting replacements from the most fertile females in your herd. Too often producers try to force a cow to fit an environment, rather than selecting for females that work within the constraints of a particular management system. Remember, the bottom line is to make a profit. One of the keys to achieving this is to select replacement females that breed and produce in an efficient manner.

This typically means selecting females that are moderate framed, easy fleshing, and have adequate milking ability. Large frames, high milking cattle tend to require too much input to be economically feasible. After several generations of proper selection, you will have a fertile herd of females.

One of the most important indicator traits of potential fertility is scrotal circumference. Scrotal circumference in yearling bulls is estimated to be 50% heritable and is highly correlated (r = 0.98) to age at puberty in heifers and potential fertility and serving capacity in bulls.

Expected Progeny Differences or EPDs are an effective tool in improving overall fertility and reproductive efficiency of your herd. Producers can select sires to utilize in improving reproduction by considering EPDs for the following traits:

  • Birth Weight
  • Calving Ease
  • Milk
  • Total Maternal
  • Scrotal Circumference
  • Cow Longevity or Stayability
  • Mature Daughter Weight and Height

Selection for low to moderate birth weight and adequate calving ease EPDs can improve reproductive performance through the reduction of calving problems or dystocia.

Too little milk and weaning weights will suffer; too much milk and cow body condition will suffer. In the Southeast production environment, moderation in milk EPDs is important. Producers rely primarily on a forge-based system, therefore, nutritional inputs are limited.

Heavy milking cows require too much nutritional supplementation for rebreeding and maintenance of proper body condition to be economically feasible. As mentioned earlier, scrotal circumference plays an important role in bull fertility, serving capacity, and age at puberty.

Commercial cow/calf producers have another effective tool at their disposal for improving reproductive efficiency. That tool is utilizing heterosis generated through an effective crossbreeding program. The use of crossbred cows in a commercial production system can enhance weaning rate, through maternal heterosis, by 7 to 12%.

That's a tremendous advantage over the use of straightbred cows, and should not be ignored. Individual heterosis (heterosis expressed through the individual crossbred calf) can account for an additional 3 to 5% increase in weaning rate. So, just through taking advantage of the principals of crossbreeding, weaning rate can be improved by up to 17%.

Herd Health

Herd health is critical to reproductive success. All breeding stock within the herd should be on a routine vaccination program that is pertinent to the particular production environment. Producers should work closely with their local veterinarian(s) to develop an appropriate herd health program.

Yearly vaccinations against diseases such as Vibrio, Lepto, IBR, PI3, BVD, and BRSV need to be implemented prior to start of the breeding season. Replacement females should still be calfhood vaccinated against Brucellosis.

At least 30 days prior to the start of the breeding season, all herd sires need to be fertility tested. Even if a bull passed a fertility test the year before does not necessarily mean he will pass one the next year.

Anything can happen in that time span. It is important that a complete exam be conducted. Scrotal circumference should be measured in young bulls, and should be a minimum of 32 cm at a year of age.

Rectal palpation for examination of the accessory sex glands, palpation of the testicles, evaluation of the penis and sheath, and estimation of a bulls' soundness (feet and legs, eye-sight, structural correctness), and pelvic area are all vital components of a complete fertility exam.

With heifers, it is a good idea to have a veterinarian examine them before the breeding season to determine reproductive tract score. Heifers that have immature reproductive tracts and are not cycling can be culled at this point.

Research indicates reproductive tract scores significantly impact heifer response to estrus synchronization and subsequent pregnancy rate. Reproductive tract score ranges for 1 to 5, and heifers should have a score of 4-5 by the start of breeding.


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