REPRODUCTION IS A MULTIFACETED SUBJECT
Successful reproduction demands a lot of expertise by the producer because many factors affect the likelihood of pregnancy:
- Cow’s fertility;
- Bull’s (semen) fertility;
- Heat detection efficiency;
- Insemination efficiency.
Pregnancy rate is the product of these four factors.
A consequence of this multiplicative relationship between the factors influencing reproduction is that improvement of one factor (let us say cow fertility) will have little overall beneficial effect on pregnancy rate if any of the other three factors has a low efficiency. It takes only one problem to severely decrease the pregnancy rate.
Cow Fertility
Cow fertility is influenced by many factors.
The age of the animal has a strong influence on fertility. Heifers and second lactation cows are usually more fertile than first lactation cows and mature cows.
Fertility is highest in the coolest months of the year, and when cows are:
- Free of reproductive diseases;
- Free of problems at calving;
- Free from nutritional imbalance—especially if the cow is not too thin or too fat at the time of calving. Fertility is also high when cows stop losing weight and begin to replenish body stores a few months after calving.
Bull Fertility
Testicular circumference is related to the fertility of mature bulls. Daily ejaculation of a sound bull over an extended period of time does not impair fertility; however, it varies with:
- Age and sexual maturity;
- Proper nutrition;
- Sexually transmitted diseases;
- Libido (sexual drive).
In the case of artificial insemination, the fertility of a bull is also affected by semen dilution, processing, storage and handling from the time it is collected to the time it is deposited in the cow’s uterus.
Heat Detection Efficiency
Poor heat detection efficiency is probably the single most important factor affecting the pregnancy rate of otherwise fertile cows. Heat detection efficiency is made up of two components: the level of detection and the accuracy of detection.
Heat detection accuracy may be low because:
- The herdsman is not familiar with the signs of heat and fails to correctly identify the cow(s) in heat;
- Heat is correctly detected, but an error occurs in determining the cow’s identification or in recording the event (e.g., incorrect date).
Insemination Efficiency
In general, insemination efficiency is close to 100% when a sound bull is used for natural service.
In the case of artificial insemination, however, this factor is measured primarily by the competence of the herdsman and inseminator to:
- Determine the correct timing of insemination;
- Handle the frozen semen correctly;
- Deposit the thawed semen accurately at the entrance of the uterus.
