Why Cows Do Not Become Pregnant
Much research has been done indicating that many cows fail to show heat early in the breeding season and also that conception rate at first service is low. If, however, proper management procedures are utilized the number of cows showing oestrus the first 21 days of breeding as well as the conception rate at first service can be high.
Factors affecting the number of cows showing heat early in the breeding season and the number conceiving on first service are:
• Showing Heat First 21 Days of Breeding
1. Time of Calving
2. Body condition of cows at calving time
3. Age of the cow
4. Suckling
• Conception Rate at first Service
1. Time of Calving
2. Weight changes of cow near breeding time
3. Bull fertility
4. Bull to cow ratio
Reproductive Rate
If the percent calf crop is to be improved, the number of cows becoming pregnant must be increased and the losses near or shortly, after birth decreased.
Time of Calving
Cows calving late in the calving season generally have a lower pregnancy rate because they do not have time to show oestrus early in the breeding season.
Cows require adequate nutrition and rest post calving in order to cycle normally. Conception rate is higher in cows bred 60 days or more after calving.
The Bull
Condition and nutrition of the bull prior to breeding are equally important to breeding efficiency.
Unfortunately very few bulls undergo any thorough breeding soundness examinations prior to the breeding season.
A breeding soundness examination would involve:
1. Conformation
2. Physical Examination
• scrotum and testicles
• scrotal circumference
• penis and prepuce
3. Semen Evaluation
• volume
• concentration
• mortality and morphology
Scrotal Circumference
Research has documented that testicular and scrotal development is directly related to sperm production and fertility in bulls. Scrotal circumference measurement properly done provides an aid in selecting sires with normal testicular development and is of considerable importance, particularly in yearling bulls.
Factors Affecting Bull Reproductive Potential
1. Testicular and scrotal development.
2. Ability to physically breed females.
3. Semen quality and volume.
4. Libido or serving capacity.
All four are of equal importance and testing would be a recommended procedure where practical before a bull is used.
Scrotal Circumference in Centimetres.
*The average scrotal circumference will vary according to breed.
