Other than milk, the main objective of a dairy farmer should be to have a calf per cow every year. Failure to this means losses arising from decreased milk yield, less calf crop due to longer calving intervals, culling of infertile cows and lack of herd replacement.
If this failure is not due to infertility by cows then it can be reduced or eliminated by correctly detecting heat and timely serving the cow. Progressive dairy farmers use artificial insemination (AI) to breed their cows and heat detection is a critical element for the operation to be successfully carried out.
A cow standing to be mounted is the crucial sign to look out for. Cows generally show signs of heat or estrus being receptive to bulls or A.I. The estrus cycle takes place every 21 days but can range from 12 – 30 days. Heat sign lasts for two to three days and is manifested by restless behavior and physiological changes around the vulva.
To time insemination accurately, it is important to know when ovulation takes place. Normally a cow ovulates 24 to 30 hours after she first stands to be mounted. She will remain on standing heat for about 12 to 15 hours. For the average cow, ovulation occurs 10 to 16 hours after it goes out of heat. It is important to inseminate a cow at least 8 to 10 hours before ovulation as it takes time for the sperm to reach the oviducts and undergo the essential process of activation which takes six to eight hours. A rule of thumb for timing insemination is as follows: –
A cow seen on heat before 6am should be inseminated the same day
A cow seen on heat after 6am should be inseminated early the next day
Using A.I. has the following advantages:
- It allows efficient control of venereal diseases.
- It is economical and eliminates purchase of expensive bulls, maintenance costs and prevents possible losses of bulls.
- Semen from bull studs or imported semen is usually genetically superior and disease free.
- It is the most efficient technique of cattle improvement. One bull can procreate 500 to 8000 offspring per year while natural servicing provides a mere 30 to 40.
- Adequate offspring for a reliable evaluation of the breeding value of a bull are available at a relatively young age.
- It necessitates accurate record-holding and a high level of management, resulting in a high degree of efficiency.
- Proven bulls are seldom sold, and their frozen semen can be distributed world-wide.
- The semen of outstanding bulls can be stored for years and thus used for subsequent breeding programs.
Disadvantages to A.I. are as follows:
- Venereal diseases can be distributed quickly if incorrect or negligent handling of A.I.
- Undesirable characteristics and heritable deficiencies are transferred to more offspring and
- The possibility of in-breeding is much greater than with natural servicing if proper records are not kept.
Using the bull
When selecting a bull to be used for mating in a breeding program a breeder should rate a bull on the basis of milk production of the dam of the bull and its pedigree. The only accurate method of identifying superior bulls is by progeny testing. When purchasing a dairy bull the rating of its progeny is evaluated based on milk yield, butterfat and proteins for 305 days lactation period
The production record for daughters of the bull being used is compared with production record of daughters of other bulls within the same herd and within the same year. The bulls’ pedigree should also be considered when selecting a bull. The bulls parentage i.e. dam should be known to calf down with ease and to be resistant to diseases such as mastitis. Only proven bulls should be used by a dairy farmer.
Bulls should be handled with care from birth to maturity. A bull should be dehorned because they can be dangerous. The bull should be exercised regularly to keep it in shape. A young bull can only be used to serve from 18 months old. Mating should be increased gradually to three times a week because more than this can exhaust and shorten the reproductive life of a bull. A bull should be kept in its own paddock and taken to female cows for mating only for a designed period of time.
If bulls are allowed to roam with female cows those on heat are served without the farmer’s knowledge. That aside, record keeping becomes virtually impossible. Inbreeding is bound to take place if proper management is not done. The bull is likely to serve young heifers that are not fully developed.
The disadvantage of using bulls is that sterility can go undetected. The bull could service cows yet no calf crop at the end of the year. If the bull was not selected properly the progeny would be of poor quality. To avoid inbreeding bulls have to be changed every to two years, and this can be very expensive. Heavy bulls should not be allowed to service young heifers to avoid injury. Bulls infected with the reproductive disease can spread the disease quickly.
Bulls are still used by majority of dairy farmers in Kenya because the bull will never miss a cow on heat. Dairy farmers should use A.I. as it is advantageous and cheaper so long as the farmer can master the technique, detect heat in cattle in time, keep proper records and manage his herd well.