The extent which artificial insemination is used to breed virgin heifers is difficult to estimate. Experience would indicate that the majority of breedings in this group is by natural service. Reasons for continued use of young sires on heifers are real, and returns from giving up these advantages need to be established.
Some of the advantages of using a young sire in natural service are as follows:
However, there are balancing factors that must be weighed in deciding whether to breed heifers AI at first breeding. One of the advantages in using AI on Holstein heifers is that there is an opportunity to reduce calving difficulties by selecting Holstein sires that contribute to less dystocia. This advantage is valid only if the breeder has already concluded that he cannot afford to sacrifice the offspring from heifers by breeding them to small breed beef sires.
If the Holstein breeder is still using beef sires, he needs to consider the following:
Typically DHI herds replace 30 percent of the cows with heifers each year. In a herd of 100 cows, these heifers would be giving birth to 30 calves. According to a study of Ohio records, the 70 cows that are not replaced would give birth to 59 calves during the year and the 30 replaced cows would give birth to 10 calves prior to removal. Consequently, 30 calves would result from first calf heifers and 69 should result from older cows in the herd. The loss of about 30 percent of replacement heifers that are born to first calf heifers bred to beef bulls would result in the necessity to introduce and keep all replacements in the herd in order to offset cows that must be removed for health and reproductive problems.
It is also likely in herds using high PD bulls that the first calf animals are the mothers with a higher transmitting ability than is to be found in the older cows. Even though the older cows have survived some culling, this is not likely to increase their transmitting value beyond an average 50 pounds of milk. On the other hand, the first calf mothers will be about three years younger than the remainder of the herd and should have resulted from sires that represent three years improvement in sire quality. Sires are improving at the rate of about 50 pounds of milk per year. These unculled two year olds then should be genetically 150 pounds superior to the older cows prior to the older cows being culled and 100 pounds superior to the older cows after culling.
The combination of removing all opportunity to voluntarily cull plus losing replacements from the best mothers makes the use of a beef sire hard to justify in a herd where plans exist for continued operation.
The best approach to reduce calving problems would be the use of AI sires identified for calving ease.
Another reason for using AI on heifers is that AI bulls have a higher milk transmitting ability than natural service sires. A summary of all sires available in 1982 through AI revealed that the average PD for milk was plus 1138 pounds of milk. At the same time the average of all non-AI sires was plus 183 pounds of milk.
This difference of about 950 pounds of milk is a measure of the actual situation, but a dairyman need not be limited to the plus 183 pound level as he selects young sires. AI organizations, by using their full resources, have been able to select young sires whose proofs averaged plus 700 pounds of milk. The individual dairyman cannot justify the expenditure of time and money to match the performance of young sires selected for AI sampling. However, he should expect to select young sires for natural service that average between plus 183 pounds and plus 700 pounds. If 500 pounds is chosen as a reasonable figure, this implies a 600 pound (1138-500) of milk advantage by AI sire usage.
The question to be answered is what is the value of having the 30 percent of the herd that is replaced each year come from heifers that are sired by 600 pound better AI bulls. The following estimate of this value is based on several data. These items of information are as follows:
The cost of semen is usually an added cash expense. However, it may not be different from the actual cost experienced when raising and maintaining a young sire. If the young sire is selected and raised from within the herd, his salvage value at two years of age following one year of service should more than offset the feed cost of raising.
On the other hand, if costs beyond feed are counted, the cost of breeding each heifer to a young sire will equal the cost of semen for AI.
If a calf is purchased from outside the herd, the cost will exceed the cost of purchased semen.
With all the above considered, it appears that the financial advantage is with those that breed their heifers AI.
In spite of the apparent advantages of breeding heifers AI, there are circumstances where a dairyman may choose to breed heifers naturally to a young sire. In this event, it behooves the dairyman to choose the best young sire available within the limits of sound economics.
In a situation where the milking herd is being bred AI and is also on DHI recordkeeping, the dairyman might well consider raising a young sire from within the herd. Like every management decision, this has advantages and disadvantages. Some of the advantages of selecting from within are as follows:
If the decision is to raise a young sire from within the herd, then the mating should be planned two years prior to need. Four or five cows should be selected as candidates and bred to the AI bull considered most desirable as the sire of a young sire.
While this decision is slightly less important than the sire selection, it is deserving of considerable care. Each cow in DHI herds has been indexed for transmitting ability. This cow index should be relied upon in screening for possible dams. The AI industry has done well relying upon the USDA index as it has selected young sires. The dairyman must be prepared for the fact that occasionally his best producing cow is not listed among the cows with the best probable transmitting ability; therefore, he should resist the temptation to use her son.
In addition to being top indexing cows (+800 pounds milk or better), they should be sound cows, especially in udders. The AI industry has limited their selection to cows classified Very Good (VG) or Excellent in mammary conformation. While this may not be possible within the herd, the udder should be average or above before a cow is to be considered.
This is the most important decision and the one for which considerable information is available. The sire used should have as high a PD for milk as possible, with a minimum of at least +1,200 pounds. Information should show that the sire is well above average in siring udders. Even though no information is available showing that a bull identified as above average in calving ease will transmit this to his sons, logic suggests that the sire of a young sire to use on heifers should be one with a good performance in each of calving. Iowa work showed no correlation between calving ease and production, so the selection for calving ease should not limit PD milk selection.
In summary, when a sire is selected from within the herd, the following guidelines appear appropriate:
If a dairyman is expecting to select a young sire from a registered cow, he will be in competition with AI organizations for sons of the top indexing cows. For limited use on heifers, expenditures to obtain sons of these cows cannot be supported. Therefore, the dairyman will have to select from the second layer of cows. For this reason he cannot expect to duplicate the AI industries' success in selecting young sires. An alternative might be to select a son of a high indexing cow that had not scored VG but is well above average in mammary system.
One other possibility exists in that there are high indexing cows in herds with medium or low herd averages for production. Such cows are sometimes passed over by AI organizations because of lack of promotional appeal of the resulting young sires. From a genetic standpoint, such cows would be a better gamble than would those that result from going too deep in selecting cows in high producing herds.
The sire of a young sire should follow the same criteria as those sought when selecting a young sire from within the herd. These are as follows:
If the dairyman has no reason to select a young sire from a registered cow, he will have fewer limitations on selection for production.
All grades on DHI are indexed the same as registered cows. These cow indexes on grade cows are sent to the owners of the animals. There is little competition for the sons of high indexing grade cows. Therefore, a dairyman should be able to select sons of the top indexing grade cows and nearly equal the success experienced by AI young sire programs without sacrificing udder conformation. Also, the cost will be less than the cost of obtaining sons of the second layer of registered cows.
By selecting a new young sire each year, the grade dairyman should be able to withstand the occasional mediocre young sire and, over a number of years, average a PD milk of 500 pounds or better. This is considerably lower than he can expect if he breeds his heifers to proven AI sires, but higher than he is likely to attain if he selects sons from afforable second layer registered cows.
In summary, it is only under unusual circumstances that a grade or registered dairy man can justify using other than artificial insemination on virgin breedings. If such circumstances do exist, a dairyman should select a young son from a high predicted difference sire and from as high indexing a cow as he can reasonably afford. If the heifers to be bred are grade, the dairyman can likely afford higher genetic potential if he selects a son of one of the high indexing grade cows that are identified in Ohio.
|If you are interested in any of the titles below, click on the title and it will take you to Amazon.com for ordering. Click on the icon at the left for more information.|
This page was last updated on November 16, 2002