Disease control is an important part of a herd reproductive management program. In addition to vaccination, efforts to isolate the herd from sources of infection are important. The use of artificial insemination permits the use of the best genetic material available without the risk of introducing new animals and diseases into the herd. The health control of animals producing semen for studs is such that little chance exists for the introduction of diseases by this route. The complete isolation of the herd is possible and gives good protection against disease introduction. When females must be added to a herd, a complete sequence of isolation, observation, and retesting should be carried out. Maintaining an environmentally closed herd, using veterinary help in a vaccination program and having prompt diagnosis in cases of suspicious animals should combine to keep a herd trouble-free.
A veterinarian should be involved in giving all vaccinations and in implementing a disease prevention program. A good reproductive health control program should include vaccinating for leptospirosis, IBR (infectious bovine rhinotracheitis), and BVD (bovine viral diarrhea).
The value of having scheduled visits by a veterinarian at designated intervals to conduct post calving examinations, pregnancy diagnosis and treatment of problem cows appears to have some advantages. Work at The Ohio State University indicated that the cost of veterinary services was not different whether the program was on a scheduled or emergency basis. However, an advantage did accrue to the regularly scheduled herd in reduced services per conception and fewer animals culled for reproductive problems. The net value of the use of a veterinarian on a scheduled basis was about $6.00 per cow per month (as of 1978). Work at other institutions has produced results that indicate the use of a veterinarian on a regular basis for routine work will return up to $5.00 for each $1.00 invested in such a program.
Cystic ovaries continue to be a problem in dairy herds. The interacting causes are not known. Inheritance plays a small role as the cause of some problems. At present, the method to minimize this problem rests with early diagnosis by post calving examination and early treatment. Cases which are detected by anestrus or irregular heat cycles require more time for correction and this time adds to that already lost in late detection.
Most cows that are culled because of reproductive failure are not permanently sterile. With the expenditure of money for treatment and loss of much production time, cows can usually be restored to a fertile state. Economics dictates that few cows are of sufficient merit to justify much of this expenditure. Many factors go into the decision to cull a cow for delayed rebreeding. These include current prices of milk, feed and cattle. The temptation to continue to salvage an aged cow that is slow in rebreeding should be tempered by certain facts.
If a cow does refreshen, her anticipated years of usefulness is determined by her age. Anticipated useful years for different ages are as follows:
Age at puberty is affected by both age and growth. Within normal ranges, the age at first breeding has little effect on conception. However, excessive delay in first breeding (3 to 4 years) results in animals with poor lifetime reproductive performances. Delays to 21 months of age for first breeding has shown no effect on lifetime performance. The most important item is the ability of the heifers to deliver a calf. Minimum weight for safe calving by breeds appears to be as follows:
Heifers bred extremely early will reach a mature weight that is slightly less than that of heifers allowed to become larger before breeding. This is due to the effect of lactation and not pregnancy. There is little evidence showing that heifers bred early have a shorter herd life, except that inferior producers are identified and culled at an early age. Heifers freshening at an earlier age will average a slightly greater lifetime production. The recommended practice is to breed heifers to calve at about 24 months of age.
The practice of breeding dairy heifers to beef bulls in order to reduce calf size has been of limited help. The size of a calf at birth is influenced heavily by the size of the dam. The influence of a sire has ranged from slight to non-existent. The average dairy cow has about three calves in a lifetime. If the first one is crossbred and unsuitable for replacement purposes, the heifer calves born from the remaining two calvings must be retained regardless of merit just to maintain herd size.
Almost all semen today is stored in liquid nitrogen at a temperature of -196° C. Two important points to remember are don't let the jug run out of nitrogen and don't remove semen from the jug until you are ready to use it. The organization from which semen is purchased should be contacted for recommendations on semen thawing and handling techniques.
A logical herd budget for semen can be made after considering certain factors:
It is recommended that about a three month supply of semen be stored in reserve (average of 50 units for a 100-cow herd). If too large a supply is maintained, some sires will be overstocked, and this can later prove to be undesirable and costly. A quarterly evaluation of bulls should be made, using information on sire merit, along with conception rates and prices. The temptation will exist to stock some bulls in anticipation of later popularity and high demand. To accomplish this, a price must be attained that will cover loss from discarding semen from other sires that prove to be undesirable. For the man with a gambling nature, this is a way to run his own lottery. Resistance will need to be maintained against the pressure from semen distributors as they compete for space in the semen storage tank. With specials and package deals, they will be trying to keep the dairyman's tank filled.
One of the limiting factors in getting heifers and some cows bred artificially has been the inconvenience and inability of watching for and detecting estrus. Heat synchronization would greatly increase the use of artificial insemination in heifers. Current work with the hormone prostaglandin offers promise that predetermined timing of breeding and breeding in groups will soon become a practical reality. Prostaglandin is secreted by many tissues in the body. It can be administered to stop the activity of the corpus luteum on the ovary and to permit immediate recycling of the animal. Animals that have been in heat within four days or are near a new heat will not respond. The rest of the females in a group, approximately two-thirds of them, will ovulate in about 90 hours following treatment. If cattle are not bred at this period but are retreated along with nonresponding ones, on the 11th day after the first treatment all will cycle together. This hormone has additional promise in helping to reduce the heat detection problem in herds. Results show that cows can be inseminated at 80 to 95 hours after administration of prostaglandin without fertility loss.
The predetermination of the sex of offspring has long intrigued observers of both human and animal reproduction. With the advent of artificial insemination, the opportunity to control the sex of the offspring by semen sexing held promise. Some modern success in separating sperm into male and female conceiving cells has been reported with rabbits. The separation of bull semen has not yet been accomplished satisfactorily. The ability to control the sex would permit more intensive selection of replacements from the top cows in the herd. Estimates suggest that if such a technique were effective, a dairyman could afford to pay $3.00 to $5.00 (as of 1978) more per service unit (straw or ampule), depending upon the expected sex ratio.
These techniques would give wider use of the genetic material from superior females. While they are possible, they have not yet been refined to the point where they can be routinely and economically used by commercial dairymen. To date they have been used mostly by the purebred cattle breeders on superior cows. The cost of these procedures often totals about $2,000 for each successful pregnancy. In order for the procedures to be justified from just the increased herd milk production that would be realized by using the best cows as dams of all the herd replacements, the cost will need to be reduced below $100. The improvements that could bring this within a realm of practicality are:
An additional possibility for using this technique would be in proving outstanding females as possible mothers of young sires. Heifers can be successfully superovulated by veal calf size. Thus, by transplanting fertilized ova from 3 to 5 months old heifers into recipient cows, offspring of these heifers could be born when the heifers were only 12 to 14 months old. The prospect of having first calf heifers and their daughters finish production records only about a year apart offers possibilities for more accurate and earlier selection of dams of young sires.
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This page was last updated on November 16, 2002