Cattle Breeding
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Production of offspring of the desired s*x using s*x-sorted semen has become an established reliable The freezability of semen varies among bulls.
Artificial Insemination (AI)
In cattle, AI is used primarily for genetic improvement of livestock and to facilitate high health replacement strategies. The worldwide adoption of AI for genetic improvement in dairy cattle was made possible by development of a progeny test system and subsequent use of milk production records as an objective measure of performance on which to select superior bulls, techniques for freezing semen, and liquid nitrogen storage refrigerators. The development of objective systems such as EBVs to measure economic traits in beef cattle (eg, growth rate, carcass conformation and composition, efficiency of feed conversion) and thus the more accurate selection of sires, as well as control of the estrous cycle, is leading to an increase in use of AI in beef cattle. Processing of frozen semen is a highly specialized technique. Attention to detail at each step is important to maintain semen quality. However, semen of high motility and morphology quality generally freezes well. Best results are obtained when semen is processed in a properly equipped laboratory by experienced staff at an AI center. Collection and Handling of the Semen Sample:
(Also see Breeding Soundness Examination of the Male.) Semen is collected using an artificial va**na or by electroejaculation (electrical stimulation of the seminal vesicles and ampullae). As long as the sample is of high quality, freezability and fertility should be normal. These techniques should not be used if the bull is unable to naturally service a cow for reasons that could be genetic. Most AI in cattle today is performed with frozen semen. Frozen semen may be maintained for years; extenders permit more insemination doses to be processed from one collection of semen, maintain the fertility of the semen longer, protect the s***matozoa from sudden temperature or pH change, and prolong viability. Semen is usually extended with citrate-buffered egg yolk or heat-treated skim milk plus glycerol, sugars, enzymes, and antibiotics. Final extension is designed to package 0.25 mL or 0.5 mL of semen containing 20–30 million s***matozoa at time of freezing. Extenders are often divided into fraction A and fraction B. The initial extension of semen is done with fraction A at the same temperature, eg, 86°F (30°C). The extended semen is then cooled to 41°F (5°C) over 40–50 min, or more slowly. Holding the extended semen at this temperature for 3–4 hr enables the antibiotics in fraction A to complete their action before being inhibited by the cryoprotectant glycerol. Fraction B contains a cryoprotectant such as ethylene glycol or glycerol (eg, 14%) and is added at 5°C in equal quantity to the extended semen. Each AI center has its own standard extenders and processing procedures. Glycerol (11%–13%) may be used with milk-based diluents. Before freezing, semen should be stored for 4–18 hr at 5°C. For freezing, bull semen is usually packaged in appropriately identified plastic straws (0.25 or 0.5 mL). Optimal freezing rates are known for many cell types, and s***matozoa can withstand a wide range of rates. In practice, extended semen is frozen in liquid nitrogen v***r before being plunged into liquid nitrogen at –320°F (–196°C). Storage in liquid nitrogen tanks is safe for ≥20 yr, and semen is transported in such tanks. The level of liquid nitrogen in tanks must be monitored to avoid semen losses, which is seen when the tanks become defective or when liquid nitrogen gradually ev***rates. Because s***matozoa do not survive for long after thawing, the semen should be used immediately. Thawing is best done as quickly as possible without damaging the semen by overheating. In practice, straws may be thawed in warm water (95°–98°F [35°–36.5°C]) for ≥30 sec and immediately placed in the cow’s reproductive tract. Recommendations by the AI center that processed the semen should be followed. Insemination Technique:
The rectova**nal method is used almost exclusively. After thoroughly cleaning the external genitalia with disposable toweling, one gloved hand is introduced into the re**um and grasps the cervix. The insemination pipette is introduced through the v***a and va**na to the external cervical os. By manipulating the cervix, along with light cranial pressure on the pipette, the pipette is advanced through the annular rings of the cervix to the junction of the internal cervical os and the body of the uterus. The semen should be expelled slowly (5 sec) to avoid s***m loss. If insemination records and consistency of the cervical mucus suggest possible pregnancy, the pipette should be advanced less than one-half of the way through the cervix, and the semen expelled. The optimal time to inseminate is between the last half of standing estrus and 6 hr thereafter, which is described as the "am/pm rule," in that cows observed beginning standing heat in the morning should be inseminated that afternoon, etc. If fertility problems arise when AI is being used, the semen should be investigated, although many factors other than semen are involved in attaining high fertility. Motility after thawing is an important criterion. An adequate number of motile s***matozoa at the time of insemination is critical. Morphologic examination also helps assess the role of semen in infertility cases. Comparisons within herds of diagnosable pregnancies resulting from the suspect semen and from semen from other bulls may be useful. Estrus detection continues to be the most important factor that influences AI efficiency. This factor should be investigated first, and inseminator proficiency second. The latter includes an evaluation of thawing temperature, time of thawing in relation to actual insemination, temperature changes from thawing to insemination, site and speed of semen deposition, and sanitary procedures. If semen is purchased from a reputable supplier, it is unusual for the cause of the infertility to be poor-quality semen, although transport and storage factors should be considered.
Crossbreeding for more profit with tropically adapted Bos ta**us
The Northern Territory Department of Primary Industry and Fisheries (DPIF) is researching whether crossbreeding with Senepol bulls is a viable way for north Australian cattle producers with Brahman herds to produce animals that will perform well under harsh northern conditions and be suited to the South East Asian live export market and the Australian domestic market. In this webinar Tim Schatz, Principal Pastoral Production Officer (DPIF), discusses the results of the research program to date and compares the:
pre and post weaning growth of Brahmans and F1 Senepol x Brahmans in the Top End of the Northern Territory
performance of the Brahman and F1 Senepol x Brahman steers in feedlots in Queensland and Indonesia
results of meat quality testing from Brahman and F1 Senepol x Brahman steers.
30/08/2022
Performance testing
Performance test is a measure of the phenotypic value of the individual candidates for selection. Since the phenotypic value is determined by both genetic and environmental influences, the performance test is an estimate, not a measure of the genetic value. The occurrence of this estimate depends upon the heritability of the trait i.e. on the degree to which the genetic value is modified by the environmental influences.
Advantages
Among simple procedures, the performance test is the most accurate.
Environmental influences can be minimised by testing candidates for selection in the same pen or in similar environmental conditions.
The measure is direct, not on a relative basis.
All candidates for selection can be tested in contrast to progeny testing where only a parent can be tested.
Generation intervals are usually short.
Testing can usually be done on the farm under normal management conditions.
Disadvantages
Accuracy become low when heretability is low.
Phenotypes are not available for one s*xor in s*x limited traits such as milk yield.
Traits which are not expressed until maturity may become expensive or difficult to manage by performance tests since most selection decisions must be made before maturity.
Performance tests should be the backbone of most selection programmes. Although much publicity has been given to other selection methods, it remains a fact that most of the progress in livestock improvement to date has been due to selection on the individual's own phenotype i.e. performance test.
B. Pedegree selection
A pedegree is a record of an individual's ancestors including its parents. This information is valuable because each individual possesses a sample half of the genes from each parent. If we can precisely know an individual's phenotype, little is gained by considering pedegree in selection. Pedegree considerations are useful when we do not have sufficient accurate records of production of the individual. Also, it is useful in the early selection when the traits in question might not have expressed themselves. It is also useful for selection of males when the traits selected for are expressed only by the female such as milk production in dairy cattle.
Advantages
It provides information when performance tests are not available for the candidates.
It provides information to supplement performance test information.
It allows selection to be completed at a young age. Pedegree records may be used to select animals for performance or progeny testing in multi-stage selection scheme.
It allows selection of bulls can be selected on the milk records of their female relatives.
Disadvantages
Accuracy, relative to alternative selection procedures is usually low.
Too much emphasis on relatives, especially remote relatives, greatly reduces genetic progress.
Progeny of favoured parents are often environmentally favoured.
Relatives often make records under quite different environments, thus introducing non random bases into the selection system.
C. Progeny testing
In this method we evaluate the breeding value by a study of the expression of the trait in its offsprings. Individuality tells us what an animal seems to be, his pedegree tells us what he ought to be, but the performance of his progeny tells us what he is.
Progency testing is, of course, a two-stage selection system because some preliminary selection determines which animals first produce progeny followed by further culling of these which produce poor progeny.
Advantages of progney testing
a. High accuracy when many progeny are obtained.
Disadvantages progney testing
a. Long generation interval.
b. Requires high reproductive rate.
c. Low selection intensity.
D. Show ring selection
Selection on the basis of show ring performance has had considerable value in the past. Essentially this selection has been directed towards bringing the conformation of the animal to some ideal conformation.
This improvement has been based on two goals:
(i) improvement conformation, and
(ii) correlated response.
Improvement of conformation has economic value because a part of the sale price is determined by the conformation of the individual. The ideal type was chosen so that, in the opinion of the judges, the animal possessing this conformation was most likely to be a profitable producer. In other words, the judges were attempting to stress traits of conformation which are corrected with productive ability.
With the advent of record keeping it was found that direct selection for performance traits resulted in much faster progress than selection through correlated conformation traits. Also, when subjected to intensive study, many of the correlations between performance and show ring were found to be of non-genetic origin.
If the correlations are of genetic origin, direct selection for performance should improve conformation as well as the reverse situation. The show ring has been a good forum for discussion of what constitutes ideal type and good management and has produced dramatic changes in the conformation of some species.
This has resulted primarily from education of the breeders, however, for most animals which are presented in the ring are good and selection differential among these animals is usually so small as to produce little change.
Advantages of show ring selection
1. It enables breeders to exchange ideas and experience.
2. It allows comparisons among superior animals both within and between breeds.
3. It allows new breeders to make contact with established breeders.
Disadvantages of show ring selection
1. Emphasis is usually placed on traits of little economic importance.
2. Clever fitting and showmanship can mask defects of various kinds.
3. Differences between exhibited animals are usually small.
4. Conformation and production traits usually have low genetic correlations.
Some of the management suggestions which will tend to improve breeding efficiency of cattle are listed below.
Keep accurate breeding records of dates of heat, service and parturition. Use records in predicting the dates of heat and observe the females carefully for heat.
Breed cows during near the end of mid heat or heat period.
Have females with abnormal discharges examined and treated by veterinarian.
Call a veterinarian to examine females not settled after three services.
Get the females checked for pregnancy at 45 days to 60 days after breeding.
Buy replacements only from healthy herds and test them before putting them in your herd.
Have the females give birth in isolation, preferably in a parturition room and clean up and sterilize the area once parturition is over.
Follow a programme of disease prevention, test and vaccination for diseases affecting reproduction and vaccinate the animals against such diseases.
Practice a general sanitation programme.
Supply adequate nutrition.
Employ the correct technique.
Provide suitable shelter management.
Detect silent or weak heat, by using a teaser bull.
The factors which influence the breeding efficiency of cattle are as follows:
1. Number of ova
The first limitation on the breeding efficiency of fertility of an animal is the number of functional ova released during each cycle of ovulation. Ovulation is the process of shedding of o**m from the Graffian follicle. In the case of cow, usually a single o**m is capable of undergoing fertilization only for a period of 5-10 hours. Therefore, the time of mating insemination in relation to ovulation is important for effective fertilization.
2. Percentage of fertilization
The second limitation is fertilization of ova. Failure to be fertilized may result from several causes. The s***matozoa may be few or low in vitality. The service may be either too early or too late. so that the s***ms and eggs do not meet at the right moment, to result in fertilization.
3. Embryonic death
From the time of fertilization till birth, embryonic mortality may occur due to a variety of reasons. Hormone deficiency or imbalance may cause failure of implantation of fertilized ova which die subsequently. Death may occur as a result of lethal genes for which the embryos are homozygous. Other causes may be accidents in development, over-crowding in the uterus, insufficient nutrition or infections in tile uterus.
4. Age of first pregnancy
Breeding efficiency may be lowered seriously by increasing the age of first breeding. Females bred at a lower age are likely to appear stunted during the first lactation, but their mature size is affected little by their having been bred early.
5. Frequency of pregnancy
The breeding efficiency can be greatly enhanced by lowering the interval between successive pregnancies. The wise general policy is to breed for the first time at an early age and to rebreed at almost the earliest opportunity after each pregnancy. In this way the lifetime efficiency is increased. Cows can be rebred in 9-12 weeks after parturition.
6. Longevity
The length of life of the parent is an important part of breeding efficiency, because the return over feed cost is greater in increased length of life. Also, it affects the possibility of improving the breed. The longer the life of the parents, the smaller the percentage of cows needed for replacement every year.
Reproduction is an important consideration in the economics of cattle production. In the absence of regular breeding and calving at the appropriate time, cattle rearing will not be profitable. A healthy calf each year is the usual goal. This is possible only by increasing the reproductive efficiency of the animals.
Successful reproduction encompasses the ability to mate, the capacity to conceive and to nourish the embryo and deliver the viable young ones at the end of a normal gestation period. In fact, interruption in this chain of events leads to failure of the cow either to conceive or the embryo to die or to have a premature delivery of the foetus.
The reproductive efficiency is a complex phenomenon controlled by both genetic and non-genetic factors, the non- genetic factors being climate, nutrition, and level of management. The reproductive efficiency varies not only between species and breeds but also among the animals within the same breed. Even the best feeding and management can not coax performance beyond the genetic limit of an inferior animal. Improving the genetic merits of livestock populations is important at all levels of management. A sound breeding programme is a necessary part of the total animal production system.
Use of Sex-Sorted S***m
Production of offspring of the desired s*x using s*x-sorted semen has become an established reliable technique in the dairy cattle breeding industry over the last two decades, where the major application is use of X-sorted semen on virgin heifers selected to produce the next generation of replacement animals. Although evolution of the technology has resulted in improved success, pregnancy rates are still somewhat lower than those achieved with conventional semen. Some of the reduction in pregnancy rate may be due to the lower concentration of s***m per dose (typically 2–4 million vs. 15–20 million in conventional, unsorted, semen straws). In superovulated cows, the use of s*x-sorted semen results in impaired fertilization rates and compromised yields of transferable embryos. Reduced fertilization with s*x-sorted semen may be due to low doses of s***m, an abnormal uterine environment due to supraphysiological concentrations of progesterone or atypical s***m transport in superovulated cows, damage to s***m during s*x sorting, or some combination of these factors. Thus, more research is required to optimize the yield of transferable embryos from s*x-sorted semen in superovulated donors.
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