The much wider gap between performance of tropical livestock species and those of the temperate climate demand a critical review and consideration by learners and practitioners of animal production. A foundation course in animal production, such as this, requires students to be acquainted with the existence of the performance gap which has often been attributed to genetic, environmental, and genetic-environment interaction variables.
The essence of familiarization with this challenge may stimulate the desire to finding ways of meeting domestic demands and reducing the performance gap. The identity and measures of productivity of breeds livestock in Nigeria compared with some exotic ought to agitate the minds of students as to what motive or factor underlies the disparity between production capacity of exotic and local breeds of stock.
Past Livestock Improvement Efforts
The temperate-zone counties particularly in Northwest Europe earlier commended livestock improvement through general improvement of environment for livestock such that at the beginning of 9th century improvement efforts were directed towards taking economic advantages of livestock.
Economic advantages were easily achieved as at then by improving on the housing facilities for livestock to prevent adverse climatic effects. Advance in livestock breeding started in 9th century particularly in the United Kingdom. The advances were however based on limited records, acute observation and trail-and-error efforts compared to modern genetic theory being used days.
Science of genetics began to gain recognition in the early 20th century revolutionizing animal breeding with the application of genetic principles combined with new knowledge on physiology of reproduction.
Today, the pace of progress is tremendous with the advent of knowledge on molecular structure of DNA (Deoxyribonucleic Acid) and location of genes on the chromosomes. Genetic engineering will soon take animal production to a new stage.
In contrast, these practices are extremely slow to be applied in the tropical countries. Although livestock owners in the tropic developed rules customs towards better breeding of their stock, but these seem to be haphazardly applied and uncontrolled probably due to inefficient grasp of the challenge pr its solution.
As such efforts to improve the productivity of livestock in the tropics have always moved in a cyclic manner perhaps for a few reasons.
One, the original domestication of most species probably occurred in the tropics and/or subtropics.
Tow, large movement of stock from their origin of domestication to isolated areas resulted in natural development of characteristics that adapted them to their new environment.
Three, breeding of animals in some cultures was restricted to cultural, magical or religious rather than economic perspective.
Four importation of improved breeds from Europe to the Americas thrived in the temperate climate but parallel importation from Europe to the tropical countries of Africa and Asia was not successful except for Criollo cattle breed of tropical Central and South America.
After a few attempts to improve the genetic make-up of stock, a new stream of importation to Africa followed without success, until it was realized that highly productive European and American breeds cannot thrive in tropical Africa and Asia unless epizootic disease are controlled and nutrition and management are improved.
Modern Approach to Livestock Breeding
A new direction is to identify tropical breeds and to initiate selection within them. Yet this has proved to be disappointing. Current efforts are towards introducing productive temperate-type livestock into the tropics primarily by cross breeding, which seems to be succeeding although at very slow rate.
This effort is not without its warning on the consequences of losing the purity of genetic resources of tropical livestock. Thus improvement of topical of livestock lies in greater knowledge of their characteristic traits and those of temperate stock as well. It also involves beings better able to control and improve the tropical environment.
The priority will however vary from an area to another. For example, in areas where epizootic diseases are still prevalent, disease control will be a priority. Elsewhere in which considerable control of disease has been achieved, nutrition and management need to be accorded priority.
It is important to note that it is needless to improve genetic merit if environmental factor remains unimproved. Also, any improvement in genetic merit implies a major step up in both feeding and other management aspects of production.
It is important to appreciate the theory that indigenous livestock breeds adapted to the tropics have achieved some level of adaptation by a natural selection against productivity.
Studies (Payne and Hancock,1957) have shown that high rates of milk production and rapid growth rate increase effects of climatic stress by increasing the metabolic heat output of the animal. In this situation, a number of breeding policy options available.
• Husbandry may select for productivity in indigenous stock.
• Upgrade indigenous stock by the introduction of exotic males or by importation of the semen
• Introduce a crisscrossing breeding system using exotic and indigenous males.
• Introduce exotic stock and attempt to select for adaptation.
• Ameliorate the climatic stress in the tropic to such an extent that exotic stock of high merit can be used (the economic viability of the option is untenable).
The choice of one or a combination of these options varies from country to country and from region to region within counties. It also depends on a number of factors such as:
• Type of indigenous livestock available
• Agricultural system prevailing in the area
• Managerial ability of the local farmers
• Type and size of the market for livestock products
In Nigeria some form of crossbreeding using indigenous (White Fulani) and exotic (Friseian) breed at 50:50 or 25:75 is being carried out at the National Animal Production Research Institute, Shika-Zaria.
An earlier report (Knudsen and Schael, 1970) has shown that lactation yields of White Fulani (840 kg) and Friesian 29,550 kg) improved after crossbreeding in the first generation offspring, Friesian/White Fulani (1.688 kg).
A complementary option to this is to intensify pure breeding of the white Fulani and other indigenous breeds to preserve their genetic resources for the future. This implies that a safeguard for the existence of purebred indigenous cattle is by encouraging the selection of the most productive indigenous stock in special bull breeding herds.
It seems there is no effort in this direction at present. However, it is of little use to upgrade indigenous cattle or any livestock species if the managerial abilities of the local farmers are not upgraded simultaneously.
Crossbreeding as Tool for Tropical Livestock Improvement
A breeding system in which unrelated livestock are mated is known as crossbreeding. The offspring (or progenies) of crossbred livestock are heterozygous for those traits that differ in their parents and the greater the degree of hetonerozygosity on the offspring.
A crossbred progeny inherit the totality of parental characteristics and tend to resemble each other. First-cross generations are usually superior in productive traits to the mean values of both parents. This phenomenon is known as hybrid Vigor or Heterosis. The degree of hybrid vigor depends on the extent to which the characteristics of the parental stock are complementary.
In general, the greater the difference in the parental genetic make-up the greater the degree of hybrid vigor which may be expressed in terms of improved fertility, viability and general thriftiness. The degree of heterosis depends also upon the level of the environment (Barlow, 1981), such that the more stressful the environment the greater the heterosis.
Hybrid vigor, however disappears when hybrids are mated and in the offspring produced. As such new parental stock are continually required if livestock owner wishes to apply or use hybrid vigor optimally.
Crossbreeding may be useful in three ways to livestock owner in the tropics. It can be used for breeding replacement stock. The indigenous and low-producing livestock can be upgraded by continually backcrossing them to more highly productive exotic/introduced stock.
New synthetic breeds can be produced by cross breeding indigenous with introduced stock and then selecting the type of animal or trait required. Both advantages: hybrid vigor and being complementary can be achieved by using some form of systematic crossbreeding between 2 or more breeds of indigenous and introduced stock.
Genetic engineering or recombinant DNA technology is a new practice likely to become needful in the near future as it is possible to use it for modification of the function of animal for better adaptation and productivity. New generation of animals may be made through this technology. Presently, the technique is being exploited in production of vaccines for used against some animal viruses.
It is possible to copy genes or manipulate to increase bulk of genetic materials by introducing genes into bacteria and inducing the same to multiply or reproduce very rapidly, attenuated and used for vaccine production. This method is known as gene cloning. Foot and mouth disease vaccine of cattle is being prepared by this technology.
Major Genetic Differences between Tropical and Temperate Livestock Breeds
Sufficient evidence exist to suggest that more than 50% of the differences in performance of tropical and temperate-type breeds of livestock are due to their inherent genetic abilities or merits. In other words, under fairly conducive environmental conditions condition, tropical and temperate stock exhibit clear difference in economic traits as a result of genetic differences.
In cattle for example, traits showing genetic difference are: age at first calving, calving percentage, milk yields, length lactation, birth weight, rate of daily live weight gain and mature body weight. In addition, McDowell (1972) listed gestation length, generation interval and carcass killing-out percentage as traits showing genetic difference between tropical and temperate stock.
Further evidences have emerged to prove that some tropical breeds such as Bail cattle are not inferior to temperate breeds with respect to some traits like calving percentage, mature body weight and carcass killing-out percentage.
In the light of genetic difference in traits, tropical livestock breeders must make efforts to adopt suitable breeds and breeding system that will address traits of economic advantage in their stock.
Option for Genetic Improvement in Tropical Livestock
1• Use of Indigenous Breed
As earlier suggested, tropical livestock breeds must depend on the use of indigenous breeds for utmost advantages since the indigenous breeds are readily available, well adapted or adapted or acclimatize to the immediate environment and possess matching genetic traits with such environment.
However, a major limitation, to this option, is that selection for increase productivity is likely to be for a lengthy period due to, previous natural selection for survival, which was at the expense of productive traits. Thus, priorities of breeding efforts in the tropical region under the option of using indigenous breed are
Another option earlier mentioned is the importation and used of exotic breeds for purposed of upgrading indigenous breeds. Consideration for importation of exotic breed should be restricted to exotic stock from temperate climate.
There could be genuine rational to import exotic stock from one region of the tropics to another. The use of exotic breed for upgrading has the unique advantage to hasten improvement of productivity where suitable exotic breeds are used and the local environmental conditions are improved.
Major limitations have to do with high cost of upgrading and loss of genetic resources of the local breeds where upgrading is done indiscriminately. Acclimatization of exotic breed to the local environment may be time consuming and expensive.
The option of upgrading with exotic breeds should focus on:
- Areas with moderate climatic, disease and nutritional stress, or montane region in the tropics.
- In case of dairy animals, lowland humid areas have sufficient forage year-round.
- Areas where to indigenous breed exists to exploit the specific peculiarity of the ecological environment. For example it may be reasonable to import water buffaloes or pigs for the creeks of the Niger Delta region of Nigeria.
- Importation is strongly suggested for livestock species whose production system can be restricted from the influence of external environment e.g. intensive poultry or swine production in tropical countries.
Crossbreeding as option has its own advantage of combining desirable traits in two or more breeds in one which is usually higher in hybrid vigor. Expressed hybrid vigor is notably in traits nit largely moderated by genetic or inherited factors but more by the environment such as vigor and fertility.
Heterosis decline with age and it influence is greater in females than males and in stressful condition than in moderately good condition. Limitations of crossbreeding option concern obtaining suitable breeds to combine, expensive and complicated management system to be evolved to obtain good results.
This possibly explains reasons where crossbreeding practices are limited to poultry, pigs and ranches in government farms or research centre in the tropics. Also, Planning a crossbreeding scheme for livestock improvement may be a very difficult exercise.
Planned crossbreeding should concern:
- Areas or breeds, which research has sufficiently approved to show tangible value, advantage or merit.
- In area infested with tsetse fly that debar livestock production, crossbreeding with trypanotolerant breeds.
4• Developing New Synthetic Breeds
Developing new synthetic breeds is an option that seems to streamline limitations of upgrading and crossbreeding options for genetic improvement of livestock in the tropics. It explores crossbreeding or upgrading of indigenous stock using a superior stock and then systematically selecting the offspring to form a breeding much.
It may be extremely long and expensive as it is also require competent personnel. It is often undertaken by very large private organization, government or international agencies.
However, it has an enduring result and may revolutionize livestock in the entire tropical regions. The option is poultry and pigs for different enterprises and for diverse production condition.
Summary / Conclusion
An in-depth understanding of the part and modern approaches to livestock is fundamental to our understanding of the challenges in animal production practices in the topics. Crossbreeding has been offered as intervention to reduce obvious gap in the genetic merits existing between temperate and tropical breeds.
There are a few other options (e.g. use of indigenous breeds developing new synthetic breeds etc) still available but have not been applied or perhaps reserved for the future.
Practitioners and students are required to appreciate the genetic constraints tropical livestock and be armed with sufficient knowledge of improvement.