Aging and Senescence
Aging is defined as the gradual decline of physiological functions and organism fitness, which leads to age-dependent fitness loss, diseases eventually mortality.
26.7.1 Oxidative Damage
Oxidative stress refers to elevated reactive oxygen species (ROS) at intracellular level where 2-3% of oxygen atoms are reduced insufficiently to ROS by the mitochondria.
The ROS oxidizes and damages cell membranes, proteins, and even nucleic acids. Over-expression of ROS-destroying enzymes in drosophila had 30-40% longer life than the control. Flies with mutant the methuselah gene live 35% longer than the wild-type files, where the mutants have developed resistance to paraquat, a poison that generates ROS within cells. Thus, genetic control can enhance aging process. Similarly, Caenorhabditis elegans mutants with the higher secretion of ROS-degrading enzymes live much longer than the wild ones. Mice lacking protein p66shc give resistance to ROS, leading to an increase in the life span of mice compared to the control. The protein p66shc is involved in apoptosis signaling pathway, their absence might play a role in the increase of the animal’s life span. Calorie restriction aids in slowing the aging process by preventing ROS synthesis. Use of ROS inhibitors like vitamins E, C, and E in the diet increases the longevity of flies and nematodes.26.7.2 Genetic Instability
Mutation in the protein synthesis process produces more altered protein; likewise mutation in DNA-synthesizing enzymes, DNA repair enzymes will affect the aging process.
Mitochondrial genome damage
Mitochondrial mutation is 10-20 times faster than nuclear DNA mutation. Mitochondrial function declines due to mutation in the mitochondrial genome which is associated with the aging process. Impacts of mitochondrial mutation are
1. Defects in energy production
2.
Production of ROS by faulty electron transport3. Induce apoptosis
All these eventually enhance the aging process.
26.7.3 Telomere and Aging
Telomeres are non-coding specialized repetitive DNA sequences located at the ends of chromosomes. Its functions are to maintain chromosome stability. When telomeres size reaches a particular smaller size, it inhibits cell division and initiates senescence processes. The size of telomeres shortens with aging. The length of the chromosomes is maintained by telomerase which prevents the shortening by adding the telomere onto the chromosome at each cell division. Telomerase may not be a factor in determining the differences in the aging rate among species. Telomere shortening might help in determining some age-related properties of organs. However, the activation of telomerase hinders a barrier to the growth of developing cancers while lack of telomerase activity provides a tumor suppressor function.
Learning Outcomes
• Growth is a complex biological process by which animals become larger over a period of time.
• Animal growth pattern is categorized into prenatal and postnatal growth which is regulated by several factors, viz., genetic, nutritional, and environmental factors.
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• Growth process might be manipulated by using various growth enhancers, feed additives, and supplementation of growth factors to enhance the meat, milk, and egg production in domestic animals.
• Growth anomalies observed in domestic animals might be due to genetic and environmental factors.
• Animals undergo aging and senescence once attain maturity.
Exercises
Objective Questions
Q1. Progressive increase in size and weight of an animal during a specific period of time is known as ?
Q2. What is hypertrophy?
Q3. What is hyperplasia?
Q4. What are periods of growth in farm animals?
Q5. What is prenatal growth?
Q6. What are the phases of prenatal growth?
Q7. Which period is considered as the most important during prenatal growth?
Q8.
Gastrointestinal tract developed from which germ layer?Q9. What is the shape of the growth curve in farm animals? Q10. What are the phases of growth curve?
Q11. Which force is responsible for rapid growth of a cell? Q12. Which point is the indicator maximum growth rate? Q13. At which point the growth rate started to decrease? Q14. What are the main factors regulating the growth of farm animals?
Q15. What are the axes governing the growth process in animals?
Q16. Which is the hormone mediating the GH effects in muscle and connective tissue growth?
Q17. Where is IGF produced?
Q18. What is the correlation between birth weight and litter size?
Q19. Growth of organs or parts of the body follows which type of growth?
Q20. What are the different phases of growth observed in birds?
Q21. Gradual loss of physiological functions and organism fitness known as ?
Q22. Which enzyme maintains the length of the chromosomes?
Subjective Questions
Q1. Describe the prenatal growth patterns in farm animals?
Q2. Write the events takes place during the pre-embryonic period of growth?
Q3. Write the characteristics of the growth curve in farm animals?
Q4. Describe biochemical and genetic determinants of growth.
Q5. Write the various factors regulating prenatal growth?
Q6. Write the various factors regulating postnatal growth?
Q7. Describe the growth in meat-producing animals and poultry?
Q8. Describe the growth manipulation in farm animals?
Q9. Describe the growth anomalies in farm animals?
Q10. Write about aging and senescence?
Q11. Describe the growth pattern in birds?
Answer to Objective Questions
A1. Growth
A2. Increase in size of a cell, tissue, or organ
A3. Increase in number of cells
A4. Prenatal and postnatal growth period
A5. Growth period between conception and birth
A6. Pre-embryonic/ovum period, embryonic, and Fetal period
A7. Embryonic period
A8. Endoderm
A9. Sigmoid or S-shape
A10.
Self-accelerating phase and self-retarding phaseA11. Growth accelerating force
A12. Point of pubertal inflection
A13. Point of inflection
A14. Genetic, endocrine, nutritional, and environment
A15. Somatotroph axis and thyrotroph axis
A16. Insulin-like growth factor 1 (IGF-1)
A17. Liver
A18. Negative
A19. Urethra
A20. Isometric and allometric
A21. Embryonic, post-hatch, prepubertal, pubertal, and adult A22. Aging
A23. Telomerase
Keywords for Answer to Subjective Questions
A1. Pre-embryonic period of growth, embryonic period, fetal growth
A2. Fertilization, cleavage, formation of blastocyst, implantation
A3. Phases of the growth curve, self-accelerating phase, self-retarding phase, negative growth phase
A4. Genetic factors, role of amino acids, role of fatty acids
A5. Heredity, hormones, maternal age, maternal nutrition, litter size, fetus sex, environment
A6. Sex of animal, litter size, plane of nutrition, hormones, environmental factors, diseases
A7. Growth of organs, muscle growth, protein deposition, fat deposition
A8. Use of different growth promotors, hormones, recombinant gene transfer, prebiotics, probiotics, organic acids, exogenous enzymes
A9. Congenital anomalies, inherited defects, developmental defects-infectious agents, environmental factors, nutritional factors, physical agents
A10. Oxidative damage, genetic instability-mitochondrial genome damage, role of telomere
A11. Growth phases, embryonic, post-hatch, prepubertal, pubertal, adult
Further Reading
Brody S (1945) Bioenergetics and growth. Hafner, New York
Buttery PJ (1983) Protein deposition in animals. Outlook Agric 12(4):172-178
Christopherson RJ (2010) Physiology of growth and reproduction in livestock. In: Hudson RJ (ed) Animal and plant productivity, Encyclopedia of life support systems. EOLSS Publications, Oxford
Gibson GR, Roberfroid MB (1995) Dietary modulation of the human colonic microbiota: Introducing the concept of prebiotics.
J Nutr 125:1401-1412Gicquel C, Le Bouc Y (2006) Hormonal regulation of fetal growth. Horm Res Paediatr 65(Suppl. 3):28-33
Gilbert SF (2000) Aging: the biology of senescence. In: Developmental biology, 6th edn. Sinauer, Sunderland, MA
Kwon H, Ford SP, Bazer FW, Spencer TE, Nathanielsz PW, Nijland MJ, Hess BW, Wu G (2004) Maternal nutrient restriction reduces concentrations of amino acids and polyamines in ovine maternal and fetal plasma and fetal fluids. Biol Reprod 71(3):901-908
Lawrence TLJ, Fowler VR, Novakofski JE (2012) Growth of farm animals. CABI, Wallingford
Miller EL (2004) Protein nutrition requirements of farmed livestock and dietary supply. In: Protein sources for the animal feed industry, expert consultation and workshop, Bangkok. Food and Agriculture Organization of the United Nations, Rome, pp 29-76
Nagashima H, Matsunari H, Nakano K, Watanabe M, Umeyama K, Nagaya M (2012) Advancing pig cloning technologies towards application in regenerative medicine. Reprod Domest Anim 47: 120-126
Owens FN, Dubeski P, Hanson CF (1993) Factors that alter the growth and development of ruminants. J Anim Sci 71(11):3138-3150
Rousseaux CG (1988) Developmental anomalies in farm animals: I. Theoretical considerations. Can VetJ 29(1):23-29
Scheaffer AN, Caton JS, Redmer DA, Reynolds LP (2004) The effect of dietary restriction, pregnancy, and fetal type in different ewe types on fetal weight, maternal body weight, and visceral organ mass in ewes. J Anim Sci 82(6):1826-1838
Wu G, Bazer FW, Wallace JM, Spencer TE (2006) Board-invited review: intrauterine growth retardation: implications for the animal sciences. J Anim Sci 84(9):2316-2337