Que 5: Write short notes on the following: (50 Marks)
- How is urine formed? Discuss the role of aldosterone and antidiuretic hormone (ADH) in this process.
- Briefly discuss different types of hormone receptors and their role in signal transduction.
- Explain how carbohydrates and proteins are digested in ruminant and non-ruminant animals.
- Enlist different blood-proteins and describe their functions in brief.
- What role is played by pulmonary circulation in the body?
How is urine formed? Discuss the role of aldosterone and antidiuretic hormone (ADH) in this process.
The kidneys filter unwanted substances from the blood and produce urine to excrete them. There are three main steps of urine formation: glomerular filtration, reabsorption, and secretion. These processes ensure that only waste and excess water are removed from the body.
1. The Glomerulus Filters Water and Other Substances from the Bloodstream
Each kidney contains over 1 million tiny structures called nephrons. Each nephron has a glomerulus, the site of blood filtration. The glomerulus is a network of capillaries surrounded by a cuplike structure, the glomerular capsule (or Bowman’s capsule). As blood flows through the glomerulus, blood pressure pushes water and solutes from the capillaries into the capsule through a filtration membrane. This glomerular filtration begins the urine formation process.
2. The Filtration Membrane Keeps Blood Cells and Large Proteins in the Bloodstream
Inside the glomerulus, blood pressure pushes fluid from capillaries into the glomerular capsule through a specialized layer of cells. This layer, the filtration membrane, allows water and small solutes to pass but blocks blood cells and large proteins. Those components remain in the bloodstream. The filtrate (the fluid that has passed through the membrane) flows from the glomerular capsule further into the nephron.
3. Reabsorption Moves Nutrients and Water Back into the Bloodstream
The glomerulus filters water and small solutes out of the bloodstream. The resulting filtrate contains waste, but also other substances the body needs: essential ions, glucose, amino acids, and smaller proteins. When the filtrate exits the glomerulus, it flows into a duct in the nephron called the renal tubule. As it moves, the needed substances and some water are reabsorbed through the tube wall into adjacent capillaries. This reabsorption of vital nutrients from the filtrate is the second step in urine creation.
4. Waste Ions and Hydrogen Ions Secreted from the Blood Complete the Formation of Urine
The filtrate absorbed in the glomerulus flows through the renal tubule, where nutrients and water are reabsorbed into capillaries. At the same time, waste ions and hydrogen ions pass from the capillaries into the renal tubule. This process is called secretion. The secreted ions combine with the remaining filtrate and become urine. The urine flows out of the nephron tubule into a collecting duct. It passes out of the kidney through the renal pelvis, into the ureter, and down to the bladder.
5. Urine Is 95% Water
The nephrons of the kidneys process blood and create urine through a process of filtration, reabsorption, and secretion. Urine is about 95% water and 5% waste products. Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid. Ions such as sodium, potassium, hydrogen, and calcium are also excreted.
The hypothalamus produces a polypeptide hormone known as antidiuretic hormone (ADH), which is transported to and released from the posterior pituitary gland. The principal action of ADH is to regulate the amount of water excreted by the kidneys. As ADH (which is also known as vasopressin) causes direct water reabsorption from the kidney tubules, salts and wastes are concentrated in what will eventually be excreted as urine. The hypothalamus controls the mechanisms of ADH secretion, either by regulating blood volume or the concentration of water in the blood.
Dehydration or physiological stress can cause an increase of osmolarity above 300 mOsm/L, which in turn, raises ADH secretion and water will be retained, causing an increase in blood pressure. ADH travels in the bloodstream to the kidneys. Once at the kidneys, ADH changes the kidneys to become more permeable to water by temporarily inserting water channels, aquaporins, into the kidney tubules. Water moves out of the kidney tubules through the aquaporins, reducing urine volume.
The water is reabsorbed into the capillaries lowering blood osmolarity back toward normal. As blood osmolarity decreases, a negative feedback mechanism reduces osmoreceptor activity in the hypothalamus, and ADH secretion is reduced. ADH release can be reduced by certain substances, including alcohol, which can cause increased urine production and dehydration.
Another hormone responsible for maintaining electrolyte concentrations in extracellular fluids is aldosterone, a steroid hormone that is produced by the adrenal cortex. In contrast to ADH, which promotes the reabsorption of water to maintain proper water balance, aldosterone maintains proper water balance by enhancing Na+ reabsorption and K+ secretion from extracellular fluid of the cells in kidney tubules. Because it is produced in the cortex of the adrenal gland and affects the concentrations of minerals Na+ and K+, aldosterone is referred to as a mineralocorticoid, a corticosteroid that affects ion and water balance. Aldosterone release is stimulated by a decrease in blood sodium levels, blood volume, or blood pressure, or an increase in blood potassium levels. It also prevents the loss of Na+ from sweat, saliva, and gastric juice. The reabsorption of Na+ also results in the osmotic reabsorption of water, which alters blood volume and blood pressure.
Aldosterone production can be stimulated by low blood pressure, which triggers a sequence of chemical release. When blood pressure drops, the renin-angiotensin-aldosterone system (RAAS) is activated. Cells in the juxtaglomerular apparatus, which regulates the functions of the nephrons of the kidney, detect this and release renin.
Renin, an enzyme, circulates in the blood and reacts with a plasma protein produced by the liver called angiotensinogen. When angiotensinogen is cleaved by renin, it produces angiotensin I, which is then converted into angiotensin II in the lungs. Angiotensin II functions as a hormone and then causes the release of the hormone aldosterone by the adrenal cortex, resulting in increased Na+ reabsorption, water retention, and an increase in blood pressure. Angiotensin II in addition to being a potent vasoconstrictor also causes an increase in ADH and increased thirst, both of which help to raise blood pressure.
Briefly discuss different types of hormone receptors and their role in signal transduction.
Major types of hormone receptors
- G protein-coupled receptors. Many peptide hormones: glucagon, hypothalamic and hypophyseal hormones. Epinephrine, norepinephrine.
- Receptor tyrosine kinases. Insulin. Growth hormone and growth factors.
- Nuclear hormone receptors. Steroid hormones. Thyroid hormones.
Hormone receptors are found either exposed on the surface of the cell or within the cell, depending on the type of hormone. In very basic terms, binding of hormone to receptor triggers a cascade of reactions within the cell that affects function. Additional details about receptor structure and function are provided in the section on hormone mechanism of action.
Role in signal transduction
Receptors for steroid and thyroid hormones are located inside target cells, in the cytoplasm or nucleus, and function as ligand-dependent transcription factors. That is to say, the hormone-receptor complex binds to promoter regions of responsive genes and stimulate or sometimes inhibit transcription from those genes.
Thus, the mechanism of action of steroid hormones is to modulate gene expression in target cells. By selectively affecting transcription from a battery of genes, the concentration of those respective proteins are altered, which clearly can change the phenotype of the cell.
Hormone-Receptor Binding and Interactions with DNA
Being lipids, steroid hormones enter the cell by simple diffusion across the plasma membrane. Thyroid hormones enter the cell by facilitated diffusion. The receptors exist either in the cytoplasm or nucleus, which is where they meet the hormone. When hormone binds to receptor, a characteristic series of events occurs:
- Receptor activation is the term used to describe conformational changes in the receptor induced by binding hormone. The major consequence of activation is that the receptor becomes competent to bind DNA.
- Activated receptors bind to “hormone response elements”, which are short specific sequences of DNA which are located in promoters of hormone-responsive genes. In most cases, hormone-receptor complexes bind DNA in pairs, as shown in the figure below.
- Transcription from those genes to which the receptor is bound is affected. Most commonly, receptor binding stimulates transcription. The hormone-receptor complex thus functions as a transcription factor.
Explain how carbohydrates and proteins are digested in ruminant and non-ruminant animals.
Energy feed digestion in the rumen
Rumen microbes digest simple and complex carbohydrates (fiber) and convert them into VFAs. VFAs mainly consist of acetic, propionic and butyric acids and provide 50 to 70 percent of the cow’s energy, see figure 1.
Diet can affect the amounts of each VFA microbes produce.
- High forage diets result in more acetic acid forming (60 to 70 percent of total) than propionic (15 to 20 percent) and butyric acids (5 to 15 percent).
- More grain or finely ground forages can cause the amount of acetic acid to decline to 40 percent, while the amount of propionic acid may increase to 40 percent.
Such changes in VFA production usually relate to a reduction in milk fat test.
Microbes digest about 30 to 50 percent of the fiber units, cellulose and hemicellulose, in the rumen. Sixty percent or more of the starch is degraded depending on the amount fed and how fast ingested materials move through the rumen. Most sugars get completely digested within the rumen.
VFAs absorb into the bloodstream from the rumen and move to the body tissues including the udder. Once in the tissues, the cow uses VFAs as a source of energy for
- Milk production
Protein and nonprotein nitrogen use in the rumen
Not all consumed proteins get broken down in the rumen, (see figure 2). Through fermentation, protein is converted to ammonia, organic acids, amino acids and other products. About 40 to 75 percent of the natural protein in feed gets broken down.
The amount of breakdown depends on many factors including:
- The ability of the protein to dissolve
- How resistant the protein is to breakdown
- How fast the feed passes through the rumen
Aside from protein breakdown, nonprotein nitrogen (NPN) sources also provide ammonia. NPN sources include urea, ammonium salts, nitrates and other compounds. Many rumen microbes need ammonia to grow and build protein. Rumen microbes convert ammonia and organic acids into amino acids to use for building protein.
Most of the extra ammonia absorbs into the bloodstream from the rumen. But small amounts may pass into the lower digestive tract and absorb there. Feed protein (not broken down in the rumen) and microbial protein pass to the abomasum and small intestine for digestion and absorption.
In animals like pigs, the lips, cheeks, palate and tongue are all involved with prehension and movement of feed in the mouth. Small feeds are usually ingested with the tongue, while the teeth shear off any large or long pieces. Pigs can also suck up slurry feeds and water. Saliva is produced by three primary glands, and its volume and consistency can change with the nature of the food. Once food has been chewed and mixed with saliva to a proper consistency it is swallowed and passed down the esophagus to the stomach. The motility of the stomach is necessary to mix the digesta with the gastric juices and to move the digesta into the small intestine.
The small intestine, comprised of the duodenum, jejunum and the ileum, is the site where the majority of digestion takes place and most, if not all, nutrient absorption occurs. The duodenum is the site for the mixing of digesta with intestinal, liver and pancreatic secretions. These secretions serve to buffer the contents as they leave the stomach, and to lubricate the bolus for ease of movement through the intestines.
The caecum and colon (hind gut) retrieve any nutrients, primarily water and electrolytes, remaining in the digesta as it leaves the small intestine. The caecum is a blind sac arising at the junction of the ileum and colon. Anaerobic fermentation of fiber in the caecum and colon produces some utilizable energy in the form of volatile fatty acids. The amount of energy produced is small in relation to the pig’s total requirement but hind gut fermentation liberates substantial nutrients in horses and rabbits.
Enlist different blood-proteins and describe their functions in brief.
Types of Plasma Proteins
The three major fractions of plasma proteins are known as Albumin, globulin, and Fibrinogen. On a finer resolution by electrophoresis, these fractions are separated as follows –
Functions of Plasma Protein
- Protein Nutrition: Plasma proteins act as a source of protein for the tissues, whenever the need arises.
- Osmotic Pressure and water balance: Plasma proteins exert an osmotic pressure of about 25 mm of Hg and therefore play an important role in maintaining a proper water balance between the tissues and blood.
- Buffering action: Plasma proteins help in maintaining the pH of the body by acting ampholytes. At normal blood pH, they act as acids and accept captions.
- Transport of Lipids: One of the most important functions of plasma proteinsus to transport lipids and lipid-soluble substances in the body.
- Blood Coagulation: Prothrombin present in ?2-globulin fraction and fibrinogen, participate in the blood clotting process as follows.
What role is played by pulmonary circulation in the body?
Blood must always circulate to sustain life. It carries oxygen from the air we breathe to cells throughout the body. The pumping of the heart drives this blood flow through the arteries, capillaries, and veins. One set of blood vessels circulates blood through the lungs for gas exchange. The other vessels fuel the rest of the body. Read on to learn more about these crucial circulatory system functions.
There Are Two Types of Circulation: Pulmonary Circulation and Systemic Circulation
Pulmonary circulation moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide. The oxygenated blood then flows back to the heart. Systemic circulation moves blood between the heart and the rest of the body. It sends oxygenated blood out to cells and returns deoxygenated blood to the heart.
In the pulmonary loop, deoxygenated blood exits the right ventricle of the heart and passes through the pulmonary trunk. The pulmonary trunk splits into the right and left pulmonary arteries. These arteries transport the deoxygenated blood to arterioles and capillary beds in the lungs. There, carbon dioxide is released and oxygen is absorbed. Oxygenated blood then passes from the capillary beds through venules into the pulmonary veins. The pulmonary veins transport it to the left atrium of the heart. The pulmonary arteries are the only arteries that carry deoxygenated blood, and the pulmonary veins are the only veins that carry oxygenated blood.
Que 6: Write in brief on the following: (50 Marks)
- Blood-brain barrier
- Growth curve
key structure of the blood–brain barrier that offers a barrier is the “endothelial tight junction”. Endothelial cells line the interior of all blood vessels. In the capillaries that form the blood–brain barrier, endothelial cells are wedged extremely close to each other, forming so-called tight junctions.
The tight gap allows only small molecules, fat-soluble molecules, and some gases to pass freely through the capillary wall and into brain tissue. Some larger molecules, such as glucose, can gain entry through transporter proteins, which act like special doors that open only for particular molecules.
Surrounding the endothelial cells of the blood vessel are other components of the blood–brain barrier that aren’t strictly involved in stopping things getting from blood to brain, but which communicate with the cells that form the barrier to change how selective the blood–brain barrier is.
Why do animal need it?
The purpose of the blood–brain barrier is to protect against circulating toxins or pathogens that could cause brain infections, while at the same time allowing vital nutrients to reach the brain.
Its other function is to help maintain relatively constant levels of hormones, nutrients and water in the brain – fluctuations in which could disrupt the finely tuned environment.
So what happens if the blood–brain barrier is damaged or somehow compromised?
One common way this occurs is through bacterial infection, as in meningococcal disease. Meningococcal bacteria can bind to the endothelial wall, causing tight junctions to open slightly. As a result, the blood–brain barrier becomes more porous, allowing bacteria and other toxins to infect the brain tissue, which can lead to inflammation and sometimes death.
It’s also thought the blood–brain barrier’s function can decrease in other conditions. In multiple sclerosis, for example, a defective blood–brain barrier allows white blood cells to infiltrate the brain and attack the functions that send messages from one brain cell (neuron) to another. This causes problems with how neurons signal to each other.
The blood–brain barrier is generally very effective at preventing unwanted substances from accessing the brain, which has a downside. The vast majority of potential drug treatments do not readily cross the barrier, posing a huge impediment to treating mental and neurological disorders.
One possible way around the problem is to “trick” the blood–brain barrier into allowing passage of the drug. This is the so-called Trojan horse approach, in which the drug is fused to a molecule that can pass the blood–brain barrier via a transporter protein.
The growth curve is a curve, which plots time against growth (can be a number of cells, the size of an animal or organ of an animal etc.).
Generally, these curves have a characteristic S-shape, also called, sigmoidal curve.
This curve has three distinct phases as:
a.Lag phase – During this phase, cell prepares for growth.
b. Log/Exponential phase – During this phase, cell actually grows.
c. Stationary phase- During this phase, the growth ceases.
It is defined as the correlated increase in the body mass at definite time interval.
- Growth generally begins slowly, which then undergoes a period of rapid increase followed by slow down or stagnant of growth. Plotting the body weight of an animal on the ‘y’ axis and the age of the animal on the ‘x’ axis produces growth curve. It is normally sigmoid shaped in all animals and man. The course of growth after birth is almost similar in farm animals. But the juvenile or the prepubertal period is very long in human when compared to that of the animals. In humans,puberty is attained when the body weight reaches 60%, whereas in animals puberty occurs when 30% of the adult weight is reached. There are few exceptions to V curve i.e. organs like gonads and mammary glands are showing cyclic growth.
The growth curve has two phases:
- It is the increasing slope of the curve, in which the growth rate accelerates to the maximum. Here the steep slope of the curve extends from the beginning of growth until l/3rd to ½ of the mature weight is reached. The following two forces acting on the growth rate which determine the shape of the growth curve:
- Growth accelerating force
- Growth accelerating force is present in the body cells and is due to hyperplasia, hypertrophy and inclusion of exogenous substances.
- Growth retarding or decelerating force
- When growth cannot continue definitely due to lack of space or food supply, the growth rate retards from this point onwards and the force that act upon is called as the growth retarding force which is found in the environment surrounding the cells.
- During the initial linear phase of growth the two opposing forces are in balance.
Decelerating phase/Retarding phase
- It is the decreasing slope of the curve. During this period growth rate declines and ultimately ceases. It is the final phase of growth and it occurs when the animal “approaches its mature body weight. There is an in built restraint on further growth, which progressively reduces the proportion of feed intake. There is stabilization of feed intake and reduction in the increase in body weight until intake equals the maintenance requirement. This may be due to the production of hypothalamic somatostatin.
- At the junction of the accelerating and retarding phase, where the growth rate stops to increase and which it begins to decrease it is called as the point of inflection. Since in all species puberty occurs at this point it is also known as point of pubertal inflection. This point indicates the time of maximum velocity’ of growth, age of puberty, beginning of increasing specific mortality and point of reference to determine age equivalents of different animals. This point occurs at 14 years in humans, 9 – 12 in cattle and 6 -7 months in sheep.
Negative growth phase
- In the old age the starts degenerating and this phase is referred as negative growth phase.
- Growth can be expressed in many ways
- Actual weight or growth curve
- Percentage increment method
- Weight gained per fixed unit of time
Que 7: Discuss the role of biotechnology in genetic improvement of diary animals. State the steps involved in embryo transfer technology and its application. (50 Marks)
Three major topics can be distinguished in the area of biotechnology applied to the genetic improvement of
- reproductive technologies,
- livestock genomics and marker assisted selection (MAS), and
- livestock transgenics.
A number of methods have or are being developed to increase the reproductive potential of livestock These include:
Artificial insemination (AI): Especially since the development of efficient semen freezing methods, AI has become the most widespread biotechnology applied to livestock and especially cattle production. By allowing for the widespread use of small numbers of elite sires, AI has had a dramatic impact on selection intensity. In addition, AI has allowed for the implementation of the progeny-testing scheme prevalent particularly in dairy cattle production, and which has had a major impact on the improvement of the herd by increasing the accuracy of selection despite the associated increase in generation interval.
Multiple ovulation and embryo transfer (MOET): By increasing the number of offspring that can be obtained from monotocous species in particular, MOET has the potential to increase genetic improvement
by enhancing the selection intensity on the female side. In cattle, however – the species in which this technology is again the most widely disseminated – the major impact of MOET might result from the reduction in generation interval vis-à-vis the conventional progeny-testing scheme, if sires are selected based on the performances of their MOET produced full-sisters rather than the performances of their female progeny: the so-called MOET nucleus scheme. Despite associated technical hurdles, MOET has the potential to play an important role in developing countries where the implementation of a large-scale AI based progeny-testing scheme would be difficult to implement.
Oocyte harvesting (OPU), in vitro oocyte maturation (IVM), in vitro fertilisation (IVF): While the number of embryos that can be obtained from a cow / year using MOET is on an average limited to the
order of 20 or less, the development of OPU in conjunction with IVM and IVF increases this number by a factor of at least 5. Moreover, OPU can be applied to pregnant animals as well as prepubic animals. The
impact of these methodologies on genetic response operates through the same channels as MOET, i.e. increase of selection intensity on the female side and increase of selection accuracy on the male and
Nuclear transfer or embryo cloning: The transfer of totipotent nuclei in enucleated oocytes theoretically allows for the production of large numbers of identical twins or “clones”. The principles underlying
embryo cloning are summarised in Figure 1. This opened the prospective to affect genetic response in a variety of ways including selection intensity, selection accuracy and generation interval. Initially, the source of totipotent nuclei were blastomeres. Despite the potential use of first as well as higher order generation blastocysts as nuclei donors, the size of the clones has remained very small. The recent generation of totipotent embryonic stem “ES”-like cells in sheep which will likely be followed by similar developments in other species, might lead to a considerable increase in the efficiency of embryo cloning
Sex selection: Recent improvements in flow cytometric sorting now allows for the effective separation of viable X and Y-bearing sperm. While the numbers of cells recovered are incompatible with conventional AI practices, they are sufficient when combined with IVF techniques. This might become the method of choice to generate embryos of a desired sex. Embryo sexing can also be achieved by micro biopsy and sex determination using polimerase chain reaction (PCR) amplified Y-specific sequences. This approach, however, is economically only justified in very exceptional circumstances.
Gamete and embryo cryopreservation: Most methods described are only effective when used in conjunction with gamete and embryo freezing methods. In addition cryopreservation plays a crucial role in conservation programmes aimed at maintaining genetic diversity.
Livestock genomics and marker assisted selection (MAS)
Advances in molecular genetics, boosted by the ‘Human Genome Initiative’, now allow for the development of unlimited numbers of genetic markers, the fundamental tool of the geneticist. These markers can be used to locate
genes underlying phenotypic traits on the corresponding genome maps using linkage strategies. This mapping is the first step in the process referred to as positional cloning which culminates in the isolation of the causal gene and mutation
Understanding the molecular biology of production traits is of importance in several respects. It is strongly believed that the identification of QTL will allow for the implementation of novel “marker assisted” selection
schemes. MAS is expected to increase genetic response by affecting all four relevant factors. Mapping genes explaining breed differences for economically important traits will allow their introgression in other populations by marker aided backcrossing, therefore increasing the genetic variation usable as substrate for selection programmes.
Probably the most publicised example of this is the search for the genes causing hyperprolificity of Chinese pig breeds. Adding information on mapped QTL on top of their own performance data and that of relatives, will increase accuracy of selection especially by explaining Mendelian sampling variance. As the marker genotype is obtainable at virtually any stage of development and irrespective of sex, there is considerable potential
for reduction in generation interval. Finally, marker genotyping will become considerably cheaper than phenotype collection allowing selection for more traits amongst more individuals than previously and therefore increasing the selection differential or intensity.
While conventional breeding strategies as well as MAS are restricted to the exploitation of genetic variation preexisting within the species if not breed of interest, transgenics has opened the exciting possibility to exploit
variants across species barriers or even create de novo.
Two major approaches for the production of transgenic animals have to be distinguished:
1) by microinjection of DNA constructs in the male pronucleus of one-cell stage embryos, and
2) by genetic targeting of totipotent cells in culture, followed by either nuclear transfer in enucleated oocytes or microinjection into blastocysts. While in the former procedure, the transgene is integrated randomly into the genome (which may affect its expression pattern), gene targeting mediated by homologous recombination is locus-specific.
Until very recently, the first approach was the only option available for livestock species in the absence of suitable totipotent livestock cell lines. The recent description of ovine “ES” cells and their use to produce chimeric sheep, however, demonstrates that gene targeting methods might become available for animal production in the near future as well.
A variety of transgenic projects are being conducted with the aim to
1) enhance growth and improve carcass characteristics,
2) increase milk production and alter milk composition,
3) increase disease resistance, and
4) improve wool production.
However, the application of transgenics applied to livestock species that has proven most successful so far is in the area of gene-pharming or the use of livestock species as expression systems for the production of high value protein products.
Embryo transfer is a bio-technique where embryos are collected from the donor females and transferred in to the uterus of recipients which serves as a foster mother for its development throughout the remainder period of pregnancy
Role Of ETT In Livestock Development And Breed Improvement.
Through ETT, one high quality cow could be made to produce up to 32 embryos per year compared to the conventional method of breeding where the farmer has to wait for twelve months for a calf that could be either male or female.
The reproductive potential of a female newborn calf is enormous and is estimated at 150,000 ova per cow. This reproductive potential has largely been underutilized.
Naturally, a cow produces about 8 to 10 calves in her lifetime. But with embryo transfer, it is possible to get 32 embryos per cow per year.
Embryo transfer is a technique that can greatly increase the number of offspring that a genetically superior cow can produce.
Under conventional ways, the generation interval ranges between 6 and 7 years, but with MOET, it can be reduced by almost half. Also useful in progeny testing programs, due to reduction in generation interval.
Very Effective for the propagation of superior genes, although factors such as lactation status of recipient animals, time of embryo recovery after insemination, site of embryo placement in recipient’s uterus, embryo quality and stage of development all influence overall conception rate.
8 Steps Involved In Embryo Transfer
1. Selection of donor
2. Selection of recipient
3. Estrus synchronization of donor and recipient
4. Superovulation of Donor with high quality semen.(release of multiple eggs at a single estrus).
5. Artificial insemination of donor
6. Embryo collection
7. Evaluation of embryo
8. Transfer of embryo / cryopreservation of embryo / Micromanipulation
Que 8: What is repeat breeding syndrome in bovines? Enlist the causes of repeat breeding. (50 Marks)
Cows that are cycling normally, with no clinical abnormalities, which have failed to conceive after at least two successive inseminations.
In practice, some will have been inseminated at the wrong time, others may have pathological changes in the bursa or oviduct that are difficult to palpate, or undiagnosed uterine infections.
Repeat breeders can be divided into two groups:
1. Early repeats
Cows that come into heat within 17-24 days after AI.
In these animals the luteal function has been shorter than normal or typical for the physiological oestrus cycle in non-bred cow. In these cows the most probable event is either failure of fertilisation (delayed ovulation, poor semen quality etc.) or early embryonic death (delayed ovulation, poor embryo quality, unfavourable uterine environment, precocious luteolysis)
2. Late repeats
Cows that come into heat later than 25 days after AI.
In these animals the luteal function was maintained for longer than the physiological luteal phase in non-bred cows. Fertilisation and initial recognition of pregnancy probably took place but for some reason (inadequate luteal function, inadequate embryo signalling, infectious diseases, induced luteolysis) luteolysis was induced and pregnancy lost.
Enlist the causes of repeat breeding
The major reasons for repeat breeding are:
- Genetics :Chromosomal or genetic abnormalities of parent and those defects that occur during the differentiation process may negatively affect fertility.
- Age : Higher incidences of repeat breeding have been seen in old cows. It is observed that fertility in dairy cows get better after the 1st or 2nd parturition, and then declines from the 4th and 5th.
- Uterine infection and repeat oestrous cycles :The uterine environment encourages the normal embryonic development. Hence, any disorder or defects like uterine infections, endometritis, pyometra, metritis etc adversely affects the survival of the embryo causing embryonic death which is also one of the major reasons for repeat breeding.
- Anatomical defects of the genital tract :The reproductive tract of cow offers a appropriate atmosphere for oocyte growth, sperm transport, fertilization and implantation. Anatomical or functional alterations of these structures can compel gestational failure and repeat breeding.
- Improper ovarian function :The problem of ovarian cysts in dairy cows is a serious reason of reproduction failure. Cystic ovarian degeneration (COD) is a cause of repeat breeding in cattle. Delayed ovulation, anoestrus are also linked with this problem. Luteal inadequacy resulting into progesterone deficiency may provoke repeat breeding syndrome.
- Nutritional causes :The conception of the cows is associated with body weight. Mandatory weight which cows should achieve before breeding is for indigenous and jersey cross heifer 240-275 kg and for HF cross heifer 260-290 kg. Underweight animals show poor rates of conception. Balanced feeding (energy, fat, protein, vitamins and minerals) is the solution for this. The trace minerals particularly copper, cobalt, iron etc. are requisite for steroidogensis. Supplementing trace minerals and Vitamins A, D3and E, can assist in treating the problem of anoestrus/repeat breeding dairy animals.
- Artificial insemination :Any disorder at any action involving bull preparation, artificial vagina preparation, semen collection, semen processing, storage, thawing, post-thaw handling of semen, incorrect insemination in relation to stage of oestrus may result into repeat breeding. If animals are not inseminated at accurate time, it may cause conception failure. We should inseminate the indigenous cows according to AM.-P.M. rule i.e. if a cow comes in heat in morning, she should be inseminated in the same day evening and if came to heat on evening she should be inseminated on next day morning. The exotic/crossbred should be inseminated in mid to late heat. It is better to give double insemination should always be done with the gap of 12-24 hours after first AI in crossbreds.