Flashcards in Animal Physiology-Growth Deck (51)
Why have farm animals been well studied?
Due to their economic importance
Mature size is when growth stops. In which order do the different tissue types develop?
Nervous tissue, bone, muscle and then fat.
Describe the 3 stages of the sigmoidal weight/growth curve.
First stage is accelerating, usually pre-natal. Then constant phase then decelerating phase as animal reaches maturity
What is the difference between the skeletal muscle growth prenatally and postnatally?
Prenatal muscle growth involves hyperplastic growth whereas postnatal muscle growth involves extensive hypertrophy (increase in size) of existing muscle fibres. There are exceptions (rats) however in most mammals there is no hyperplastic growth after birth
What is myogenesis?
Myogenesis is the development of muscle fibres during the embryonic stage (pre-natal). Muscle fibres arise from individual embryonic muscle cells called myoblasts, which are mono-nucleated precursor cells.As the foetus develops myoblasts proliferate and fuse to other myoblasts creating elongated multinucleated myotubes, which synthesise muscle protein forming a muscle fibre
Postnatally, hypertrophic growth of the skeletal muscle occurs. What sort of cells activate this kind of growth?
Satellite cells (discovered by Mauro) increase DNA accretion through proliferation followed by differentiation and fusion with existing muscle fibre content and can be used to replace damaged myofibres. IGF activates them from being dormant underneath the cell membrane
In terms pigs' final body weight, what is the difference between those who were born with a low or heavy birth weight?
The LW pigs took a lot longer to reach the same final body weight as the HW pigs. It has been found that the smaller piglets displayed more hypertrophic growth throughout their lives compared to the heavier piglets as they try to compensate for having lower fibre numbers at birth
How do adipocyte tissues develop (adipogenesis)?
Adipoblasts multiply and differentiate to form pre-adipocyte cells which contain only a few lipid droplets and lipogenic enzymes. They then further develop into an adipocyte cell which is our fat cell containing a single large lipid droplet (90% of cell cover)- beige adipose tissue is thought to develop from these WAT by cold activation
Does adipocyte tissue have clean cut prenatal hyperplastic growth and post natal hypertrophic growth?
No, these overlap and occur in both pre natal development and post natal. Hypertrophy occurs as lipid is deposited in the cell increasing the cell diameter and volume, therefore the rate of hypertrophy depends on the relative rates of esterification (trigylceride levels) and lipolysis, hypertrophy being absent if the two rates are equal. In turtles, We can see hyperplastic growth from 1-4 months and hypertrophy growth 3-7 months.
What is the difference between WAT adipogenesis and BAT adipogenesis?
BAT pre-cursor cells are not the same as WAT, they are actually more similar to those of the myoblasts. These then develop into brown pre-adipocytes and then into the mature adipocytes then activated by cold activation. BAT has smaller lip droplets and no mitochondria
Why should a pig be slaughtered at around 100 kg?
This gives a leaner carcass as both lipid and protein deposition increases up until then, after protein deposition starts to decrease but lipid still increases
What is growth hormone controlled by?
Growth hormone (GH) is released form the anterior pituitary gland. Its release is stimulated by growth hormone releasing hormone (GHRH) and decreased by somatostatin (also known as growth hormone-inhibiting hormone) which are produced in the hypothalamus
What are the direct effects GH has on lean growth (increasing it)?
Decrease in lipid accretion – more nutrients, such as glucose are available for lean growth
Decreases the uptake of glucose for lipid synthesis through decreased synthesis of the glucose transporter GLUT4
Decreases the synthesis of lipogenic enzymes
Acetyl-Co A carboxylase
Decreases the stimulatory effects of insulin on glucose uptake and utilisation by adipocytes
Basically stopping lipid/ fat formation to allow lean growth
What are the indirect effects GH has on lean growth (increasing it)?
Stimulating growth is mediated via insulin-like growth factor-1 (IGF-1). High blood levels of IGF-1 decrease the secretion of GH by direct negative feedback action on the pituitary and also by stimulating SS production by the hypothalamus
-IGF-1 increases the proliferation of chondrocytes to increase bone growth
-Increase proliferation of satellite cells
This is highlighted in studies where cows had free access to food showed high levels of IGF-1 whereas those with restricted access had low levels of IGF-1 indicating they would have less lean growth
What is leptin?
Leptin is a protein hormone that plays a role in the control of feed intake, energy balance and body composition.Leptin is secreted from fat tissue (adipocytes) and has the ability to regulate feed intake so as fat deposition increases so does leptin concentration. Fat animals have more leptin and by negative feedback are told to reduce their energy intake.
What is BUN and what can it be used to indicate?
Blood urea nitrogen (BUN) can be used to indicate how efficiently animals utilise protein in the diet for lean growth. If amino acids are consumed in excess, the extra amino acids undergo transamination and deamination and the nitrogen is converted into urea.High BUN is also associated with a low efficiency for amino acid deposition of lean meat and a high nitrogen excretion. So basically a very lean animals have low BUN and fat animals have high BUN (it is important to know what the animal is eating as high BUN can indicate that the animal is starving and therefore breaking down its own protein)
What is creatinine? What can it indicate?
Creatinine is a waste product formed after dephosphorylation of phosphocreatinine to creatine in muscle
Creatinine is therefore released from the muscle in amounts proportional to muscle mass
What are NEFAs? What can they indicate?
Lipid is stored as triacylglycerol which is hydrolysed (lipolysis) to Non- Esterified Fatty Acids (NEFAs) and glycerol. Serum NEFA can therefore be used as an indicator for rate of lipolysis
What test can be used to measure the levels of metabolites such as leptin in samples?
Radioimmunoassay (not as used anymore), ELISA tests and Colorimetric assays
What is the link between gender/sex and growth?
Males generally have
-Grow more rapidly
-Use their feed more efficiently for growth
-Have increased lean-to-fat ratios in the body
What is the link between genotype and growth?
Certain breeds will be naturally leaner than other. All breeds have a maximum protein deposition maximum where protein deposition plateaus
What is the link between nutrients and growth?
Too little or too much food intake/nutrients will reduce energy used for growth (too much means that energy will be used to break down the excess nutrients instead of growth)
What is the link between geographical location and growth?
Depends on food availability, climate and population density
What is the link between disease and growth?
Disease (even when sub-clinical) prevents an animal from growing to its full genetic potential and the reduced feed intake and ADG observed results in considerable economic loss. During an immune response, nutrients are diverted away from growth and redistributed towards tissues and cells involved in the immune response #
side note- Cholecystokinin (CCK) is secreted by the duodenum and makes you feel not hungry. There is a peak in this during disease and so this lowers food intake
Do elephants exhibit determinate (like most mammals) or indeterminate growth?
It was thought that they showed indeterminate growth due to males' body weight increasing up until death however it was found their height did not and so they show determinate growth
What is 'Compensatory growth'?
A phenomenon in which an animal accelerates its growth above normal rates after a period of suppressed growth, usually caused by feed restriction (also called 'catch-up' growth)
Seen in cattle, sheep and rats (and humans)
How did a study in 1940 by McMeekan show compensatory growth to be real?
The classic study carried out by McMeekan (1940) demonstrated accelerated growth rates in pigs following removal of feed restriction. In the experiment feed intake was restricted from birth for 16 weeks
At the end of the 16 week period, restricted pigs were approximately half the body weight of control pigs. When the restricted pigs were fed ad libitum, accelerated growth rates were observed
How is compensatory growth exploited by farmers?
It is cheaper to restrict the animals feed first then allow access to food as they will compensate for their growth with overall less food. This does not always happen though so some animals may just end up smaller than if they had no restriction. In addition, the compensation is due to increase in fat and organ weight rather than lean muscle
Compensatory growth can be as a result of restricting feed intake or nutrient intake. Why may this be beneficial environmentally and economically?
Due to the high cost of protein sources, protein restriction is often used in compensatory growth feeding strategies, with major emphasis on lysine, the first limiting amino acid
Protein restriction is also of environmental interest since it reduces nitrogen output