Lecture 12 - Ruminant Nutrition 2 Flashcards
What are the major functions of calcium?
- Vital component of milk
- Actin-myosin coupling (muscle activity)
- Hormone and neurotransmitter release
Calcium absorption in the body is largely facilitated by activated vitamin ___ and ___________ hormone
D; parathyroid
What are three factors that can affect calcium absorption?
- Phosphorus and magnesium content
- High dietary zinc
- Oxalates
True or False: Oxalates can be poisonous to ruminants, but the rumen can detoxify them up to a certain ingested amount
True
What can occur when there are too many oxalates in the bloodstream?
They can form insoluble salts that will precipitate in the kidney and cause kidney failure
True or False: Sheep are most susceptible to oxalate poisoning, followed by cattle, but livestock can develop a tolerance for oxalate-producing plants with gradual exposure in the diet
True
(Extra note: Gradual exposure to oxalates allows the rumen to build up a concentration of oxalate-degrading bacteria)
How much soluble sodium oxalate does the Halogeton plant contain (on a dry matter basis)?
(Give the percentage range)
30 to 40%
How do Rumex spp. plants cause hypocalcemia?
Oxalates bind calcium, which can lead to hypocalcemia if the plant is consumed in large amounts
What percentage of extra-cellular calcium in the blood is ionized? Where is the rest of the calcium found?
- 55% ionized (the metabolically important calcium)
- 35% bound to albumin
- 10% bound to phosphate, citrate, HCO3-, and other ions
True or False: Acid-base status influences albumin-to-calcium binding. For example, more calcium binds to albumin during acidosis, resulting in slightly lower Ca2+ in the blood and ECF
False; more calcium binds to albumin during ALKALOSIS
(The rest of the statement is true)
Which metabolic abnormality often accompanies diseases that impair abomasal emptying, causing HCl to be trapped in the abomasum and forestomachs?
Metabolic alkalosis
Why might acidosis trigger an increased release of calcium from the bone?
Less calcium binds to albumin during acidosis, so calcium may be released from the bone to act as a buffer and attempt to maintain calcium homeostasis
What is the role of parathyroid hormone (PTH) in calcium regulation? Which cells release it?
- Increases Ca2+ in ECF back to the desired concentration (“normal range”)
- Promotes bone resorption to provide Ca2+ to the ECF
- Released by chief cells in the parathyroid
PTH promotes a loss of _________ ion in the saliva and urine, resulting in an increase in ionized calcium and a decrease in ____________.
Phosphate; phosphorus
Which hormone promotes the transformation of 25-hydroxyvitamin D to 1,25-hydroxyvitamin D (active form)?
PTH
What is the function of calcitonin? Which cells release it and when?
- Promotes deposition of calcium INTO bone and calcium loss in urine to decrease Ca2+ in the ECF
- Released from thyroid C cells during hypercalcemia
An acute flaccid paralysis that results from depleted serum calcium as it is lost into colostrum and milk
Milk fever
When can periparturient hypocalcemia occur?
Before, during, or after calving (anytime around birth)
Which stage of milk fever exhibits clinical signs such as standing, apprehensiveness, hypersensitivity, and tremors?
Stage 1
(Reflects loss of the dampening effect Ca2+ has on axonal sodium channels)
Which stage of milk fever exhibits clinical signs such as recumbency, weakness (to degree of inability to stand), and head turning into flank (because too heavy to lift)?
Stage 2
(Continued loss of calcium influx at axonal motor end plate lowers ACh release per AP; also, less Ca2+ available in ECF to participate in muscular response to ACh)
What occurs during stage 3 of milk fever?
Coma and death due to cardiac or respiratory failure; may regurgitate rumen contents and aspirate
Why is it important to administer IV calcium solutions slowly?
Rapid infusion can lead to cardiac arrest (stone heart syndrome)
When treating milk fever with calcium borogluconate, why will you likely see eructation, increased alertness, and a slower heart rate?
Muscle contractions will slow down but strengthen with a higher availability of calcium in the body
What are two possible methods for preventing milk fever?
- Feed a diet low in calcium 1 month pre-partum to boost PTH and Vit D3 homeostasis early
- Feed anionic salts for 2 weeks pre-partum to induce mild metabolic acidosis
(Extra note: Do not forget to also supply adequate Mg2+ as it is a necessary cofactor for PTH release!!)
What is the benefit of inducing a mild metabolic acidosis 2 weeks pre-partum?
Increases gut calcium absorption and bone utilization to maintain calcium homeostasis
What is the primary role of Mg2+, and what does it compete with/inhibit?
Acts as a cofactor for multiple enzymes (including acetylcholinesterase) and for release of PTH from the parathyroid gland; competes with Ca2+
True or False: Animals must consume Mg2+ in their diet, because Mg absorption from the GI tract is the only regulatory mechanism for ECF [Mg2+]
True - unlike calcium, Mg does not have specific hormones to regulate its ECF concentration, so it must come from the diet!
What are considered good sources of dietary Mg?
Plant-based: legumes, nuts
Animal-based: animal tissues, liver
How is Mg absorbed in ruminants?
Across rumen wall via energy-dependent processes
High nitrogen and K+ in a ruminant’s diet will _________ Mg absorption from the rumen
Reduce
Metabolic disease of ruminants characterized by abnormally low ECF Mg2+ and calcium; affected animals exhibit uncontrolled/repetitive muscle contractions, hyper-irritability, and convulsions
Grass Tetany / Hypomagnesemic Tetany
What does “early” vs “late” hypomagnesemic tetany look like in affected animals?
Early = muscle fasciculations, hyperesthesia, stiff gait, irritability/excessive alertness/nervousness
Late = recumbency and convulsions; death may occur from respiratory or cardiac arrest
Why are Mg salts often mixed with salt and grain when given as a dietary supplement?
They are not very palatable, so mixing with salt/grain helps to ensure consumption
True or False: Plant uptake of Mg is not affected by the PO4(2-) content in the soil
False; Mg uptake is facilitated by adequate PO4(2-) in the soil
A mineral that is a component of bone mineral and tooth enamel; 85% of total amount in the body lies in hydroxyapatite; dietary sources include grains, wheat bran, and supplements
Phosphorus
____ calcium and _____ phosphorus in the blood triggers chronically elevated PTH, which can lead to a condition called “rubber jaw”
Low; high
Where does phosphorus excretion primarily occur in the ruminant? What is the benefit of this?
In the gut via phosphorus being moved into saliva and lost into the GI tract; this process supples rumen bacteria with phosphorus (for ATP) and allows for phosphorus to be recycled into the blood, minimizing losses in urine
A medical condition affecting ruminants on high-grain diets that is associated with the development of phosphate-based urinary calculi if urine becomes too highly concentrated
Urolithiasis
Possible complication of milk fever with failure to respond to conventional therapy; affected cows are alert but show severe muscular weakness (may attempt to move by pushing partially up and moving around on their abdomen)
Hypophosphatemia
How can the onset of lactation cause hypophosphatemia?
Lactation causes heavy calcium losses, triggering more PTH secretion, and PTH can move a lot more phosphate to the urine than usual
What is the physiology behind hypophosphatemic rickets in young camelids?
Inadequate vitamin D leads to inadequate Ca and P absorption from the gut to mineralize bones (leading to micro-fractures which cause lameness and long bone deformities)
True or False: In hypophosphatemic rickets, serum calcium may be completely normal even though phosphorus is noticeably reduced
True
