Let down The science behind getting the milk out
Aug 24, 2016 11:44:27 GMT -5
hazelsmilker, richard olson, and 11 more like this
Post by saysfaa on Aug 24, 2016 11:44:27 GMT -5
This is a rewrite of a research report (see bottom for a link to the actual article). I tried to keep all of the meaning but put it into the way I think. This subject seems to have come up a lot lately and I thought it might help someone. Besides, I think it is very interesting anyway.
Milk is made in the lining of the tiny sacs within the udder. It is stored in those sacs, and in the cisterns and in the ducts between the sacs and the cisterns.
This pdf www.uvm.edu/extension/agriculture/faccp/files/aglabor_bilingual/milk_quality_posters.pdf talks about something else but has a reasonable diagram on the first page showing the relationships between the structures in the udder. (lobules are just small lobes filled with the tiny sacs (which are called alveoli))
edit to add links to other images because that link doesn't work anymore, still wanting just the images - not what else they are talking about.
articles.extension.org/pages/62147/are-us-dairy-farms-ready-for-a-drop-in-the-scc-legal-limit
i1.wp.com/cmapsconverted.ihmc.us/rid=1NG7D7HW4-13YCVXK-16TN/udder%20anatomy.gif
bclearningnetwork.com/LOR/media/sr12/Module_4/Section_42/Lesson_42a/42a01_topic1.html
An udder filled with milk usually has more than 80% of that milk stored in the tiny sacs and the small ducts. This is important because this 80% can only be removed from the udder through "activation of the milk ejection reflex" (also called let-down). The other 20% is stored in the big ducts and the cisterns. That 20% can be removed by overcoming the teat sphincter barrier.
Touch of the teats stimulates pressure and touch-sensitive nerve endings in the teat skin. Those receptors fire off signals which travel to the brain resulting in a release of oxytocin into the blood. The blood carries the oxytocin to the tiny muscles surrounding each tiny sac within the udder. The hormones prolactin, cortisol, and various stomach/intestinal hormones are also released. Their roles are unclear. There is some evidence to suggest prolactin plays a role in maintaining milk secrection and cortisol contributes to making amino acids and other fatty acids available for milk production. As for the stomach/intestinal hormones - "probably...activates of the vagal nerves in order to adapt the food intake and metabolism" [to match the added demand on her resources due to producing the milk].
(skip this paragraph if you want the simple version - this is just a detailed description of the above paraphraph) "nerve impulses which travel via segmental pathways in the CNS (central nervous system) to the PVN (paraventricular nulei) and SON (supraoptic nuclei) in the hypothalamus resulting in a release of the pituitary hormone oxytocin. Oxytocin is a nonapeptide consisting of nine amino acids and it is produced in the SON and PVN in the hypothalamus. Via carrier proteins (neurophysin I) oxytocin is transported from the cell bodies PVN and SON through the pituitary stalk. From the pituitary it is released into the blood and transported to the udder where it attaches to the receptors at the myoepithelial cells surrounding the alveoli. As a result the myoepithelial cells contract to expel the milk."
The kind of touch is important. Warmth matters. Pressure matters [not just squeezing the teats, but rubbing and bending them]. Studies in the 1950's found 30% difference in milk production between minimal teat stimulation and optimal teat stimulation. Later studies showed less difference probably because of years of breeding for milkability [something to keep in mind if you are milking a beef cow or beef cross cow].
It is the timing between the beginning of the touching and the beginning of the milking rather than the amount of oxytocin released that is important for efficient emptying of the udder. From the beginning of the touching until the beginning of the milk ejection is about 1 to 2 minutes. Significantly more milk is left in the udder if milking is started 5 minutes after the start of the touching vs 1 minute.
Touch is not the only stimulant that is important. It is the most efficient stimulant but the milk ejection reflex can also be activated by visual or auditory stimulation of the calf. Feeding also induces a release of oxytocin. Feeding 1.5 hours before milking gave higher milking-related release than when the cows were fed 1.5 hours after milking and incremental feeding during milking has a positive influence on milking parameters such as milking time, milk flow and amount of residual milk
And there are also inhibitors.
Stress activates the release of adrenaline which counteracts the oxytocin by blockading the oxytocin receptors in those tiny muscles surrounding the little alveoli sacs. This means milk flow into the cisterns is cut off (or reduced, depending on how much adrenaline is flowing around). This is peripheral inhibition because the stoppage mechanism is active out away from the brain.
And there can be central inhibition (the stoppage happens inside the brain). The disturbed milk ejection reflex was a lack of oxytocin being released even though the other hormones (prolactin, and so on) were being released as expected. This is the kind that happens immediately after calving, during heats, and when milking happens in unfamiliar surroundings.
www.nmconline.org/articles/milkejctn.pdf
to give credit and allow later checking of facts or understanding.
Milk is made in the lining of the tiny sacs within the udder. It is stored in those sacs, and in the cisterns and in the ducts between the sacs and the cisterns.
This pdf www.uvm.edu/extension/agriculture/faccp/files/aglabor_bilingual/milk_quality_posters.pdf talks about something else but has a reasonable diagram on the first page showing the relationships between the structures in the udder. (lobules are just small lobes filled with the tiny sacs (which are called alveoli))
edit to add links to other images because that link doesn't work anymore, still wanting just the images - not what else they are talking about.
articles.extension.org/pages/62147/are-us-dairy-farms-ready-for-a-drop-in-the-scc-legal-limit
i1.wp.com/cmapsconverted.ihmc.us/rid=1NG7D7HW4-13YCVXK-16TN/udder%20anatomy.gif
bclearningnetwork.com/LOR/media/sr12/Module_4/Section_42/Lesson_42a/42a01_topic1.html
An udder filled with milk usually has more than 80% of that milk stored in the tiny sacs and the small ducts. This is important because this 80% can only be removed from the udder through "activation of the milk ejection reflex" (also called let-down). The other 20% is stored in the big ducts and the cisterns. That 20% can be removed by overcoming the teat sphincter barrier.
Touch of the teats stimulates pressure and touch-sensitive nerve endings in the teat skin. Those receptors fire off signals which travel to the brain resulting in a release of oxytocin into the blood. The blood carries the oxytocin to the tiny muscles surrounding each tiny sac within the udder. The hormones prolactin, cortisol, and various stomach/intestinal hormones are also released. Their roles are unclear. There is some evidence to suggest prolactin plays a role in maintaining milk secrection and cortisol contributes to making amino acids and other fatty acids available for milk production. As for the stomach/intestinal hormones - "probably...activates of the vagal nerves in order to adapt the food intake and metabolism" [to match the added demand on her resources due to producing the milk].
(skip this paragraph if you want the simple version - this is just a detailed description of the above paraphraph) "nerve impulses which travel via segmental pathways in the CNS (central nervous system) to the PVN (paraventricular nulei) and SON (supraoptic nuclei) in the hypothalamus resulting in a release of the pituitary hormone oxytocin. Oxytocin is a nonapeptide consisting of nine amino acids and it is produced in the SON and PVN in the hypothalamus. Via carrier proteins (neurophysin I) oxytocin is transported from the cell bodies PVN and SON through the pituitary stalk. From the pituitary it is released into the blood and transported to the udder where it attaches to the receptors at the myoepithelial cells surrounding the alveoli. As a result the myoepithelial cells contract to expel the milk."
The kind of touch is important. Warmth matters. Pressure matters [not just squeezing the teats, but rubbing and bending them]. Studies in the 1950's found 30% difference in milk production between minimal teat stimulation and optimal teat stimulation. Later studies showed less difference probably because of years of breeding for milkability [something to keep in mind if you are milking a beef cow or beef cross cow].
It is the timing between the beginning of the touching and the beginning of the milking rather than the amount of oxytocin released that is important for efficient emptying of the udder. From the beginning of the touching until the beginning of the milk ejection is about 1 to 2 minutes. Significantly more milk is left in the udder if milking is started 5 minutes after the start of the touching vs 1 minute.
Touch is not the only stimulant that is important. It is the most efficient stimulant but the milk ejection reflex can also be activated by visual or auditory stimulation of the calf. Feeding also induces a release of oxytocin. Feeding 1.5 hours before milking gave higher milking-related release than when the cows were fed 1.5 hours after milking and incremental feeding during milking has a positive influence on milking parameters such as milking time, milk flow and amount of residual milk
And there are also inhibitors.
Stress activates the release of adrenaline which counteracts the oxytocin by blockading the oxytocin receptors in those tiny muscles surrounding the little alveoli sacs. This means milk flow into the cisterns is cut off (or reduced, depending on how much adrenaline is flowing around). This is peripheral inhibition because the stoppage mechanism is active out away from the brain.
And there can be central inhibition (the stoppage happens inside the brain). The disturbed milk ejection reflex was a lack of oxytocin being released even though the other hormones (prolactin, and so on) were being released as expected. This is the kind that happens immediately after calving, during heats, and when milking happens in unfamiliar surroundings.
www.nmconline.org/articles/milkejctn.pdf
to give credit and allow later checking of facts or understanding.