The milk of the dairy cow is a valuable food source for animals and humans. It is a complex mixture of nutrients, including fat.
Dairy milk production is dependent on a number of factors such as feed, climate, accommodation, species and age of the cows. If you are able to optimize these variables, milk production can be greatly increased.
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Bovine somatotropin (bST)
Bovine somatotropin (bST) is a protein hormone that increases milk production in dairy cows. It is injected into the cow and is released gradually over time.
In addition, bST increases the levels of bovine insulin-like growth factor I in cows’ milk. These two proteins are nontoxic and do not cause health problems.
Using bST on a cow requires injections of a small amount of bST into the mammary gland every few days. This treatment is similar to the way that insulin must be injected into people with certain types of diabetes.
However, bST is not effective on its own and needs to be used along with proper nutrition, health programs, milking techniques, and environmental conditions. If these are not followed, the results will be disappointing.
Some activists have questioned whether the FDA has done enough testing before approving bST for use in dairy herds. Others have cited animal rights issues or the persistent oversupply of milk and dairy products as reasons to block its use.
Milk ejection
The oxytocin-induced milk-ejection reflex is the primary mechanism of milk removal from the mammary gland. It is initiated by stimulation of the teats or milking machine (or both) and transmits into the systemic circulation through hypothalamic nuclei located within the supraoptic and paraventricular lobes of the brain.
A dramatic increase in activity occurs in the oxytocin-producing neurones some 2-4 sec after tactile stimulation of the teats. This acceleration enhances by a factor of 100 the hormone released by each action potential.
This increased activity in the oxytocin-producing neurons causes contraction of myoepithelial smooth muscle cells that surround and run the length of smaller ducts. These cells expand the bore of their ducts and increase intramammary pressure, which forces milk into the cistern from where it can be removed by suckling or milking.
Oxytocin also stimulates the production of uterine oxytocin (OT). Deficiency in OT in dams results in a complete inability to lactate, indicating that oxytocin is the primary mediator of the oxidative process involved in OT function.
Oxytocin
Oxytocin is a hormone that helps to stimulate the uterus during childbirth and help milk ejection during lactation. It is also a neurotransmitter that affects behaviour in both animals and humans.
When cows are milked, oxytocin is released into the bloodstream to induce milk ejection from the mammary gland. It is a small octapeptide hormone that causes contractions of smooth muscle and the myoepithelial cells surrounding the milk secreting alveolus.
There are many factors that can inhibit the release of oxytocin. These include the occurrence of stress (feeding, barn noises, calf sight) or the stimulation of the sympathetic nervous system via emotional stimuli such as dog barking.
The practice of oxytocin injection is commonly used to increase milk production in cattle but this has many drawbacks. Regularly injected animals become habitual to the drug and it is difficult for them to let down the milk without its administration.
Feed intake
Cows produce milk based on nutrients including carbohydrates, proteins, fats, vitamins and minerals. These nutrients provide energy to the mammary gland to perform its functions.
Intake of supplemental energy by lactating dairy cows is a critical factor in optimizing milk production and maintaining body condition score. Negative energy balance experienced during the early period of calving results in a loss of body weight and negatively impacts milk fat and protein composition.
During positive energy balance, cows regain their body weight and produce milk of normal fat and protein content. This is related to increases in total feed intake.
Feed intake also depends on the dietary fiber content. Dietary fiber level and particle size influence rumination, salivation, and milk fat and protein composition.
Low dietary fiber, high non-fiber carbohydrates and poor forage panicle length increase milk protein percent and reduce the milk fat test. Additionally, these feeding practices lead to acidosis, lameness and chronic feed intake fluctuations.
