[MUSIC] So, let's go back to our list here and take a quick look at this again. I've indicated that these are nutrients. This is one perspective in how to think about milk and milk composition, but there are many, many other ways of thinking about this. So let's take a look at some of those and kind of see what we're talking about. Clearly, the first one at the top of the list there is value to the neonate. The neonate's getting some value, nutrients, protective factors, etc, etc, that's one perspective we can think of. Another perspective is just simply thinking about what's the chemical nature of each of those components? What's the biochemical nature, what is a physical chemical relationship of those? How are they fit in to say with pH or acidity of the milk and so on and so forth? Component interactions, a lot of these things are not by themselves they interact with each other in different ways. Whether it's be during synthesis, whether it be say the calcium fosters are tied up in what we call casing my cells, so they're tied up with the protein casing so some interactions there. Synthesis and secretion, how are they synthesized in the mammalian cells? How are they secreted out of the cell? How do they become what we think of is milk? Variation across and within species, and we're going to kind of touch on that as we get into each of the different components. Tremendous variation in some of the components, for example, fat. Enormous variation in the amount of fat in milk of different species. Lactose on the other hand is not quite as variable, for example. Even within a species, so we're talking about breed differences and we're giving a few examples of dairy breeds. [COUGH] Impact, what I've indicated here, impact of internal factors. And here what I'm talking about is how old is the animal. Which stage of lactation is she. What parity that is how many lactation is she going through those kinds of things. The physiological factors that underlie that lactation can potentially impact both milk yield as well as milk composition. Impact of external factors. So here we're talking about temperature, humidity, and nutrition. Nutrition is basically an external input into the animal. And so how does nutrition, nutrition indeed can affect some of those components very substantially. And then, I've just kind of rolled it altogether, the role in milk-based products. So milk, cheese, yogurt, etc, again, there's volumes and volumes written about how milk composition relates to developing those kinds of milk-based products. So again, this is just to emphasize, this is a very simplistic way of thinking about milk composition and we're going to start dissecting some of these a little bit more. There is one prospective that I want to share with you. And so get a slide up here. And that's to think about this is an example. So, these are some baby pigs nursing the mum and if you understand the behavior they're actually getting milk, right, this moment in this picture. When this picture was taken they're getting milk out of the mammary gland of the mom. Let's make a couple of assumptions here first of all lets assume that when these guys are nursing mom that they actually emptied all the milk out of the mammary gland. That's not actually true but for our purposes we'll assume that is the case. So they empty the milk out of the mammary gland. The other thing, I want to do, is to assume that the interval between nursings is 50 minutes. And that's not at all unreasonable. That's a fairly standard time for most sows and most litters to nurse. About every 50 minutes they are removing milk. Okay, so let's assume that these guys are nursing right now here and they removed all the milk. We're going to make that circle a little bit bigger so you can see it. And, So this is about 50 minutes. So one nursing another nursing. Assuming that they have emptied the mammary gland. That means at this moment that mammary gland's going to starting to make more milk, new milk, essentially. And so the first little bits, first droplets microliters of milk that are being produced, are being produced right away, it doesn't stop just because milk is being removed, it keeps on going. And accumulates and accumulates and accumulates and accumulates and then, they're going to nurse again. This milk then goes into the stomach of the neonate, of the piglet forms a curd, that curd is gradually broken up and goes through the intestine. And then 50 minutes later, These guys are going to nurse again. Which means that whatever they ingested here, pretty much has to be digested and gone to make room for the next bout of milk, all right. By the way, just as an aside, the amount of time that they're actually getting milk from her mammary gland, here, is about 15 seconds. So, milk ejection, in this species, therefore milk removal in this species here and here is only lasting for a very few seconds. So again this is interval of 50 minutes. So what that means is, if pretty much all those nutrients that are initially synthesized in the mammary gland here are completely digested and absorbed here in the neonate. So they only lasted for about an hour and a half or a little bit more than an hour and a half. Milk is very very perishable. It's a very perishable product. It evolved to be rapidly synthesized, rapidly ingested, rapidly digested and absorbed. It did not evolve to last for two weeks in your refrigerator. So an enormous amount of work has been done on dairy chemistry, dairy foods, taking all these things into account, to make sure that we can actually store this stuff for an extended period of time. Whereas in nature, again, this is kind of an extreme example if this were a calf, for example, nursing every four to six hours then we would have been talking about, 8 to 12 hours something like that, with that same concept. So again it starts to fall apart, some species, baby rabbits for example, only nurse once a day. So the milk in the mom is produced, accumulated over a 24 hour period, they nurse again and so on. But nevertheless, it is a very perishable product. The other thing I want to throw in here right now while I'm thinking of it is the idea that during this whole process, regardless of what species it is, milk is never cooled down in nature. It never cools down. It's in her body. It's in the body of the neonate. It's always going to be running at about body temperature, whatever that is. So it's never cool down like we would put this in a refrigerator. So again, this idea of how even just refrigerating milk starts to change little bit characteristic versus what we're seeing here in nature. So we've introduced this idea of milk composition. We've introduced some of these, and now in our next set of video we are going to start again looking more carefully at each of these particular component. [MUSIC]
