Welcome back. In some of the videos in this series on swine, we've talked about milk removal in a number of different ways. And here in this video, what we talk about is what happens when milk is not removed from the gland. And there are two situations where that may occur. One, it occurs at weaning. So when the - when lactation is done, the - the - the piglets are weaned, what happens to that mammary gland at that point? And we'll get to that here in just a moment. And the other was actually during lactation, especially during very, very early lactation when the milk is not removed from the gland. So again, if a piglet is not suckling a gland, that gland will involute, even though all the other glands are being suckled and - and lactating at that point. So we want to kind of take a look at what - what happens in those cases. So let's go to the next slide. This is five pictures of exactly the same cell. Day zero, we're calling here lactating. So this is the last day - so just immediately after she was weaned. So you can see the full line of mammary glands are fully developed. Take note of that little blemish right there, just as - just as a marker, really, just in terms of these other pictures - it's just to prove it's the same cell. By day two, it's already regressed quite a bit. Day three, day five, it almost looks like it never lactated and certainly by day seven, it's - it's pretty much completely involuted. So again, these are - are - day two, three, five and seven are days after taking the litter away. So again, substantial regression from lactating, even by day three and certainly by day seven, very substantial drop in the - the mass of the mammary gland. So the next slide. What we've done here is we would take a cell like this, if we sacrifice a cell, take that slab of mammary glands off, take the skin off and slice it down in the middle so we're getting a profile here, basically, of a series of what looks like three or four glands here. Again, these are these glands, that's the mammary glands of the skin; the nipples have been removed. The glands actually have grown so much they've grown up against each other. On the other hand, if we take the same kind of a slab of tissue, a cross-section of the tissue through the mammary tissue from one that's been involuting for seven days, substantially regressed and you can actually see the point where they've regressed to the point where right in between these glands there's a little bit of fat pads reformed in there. So again a very big difference in terms of not only size, but also the consistency of the tissue. Let's go to the next slide. Now what we fairly consistently see is in this seven day period, there's about a two-thirds reduction in wet weight. So loss of many, many cells through apoptosis, loss of - and again, regression in - in many sorts of ways. So wet weight drops by about two-thirds. Go to the next slide. And so what I have done is here to pull out one gland example and these are approximately to scale. In this case, the nipple would have been on top up here. Same way here. At day zero, it's the same gland, it's the fourth gland on the left side. So it's the same spot - two different cells, but the same spot. Again, this would be lactating tissue and this would be approximately the average size compared to this one of - of a gland that had involuted after weaning; seven days after weaning. That gives you an idea of just how much this thing has regressed during that time period. What we just saw a moment ago was what happens with mammary gland when you wean all the piglets at the end of lactation, essentially. But what happens to glands that are not suckled from the very beginning? So just what we're going to look at here again is farrowing - all the glands are - when they have the piglets, all the glands are functional, they've all got - they're all secreting colostrum, they're all ready to make milk, they're ready to go. During lactation, on the other hand, of course, those glands that are suckled are - grow, they either maintain and grow. On the other hand, glands that are not suckled, regress. And so we want to look at that process just a little bit more here. Next slide. So if we can plot out wet weight - approximate gland wet weight here. They - and again, kind of on average, they start out atroughly the same point, although again, remember, some of the middle ones are bigger than the anterior ones, et cetera, et cetera. But if we kind of put all that together, they start out essentially the same spot; those that are suckled grow, obviously making more milk, but they also grow; on the other hand, those that are not suckled decline. And so they - again, by roughly about day seven here, maybe slightly after day seven, they've pretty much gotten down to a point of where they're not going to regress any more. That's pretty much baseline. So again, suckled gland here, non-suckled gland, this - this obviously would be after probably seven, eight days, 10 days, something like that of lactation, that particular picture would be out in this time frame right here. Go to the next slide. And also to remind you, 'cause we talked about this in an earlier video on this series on the cell, is that by day three, if we tape off that gland and then take the tape off on day three, put a piglet on it, there is no milk. The piglet can't get any milk because there's nothing being produced. So functionally, the gland is pretty much done by day three; in fact, probably even before day three - physically though, day seven-ish, something like that. So even early on, it's losing its functionality and then continues to regress in the next several days after that. Another feature I want to point out on this curve is to present an idea to you. And that is, if we get an idea that suckled glands are going to grow, non-suckled glands are going to involute. And what this might suggest to us - one of the things that might suggest to us - is that then, when the animal is done lactating, is bred and starts - the mammary gland starts growing again in the next lactation, that the ones that had been suckled before, in fact, start from a higher - let's say higher plane. There's - there's more - a little bit more tissue there for them to grow from than the ones that were never suckled to begin with. And what we're going to see in other videos is the idea that that's - that's true. If we then follow that out into the next lactation, the glands that were suckled in the first lactation are producing a bit more milk than the glands that were not suckled in the first lactation and then suckled in the second lactation. So there's a difference there. So this difference may carry out further on beyond this. So again, part of the potential significance of a gland being suckled in the first lactation versus not suckled in the first lactation. Let's quickly review what we've talked about in this video. Mammary involution at weaning progresses very rapidly after milk removal was stopped. And so we see by about seven days post-weaning, glands have lost about two-thirds of their mass, or their wet weight. So again, involuting very, very rapid rapidly. Glands that are not suckled at farrowing also regress. So here we're talking about after weaning, here we're talking about after they have their young, but a gland - one gland or several - are not being suckled and that gland is going to regress. And in fact, it - even within two to three days, has lost its functional - functionality - is no longer producing milk. And then certainly by seven days, it's more like what we're talking about up here, it's pretty much completely regressed at that point. So quick - obviously, milk removal is absolutely critical for maintaining lactation. And in this species, as in many other species, we can see how very, very fast that mammary secrete - the - when milk removal does not occur, that lactation function is declining and the gland starts to be regressing.
