[SOUND]. Welcome, I want to take some time and have us think about milk yield and somewhat of a lactation curve and what's driving the lactation curve in a cell. So to start with, I just want to remind you what a lactation curve would look like for a dairy cow. And so again, you have this ascending part of the curve. And there are factors we'll get to here in a second that are causing that. You have peak lactation and a gradual decline. So again, for a cow, we're talking about maybe a 10 month period of lactation before we dry them off. And hopefully soon there after they have another calf, start another lactation. Early on, the ascending part of the curve, two things that seemed to be happening there is, we get an increase in cell numbers. So there are more and more epithelial cells making more and more milk. And then more of milk yield per cell. So this differentiation of the cells starts to increase. There's not any more cells but each cell is then making more milk. And those are things contributing to these rise in milk yield. Hits peak and then the declining phase of lactation. The biggest thing that's going on is you're starting to get loss of cell numbers during this phase. Let's go to the next slide. I put this up here to compare the cow in the white versus the sow in the yellow. And just to kind of make you understand that lactation in a sow is relatively short compared to the cow. I put this arrow here at peak lactation which is approximately 21 days. It varies a little bit, but in that ballpark, roughly about 3 weeks. The other thing you need to understand is that in most commercial systems in this country and in other places too, we're weaning them about this time period. Maybe three, maybe slightly over four or maybe slightly after about three weeks. We’re actually weaning them, so we don't see that many cells that are continuing to lactate in this declining phase of lactation. Let's go to the next slide. So what do we know about this? So what else I've done here is expand this out to instead of months down here, I have seven weeks of lactation. And again, they're peaking at about three weeks of lactation. What's causing that? We do have evidence that in fact cell numbers are going up. So the mass of the number of epithelial cells are contributing to this. We don't really have a lot of good evidence just because studies haven't been done really yet to clarify whether, in fact a differentiation state of each cell was going up, so we're getting more milk yield per cell. Likely that it is happening but again, we don't have a lot of good data yet on that to demonstrate that. One of the major things that is driving the continuation of lactation, the maintaining of lactation, galactopoiesis, is milk removal. So, to remind you of a few things again, milk removal, we've got up here. So we want to examine milk removal, start to examine milk removal a bit more in the pig. But to start and again I need to remind you of some things. We have what are called systemic factors. So typically, we're talking about systemic hormones and especially prolactin. Prolactin is our best example of this because it's involved in refilling or filling that mammary gland between milkings, between nursings. We also though as milk is secreted from the epithelial cell into the lumina alveolus. We have an accumulation of this Feedback Inhibitor of Lactation, FIL. It's a part of the normal process of making milk. The more that's accumulated in the alveolus, it feeds back and then shuts down further milk production. So on the one hand, you have systemic factors in the blood flowing through all the glands. Each gland, of course, is going to be different here and we can see that. For example, if milk is not removed, the gland involutes. If milk is removed, we kick this back around to here and we start refilling the gland and so on. So again, we've covered that in some other videos in some other modules. The intensity what I've called here, milk removal intensity and that we'll start to finding that here in a moment, has an impact on both of these factors and especially on this factor. Let's go to the next slide. So I started to list some of these kinds of things in terms of milk removal. Suckling intensity is what I've called this in this particular case. So here's three factors and there are other factors, but here's three factors that come into play. Litter size, piglet size, and frequency of suckling. And for the rest of this video, we're going to focus on looking at and thinking about litter size. So let's go to the next slide. We know that milk yield in the cell, total milk yield will increase from, and people have done studies with variable litter size numbers. But in this case we kind of generically plot it out from 4, litter size of 4 and up to 14. And we know that as that litter size increases the amount of total amount of milk that she's producing, let's say in a day, increases. So that's fairly consistently observed. Let's go to the next slide. On the other hand, it's not kind of one to one, because what we see is, milk yield per gland. So not just taking total milk yield, but per gland, actually declines as litter size goes up. So let's go to next slide and see if I can illustrate that in another way. So what I've done here is to kind of indicate. Again, here's the cell, seven mammary glands on a side. Seven mammary glands on a side. This cell is nursing six piglets. And what happens is, in a species like this, they have very strong teat order. So this piglet only nurses that one remember, this pig can only nurses this one, so they don't shift around. So any gland that is not suckled starts to regress. Each gland is bigger, it grows quite a lot here. So that's why these circles are fairly big. So I'm just suggesting that they're nursing these top six glands, but it's not necessarily the case. On the other hand, if the sow has 14 piglets, 14 glands, so each gland is being nursed, all the glands continue to grow. They continue to make milk, none of them are regressing. On the other hand, each gland is a little bit smaller than this one over here. So again, that's as we saw that graph, this is representing really the mass of the mammary gland. But that's going to be highly correlated with the milk production of that mammary gland. So both of those factors, the size of the mammary gland, the mass of the mammary gland, the milk it produces gradually is going to go down with increasing litter size. And so we're kind of demonstrating that here with the comparison of these two sows. Now let's review what we talked about in this video very briefly. Sows typically are weaned at or shortly after reaching peak lactation. So again, many times they'll be weaned at approximately three weeks of lactation, which is about the time of peak lactation, sometimes maybe a little after. Sometimes a bit before, but they're certainly not going very much beyond that peak lactation period. Litter size significantly affects milk yield. So, the greater the litter size, the more total milk that's produced, in let's say in a 24 hour period. On the other hand, the amount of milk that is produced that's consumed by each piglet declines. So total milk yield goes up, milk yield per piglet is coming down. The same thing is true for then looking at mammary development or mammary mass, or the number of epithelial cells, for example, in a mammary gland. Same idea, greater total mammary mass is occurring at the same time the lower mammary mass per gland. So there's not as much stimulation per gland. We've shown examples of both of those kind of things in this video. [SOUND]
