I want to introduce you to another concept that relates to milk removal and relates to frequency of milk removal. And this is particularly true for the dairy cow as well as the number of other species including a number of dairy species, sheep's, goats and so on. So let's take a look at the next slide so something to remind you about the anatomy of the mammary gland and that is in a cow, this is a cross section of a dairy cow. I've kind of outlined the cisternal ducts, the teat cistern and the gland cistern here. And then these cisternal ducts are the major ducts coming down. Those are not secreting milk. The alveolar part, on the other hand, up here, is secreting milk. So we might say, well, what that means is that any milk that's down here where the yellow is indicated feedback inhibitor of lactation is in that milk just like it is on all the milk. But there's nothing to feed back on because there's nothing there secreting milk. On the other hand, feedback inhibitor lactation up here is going to feedback and then impact that secretion rate like we just we saw in the graphs a few moments ago. So the proportion of cisternal volume, what they call cisternal volume versus alveolar volume, can impact the ultimate milk production of a cow, again a goat, sheep and so on. So animals that have this cisternal volume in them. Compare that say, to a pig, and remember in the case of the pig, they don't have cisterns, they might have a lactiferous sinus. Again there would be two of those coming out of the nipple here. But there's really no milk collecting area, so essentially all the feedback due to lactation is up here in the alveolar tissue. So if you don't get all the milk out, that's going to feedback and impact secretion rates. So again, this animal we're milking two, three, four times a day. This animal's being nursed roughly once an hour or once every 50 minutes, something like that, and getting that feedback of lactation very quickly. [COUGH] So I want to examine that a little bit better here, and in a little more detail of what the impact of that is. So let's go to the next slide. [COUGH] So what I've done is to set this up in kind of like pools of milk. So the white area up here, in each case, cow A, B and C here, represents the alveolar area. So again, alveolar volume's in white. Yellow represents cisternal volume. So if we compare Cow A and Cow B, both of them have the same total volume In that sense. So the pull of milk in both of these is the same because the total box size is the same. However, this one has a smaller Alveolar Volume but a larger Cisternal Volume compared to Cow B. We might actually expect, even though this has a smaller alveolar volume, we might expect that these cows to give roughly the same amount of milk. Because, remember, milk is being secreted here. So again, remember, this pink arrow indicates milk that's in the alveolar volume, that has the feedback inhibitor lactation, is feeding back and impacting further milk secretion. Whereas, the stuff in the yellow It's nothing to feedback on, so it's kind of out of the way. So again we might expect cow a and cow b to end up producing the same amount of milk or pretty close the same amount of milk. Again, even though this one has a smaller alveolar volume compared to cow b. If we then go to cow c, we see that she has basically the same alveolar volume as cow B. Excuse me, cow C has the same alveolar volume as cow B but has a bigger cisternal volume. Again, we might expect this cow to give even more milk because again, lot more alveolar volume as well as somewhere for that to go in terms of the cisternal volume. What else do we know about cisternal volume, alveolar volume? So a couple things that people have found for example, cisternal volume is a proportionate total. So again, this would be total, and the cisternal volume would be the part in yellow here, down in those cisterns. It tends to increase as the animal gets through more and more lactations, tends to increase with parity. In terms of a proportion. Cisternal volume as proportion of total volume tends to decrease the stage of lactation. And ultimately this is going to influence the impact of changing milking frequency. So, how the milk is distributed can impact how that animal is going to respond going say from two times a day, to three times a day milking. Or vice versa, three times a day back to two times a day milking and so on. So this is part of the whole story as we think about milking frequency, this idea that there are multiple pools of milk in there. This alveolar milk which again, feedback inhibitor of lactation's impacting further milk secretion whereas the cisternal volume feedback inhibitor of lactation's there, but there's nothing to feedback on. Before we go on, I want to tell you a little story, personal story. For many, many, many years, I looked at this idea of cisternal milk as being, yeah, okay, it's there, it doesn't do much. In the milk ejection module, we will see that actually as milk is ejected and pushed down, this volume expands for a moment, temporarily till the milk comes out. So it is fairly dynamic. And now we've now seen that physiologically there's an impact of having the cisterns again compared to species like the pig. A number of years ago, I was privileged enough to spend sometime at the Hammond Research Institute in Scotland. It's now been dissolved. It's gone. And went in to one of my colleagues there, Colin Wild, and was asking about another colleague, Chris Knight, who was at that a time there. He's currently at the University of Copenhagen. [LAUGH] And, I kind of asked Dr. Wild, what's Chris up to. And he was talking about, well he's looking at the relationship, the anatomy of the mammary gland, with regard to milking frequency and those kinds of things. And I thought to myself, what were you talking about? It's anatomy, it doesn't change. There's nothing, it just there. So I went up to Chris and he started explaining this idea of alveolar versus cisternal milk to me. And yeah, that makes complete sense. because again, they're some of the people who have come up with this feedback in a lactation concept. And so it started to make a great deal of sense. So that's my personal introduction to this alveolar versus cisternal. And the recognition that again, for many many years, the cisternal part of the mammary gland was very very boring, because it didn't change. And now we know that in fact it's extremely important to thinking about the total physiology of that mammary gland. Both with regard to again the milk ejection process but also with regard to this how the feedback lactation impacts the mammary gland. How we think about milking frequency, milk removal, and those kinds of things.
