[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.