Mammal milk! Comparative study blogged!

I am excited (dare I say thrilled) to report that a paper I was involved with got blogged about!
 *Forgive the self-enthusiasm.  This is a first for me!*

This paper examines lactation in 129 species and was published this year (2013) in the Journal of Animal Ecology.

The paper is titled: "The evolution of the nutrient composition of mammalian milks" 

Authors: Amy L. Skibiel, Lauren M. Downing, Teri J. Orr and Wendy R. Hood

Article Summary:  
"1. In mammals, nutrient allocation during lactation is a critical component of maternal care
as milk intake promotes juvenile growth and survival, and hence maternal and offspring
fitness.
2. Milk composition varies widely across mammals and is hypothesized to have arisen via
selection pressures associated with environment, diet and life history. These hypotheses have
been proposed based on observations and/or cross-species comparisons that did not standardize
for stage of lactation and did not consider evolutionary history of the species in analyses.
3. We conducted the largest comparative analysis of milk composition to date accounting for
phylogenetic relationships among species in order to understand the selective advantage of
producing milk with specific nutritional profiles. We examined four milk constituents in association
with species ecology while incorporating phylogeny in analyses.
4. Phylogenetic signal was apparent for all milk constituents examined. After controlling for
phylogeny, diet and relative lactation length explained the greatest amount of variation in
milk composition. Several aspects of species’ ecologies, including adaptation to arid environments,
reproductive output and maternal body mass were not associated with milk composition
after accounting for phylogeny.
5. Our results suggest that milk composition is largely a function of evolutionary history,
maternal nutrient intake and duration of milk production. Arriving at these conclusions was
made possible by including the evolutionary relationships among species."



Read the blog entry by Katie Hinde here at:
http://mammalssuck.blogspot.com/2013/11/mega-mammal-milk-analysis.html

This paper was part of Amy Skibiel's dissertation work under the direction of Wendy Hood.  I've written about these two lovely ladies before as they were instrumental for helping me get my bat milk work up and running during my dissertation! 

Bat souffle anyone? Milk assays in-progress

It has been some time (and then some) since I have posted anything but I figured a quick update about my current endeavours: bat milk analysis would get me back to posting more regularly. Besides classes start up tomorrow so I am back to my regular schedule and so too blogging.

Because I am interested in the costs of reproduction in bats I am also very interested in the quality of the milk bats produce. This is in part because lactation is arguably the most expensive task that mammals do! Females will deplete their fat stores and even start to break down their own skeletons to make milk for their young.

But here is the issue. Bats are MUCH smaller than cows.

So say I want to know the percentages of fat, sugar and protein or total calories in bat milk... I will need a LOT of milk or very specialized techniques to evaluate these components. This is where an amazing group of people come in one of which is Dr. Wendy Hood at Auburn who has developed methods to analyze very tiny volumes of milk!

Thank you Dr. Hood! So since last September I have worked off and on to develop my own versions of these tests using the methods and protocols of Dr. Hood.

My standard for all my tests (to be sure they are working) happens to be regular 'ol cow's milk. Luckily the values for all the parts of cow milk are all well known (thank you now to the USDA!) * see label above for an example.

The idea (one that takes more work than it sounds) is to get the same numbers for your cow milk as the contain of milk suggests... if you can do that your assays are working!

The parts I analyze are:

• dry mass (how much water is in the milk)


• fat


• carbohydrates (sugars like lactose) and


• protein

If you know these components you can calculate the amount of energy in your milk!

I will explain each of these in part but the bat souffle will be first so... keep posted!

Back to field planing! (and milking bats)

Ah it is 'that time' again the birds are singing, the bees are buzzing and the bats are lactating! Yes, considering that the Artibeus were all pregnant (late-stage) during my mid-march visit if I plan on collecting milk it is time once again to schedule a trip to the field for the 'last' milk collection of my dissertation (assuming all going according to plan). This next trip my lab mate will accompany me which will be an added bonus. Now all that said I imagine one question came to mind rather quickly 'wait... milk bats?' Yes... this is actually not as difficult as it sounds. Basically the mother and pup are captured, kept away from each other for a short while (~1 hour) so she accumulates milk which is natural if the mother is away from her baby. (Also the mother and pup are accustomed to being separated from each other for longer periods of time because the baby that cannot fly must stay behind while its mother is out for several hours every night searching for food.) After about an hour, I inject the mother with a small amount of a hormone called oxytocin. Oxytocin increases milk let down (i.e. lactation) so this combined with what is essentially a miniature version of milking a cow allows me to collect milk from the female before letting her and her baby return to their roost. I then upon returning analyze many nutritional components in the milk (dry mass, protein, fat, and carbohydrate (sugar) content).