Investigating Seasonal Component Fluctuation

00:53:00 – How did your path of research take you to seasonal changes in production in dairy cows and what piqued your interest in it?

Dr. Baumgard’s PhD brought him to look at milk fat synthesis, and specifically at dietary situations that cause milk fat depression. He learned that the number one constraint to profitability is heat stress, and that’s where the two came together. 

He started working on heat stress and what causes a reduction in milk yield during heat stress, and looking at different season patterns of milk components.

01:41:00 – From the first hypothesis you had in Arizona about what causes changes, how does that differ to how you look at it today?

At first, Dr. Baumgard and his team thought there was some inner control of heat stress that causes reduction in productivity. Then they had this idea that reduction in feed intake only explained about 50% of reduction in milk yield. They’ve been spending the last 15 years trying to chase down these other components that contribute to poor productivity during summer time. 

02:47:00 – What did you come up with to explain why butter fat and protein go down from around April to August?

The answer is not known. There are just so many different theories and dairy scientists have been looking at this issue for over a hundred years. Nothing stands out.

04:29:00 – Have we looked at other milking mammals?

According to Dr. Baumgard someone probably has, but he’s not familiar with it. 

04:43:00 – So when we see that milk fat and protein drop, can we explain part of that from heat stress?

We can’t be sure. For example, if you look at the national milk fat content in Canada, it starts to go down long before there’s any heat stress going on (from March-April). We don’t know what’s causing it.