Dairy cattle reproduction is a multi-faceted challenge for farmers, nutritionists and veterinarians alike.

Key aspects of a nutritional program that could change reproductive performance are inadequate nutrients, high feed intake and excess nutrients or other dietary components. An area coming under increased scrutiny is high feed intake.

High feed consumption and reproductive efficiency appear to be linked by high hormone metabolism. A model developed by Milo Wiltbank, dairy cattle reproductive physiologist at the University of Wisconsin, may help explain some of the changes in reproduction. Lactating cows have greater energy requirements than non-lactating cows. The high feed consumption required to meet these energy requirements leads to a dramatic increase in blood flowing to the digestive tract to pick up these nutrients. All blood that flows through the digestive tract has to flow through the liver. There will be a very high amount of blood flowing to the liver in cows with high feed consumption (such as high-producing dairy cows). This may seem trivial, says Wiltbank, but the liver is the organ that rids the body of many compounds, including hormones like progesterone and estrogen. Therefore, high feed consumption, through this simple pathway, will lead to a very high amount of the estrogen and progesterone in the body being broken down in the liver. This would cause lower estrogen and progesterone in the blood and could cause problems with many different aspects of reproduction, says Wiltbank. It is not yet clear how the reproductive problems with high feed consumption can be alleviated. However, it should be stressed that high feed consumption should not be mistaken for excessive feed consumption, causing fat cows. This is a separate problem that could be considered as excessive nutrient intake, says Wiltbank.

Read the paper that Wiltbank presented at the 2009 Penn State Dairy Cattle Nutrition Workshop.