Switching from warm-season grasses to cool-season forages can give livestock bellyaches, in some cases, deadly ones, according to Texas AgriLife Research scientists.

How diet changes affect cattle's digestive tracts microbially – and how these changes may increase risk of disease – are being researched by Bill Pinchak, Texas AgriLife Research animal nutritionist at Vernon. Specifically being studied: frothy bloat of cattle grazing winter wheat pastures.

Pinchak, head of the Bloat Research Project, says bloat is a costly and sometimes fatal disease of cattle, with an estimated $400 million negative impact on the beef cattle industry. He and a team of scientists are working to determine the interactions among rumen microbes that lead to the onset and duration of disease.

To reach that goal, the researchers are using state-of-the-art technology, called metagenomics, which is a field of molecular microbiology where the presence of a microbe is determined by identifying its DNA in a sample rather than trying to grow the organism in culture.

Metagenomics is an ideal approach to studying microbial communities because less than 10% of rumen microbes can be grown in culture using routine anaerobic methods, says Jason Osterstock, AgriLife Research ruminant animal health scientist in Amarillo and part of the research team.
The bloat team recently completed the first genomics-based characterization of bacterial populations from steers associated with changing from a warm-season grass-hay diet to a cool-season grazed-forage diet. Their study included 14 steers sampled at two time points, the largest study of its kind to date, the scientists say.

They found that the distribution of bacterial genera changes dramatically when stocker cattle transition from bermudagrass hay to winter wheat forage diets, Pinchak says. Analyses also determined that bacterial communities were clearly different in the fiber, liquid and whole rumen fractions within the rumen.

Overall, more groups of different bacteria occurred on bermudagrass hay than on wheat forage diets, which is consistent with the increased rumen retention time of the less-digestible bermudagrass hay, Pinchak says. Specific bacterial groups would increase, decrease, appear or disappear from one diet to the other, highlighting the complexity, plasticity and specificity of rumen bacterial populations, he says.

hese results point toward the potential to use deeper metagenomic sequencing, including characterization of non-bacterial microbes, to gain better resolution and begin to unravel more complex relationships in future studies, Pinchak says.