Novel research published in 2018 in the Journal of Dairy Science detailed the effects of the calving transition on the rumen epithelium, according to Lallemand Animal Nutrition, and now this study has been supplemented with metagenomics data that confirm the association between changes in the rumen microbiota and feed efficiency improvements around calving.

The transition period in dairy cows spans three weeks pre-calving to three or four weeks following calving, Lallemand said. It represents a critical time for the cow with major dietary, metabolic and physiological changes. In particular, the transition from a high-fiber diet to a diet high in rapidly fermentable carbohydrates represents important challenges for rumen health, the company said. It can also have a negative effect on the cow’s inflammatory status.

Lallemand conducted a trial in partnership with Alex Bach at the Institute of Agrifood Research & Technology's (IRTA) Blanca Experimental Farm in Spain on the impact transition challenges have on rumen health and microbiota profiles as well as the effect of live yeast.

The trial was conducted with 21 Holstein dairy cows from 21 days before calving until 21 days after calving. The diet changed from 28% concentrate before calving (51.2% neutral detergent fiber [NDF] and 13.2% crude protein [CP]) to 64% concentrate after calving (34.8% NDF and 15.2% CP).

Understanding metagenomics data

Metagenomics is the genetic identification of the whole microbiota of a host and their relative abundance. These technologies generate millions of genetic sequences. Thanks to biostatistics analysis, these data could be pooled together according to bacteria genus, which shows more than a hundred different bacteria types, Lallemand said. Such an analysis can help microbiologists have a better understanding of the complex composition of the microbiota, like that found in the rumen.

In the case of transition cows, the goal was to focus on the relative abundance of functionally relevant bacteria, the company said. Results from two main categories of microbes were combined: (1) bacteria that degrade complex carbohydrates, such as fiber, and (2) bacteria that degrade rapidly fermentable carbohydrates, like starch (Figure 2).

According to Lallemand, the data show that:

* Before calving, the relative proportion of the fiber-degrading bacteria was higher than the proportion thriving on rapidly fermentable carbohydrates.

* Post-calving, there is a rapid shift toward a higher proportion of bacteria degrading rapidly fermentable carbohydrates.

Protective role of live yeast

The first part of the study published in 2018 showed that feeding Saccharomyces cerevisiae CNCM I-1077 to dairy cows beginning three weeks pre-calving positively improved the rumen dynamics by:

* Reinforcing rumen epithelium integrity, thanks to higher tight junction gene expression before the challenge, and

* Increasing resistance to a lipopolysaccharide challenge, leading to less inflammation after calving.

The metagenomics data further indicate the protective role for the live yeast, because before calving, the relative proportion of fiber-degrading populations was significantly higher (P < 0.05), while post-calving, the live yeast group showed higher dry matter intake, leading to a 1.21 kg-per-day increase in non-fiber carbohydrates.

This would have negatively affected rumen pH and microbial balance, leading to a higher proportion of rapidly carbohydrate degraders, Lallemand said. Instead, there was no statistical difference with the control group that consumed fewer fermentable carbohydrates.

Since the cows fed S. cerevisiae CNCM I-1077 "consumed more feed, a lower rumen pH and greater relative abundance of Prevotella -- rapidly fermentable carbohydrate degrader -- would have been expected, unless (S. cerevisiae) had exerted a positive effect on rumen pH,” Bach explained.

Lallemand concluded that the live yeast — by stabilizing the rumen pH despite higher non-fiber intake — limited the burst of rapidly fermentable carbohydrate degraders.