Dairy farms can pay a heavy toll to thermal stress, even under moderate climate. The cow comfort zone is between 5-20°C and it is now admitted that even moderate heat stress can affect dairy production and cows health status.
Heat stress, as other stress factors for livestock, also affects the rumen balance and function, translated into a loss of digestion efficiency and increased acidosis risks.
A new study conducted by scientists at University of Bologna and presented last July at the ADSA-ASA joint annual meeting, confirms the benefits of ruminant specific live yeast SC I-1077 (LEVUCELL® SC, Lallemand Animal Nutrition) under moderate heat stress (Average Temperature–Humidity Index=70, just below the 68 threshold):
- On milk yield: + 6.7% Energy Corrected Milk Yield, equiv. to an extra 1.7 Kg ECM/day (Fig.1).
Figure 1: Effect of supplementation of dairy cows diet with LEVUCELL® SC on energy corrected milk yield under moderate heat stress (Fustini et al., 2013).
- But also on cow digestive comfort and rumen function. In this original trial, several indicators of rumen function were also measured: rumen pH was continuously recorded (use of rumen pH bolus); rumination activity was monitored (RuminAct, see picture), and NDF (fibers) digestion was evaluated. All these parameters were improved with the supplementation, when compared to the control cows, indicating a reduced impact of heat stress on cows digestive comfort:
- Cows spent on average a shorter time with a rumen pH below the critical value of 5.8 (Fig. 2), while control cows were impacted by the THI.
Figure 2: Correlation between environmental conditions and rumen pH. a) Variations of the temperature-hulmidity (THI) index during the trial. b) rumen pH variation for the control and Levucell SC groups (Fustini et al., 2013).
- More cows were spending more time ruminating, which is a good indicator of digestive comfort and welfare. It is generally admitted that optimal rumination is between 400-500 min/day, sign of good rumen function. Under 400 min/day, it could be a sign of poor rumen health and probably acidosis. In the trial, the number of cows achieving optimal rumination time is increased by 35% with the live yeast. This increased rumination will induce and increased saliva production helping the animal to maintain rumen pH.
- Fecal fiber analysis shows an increase of NDF degradation with the live yeast (+4%), also a sign of enhanced rumen function.
This new study complements previous heat stress trial, showing that under severe heat stress the live yeast SC I-1077 has a positive impact on dairy production and feed efficiency (Figure 3).
Figure 3: Effect of LEVUCELL SC on feed efficiency under severe heat stress (Marsola et al., 2010).
Moreover, this trial also enabled to look closer at what happens inside the rumen and the impact on animal behavior: both rumen pH and rumination activity were improved, signs of improved rumen function, which is corroborated by an improved fiber degradation. This is translated into higher direct milk revenue for the producer (+0.28 € / cow/day). To this, we must add the benefits on animal welfare (increased comfort, reduced acidosis and bloating risks…).
In conclusion, dairy production can be heavily impacted by heat stress and the recent re-evaluation of heat stress threshold indicates that dairy cows could be affected earlier than previously suspected. Latest study on live yeast shows that, when the best herd management practices are respected (housing and nutrition...), the additional help of this natural rumen modifier could benefit the dairy producer by further helping to manage and limit the impact of heat stress on rumen function and digestive comfort, whether under severe or moderate heat stress.