As dairy farms increase their use of digital monitoring tools, new patterns are emerging in how warm weather and TMR stability shape feeding behaviour and performance. Recent findings confirm that managing aerobic stability is becoming just as important as formulating the right ration, particularly as temperature fluctuations and heat events become more common.
Heat stress begins earlier than expected
Research shows that dairy cows begin experiencing heat stress at temperatures as low as 16–19°C, depending on humidity (THI > 62). Even moderately warm conditions can reduce rumination, shift feeding behaviour toward cooler night hours, and depress dry matter intake, directly contributing to milk yield losses. Up to 50% of seasonal milk decline is linked to intake reduction alone.
With more farms relying on rumination and intake sensors, these shifts are now easier to detect, and much harder to ignore.
TMR heating: An underestimated driver of intake variability
Aerobic deterioration remains a year‑round issue. A survey of 30 US farms showed half of sampled rations deteriorated within 12 hours at 22°C, highlighting how quickly nutrient quality and palatability can drop once the TMR is exposed to oxygen.
The spoilage cycle follows a predictable pattern:
- Wild yeasts activate first, after which moulds and aerobic bacteria start to grow.
- Microbial activity generates heat, often pushing feed temperature above ambient.
- Nutrient losses occur – dry matter, sugars, starch, digestible fibre.
Figure 1 – Spoilage cycle
In warmer weather, this cycle accelerates, compounding the cows’ behavioral effects of heat stress.
Why intake matters more than ever
A landmark study in Livestock Science confirmed that DMI remains one of the strongest predictors of milk yield, with high‑producing cows consistently consuming more feed and taking larger meals regardless of parity. During warm conditions, when cows already tend to eat less, any additional loss of palatability due to heating becomes critical.
Practical impacts at the feed bunk
As TMR warms:
- Cows reduce intake
- Sorting increases
- Feed wastage rises
- Nutrient delivery becomes inconsistent throughout the day
Groups fed less frequently (dry cows and heifers) are the most exposed, as their rations remain exposed for longer periods.
A focus on aerobic stability: Where additives fit in
With farms seeking practical tools to maintain ration quality between mixing and ingestion, TMR stabilisers added directly into the mixer wagon have gained attention. They can be liquid or solid. Powder versions seem to be preferred due to practical management and safety.
According to a Danish study, the solutions available in the market show variable levels of stabilisation. Among those, FreshFoss:
- Reduces wild yeast counts (from 8.1 to 7.1 log₁₀ CFU/g)
- Lowers aerobic bacteria (from 8.4 to 7.4 log₁₀ CFU/g)
- Improves aerobic stability by +18 hours at 20 °C versus the non-treated TMR
Figure 2 – Control = no treatment, Freshfoss = treated at 1kg/t. Aerobic stability of TMR is the time spent to rise above 2.5°C in controlled conditions (here incubation at 20°C). Kristensen, 2019.
In an internal trial, when looking at the nutrient content of the TMR, the higher stability of a TMR treated with FreshFoss was associated with:
- Higher total dry matter (+2.2%)
- Higher starch and sugar content (+8 g/kg and +14 g/kg TMR)
- Greater metabolisable energy available for milk production
Key takeaways
- Heat stress begins at lower temperatures than commonly assumed.
- DMI is the primary driver of milk yield, making behavioural changes under heat highly consequential.
- TMR heating amplifies warm-weather intake drops, reducing energy supply exactly when cows need stability.
- Aerobic stability solutions, including TMR additives, offer practical protection against nutrient losses and palatability decline.
