Preventing milk fat depression this summer

Maintaining milk butterfat levels through the spring and summer grazing season is an annual challenge for dairy units across the UK (Figure 1) and Ireland.

Yet with the right adjustments to buffer feeding, it’s possible to reduce the impact and protect valuable butterfats, claims Kayley Barnes, AB Vista’s GB&I Ruminant and Equine Technical Manager.

Summer grazing season milk butterfat
Figure 1: Average UK milk butterfat content in 2018-19 and 2019-20. (DEFRA)

Figure 2: Average analysis from multiple samples of April 2020 fresh grass taken using AB Vista’s portable NIR 4 Farm device
Maintaining butterfat levels through the spring and summer grazing season is an annual challenge for dairy units

“The main component in milk butterfat production is the volatile fatty acid ‘acetate’, which is produced when dietary fibre is fermented in the rumen,” she explains. “The problem is that although young spring grass provides a great source of both energy – in the form of rapidly fermentable carbohydrates or sugars – and protein, it’s structurally immature (Figure 2).

“As a result, fibre levels are extremely low compared with older, more mature grass. This limits the amount of acetate produced in the rumen, which in turn reduces milk butterfat levels.”

The positive impact of stabilising rumen pH

Good rumen function is also critical, with fibre digestion in the rumen impaired whenever rumen pH drops below 5.8. This not only further cuts acetate and milk butterfat production, but can reduce feed intakes, overall nutrient supply and milk yield, as well as increasing the incidence of health problems such as laminitis.

“The high levels of rapidly fermentable carbohydrates and sugars in spring grass, combined with low levels of structural fibre, can result in extended periods of low rumen pH,” Ms Barnes continues. “If the rumen drops below pH 5.8 – the threshold for sub-acute rumen acidosis or SARA – the impact is even greater.”

Low milk butterfat is an indicator for SARA at any time of the year, but in the spring, when butterfats are already depressed, it can be harder to spot.

“One of the best ways to reduce the rate and extent of any rumen pH drop is to add

Acid Buf
slow-release rumen conditioner and Vistacell live yeast to the diet or the buffer feed offered at grass. The benefits, in terms of improved rumen conditions, as well as milk butterfat production and milk yields, have been proven in numerous peer-reviewed research and commercial trials over the years,” she adds.

Ration tips to boost acetate production and milk butterfat:

  • dietary fibre

    Balanced concentrate feeding with good levels of dietary fibre from sources such as soya hulls, sugar beet pulp or high-fibre moist feeds.

  • concentrate

    Feed a concentrate that compliments the energy coming from lush grass combined with feeding a long fibre (hay or straw) to stimulate cudding and help release acid-neutralising saliva.

  • condition the rumen


    Acid Buf
    slow release rumen conditioner and Vistacell live yeast to stabilise rumen pH, minimising the time spent in acidic conditions (below pH 5.8) when fibre digestion is compromised.

Increasing butterfats with live yeast and conditioners

In a 2014 trial, the addition of

Acid Buf
and Vistacell to cows receiving a 65:35 forage-to-concentrate ratio diet increased both milk fat production (1649 g/ cow/day vs. 1462 g/cow/day) and fat-corrected milk yield (38.9kg/cow/day vs. 37.1kg/cow/day). The result was due to a substantial reduction in the time the rumen spent at low pH (Figure 3), which improved fibre digestion and produced a significant increase in acetate concentration in the rumen (63.1% vs. 61.9%).

“The trial results highlight the value of properly supporting rumen function and fibre digestion when looking to maintain butterfat production when grazing,” Ms Barnes concludes.

“Whether used individually or together, the addition of

Acid Buf
and Vistacell, along with extra digestible fibre, can substantially improve butterfat percentage, and subsequent herd performance.”

[geot country="US"] CalMin[/geot][geot country="CA"] ProMin[/geot][geot exclude_country="CA, US"] Acid Buf[/geot] optimises rumen pH
Figure 3: Effect of
Acid Buf
and Vistacell use on rumen pH versus control (Source: Schothorst Feed Research, 2014)

Benefits & Conclusions

Maintaining butterfat levels at turnout can be challenging due to the reduced fibre content of the lush grass. The inclusion of

Acid Buf
optimises rumen function for over 8 hours, by stabilising the rumen pH and increasing the performance of the beneficial rumen microbes.

[geot country="US"] CalMin[/geot][geot country="CA"] ProMin[/geot][geot exclude_country="CA, US"] Acid Buf[/geot] rumen buffer reduces the risk for milk butterfat depression during the summer grazing season.
The efficacy of
Acid Buf
is supported by independent peer reviewed research

Acid Buf

  • buffers the rumen

    Buffers the rumen for a minimum of 8 hours – minimising the time spent below pH 5.8.

  • improves feed efficiency

    Improves feed conversion efficiency (FCE) – more production from the ration.

  • saves space in a diet

    Can be offered at relatively low feed rates – freeing up dietary space.

  • bioavailable minerals for the rumen

    Contains a source of highly bioavailable magnesium and calcium – helping restore cow magnesium levels, reduce incidence of grass tetany (staggers) and improve butterfat levels.

This article was published by British Dairying I Editor Kayley Barnes, Technical Manager AB Vista I May Edition 2020, pages 40-41
Celtic Sea Minerals

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