Unintended drop in milk fat – when biohydrogenation in the rumen becomes a problem
Almost all types of feed for dairy cows contain fats – but the quantity and composition of the fatty acids they contain can be very different. Unsaturated fatty acids in particular are subject to a transformation process in the rumen: they are biohydrogenated in the rumen by microorganisms. This affects unprotected fats from forage and concentrates as well as calcium soaps.
It becomes problematic if too many unsaturated fatty acids are consumed:
- They disturb the balance of the rumen bacteria
- There are shifts in the microbial composition
- As a result, a so-called ‘milk fat depression’ (MFD) can occur – an undesirable reduction in the milk fat content
Biohydrogenation can shift the composition of the rumen bacteria
There are two different metabolic pathways for the biohydrogenation of fatty acids in the rumen, depending on which bacterial species dominate (see figure). The resulting intermediate products – the so-called trans fatty acids – differ in the position of the double bonds and their effect in the cow’s metabolism.
- The normal biohydrogenation pathway transforms e.g. linoleic acid into stearic acid via the intermediate stage cis-9, trans-11 CLA
- This form of CLA has no influence on milk fat synthesis in the udder
Figure: Alternative pathways of biohydrogenation in the rumen (Griinari and Baumann, 1999)
Disruption of natural biohydration due to unbalanced feeding
An excess of unsaturated fatty acids in the ration and a low rumen pH value – caused by high levels of rapidly fermentable carbohydrates (e.g. starch or sugars) – can significantly alter natural rumen biohydrogenation. Under these conditions, the normal pathway is interrupted and an alternative biohydrogenation pathway is activated (see figure above).
The trans-10, cis-12 CLA is formed as an intermediate product, while the complete conversion of the fatty acids to stearic acid is inhibited. Consequence: Inhibition of milk fat synthesis
Even small amounts of trans-10, cis-12 CLA are sufficient to specifically inhibit milk fat synthesis in the udder – an effect that can be utilised in a controlled and targeted way with BEWI-FATRIX® CLA.
However, if this effect is unintentionally triggered by incorrect feeding – for example by an oversupply of starch and a simultaneous drop in pH in the rumen – the rumen metabolism becomes unbalanced. Possible consequence: rumen acidosis.
RUFAL value as an indicator for unwanted milk fat reduction
A key factor in milk fat depression (MFD) – i.e. an undesirable reduction in milk fat content – is the intake of unprotected, unsaturated fatty acids. The RUFAL value (Rumen Unsaturated Fatty Acid Load, according to Jenkins et al., 2009) was introduced to assess this effect.
The RUFAL value shows the intensity to which the rumen is burdened by unprotected, unsaturated fatty acids – and the risk of a reduction in milk fat.
The RUFAL value includes all unsaturated fatty acids. The most important ones include:
- Oleic acid (C18:1)
- Linoleic acid (C18:2)
- Linolenic acid (C18:3)
| Feed, typical values | Fat content (g per kg DM) | Oleic acid (% in fat) |
Linoleic acid (% in fat) | Linolenic acid (% in fat) | RUFAL (% in fat) |
RUFAL (g/kg DM) |
| Maize silage | 35 | 19.2 | 47.7 | 8.3 | 75.2 | 26 |
| Grass silage | 40 | 3.8 | 20.0 | 44.3 | 68.1 | 27 |
| Maize meal | 45 | 24.1 | 55.7 | 1.6 | 81.4 | 37 |
| Brewer’s grains | 90 | 14.6 | 48.9 | 4.6 | 68.1 | 61 |
Tablevalues for the fatty acid composition of individual feedstuffs and RUFAL values
Keep an eye on the ration as a whole
When RUFAL values are high, attention is often focussed on concentrate feed or added fats. This underestimates the significant contribution that basic feedstuffs such as maize silage or grass silage make to the daily RUFAL intake – primarily due to the quantity fed.
Example:
Just 8 kg DM of maize or grass silage already provides over 200 g RUFAL per day.
Calcium soaps also have high RUFAL values (~50 % in fat), which can lead to a daily load of around 400 g RUFAL/kg DM – despite supposed rumen protection.
The amount of unprotected, unsaturated fatty acids in the feed should preferably remain below 600-650 g per day or below 3 % of dry matter. However, recent studies (Mannai et al., 2016) show that the negative effect of increasing RUFAL levels is continuous and increasing. There is therefore no correct limit value for the content of unsaturated fatty acids.
Therefore, the lower the RUFAL value, the better. This avoids negative effects on the milk fat content.
Rumen-protected fat powders do not increase the RUFAL value
BEWI-SPRAY® fat powders based on palm or rapeseed supply additional energy via fatty acids without having any negative effects on the milk fat content.
BEWI-FATRIX® CLA enables targeted regulation of the milk fat content, with positive effects on metabolism and fertility, without disturbing the rumen microbes.
Unsaturated fatty acids in the fat powder are rumen-protected and do not increase the RUFAL value!
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