Skip to main content

Methane: What influence does cattle breeding have?

By Prof. Dr habil. Wilfried Brade, Professor emeritus of Animal Breeding at the TiHo Hannover

Genetic selection of dairy cows with lower methane emissions is one of the frequently discussed strategies for reducing methane emissions (CH4). However, it is extremely difficult to establish direct genetic selection of ruminants for CH4 emissions. In principle, the desired reduction in methane emissions must be achieved without compromising the cow's health and performance. This is another reason why it is important to understand the genetic background of the various methane traits and their relationships to other traits (e.g. health and production traits). Unfortunately, genetic-physiological correlations of CH4 formation during lactation have so far only been investigated on an animal-specific basis in studies conducted abroad over several years.

The genetics of CH4 emissions

The most comprehensive recording of animal-specific CH4 emissions to date was presented by the Danish Cattle Research Centre (DCRC) for more than 600 Danish Holstein cows. A very similar experiment was also carried out in France, but not on the same scale. In addition, CH4 emissions were determined in terms of production (MeP, in g/d), yield (MeE, in g/kg DM) and intensity (MeI, in g/kg FPCM (fat and protein corrected milk).

It is known that a cow's feeding behaviour has a strong influence on daily methane emissions. The diurnal fluctuations with an automatic feed distribution between 9 am and 5 pm were confirmed in the French study. CH4 emissions rose sharply with the start of TMR feeding in the morning and fell significantly at night. Since methane is formed in the rumen due to the fermentation of the feed consumed, it is not surprising that MeP follows the familiar pattern of a feed intake curve over the course of lactation (with a sharp increase from early to mid-lactation). Also, as expected, MeP is significantly higher for second-calving cows than for first-lactation cows. Instead, MeI is lower for older cows, as milk yield increases regularly from the first to the second lactation. In addition, MeE increases slightly within the two lactations.

How can methane be recorded?

Methane emissions can be expressed in very different ways:

  • Methane production (MeP) measures CH4 emissions per animal per day (in g/d).
  • CH4 intensity (MeI) characterises the CH4 production per kg of milk (in g/kg milk).
  • And the CH4 yield (MeE) records the CH4 emission per kg (feed) dry matter intake (DM), expressed in g/kg DM. 

Animal-specific differences in methane formation

As ruminants themselves do not possess genes for CH4 formation, this is referred to as "indirect" heritability. For MeP, the estimated (indirect) heritabilities (genetically determined variance components of the total variability) in Danish Holstein cows vary between 0.14 and 0.25 at the beginning of lactation, between 0.28 and 0.47 in the middle and between 0.11 and 0.29 at the end.

The pairwise correlations (rg) determined in the Danish study are moderate to high during early lactation with a peak value of up to 0.90 around the 32nd week. This is followed by a decrease in correlations to rg ≤ 0.5 by the end of lactation. It can be concluded that MeP is obviously not the same trait across both lactations, as the associated genetic correlations deviate significantly from 1 (rg ≤ 1) in numerous lactations.

The influence of genetics on CH4 emissions

The genetic correlations between MeP and energy corrected milk yield (ECM) and dry matter intake (DM) were moderately positive (> 0.5) for most of the lactation in the Danish study. In contrast, the correlation between MeP and body mass (BM) was close to zero. It has only a slight positive increase from the 32nd week and a decrease to the negative range at the end of the first lactation. A British study also found moderate genetic correlations (rg = 0.38 to 0.57) between MeP and milk yield throughout lactation, with a maximum in the middle (20th to 30th week of lactation) in high-yielding HF cows. It also reports genetic correlations between MeP and KM close to zero during lactation.

Evaluation of the various CH4 traits from a breeding perspective

The methane yield offers the possibility of reducing CH4 emissions per kg DM. It would therefore be a very attractive trait, provided it is not associated with poorer feed conversion. The utilisation of MeI means, above all, opting for a reduction in CH4 per kg of milk. The desired CH4 reduction can be achieved by reducing CH4 emissions per animal or by increasing milk yield.

Since milk yield has a generally higher heritability than CH4 emission and is already subject to strong selection in all modern Holstein populations (with sometimes very unfavourable reactions to functional traits), this target criterion brings little innovation to a modern breeding programme. However, it could be interesting for animals/breeds or systems with low performance. Intensive selection for reduced methane production (MeP) should lead to a reduction in CH4 emissions per animal. And this is likely to occur in several ways, such as a decrease in performance and feed intake. In the case of targeted selection for reduced methane production, both milk yield and feed intake must in turn be balanced out by additionally emphasising these traits in a breeding goal.

In the context of currently practised multi-trait selection, methane yield with its relative independence from the other traits seems to be the most attractive target, despite its lower heritability and the difficulties in continuous data collection. In fact, it is the only trait that really adds new information to the breeding goal. Considerations on optimal body mass of dairy cows and measures to increase longevity and animal health could further enhance the genetic gain for trait MeE, as this information is not included in MeE.

Possible measures for lower CH4 emissions

Establishing direct genetic breeding selection of ruminants for CH4 emissions, as is often called for, is extremely difficult. The Canadian initiative of April 2023 to create an additional breeding value for methane emissions for Holstein cattle should rather be seen as a targeted "advertising strategy".

Based on the current state of knowledge, great caution should be exercised in the intensive, one-sided selection of low CH4 excretors in breeding programmes with ruminants, as this can also lead to reduced efficiency of cell wall and thus roughage utilisation in ruminants.

CH4 reduction strategies can already be implemented through a wealth of targeted feed-related and husbandry measures that are far from being exhausted.

The CH4 emissions of lactating cows can now also be indirectly estimated (with limited accuracy) using the spectra of the mid-infrared (MIR) in standard milk analyses. This data should currently be used as a supplement, especially in the context of herd and feeding control.