Another new breeding value, is that necessary? Yes, says Dr. Stefan Rensing from vit in Verden, because higher feed efficiency brings farms hard cash. They can save on feed costs and reduce CO2 emissions. However, it will be some time before RZFeedEfficiency is integrated into the overall breeding value.
An increase in feed efficiency not only saves feed costs, but also reduces the amount of manure and lowers CO2 emissions per kg of milk. With the April breeding value estimation, the breeding value feed efficiency (RZFutterEffizienz) is now also reported in Germany. We spoke to Dr. Stefan Rensing from Vereinigte Informationssysteme Tierhaltung (vit) about what the breeding value records and what advantages farms have if they take it into account when selecting bulls.
Dr Rensing, what does the new breeding value for feed efficiency entail?
The breeding value RZFeed Efficiency describes how much less or more feed (kg dry matter) a cow eats for her productive performance compared to the expectation. The breeding value defined in this way is therefore usually referred to as ‘feed saved’. Productive performance is not only the milk yield as ECM (energy corrected milk), but also the body gain, which ultimately generates income as a carcass. The RZ feed efficiency refers to the average of three lactations and therefore represents the productive life of the cow.
Other countries already have feed efficiency breeding values. Why is Germany only now following suit?
The initial feed efficiency breeding values, e.g. in the Netherlands, the USA or Denmark, were essentially based solely on the differences in maintenance requirements, i.e. weight. This is because at that time there was no or very little data available on individual feed intake. And weight was usually not actually measured, but only estimated using correlations with linear body characteristics.
Is the required data basis now sufficiently available?
A data basis for meaningful breeding values on the actual individual feed efficiency of cows has only been available since last year. It is based on an exchange and thus a common data pool from the USA, Germany, Canada, Denmark, Switzerland, Spain and Australia. This brings together data from around 15,000 Holstein cows (excluding Australia). For the most part, feed intake as well as milk quantity, ingredients and weight were measured daily in herds from experimental farms with feed weighing troughs. The data from these 15,000 cows not only covers the first lactation well, but also the later ones. The number of animals with data on actual individual feed efficiency is not very high compared to other traits, but it is the largest learning sample available internationally. As the three traits involved - dry matter intake, ECM and weight - are all relatively highly heritable, the so-called single-step method achieves a good 40 % reliability of the genomic breeding values for RZ feed efficiency.
What is the single-step method?
The single-step procedure is an innovative estimation method for determining breeding values simultaneously and with mutual consideration of both classic phenotypic data and genomic data (SNP). Until now, genomically supported breeding values have been a combination of separately estimated classical breeding values and direct genomic breeding values. The single-step procedure directly estimates a genomic breeding value based on all information.
With the given data distribution for the feed efficiency measurements with values from only 15,000 cows, but 1.5 million typed animals for which genomic breeding values are estimated, the single-step method is particularly suitable. This is because it utilises the available data more effectively and achieves a higher level of certainty for the genomic breeding values.
For feed efficiency, practically all bulls that are reliably daughter-tested for milk have only one genomic RZ feed efficiency. This is because only a few bulls just happen to have individual daughters on (German) test stations.
Which breeding goal traits is the RZ feed efficiency related to?
This is perhaps somewhat surprising: feed efficiency has practically no correlation with the previous breeding target traits and therefore also not with the overall breeding value RZG and the economic breeding value RZ€. Successful breeding for ever higher performance has led to a significant increase in output (more milk, but also higher weight), but obviously the input not previously considered, feed intake, has increased proportionally in the same way. Thus, feed efficiency has remained roughly the same despite the higher absolute milk yield. There are only slightly to moderately negative correlations with body traits. The higher absolute yield was partly achieved by increasingly heavier cows, which produce more on average, but have a disproportionately high energy requirement for maintenance.
What effect does selection have on feed efficiency within the best RZG bulls?
There is practically no difference between efficient and less feed-efficient cows in terms of milk yield or body weight gain (efficient animals are slightly lighter overall). However, they eat considerably less for the same performance.
This also applies within the best bulls according to RZG, i.e. the feed-efficient bulls do not differ from the less efficient bulls in terms of milk yield and the other traits in RZG/RZ€, but their daughters eat significantly less for the same performance. Within the best bulls by RZG, there are some with differences of two standard deviations for RZFeed efficiency (88 to 112). So your daughters will differ by one standard deviation (or 12 points) for feed efficiency. And this corresponds to about 247 kg dry matter intake per lactation or 3.5 % of total feed intake.
When is the breeding value feed efficiency taken into account in the Holstein breeding goal?
The composition of the overall breeding values for Holstein is the responsibility of the Bundesverband Rind und Schwein (BRS) as the umbrella organisation of the breeding organisations. This organisation has decided to initially publish the RZFutterEffizienz on its own. A decision on integrating it into the RZG or RZ€ will be made after some time of gathering experience through practice and in the organisations, i.e. probably not until 2025.
Will the breeding value feed efficiency be extended to other breeds?
Unfortunately, there are currently no prospects for the smaller dairy breeding value estimation breeds in vit (Angler, Rotbunt dual-purpose, Deutsches Schwarzbuntes Niederungsrind, Jersey) - similar to genomic breeding value estimation - as there is not enough data available.
There are also currently no concrete plans for a breeding value for feed efficiency for Fleckvieh, the largest dual-purpose breed. Although there is feed recording data for Fleckvieh cows from experimental farms in southern Germany (and presumably also some from Austria), these are significantly smaller in scope than for the current 2,500 Holstein cows from Germany and there is a lack of other potential partners for an international exchange.
