The new RZG – The key to better health and performance of dairy herds worldwide

The April Sire Summary 2021 shows the German Total Merit Index, RZG, published in a new combination. The last revision took place in 2008. The RZG (Relativ Zuchtwert Gesamt) is applied to improve all traits according to their relative importance in the overall breeding goal. Starting in April 2021, the German health breeding values, RZHealth and RZcalffit, which have been increasingly influencing bull selection on farms since their introduction in 2019, are now directly included. In the past, the cows‘ health has been considered within the RZG via secondary traits such as the RZS (Somatic Cell Count), the RZR (Reproduction Index) and the RZN (Functional Herd life Index). The RZM (Milk Production Index) is reduced to a weight of 36% which is still ahead of the health breeding values but remains the most important trait within the new RZG. Today‘s excellent milk production recorded in the German Holstein population, allows a shift in weighting towards more health, which additionally brings economic advantages by avoiding treatment costs and performance losses due to diseases. With this new revision of the Total Merit, Germany sets out a clear focus, with emphasis on animal health and animal welfare.

The inclusion of the RZHealth allows the removal of the secondary trait RZS from the RZG, as the RZHealth acts as a direct trait for udder health. In addition, RZN and RZR lose weight in favor of RZHealth and RZcalffi t. Since the two new breeding values have a positive eff ect on these traits, their lower weighting will not reduce the breeding progress for longevity and udder health.

Other minor changes are extended by the complex „body“ to account for the fact that body structure plays a key role for the functionality of a cow. Extreme characteristics like excessive stature will be respected negatively. In addition, the maternal calving trait RZKm is supplemented by the direct calving trait RZKd. Within both calving traits the weighting for stillbirth has been increased, since stillbirth has a larger variance and therefore a higher information value. All included traits and their relative weights within the RZG are shown in the diagram above.

To summarize, the new RZG enables farmers to breed specifically for high milk yields and good health of their animals and at the same time meets the changing demands of modern dairy farming. The new RZG remains standardized to a mean of 100 in the base (cow base with all cows who are 4-6 years old, born 2015-2017) and a genetic standard deviation of 12 points.

Improving production efficiency and thereby increasing profitability has become a necessity for today’s dairy producers to remain competitive and successful in the market. To be profitable, farmers need long lasting cows that produce high quality milk, calve easily and are healthy, fertile and feed efficient. In August 2020 Germany published a new economically focused total net merit called RZ€ to achieve this. This important additional index includes all economically relevant traits derived from an extensive breakdown of the complete income and cost structure of dairy farming. Different to the well-known German RZG, the RZ€ does not include conformation traits and somatic cell count. The reason for this is that the direct economic weight of type traits is rather small and made insignificant through the correlation with other traits like longevity. There is also no direct economic weight for cell count (EBV RZS) independent from the incidence rate of mastitis. The importance of the new German health traits for a herd’s profitability is highlighted by their total weight of 16 % within the new RZ€.

In addition, the calf fitness trait RZcalffit counts for another 6 % of the RZ€ which refers to young stock losses in the period between 3 and 458 days of life. The exact composition and relative weighting of the included traits within the new German Economic Total Merit are shown in the graph above. The RZ€ is calculated for all Holstein animals and expressed in Euro difference in margin during the lifetime of a cow (about three lactations) compared to an average cow alive (basis 4-6 years old cows). Therefore, the differences in RZ€ directly shows the monetary advantage based on the genetic level between two animals during their entire life. The higher the Euro value for RZ€ the better the animal potential is. The daughters of a bull realize half of the differences of the sires RZ€. Selecting for the German RZ€ provides our worldwide clients a perfect, state-of-the-art tool to breed even more productive, healthier cows and assures a maximum progress in herd profitability for most dairy farms.

For organizations operating in international markets like MASTERRIND it is fact, that many countries still put a lot of emphasize in their sire selection on milk production as this is generally a field of high economic importance and where emerging markets quite often need to catch up compared to the existing production level in the key Holstein countries of Europe and North America. Within the current German Total Merit Index, RZG, production (RZM) has the highest weight as this index is particularly based on economic considerations but also takes into account the genetic correlations between traits and reliabilities of estimated breeding values (EBV’s) into account in order to maximize the overall return for the breeder.

Estimation of breeding values for milk production traits
Since May 2003 Germany is using the most enhanced Random Regression Model to estimate breeding values for milk production traits and somatic cell scores. This is a reliable model that even estimates individual genetic lactation curves. All official test day records of cows with an initiated first lactation since year 1990 are considered in the current German genetic evaluation.

Method
There are many advantages of a Random Regression Model like in Germany compared to Single trait or Multi-trait Animal Models in use by other key countries, like the USA. This includes the possibility of using the test day records directly instead of 305-day lactations, a better consideration of management effects or the possible estimation of individual lactation curves instead of a constant deviation from the beginning to the end of a certain lactation. Finally, the individual lactation curves are predicting the EBVs more flexible, especially when only early lactation information is available which helps to avoid over-or under estimation of proofs based on records in progress. Nevertheless, the Random Regression Model remains to be a multiple lactation model, where the lactations 1, 2 and 3 are still considered as genetically different traits. That means for all animals, with and without records, the model estimates breeding values of the fi rst three lactations.

Definition of estimated breeding values
There are 5 breeding values for production in Germany available: milk yield, fat yield, protein yield, fat content and protein content. The breeding value on lactation base is the sum of the EBVs from test day 1 to 305. The published breeding values for milk, fat and protein yield in Germany are defined as the average breeding value of lactation 1 to 3. This is important as it already takes into account that today’s farmers are more and more often breeding for high lifetime production per cow. The breeding values for fat and protein contents are calculated on the base of total breeding values for the yield traits and phenotypic means (F%, P%, Milk kg) of cows in second lactation included in the German base.

The composition of the German Relative breeding value milk production (RZM)
The German RZM for milk production combines the estimated breeding values for selected production traits, with a breed-specific weight according their economic importance. Within the index it gives the first, second and third lactation the same weight. For Black & White, as well as Red & White Holsteins, the RZM includes the following traits and corresponding weights within the RZM index:
Fat kg (70 %), Protein kg (25 %) and Protein percentage (5 %).

The yield traits, fat kg and protein kg, are included using the ratio of 1:4. The RZM is standardized to a yearly rolling base of cows at an age of 4-6 years (2016: cows born 2010-2012) with a mean of 100 and a genetic standard deviation of 12 points. The following percentage of Holstein bulls reaches each RZM group level:

50.0 % of the bulls have an RZM >100,

17.0 % of the bulls have an RZM >112,

2.5 % of the bulls have an RZM >124,

0.5 % of the bulls have an RZM >136.

(Source: Based on German Evaluation Center VIT, Verden)

Mastitis remains to be one of the main reasons for involuntary culling on today’s dairy farms. Besides the veterinary costs for udder treatment and the related loss of milk income, it also leads to indirect herd replacement costs. Therefore, modern dairy producers need to pay high attention to a good udder health status due to its big effect on milk quality, overall animal health and the general profitability of their dairy herds. The German milk recording service includes the analysis of milk samples for somatic cell count on a standard base, which is an indicator trait of clinical and subclinical mastitis. With the level of milk recording in Germany approximately at 88%, higher than in any other country in the world, it means that the large and unique data base is used to provide very accurate Somatic Cell Score (SCS) genetic evaluations for bulls and cows.

Estimated breeding values (EBVs) for Somatic Cell Scores

The German genetic evaluation for Somatic Cell Scores was established in 1996 by the German Evaluation Center VIT, using a Fixed Regression Model. Since May 2003, the genetic evaluation model has changed to an enhanced Multi-Lactation Random Regression Animal Model to estimate the breeding values for somatic cell scores and milk production traits. It is scientifically proven that the Random Regression Model used in Germany has many advantages compared to Single trait or Multi Trait Animal Models in use by other key Holstein countries. The Model remains to be a multiple lactation model, where lactations 1, 2 and 3 are considered as genetically different traits. So for all animals, with and without records, the model estimates breeding values of the first three lactations.

Estimated breeding values (EBVs) for Somatic Cell Scores

The data for SCS in Germany is the same as for milk production traits because SCS is available for all test day samples. Test day records of cows with first lactation initiated since 1990 are considered in the genetic evaluation. All official test day records are included if:
• the age of calving is: 20 – 40, 30 – 56 and 44 – 75 month for lactations 1, 2 and 3, respectively
• the days in milk are between the 5th – 330th day after calving.
Since the original data for cell count from the laboratory is expressed in cells/ml milk, this data needs to be transformed to get a standard normal distribution by using the following formula: SCS = log2 (Cell count / 100000) + 3

German genomic breeding values for SCS

Based on the unique German database for SCC, the German genomic proofs on young Holstein bulls and heifers for SCS are already very reliable at 75% reliabilty, which is even higher compared to the reliability of the gEBV’s for production traits (73%). Furthermore, the achieved reliability of gEBV’s for SCS on young Holstein bulls from the enhanced German genomic evaluation system is already comparable to that of a first crop daughter proof with about 85 daughters and 5 milk recordings.
Expression of German proofs for Somatic Cell Scores – The German RZS

The German model provides separate Estimated Breeding Values for Somatic cell score in the first three lactations. These individual EBVs are combined into an overall EBV for SCS by index weights of 0.26, 0.37 and 0.37 for EBV for somatic cell scores in lactations 1, 2 and 3, respectively.
German SCS proofs are expressed as relative EBV Somatic Cell Score, called RZS. The scale of the relative breeding value RZS is reversed to better indicate desirable proofs (low SCS) with RZS values above 100 as with all other traits. The RZS is standardized within the breed to a mean of 100 and a genetic standard deviation of 12 points for all 4-6 years old cows.
Selecting for RZS is an effective way to make genetic improvement on udder health. A German study by VIT has shown that there is a definitive link between a sire’s breeding value for RZS and the cell count of his daughters. Daughters from sires with a high EBV (111.8 RZS) had 101,000 less cells per ml in their third lactation compared to daughters from sires with a low EBV (88.2 RZS) within the same herds (see graph below):

Since 1997, the RZS has been an essential part of the German Total Merit Index (RZG), which combines all economically significant trait composites according to their importance within the German breeding goal; a balanced combination of production, health traits and functional type. The current weight of the RZS in the German Total Merit index RZG is 7%. Since 2009 Germany introduced the combined fitness index, RZFit to better identify bulls with with the best fitness traits among a larger number of proven Holstein bulls. Within the RZFit, the udder health proof RZS has an even higher weighting of 10%.

(Source: German Proof Center VIT, Verden)

Since dairy producers demand bulls siring productive, healthy and trouble free cows which last as long as possible, the longevity trait of a bull becomes of increasing importance. Thus, longevity is one of the most important components of dairy cow profitability. It basically describes how long the daughters of that specific bull last in comparison to the breed average under similar environmental conditions. To define that trait, a difference has to be made between voluntary culling (decision by farmer) and culling related to health (involuntary). For breeding purposes herd life corrected for voluntary culling is more informative, because it is a more precise indicator of the genetic vitality, health, robustness and fertility. Voluntary culling is often related to the milk production level of a cow compared to the herd mates, i.e. farmer cull low producers earlier compared to high yielding cows even when both have the same health status. Therefore the productive life is corrected for the yield deviation within the herd (protein + fat kg) to achieve an unbiased trait for the genetic ability of a cow to resist involuntary culling.

This is called functional herd life (fHL) and is defined as the ability of a cow to remain sound and healthy in a herd, independently from different voluntary culling strategies of the farmer.

Selecting and breeding for fHL has the problem, that for cows still alive the definitive life span is unknown. Animals currently interesting for breeding would be excluded from the evaluation by waiting until culling has occurred. This would lead to an extremely long generation interval and genetic improvement would practically be impossible. Therefore cows still alive are also included in the evaluation as censored observations.

Method and Model
Survival analysis offers the possibility to consider the longevity of animals alive up to a certain date (proof date) statistically as a censored observation. Thus live animals deliver information as well as culled animals, but are given less weight in the evaluation because their information is not yet complete. The estimation of breeding values for fHL in Germany is using the Weibull regression model as a well-known method of survival analysis. The evaluation at the German Proof Center VIT is based on a model, in which a combined effect of a bull is estimated as sire and maternal grandsire. Relationships among bulls are taken into account through their sires and maternal grandsires. The solutions from this estimation system relate exclusively to the direct fHL (based on culling/survival information). These solutions are not published, but are summarised with information from auxiliary traits to combined proofs for fHL.

Combined breeding value for functional herd life
Studies have shown that certain traits have a high correlation to the direct longevity of a cow and can be used as additional information in the proof system for functional herd life. Currently, estimated breeding values for somatic cell score, body depth, feet & legs score, udder depth and maternal calving ease are considered as information traits. Among the information traits the proof for somatic cell score is by far of most importance, as it is closely related to fHL and estimated accurately at an early stage. The solutions from the direct evaluation of length of productive life are combined with the evaluations of auxiliary traits through selection index to increase the accuracy of the RZN proofs. The importance of the auxiliary traits in the combined RZN decreases with increasing reliability until culling/survival information is 100 % determining RZN at maximum reliability.

Relative breeding value functional herd life (RZN)
Breeding values of bulls are published in proof lists and direct data access as relative breeding value fHL (RZN). For interpretation purposes approximated fHL in days of herd life are published too, assuming that the average culling rate in first lactation for all cows is 20 %.

(Source: German Proof Center VIT, Verden)

The modern Holstein dairy cow has the ability to produce large amounts of milk. The increasing production level has been accompanied by a significant improvement in type and udder quality among Holsteins with the result that involuntary culling for poor type or poor udder has become quite rare. Nevertheless the intense type selection has led to a compounding increase in stature for Holsteins and raised discussions in relation to feed intake efficiency and the necessary, optimized cow comfort. Therefore significant measures have been taking in recent international breeding goals to at least stop that trend of taller cows & higher body weights and to increase the emphasis on functional conformation and lifetime productive efficiency. Foreseeing that trend towards more efficient, long lasting, profitable cows Germany decided already in 2013 to leave body traits out and only include the total composites “feet & legs” and “udder” when calculating the Total Merit Index RZG for a Holstein bull. In April 2017 the body trait “Stature” was among others defined as optimal trait within the total conformation index RZE to underline the fact that extreme values are not desired when selecting towards higher dairy cow profitability.

Estimation of breeding values for conformation traits

Starting in June 1993 linear type traits are routinely evaluated using a Best Linear Unbiased Prediction (BLUP) animal model. The estimation is carried out for German Holsteins and German Red Holsteins together in one run.

Data base and classification

The German breeding value estimation for conformation traits is calculated for 19 linear type traits (incl. BCS) and 4 general scores for the characteristics dairy type, body (incl. rump), feet & legs and udder. The 18 international standard traits as well as the trait “quality of hocks” are considered between the biological extremes on a scale from 1 to 9, while the four general characteristics are classified with a score of 65 to 88. The German type evaluation uses classification of cows in first lactation recorded since 1998. The linear assessment is the core of the conformation assessment of the sires’ progeny. The classifications are carried out by approved and experienced German Holstein classifiers who work in accordance with international regulations. These classifiers are regularly trained and supervised by the German Holstein Association (DHV). A steady data monitoring guarantees the compliance with the guidelines issued by DHV.

Definition of breeding values

The breeding values for the linear figures and the 4 composites are expressed as relative breeding values with an average of 100 and a genetic standard deviation of 12 for all in first lactation linear scored 4-6 year old cows (2017: cows born 2011-2013). Estimated breeding values for type on a bull will be published by the German evaluation center VIT if he has received data of minimum 10 classified daughters in 10 different herds.

Linear composites and definition of optimal traits

In a first step the breeding values of the single linear traits are combined to Linear composites for dairy type (1 trait), body (5 traits), feet & legs (5 traits) and udder (7 traits).
By combining the linear traits as an index most of them follow the pattern as higher an EBV the better. But there are some traits where extreme values in both directions are undesired. These are named “optimal traits”. Thereby the optimum is not always the average of the population but to some extent in the moderately positive range. In the weighting of the respective composite the following traits in Germany are considered as optimal traits (last revised in April 2017). The optimum is shown in brackets, displaying the EBV which leads to the maximum contribution to the index:

Stature (optimum 112)                                  Teat placement rear (optimum 100)
Rump angle (optimum 100)                          Teat placement front (optimum 112)
Rear leg set side view (optimum 100)          Teat length (optimum 112)

EBVs being above the optimum will result in a minor contribution to the index according to the distance from the optimum for that trait. For example an EBV of 112 for rear leg set side view (optimum = 100) provides the same minor contribution to the feet & legs index as an EBV of 88. Furthermore the contribution of the EBVs for body depth and chest width to the body composite are weighted linear positive up to 112, but no more credit is given for values above 112. This means that EBVs above 112 do not provide a further contribution to the body composite but they are rated as 112. This measure should account for the fact that body weight of the next generation of cows should be rather consistent with the current population and not increase further. Additionally, changes in the physical characteristics of the mammary system such as teat placement and teat length needed to be addressed, as a cow’s general milkability, milking time or the likeliness of getting an udder infection all have a strong impact on her productive lifetime and thus overall profitability.

The total type composites

In a second step the breeding values (EBV) for the linear composites and the EBV’s for the general scores for dairy type, body, feet & legs and udder are combined to receive the 4 total type composites. The weighting is 25% for the EBV general score and 75% for the linear composite with the exception for dairy type, where the EBV general score as well as the single linear trait composite dairy character have each a weight of 50% (see table 1):

Table 1: Combining the EBV of linear composites and general scores to total composites

All composites are standardized to an average of 100 and a genetic standard deviation of 12, where higher values are rated positive and desirable.

The composition of the German Relative breeding value total conformation (RZE)

Finally the published relative breeding value for total conformation RZE is not an EBV calculated on the basis of a total score, it is a combination of the 4 total composites by using the following relative weights:

10% Composite Dairy Type
20% Composite Body (incl. rump)
30% Composite Feet & Legs
40% Composite Udder

Different to overall conformation calculated from rather subjective total scores, the German RZE assures that the composites are always weighted as defined. This corresponds to the procedure of the classification where the classifier assigns four general scores for the composites while the total score is always calculated automatically by using the above stated weighting.

Selecting for the German RZE allows for improvement in functional conformation to account for the fact that dairy producers need long lasting cows that produce high quality milk, calve easily and are healthy, fertile and feed efficient.

(Source: Based on German Evaluation Center VIT, Verden)

Enhanced Daughter Fertility evaluation in Germany
Since January 2008, the new multi-trait-model for evaluating daughter fertility was introduced in Germany including new traits and trait definitions. It replaced the old model where the only trait evaluated for daughter fertility was the 90-day Non-Return-Rate.

In the new model daughter fertility is described in much more detail:
a) Heifer and cow traits are (partly) treated as independent traits.
b) The ability to conceive is evaluated by two traits, the Non-Return-Rate 56 days and the number of days from first breeding until successful breeding.
c) The ability to return to estrus function following calving is now evaluated with the trait “time from calving to first breeding”.

Detailed trait definition and abbreviations are:

NRh/NRc = Non-Return-Rate-56. It records if re-breeding is registered within 56 days after the first insemination, (heifers (h)/cows (c)).

FLh/FLc = Time from first to successful breeding in days. It’s only calculated if the following calving has taken place within a logical pregnancy length, (heifers (h)/cows (c)).

CFc = Time from calving to .rst breeding in days for cows (c). DOc = Days open is not a direct evaluation trait, but this Interbull trait is calculated from the EBVs CFc + FLc (time from calving to first breeding plus time from first breeding to successful breeding).

Germany provides all of the above indicated single-trait data to Interbull while many other countries have only one national fertility trait or at least not all traits converted by Interbull. For the current genetic evaluation, all breeding (inseminations and natural services) since 1995 on all heifers and cows from the milking breeds in herds under milk recording are used. The data from lactations 2 and 3 are utilized as repeated observations.

Conception Index CON as part of the Reproduction Index RZR
The four conception traits are summarized in the conception index CON, which gets a significant relative weight of 75% within the overall Reproduction Index RZR (R = Repro-duction). A cow’s ability to cycle after calving is represented by the trait ‘Time of Calving to 1st Insemination’ and gets the remaining 25% weight within the RZR index. Both composite indices cause about half of the genetic variation for calving interval, but the costs for a prolonged calving interval by poor conception are higher. Besides lower milk yield, longer calving interval from poor conception causes extra costs in repeat breeding. The RZR breeding values are published as relative breeding values with an average of 100 in the breed base and a genetic standard deviation of 12.

The composition of the Reproduction index RZR is shown in the graphic below:

For many years, mainly production and type have been key criteria’s in sire selection of dairy farmers. In the last years the focus changed towards functional traits and those traits that can reduce costs and increase dairy cow profitability. Among those, non-problem calving and calf viability have a significant impact on the financial success of the dairy herd. Easy calving will minimize the veterinarian and labor costs and increase the total revenue as fewer animals will be lost and less subsequent performance reductions occur as a frequent result of calving complications. Furthermore, research has shown that difficult calvings compromise animal welfare and thereby consumer acceptance of dairy management systems.

Despite the lower heritabilities of calving traits and the sensitivity of phenotypes to subjectivity due to often categorical scales, genetic selection can improve calving performance.

Method and Model
The German evaluation center VIT has collected a large data set of first to third calvings from heifers and cows which has allowed the center to obtain sufficiently accurate estimates for calving traits. Only calvings since 2000 are included in the current genetic evaluation.
The German enhanced calving evaluations includes routinely calving difficulty and stillbirth and for both the direct and maternal effects. Calving difficulty is recorded in four classes for all cows under milk recording in all parities. These classes are: Easy, Normal, Heavy and with Veterinarian / caesarean. The Still Birth rate is defined as “All-or-None” trait. A calving where the calf was born dead or died within 48 hours is considered as stillbirth. The direct effect describes the calf’s contribution arising from its size, form and weight (bull is father of the calf born) while the maternal effect stands for the dam’s contribution as result e.g. of rump measurements and the ability to respond to parturition signaling (bull is sire of the calving female).

Since April 2012 a linear multi-trait BLUP animal model is used in Germany for evaluation of 12 calving traits in total:
– Calving ease and Still Birth rate
– each for 1st, 2nd, 3rd calvings plus
– each the direct (d) and maternal figure (m).

The German Breeding values to compose RZKd and RZKm
It has been proven that calving difficulties occur more often during the first calving of an animal and farmers are using calving proofs primarily when selecting bulls to breed their heifers. For that reason Germany defined the EBV for first calving as the goal trait within the calving evaluation.

On each bull Germany publishes Estimated Breeding values (EBV) for the following four single calving traits: (1) Calving Ease direct (CEd),
(2) Calving Ease maternal (CEm),
(3) Still Birth rate direct (SBd) and the
(4) Still Birth rate maternal (SBm).

Information from 2nd and 3rd calving’s contributing to the published EBV for 1st calving via the high correlations between them (see table below).
For practical selection the two direct EBVs are combined into the “Relative Index Calving direct RZKd” = 50 % EBV for Calving Ease direct (CEd) + 50 % EBV for Still Birth rate direct (SBd).
Similar to that the two maternal EBV’s are summarized into the “Relative Index Calving maternal RZKm” = 50 % EBV for Calving Ease maternal (CEm) + 50 % EBV for Still Birth rate maternal (SBm).

All published EBV’s are relative breeding values and standardized to a mean of 100 and a genetic standard deviation of 12 (true breeding values). The base is defined as for all relative breeding values (currently for Holstein and Red Holstein A.I. bulls born 2004-2006; for small breeds born 2000-2006) and base change every year in April.
Estimated breeding values for calving above 100 generally indicate desirable proofs which means less difficult calving’s and less still born calves. Farmers are advised that in practice bulls with direct EBV’s for Calving ease of one genetic standard deviation and above (CEd 112+) are considered to be particularly suitable for breeding heifers. Nevertheless the focus just on direct calving traits is not recommended. These particular “Calving ease sires” mainly transmit lower values for certain body traits, especially rump width which just transfers the problem into the next generation as resulting females will have more problems of giving birth due to smaller pelvic measurements. Therefore the selection focus should be to identify and exclude bulls with low direct calving proofs particularly when mating heifers and use bulls which offer positive figures for both, direct and also maternal calving traits on cows.

Table: Correlations between parities/calving number within trait

The development of genetic strategies to improve animal health has always been of high importance in Germany to further increase the lifetime productivity of our future cow generations in dairy herds. With the design of the German Total Merit Index towards balance and profitability Germany has already seen since 2002 a positive genetic trend for overall health due to the precise selection for somatic cell score (SCS), daughter fertility (RZR) and longevity (RZN) which together made up 37% of weight in the Total Merit Index RZG since a longer time. In several German projects and in particular through KuhVision (CowVision, the whole herd genotyping project), a large number of standardized health data has been collected in order to identify new selection traits for cow health. As a result, 4 major disease complexes have been identified as the main areas of health problems in dairy cattle. Besides udder health and hoof health this includes metabolic stability and reproductive health.

Breeding values for direct health traits

Based on standardized animal health recording in herds via farmers, veterinarians and hoof trimmers plus additional information for several health disorders around calving from the
German identification information system for animals (HITier), Germany was able to calculate and publish breeding values for direct health traits for Holstein and Red Holstein since the April Sire Summary 2019. The definition of these health traits is based on the German version of the ICAR Health Key, facilitating the best possible use of the differentiated information on animal health.
A total of 13 health traits are relevant and have been added to the German genetic evaluation which can be assigned to the 4 important complexes: udder health, hoof health, reproductive health and metabolic stability. Therefore, the German system covers all trait complexes including 6 hoof health traits and metabolic diseases. For the genetic evaluation a multi trait animal model within the composites including repeated measures is applied.
In addition to the direct health traits, Germany performs an evaluation for 4 culling reasons corresponding to the 4 composites for direct health traits. Unique in the world in Germany standardized culling reasons are recorded for all cows under milk recording since decades. Internal breeding values for the 4 culling reasons ‘Udder health problems’, ‘Foot & Leg problems’, ‘Infertility’ and ‘Metabolic disease’ show high correlations to direct health traits. By combining these information with the estimates for direct health traits the reliability has been significantly increased. This is especially true for the genomic breeding values for health traits because for culling reasons all bulls have information from all daughters, i.e. perfect reference population.

Publication of breeding values for direct health traits

The EBV’s for individual health traits in Germany are summarized and the following breeding values are published:

• RZudderfit (Ufit): resistance to mastitis
• RZhoof (Hoof): resistance to hoof disorders
• RZrepro (Rep): resistance to reproduction disorders and infertility
• RZmetabol (Meta): resistance to metabolic diseases
• DDcontrol (DDc): resistance to digital dermatitis (hairy foot warts) disease.

Besides being part of the hoof health index RZhoof the EBV “DDcontrol” is published separately. Furthermore, the elite 10% of bulls for DDcontrol i.e. digital dermatitis disease, do carry the label “DDpremium” while the 25% best bulls will carry the label “DDcontrol”. The before, highlighted 4 sub-indices are further combined into the

• Total Health Index (RZhealth) according to their economic importance.

The compositions of the 4 complexes as well as the index for total health are shown in the following table:

Table 1 – Overview of the individual traits and complexes in the genetic evaluation for direct health traits

All of the new German breeding values for health traits will be expressed as usual on a relative scale with a mean of 100 and a genetic standard deviation of 12 points. Higher EBV’s are more desirable, indicating that daughters are less affected by the identified diseases. Since April 2019 Germany has herewith offered a state-of-the-art system which does allow our global clients to enhance their selection on cow health and to have the opportunity to make significant genetic improvement in all important fields of animal health in their herds.

(Source: Based on German Evaluation Center VIT, Verden)

Over the past decades, the commercial use of Robotic milking systems is steadily increasing around the world. These enhanced milking robots are popular with farmers for their operating efficiency and robust 24-hour performance. Besides significant advances in the robotic milking technology, experience shows that farmers who work with milking robots need cows with specifically good udder health, great mobility, not too narrow in rear teat placement, optimal teat length & shape, plus good milking speed for best performance in such systems.

Method and Formula
In 2014, the German Holstein Association (DHV) in cooperation with the German Evaluation Center (VIT) developed a special Robot index (RZRobot) to select bulls that produce cows suitable for robot milking. In order to increase herd profitability, farmers with milking robots should continue to first select for total merit (e.g. RZG), but in a second selection step they now can exclude certain high RZG bulls that produce daughters that do not work well in Robotic systems due to teats that are too short or rear teat placement that is too narrow to be milked properly. For calculating the German RZRobot index the following traits are used with the listed weightings:

– Milking Speed (RZD) 20 %
– Somatic Cell Count (RZS) 15 %
– Total Feet & Legs Composite 15 %
– Total Udder Composite 10 %
– Rear Teat Placement 20 % (narrow=negative)
– Teat Length 20 % (short=negative)
The RZRobot index takes a different approach compared to other summarizing indices. In addition to the overall weightings shown before, additional parameters must be fulfilled, which are:
Milking Speed (RZD) ≥ 94
Rear Teat Placement ≤ 106
Teat Length ≥ 94
These additional criteria’s help avoid situations where lower values for one trait (ie. milking speed) would be compensated by extremely high figures for another trait (ie. udder health). Furthermore, a RZRobot index value is only published if ALL minimum requirements are fulfilled PLUS the calculated relative index must be above 100. For that reason just 30-40 % of the active German AI bulls receive an RZRobot value, which means that all bulls having an RZRobot value are suitable for management systems with robot milking. The end result is that bulls with higher RZRobot values are more suitable for use to develop cows that are more profitable in automated milking environments.
With each Sire Summary the German evaluation center VIT publishes on its website (www.vit.de), the list of active Holstein bulls that are specifically suitable for farms using automatic milking systems. This includes separate lists for daughterproven and genomic bulls as well as for Holstein and Red Holstein sires. MASTERRIND’s Top 5 daughter-proven bulls for RZRobot as well as MASTERRIND’s Top 5 genomic bulls for RZRobot are listed below.
(Source: Based on German Evaluation Center VIT, Verden)

RZcalffit – Introduction
Animal welfare has a continuously growing impact on the German dairy industry. Healthy and long-lasting dairy cattle are just one part of this development. The other aspect is to reduce the mortality of the calves. To improve the productive life of our dairy cows, breeding values have been available for almost 20 years, which are used intensively for selection. For calves, however, there is only the breeding value for stillbirth rate, which includes losses up to 48 hours after birth. The German index for longevity (RZN), starts measuring just after the first-time calving. In conclusion, the rearing period has been a black hole for breeders. With the official introduction of RZcalffit, the new German breeding value for calf survival, these unknown rearing periods are
no more!

Trait definition and data base
RZcalffit represents the genetic ability of a calf to survive the rearing period, from day 2 up to the age of 15 months, around the
age of the first breeding.
The pure genomic RZcalffit score has an accuracy of 51 %. Calf mortality at different ages is genetically not the same trait because different diseases are predominant at different ages.Therefore, the total timespan until 15 month of age is divided into 5 periods (see table).
Within RZcalffit the EBV’s for these five periods are weighted equally with 20 % each.
The data is derived from the mandatory registration and traceability data for all cattle in Germany, the animal origin and information system HIT. Data of approx. 8 million female calves born since 2006 are the base of the breeding value estimation. Information from male calves are not used because most of them leave the dairy herd just after beeing two weeks old.

Published breeding value RZcalffit
The breeding value RZcalffit is expressed on the usual relative scale with a mean of 100 and 12 points for one genetic standard deviation. Higher values correspond to fewer calf losses. The mean value of 100 corresponds to approximately 93% survived animals from day 3 up to 15 months, with 60% of the young animal losses occurring in the first two age segments up to 60 days. 12 points RZcalffit (one genetic standard deviation) is the equivalent to around 3 % of calf losses/survival.

MASTERRIND’s Top sires for RZcalffit are listed in the table below.