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The authorities of the Federal states in Germany are responsible for the estimation of the official breeding values. The independent German Evaluation Center VIT is responsible for the genetic evaluations of the Dairy breeds German Holstein Black &White and German Holstein Red &White. Based on an unique and accurate dataset, VIT thereby uses some of the most enhanced calculation models globally available to calculate proofs for an increasing number of traits with economic importance including milk production, somatic cell scores, conformation, longevity, reproduction, fitness or suitability for milking robots. All breeding values and summarizing indices with the exception of the milk production traits are published as relative breeding values with the mean of 100 and a genetic standard deviation of 12 points. By doing so the figures are directly comparable across traits and the higher individual proof value always indicates a better breeding performance for that trait.
Definition of terms
To achieve the maximum overall genetic gain in dairy cattle breeding, a Total Merit Index is applied to improve all traits according to their relative importance in the breeding goal. This Total Merit Index is called RZG (Relativ Zuchtwert Gesamt) and is applied to Holstein and Red Holstein. Relative weights for included traits were last revised in August 2008 to put more emphasis on functionality and health traits.
The derivation of the Total Merit Index (RZG) is based on selection index theory. This is providing the optimum overall selection response in all traits. The relative breeding values (composites or indices) are considered as information traits. Included traits and relative weights are given in the diagram (see below).
The RZG is only published if a bull has an official index for production (RZM), somatic cell score (RZS) and conformation traits (RZE). The RZG is standardized to a mean of 100 in the base (cow base with all cows who are 4-6 years old, born 2011-2013) and a genetic standard deviation of 12 points. The official ranking of Geman top bulls is by RZG. Breeding values of Holsteins and Red Holsteins in Germany are estimated three times a year.
(Source: German Evaluation Center VIT, Verden)
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.
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)
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
|EBV linear composite||+ EBV general score||= published EBVtotal composite|
|50% Dairy type||50% Dairy type||Dairy type|
|75% Body||25% Body||Body|
|75% Feet & legs||25% Feet & legs||Feet & legs|
|75% Udder||25% Udder||Udder|
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 popular German indices RZM or RZE are designed to help selecting bulls with the main breeding focus on milk production traits or conformation respectively. With the new RZFit it is possible to select from a large number of proven Holstein bulls with the best traits for fitness (health traits). Therefore, German Holstein breeding, the MASTERRIND breeding program in particular, can offer bulls, breeding extremely positive for health traits, resulting in desirable improvement.
The RZFit is calculated in Germany using official EBV’s for all included traits. The functional traits included and their relative weights are shown in the diagram above. Daughter fertility and calving traits get most relative weight within the index. A 10% weight on the production Index RZM allows for keeping the selection differential for production close to zero while selecting for RZFit. Since August Sire Summary 2015 the RZFit is calculated and published also for German genomic sires. Top ranking bulls for RZFit demonstrate transmitting superiority in all functional traits.
(Source: German Proof 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)
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