Section 06 – AI and ET Data and Fertility Analysis
Bovine Semen Straw Marking
Objective
The guidelines define the minimum information to be printed on a bovine semen straw.
If additional information is to be printed, general recommendations are also given in order to help the users.
Field of application
The guidelines apply to bovine semen straws used for international trade, for either fresh or deep-frozen semen.
Definitions
To code the identification of semen in bars and print it on semen straws for an use on field during the insemination act by AI technicians or farmers in do it yourself, following recommendations have to be implemented:
- “2a” means two digits with an alphanumeric format.
- “3n” means three digits with a numeric format.
- “Bovine” means domestic animals of the genera Bos, Bubalus and Bison (include in particular the bovine species Bos taurus, Zebu Bos indicus, Indian buffalo Bubulus bubalis, American bison Bison bison and European bison Bison bonasus).
- “Bull” means a bovine male as defined above.
- “Ejaculate” means the semen released by one ejaculation.
- “Collection” means the entire successive ejaculates from the same donor in the same day.
- “Collection sequence for a given location and a given day” means the rank of the ejaculate within the bull collection (/n) or for all the bulls (/nn). It is also called charge number.
- “Semen collection centre” means an approved and supervised establishment in which semen is collected and processed for use in artificial insemination.
- Semen processing centre” means an establishment in which semen is processed for use in artificial insemination.
- “ISO country code” refers to the 2a list of codes ISO 3166.
- “International identification” means a unique registration number provided by the country for all the bovine animals and preceded with the ISO country code.
- “Bull code” means any code used to identify the bull for the management.
- “Uniform bull code” means the unique identification used by NAAB comprising the so-called “stud code” (3n), the breed (2a) and a number (5n) unique within the “stud” and the breed.
- "Bar code" means a system for coding alphanumeric numbers in bars deciphered by reader.
- "Batch of semen" means a group of semen straws produced from ejaculate(s) of a specific bull, on a specific day, in a Semen Collection Centre (SCC), with the same specific treatment (ie extenders, sexing, specific dilution...).
- "Batch identification" means a unique number to identify a batch of semen within a SCC either a serial number or combination of bull ID, collection date, ejaculate number. The Batch identification format is left to the action of SCC.
- "Stud or marketing code" means a unique code assign by the NAAB (National Association of Animal Breeders) to identify SCC or AI marketing organisation. A fee is paid at first registration and then each year in case of commercial activity in the US.
- r. "Barcode number" means a stud or marketing code + batch identification.
Straw identification
Summary of the straw identification as a minimum requirement
- Semen collection or processing centre code
- Breed (2a).
- Identification of the bull-
- Collection code (yyddd).
Printing
The printer should be an ink jet printer to ensure the legibility of the information.
Order
Guidelines do not address the order of the information.
The collection or processing centre from which semen is issued should be identified with a code. According to legal basis or to industry agreement this code should be either the collection code or the processing code. Within a country, centre codes printed on straws is either processing or collection and this information is available on reference lists.
If the semen is intended to be used within the European Union (EU), according to the Directive 88/407, the code should be the official EU code assigned for the approved “semen collection centre”.
Outside of the EU another code to identify the processing centre can be used, for example the “stud code” assigned by the NAAB.
Breed
The recommended format is 2a.
The ICAR list of the most relevant breeds for the international trade in semen is maintained by the Interbull Centre and available here on the Interbull website. The breed code can be presented alone or as an integrated part of the uniform bull code.
Identification of the bull
It can be either the Interbull international identification (IID) code or a world-wide unique bull code.
The international identification comprises the ISO country code (2a) and a registration number of the bull within the country (max 12n), for instance FR1234567890. This international identification is used for any purpose including traceability. It may or may not be the HB number.
If a bull code is used, it must be cross-referenced on the transport documents with the international identification of the bull.
This bull code can be:
a. The “uniform bull code” from NAAB (example 132HO12345).
b. A unique national bull number preceded by the ISO country code (example FR12345) .
1.7.1 Collection code
It is recommended to print the collection date with the Julian format “YYDDD” where YY is the two last digits of the year (99, 01) and DDD is the day number (from 001 to 366).
The collection sequence is considered as an additional information, but if it is printed, it should be adjusted to the date separated with a slash “YYDDD/1”.
1.7.2 Format for additional information
a. Name. Either the short name (commercial name) or the full name can be used.
b. Collection sequence. It should be adjusted to the date separated with a slash “YYDDD/1”.
c. Compulsory information. Within the EU, semen produced has to be labelled with its IBR status. The format for this has to be defined by the European Commission and will be part of this recommendation as soon as it is available.
1.8 Barcode identification of straw
To code the identification of semen in bars and print it on semen straws for an use on field during the insemination act by AI technicians or farmers in do it yourself, following recommendations have to be implemented.
1.8.1 General rules
a. Barcode doesn't substitute for official visible identification of semen straws that is printed according to ICAR Guidelines, in 1.4 above, page 6.
b. Barcode with the system 128C (see a. in 1.9.6 on page 10 below) is highly recommended.
c. The barcode must be as short as possible because it's the principal factor to obtain a high percentage of success when reading it. According to the state of art in 2008, for an easy reading on field, a maximal number of 13 digits is suggested.
d. Barcode is recommended to contain only numeric characters (see b. in 1.9.6 on page 10 below).
e. Some characteristics of the straws (ie colour…) affects the readability of the barcode. So it's recommended to test straws before use with barcode.
f. The barcode number (n. in 1.3 on page 5 above) refers to an unique ID for any batch of semen (see p. in 1.3 on page 5 above).
g. The format of this number
- Refers for it's first 3 digits to an unique reference number of SCC allocated by ICAR as described in 1.7.1 on page 7 above and defined in h. in 1.3 on page 5 above.
- Refers for the other digits to an unique batch identification as defined in p. in 1.3 on page 5 above.
h. The list of ID of SCC utilising a barcode system is maintained by ICAR. This list is unique in the world and consistent with the list of SCC ID (Stud and marketing codes) allocated by the NAAB.
1.8.2 Allocation of ID of SCC and publishing barcode format
a. Any SCC utilising a barcode system for international usage has to inform ICAR. ICAR will allocate a unique ID to the SCC.
b. SCC provides ICAR with the ID stud or marketing code allocated by the NAAB if it already has one.
c. An allocated ID will be valid for 20 years after the day when the SCC stops its activity to guaranty its uniqueness in bar coding. It doesn't change if the SCC modifies its system of barcode.
d. At the same time, the SCC informs ICAR of the format of the barcode number. ICAR publishes this format on the web site and renders it accessible to any user (§4).
e. ICAR and NAAB manage together the system of allocation of ID SCC and fix various problems arising in using an unique ID for the 2 organisations:
1.8.3 Management of barcodes within SCC and for the movements of semen
a. Any SCC running a barcode system maintains a data base where any barcode number on straw is cross referenced with the official data printed on straws. Optional information may also be attached to the data base.
b. Any client receiving semen may get from its supplier (distributor, AI Company…) the necessary data to cross reference barcode number with the official straw identification in accordance with these ICAR guidelines and eventually optional requested information.
c. After reading it is highly recommended that the barcode number is stored in the user data base as a raw data.
1.9 Explanatory notes
Comments on the recommendation
1.9.1 History of the discussions
Several attempts have been made to define an international recommendation for straw identification from which are the following:
a. ICAR proposal of September 1995
b. IFAB proposal of June 1998
c. QualiVet proposal of November 1998
All these approaches were to define precisely the entire sequence to be printed on the straw and tried to combine the requests of the different countries. As a result, the previous statements resulted in rather long identification and eventually failed to reach a full agreement from the different countries.
The actual recommendation tries more to set up the principle of the identification rather than to reach a full agreement on the sequence printed on the straws.
Basic ideas were:
a. The straw should not be considered like a database by itself.
b. The minimum information for official recording purposes is ‘centre/bull/date’ and for field recording by the technician ‘bull/date’.
c. For ease of use by the technician on farm and accuracy, the number of data items should be kept as few as possible and in large print.
1.9.2 Semen collection centre
The “semen collection centre” is a specific facility for the collection of bull semen and should not be confused or replaced by the ‘owner identification’.
It is the approved and supervised “semen collection centre” which should be under an obligation to ensure that the semen has been obtained from animals whose health status is such as to ensure that the risk of spread of animal disease is eliminated, and has been collected, processed, stored and transported in accordance with hygienic rules and rules which preserve its health status.
1.9.3 Collection code
Printing a date instead of a code is advisable for transparency to the customer.
Most people prefer having a “real” date like “11 March 99” than a Julian date YYDDD comprising year + day in the year.
The main reason why the Julian format was chosen was the ambiguity of the information 02/05/03 that could be naturally interpreted in different countries as DDMMYY YYMMDD or MMDDYY. Another reason is the compactness of the Julian format (5n) and the ease of reading with the sequence number (99032/1).
The collection sequence is considered as additional information because lots of centres mix the ejaculates of the same collection and thus do not want to systematically print “/1” for nothing.
1.9.4 Name
Some people support a short name that is easy to read for the technician and others prefers a full name to avoid confusion between bulls. No agreement could be reached for the format.
1.9.5 Identification
The international identification is up to now the only identification universally accepted world-wide. It was logical to recommend that this be the minimum printed on the straw. But since this identification is long, it is not practical to read it in liquid nitrogen neither to record it on farm for the insemination. Every country is thus using either the bull name or a bull code. An agreement was reached to not impose the international identification for those countries used to managing unique bull codes, but it can also be used when required.
1.9.6 Barcode identification of straw
a. We choose to recommend the type of barcode for several reasons: readers are not able to read all the types of barcodes and the 128 C type is compact (about 17 mm long for a 10 digit numeric barcode and 23 to 25 mm long for a 13 digit numeric code). However as technologies advances this recommendation may change.
b. In a barcode 128C, alphanumeric characters take 3 to 4 times more space than numeric characters. Considering the elements to write on a straw, numeric characters are presently more compatible with the available space.
1.10 Procedure to handle breed codes on semen straws
1.10.1 Article 1 - Purpose
The general purpose of the list of breed codes is to facilitate traceability of semen that is traded across country borders. The code should thus be used to identify the breed of the bull on semen straws that are used in another country than the country of origin (sampling).”
1.10.2 Article 2 - Exceptions
The breed codes printed on straws do not apply:
a. To identification of breeds in the international genetic evaluations for bulls offered by Interbull.
b. To procedures of registration of the progeny: the use of the breed code printed on the straw doesn’t make provision for the breed of the calf born out of the insemination using the semen unit nor it’s registration in the Herd-Book of the breed of the sire.
1.10.3 Article 3 – New Breed Codes
Breeds can be added to the code list, provided semen from bulls of the breed is exported in a significant number and to a significant number of countries.
In 2004 “significant number” means that more than 10 000 doses have been exported in more than 3 countries. These figures may change according to the experience in processing such demands; then new rules will be published.
1.10.4 Article 4 – Evidence Required
Any party requesting that a breed is added to the list of codes should provide unequivocal evidence that:
a. The breed does not belong to a breed already on the list.
b. The breed is recognized as a separate breed, e.g. recognized by a breed society.
c. There is significant international exchange of genetic material from the breed, e.g. by showing country of origin, number of doses (semen straws) produced in country of origin, number of doses (semen straws) exported, according to article 3.
1.10.5 Article 5 – Other Party Support
Any party requesting that a (local) breed is added to an already existing group of breeds should provide unequivocal evidence that the request is warranted. The request should be seconded by at least one other party representing a breed already included in the group.
1.10.6 Article 6 – Unique and Relevant
New breed codes should be unique and should be assigned based primarily on the name and/or abbreviation of the breed used in the country of origin. The second character in the breed code should be exchanged if the most logical 2-character code is already in use.
1.10.7 Article 7 – Interbull Centre Role
The list of breed codes is maintained by the Interbull Centre. Requests for updating or adding breed codes should be submitted to the Interbull Centre by e-mail, fax or letter. Requests, and results of requests, should be officially announced on the Interbull web-site accommodating the breed code list.
1.10.8 Article 8 – ICAR Website
This procedure is published and up-dated on the ICAR web site as part of Section 6 of the ICAR Guidelines.
1.10.9 Article 9 - Appeals
If a requesting party disagrees with the result of the procedure handled as describe before it may submit the case to ICAR board, that will make the final decision.
2 Bovine Embryo Production and Transfer
2.1 Object of the recommendation
The purpose of this recommendation is to improve quality of data in Embryo Production and Transfer on cattle in respect of assessment parentage of calves born out of this technology. It takes into account existing rules or guidelines already laid down to guaranty high level of exchanges at international level and is considered as an extension of those rules. It recommends the minimum items that should be recorded for using embryo data and the minimum of controls that data must undergo for being declared as valid.
It is a complementary addition to international rules governing embryo trade such as:
a. Veterinarian requirements issued by EU or other national/international bodies.
b. Zootechnical requirements issued by EU or other national/international bodies.
c. Technological guidelines adopted by the IETS.
2.2 Field of application of the recommendation
The recommendation applies usage of embryo data to establish parentage of calves born out of embryos prior to registration in the herd-book. It also provides elements to insure embryos traceability.
It applies on females from which embryos are recovered, their sires and to the recipient female whatever the technology used to produce embryos subject to future transfer, such as classical production technique, IVF, splitting, embryonic cloning.
It applies for embryos produced within country or imported from the other countries
It doesn't apply to recording of data used for technology purposes such as:
a. Assessment of embryo's quality.
b. Processing of embryos for freezing, or other technique (splitting, sex assessment) Then IETS guidelines including forms have to be used for international exchanges of embryos.
DNA references (or blood types as exceptions) have to be provided for the genetic parents of embryos. DNA references are the ISAG list of markers.
2.3 Definitions
a. AI: insemination to produce embryos from a donor female, heifer or cow.
b. Donor female: female chosen as genetic mother of future calves born out of embryos.
c. Double AI: two AI carried within a short lap of time, e. g 48 hours, on the same female with or not the same bull often to produce embryos. This information is recorded to avoid rejection when verification of dates.
d. Embryo transfer: Implantation of embryos produced in vivo or in vitro into a recipient female
e. IETS: International Embryo Transfer Society: professional forum for the exchange of information among practitioners, scientists, educators regulatory officials. IETS is providing a handbook of forms and certificates for the benefit of practitioners. The updated IETS forms are available on www.iets.org
f. IVF: in vitro fertilisation. Technique used to fertilize oocytes recovered from donor females with bull semen outside the genital tractus of donor female on the lab. Oocytes may be recovered either by ovum pick up either at the abattoir.
g. Operator: Person qualified to recover embryos from donor females and or to perform transfers of embryos. Also person qualified to carry out OPU of IVF. An operator is a member or acts under the responsibility of a team.
h. OPU: Ovum pick up. Technique allowing recovering oocytes out of an ovary from a living donor female. Then oocytes are fertilized on the lab by bull semen.
i. Recipient female: Female treated to be subject to embryo transfer. After calving she will be called as "non-genetic mother".
j. Recovering embryos: Technique used to recover embryos by flushing a donor female inseminated with semen from one or two bulls.
k. Registration: In the sense of this recommendation "registration" of an animal, recipient , donor cow or bull, refers to an animal with an unique identification notified to a data base. The same term applies for herds.
l. Reproductive cloning: technique used to multiply nuclei of embryos produced in vivo or in vitro.
m. Teams: Officially approved bodies to collect embryos or oocytes and/or to transfer embryos. References of approved teams are published by national or international authorities (codes, address, responsible person), with the scope of approval: nationally- internationally.
2.4 Recording of relevant data
Data that have to be recorded in order to insure the parentage of calves born out of embryos and the traceability of embryos refer to:
a. Recovering embryos, including IVF procedures (see 2.4.1 below).
b. Embryo transfer (see 2.4.2 below).
Moreover it will be mentioned minimum items that should be mentioned on straws containing frozen embryos (see section 2.4.2 below)
The provisions to follow movements of embryos is given in Annex 3. Embryos storage and movements on page 20 below.
2.4.1 Recording data at different steps of embryo production
2.4.1.1 Summary of items to be recorded when embryos are recovered
When embryos are recovered, some items have to be registered compulsory, by hand (paper form) or by electronic devices (as example laptop computers, PDA.). Those data will be used to constitute the basic databases to trace back embryos history according to the various situations.
When embryos are imported, relevant data have the same status as recovering data.
Requested data are, either on farm recovering or importation:
In any situation:
a. Recovering's references of the approved team and/or operator carrying out operations.
b. Date of collection (or date of importation).
c. Date of freezing (if different).
d. ID Herd of the donor at time of embryo recovery.
e. ID Donor female.
f. Nature of recovering: embryos or Oocytes.
Only for embryos recovering:
a. Possible ID sire(s if double AI have been carried out with 2 different bulls).
b. Age of embryos.
Only for Oocytes recovering:
a. Nature of recovering: abattoir or OPU.
2.4.1.2 Summary of items to be recorded at fertilisation process or reproductive cloning (when relevant)
These items address any embryo (or on straw to identify embryos):
a. Lab of fertilisation.
b. Date of fertilisation.
c. Possible ID sire(s).
d. Operator of cloning.
e. Date of cloning.
2.4.1.3 Extra information
a. Indication of genotyping by biopsy.
b. Technical data such as codes requested by the IETS forms set.
2.4.1.4 Data for parentage validation
a. Embryo reference number ( which may contain recovering reference number).
b. Identification of the approved team and / or operator.
c. Date of freezing.
d. Embryo's sire(s): ID + breed code.
e. Embryo's dam: ID + breed code.
f. ID Herd of the donor.
g. Age of embryo (s).
If embryos are imported relevant data may be obtain from documents accompanying embryos:
a. Herd Book pedigrees.
b. IETS appropriate forms.
Recommendation does not address the order of items. The description of order has to be mentioned when data are exchanged.
Note
DNA has to be collected from parents, markers (or blood types) have to be provided along with the other data.
2.4.2 Identification of embryos on straws
On each straw containing embryos, an unique reference number has to be printed or hand-written in order to set cross-reference with following items on papers or accessible electronic files, that render possible to follow physical movements of embryos:
a. Identification of the approved team/operator that has recovered embryo(s).
b. Date of freezing.
c. Embryo's sire(s): ID + breed code.
d. Embryo's dam: ID + breed code.
e. Number of embryos per straw.
In addition to the unique reference number, more information may be laid down on straws according to the needs of the clients or the breeding organisations. This recommendation does not address the order of items.
The structure of the unique reference number isn't requested by this recommendation. It includes usually the team / operator code, the reference of recovering intra year and the rank within recovering operation.
In situation of embryos produced for export purposes it is strongly recommended that teams implement the IETS identification system.
2.4.3 Summary of items to be recorded when embryos are transferred
When embryos are transferred into recipients, some items have to be registered compulsory, by hand (paper form) or by electronic devices ( such as laptop computers, PDA.). Those data will be used to constitute the basic database to assess parentage of the calves born out of embryos allowing distinction between genetic mother and biological mother.
Items addressing any embryo are:
a. Operator.
b. ID Herd of recipient.
c. ID Recipient female.
d. Date of transfer.
e. Embryo's identification.
Recommendation does not address the order of items. The description of order has to be mentioned when data are exchanged.
2.4.4 Details on recorded items
2.4.4.1 Recovering reference number
Reference of the officially approved team that has recovered embryos and the intra team year number.
2.4.4.2 Embryo's reference number
Refers to recovering reference number to describe produced embryos: number of embryo produced intra team by an approved team.
2.4.4.3 Operators
Technicians or vets working under the responsibility of approved teams for recording or transfer embryos. Recording of individual operators is not compulsory.
2.4.4.4 Dates
The date of each operation has to be recorded. Dates of recovering embryos and freezing are usually the same.
2.4.4.5 Identification of herds and females
Herds and females have to be identified within the national system of registration dedicated to genetic data processing. The identification number of females including country code has to be recorded for each donor or recipient female.
2.4.4.6 AI bull
Donor females have to be inseminated by semen of AI bulls, known through the reference of their semen. The bull's identification is that defined by the "ICAR guidelines for straw identification for bovine semen" as the international identification code or a world-wide unique bull code (refer to 1.6.2 on page 7 above).
2.4.4.7 Double AI
The existence of a double AI has to be mentioned, either by recording of a code, either automatically.
2.4.4.8 Breed codes
Those of the ICAR list (available here) for bulls and donors have to be used for international trade. In case of production of embryos, from breeds that are not on the list, teams are free to use any other code, provided that they not already on the list.
2.4.4.9 Herd
A herd may be either a farm or a station.
2.4.4.10 Age of embryos.
Embryos produced in vivo or in vitro, are transferred at stage of blastocytes, usually 7 days.
2.5 Transmission of embryo data for parentage assessment
a. Data have to be transmitted on a regular frequency to the database where there will be matched with birth data.
b. Embryo identification data and AI data have to be available in the database.
c. Transfer records have to be available in the database prior to birth data.
d. Birth data have to be transmitted by the person in charge of the recipient at calving (sex of the calf is declared at birth and not by molecular analyse).
2.6 Parentage assessment
After calving of a female known as a recipient by indication of embryo transfer instead of AI (or natural service) as reproduction event, the system of parentage assessment has to establish the genetic parents of the calf . Two methods are possible according to the data processing organisation implemented within countries:
a. Either parentage assessment requires that both parents and the calf are compulsory analysed for Micro satellite or SNP markers or blood types consistency on the basis of recorded data described in 2.4 on page 13 above.
b. Either parentage assessment requires that relevant data undergo successfully tests described in Annex 4. Validation of data on page 21 below and transmitted to the database according to 2.5 above, prior to the transfer data being matched with birth data.
If dates of implantation and of birth are consistent with the gestation length of calf's breed, taking into account the age of the embryo, the genetic parents may be attributed the born calf.
It is recommended that parentage for the more valuable animals of the population should be confirmed using DNA analysis.
Note
Parentage of AI bulls, born out of AI or ET, has to be compulsory checked for checked for Blood typing, Micro satellite, or SNP parentage analysis in most countries.
2.7 Quality controls
The efficiency of any information system depends on the quality of data proving that the expected result fits with the goal. For embryos, it deals with the accuracy of the records and with the proof that the progeny from embryo transfer was born from foreseen parents.
It is recommended that the organisation in charge with data processing aimed to assess parentage from calves born out of embryonic techniques carries out controls and implement relevant indicators for failures on each test suggested above, in terms of completeness, integrity, coherence and likelihood of recorded date.
Note
Those quality controls are independent of those requested for the renewal of approval of ET teams.
3 Fertility Reporting for AI organisations
3.1 Scope
Non-Return Rates (NRR) as a management tool for AI industry to characterise bull fertility and technician performance or to compare different semen treatments.
The reproductive performances of any herd or flock is out of scope.
3.2 Aims
a. To facilitate the understanding of the “Non-return rates” usually provided by AI organisations, recommending a precise description of the method used for the calculation of NRR.
b. To suggest guidelines for calculations of NRR, in order to facilitate the harmonisation of the calculations between countries or AI organisations.
3.3 Definitions
First insemination = First insemination to breed an heifer or to breed a cow after the end of each pregnancy.
Non-Return Rate (NRR) = Percentage of females that are inseminated for the first time during a given period of time (such as a month) and have not been recorded as having returned for another service within a specified number of days (e.g. 24, 56, 90).
3.4 Rules for calculation
3.4.1 Services to consider
Only first inseminations should be considered for the calculation of NRR (agreement for bull fertility in 5th ICAR meeting at TRENTE, 1964).
3.4.2 Females to consider
In a given herd, all females inseminated should be used for NRR calculation (without selection on reproductive parameters).
Female breed(s) should be indicated.
3.4.3 Day of insemination
The day of insemination is Day 0.
3.4.4 Interval of returns
Calculation of a NRR (e.g. 56 day NRR) commonly excludes early returns according to the objective of the NRR (e.g. returns within 3 days after the insemination are excluded since it is considered usually as a problem due to females and not to the males).
Thus, both limits of the considered interval should be indicated (e.g. 3-56 day NRR).
3.4.5 Limits on the interval of returns
As a rule, the limits given should be inclusive.
For instance, for a 3-24 day NRR, if an insemination has occurred on Monday (D0), an early return recorded on Tuesday (D1) or Wednesday (D2) is excluded, and a return recorded from Thursday (D3) to D24 is considered.
3.4.6 Exclusion of short returns
The females with short returns, excluded as stated above, could be considered either like non-returned females (“pregnant”) or like non-inseminated females. The former will lead to a slight overestimation of NRR, the latter represents a better option but might be more complicated to implement.
As a rule, short returns should be considered like non-inseminated females, i.e. should be eliminated from the file for the given year of calculation. Otherwise the chosen option should be indicated.
3.4.7 Number of first AI
The number of first AI should be indicated for any NRR, since it is related to the precision of the estimation. For example, a NRR of 50% based on 100, 400 or 1600 AI will have a standard deviation of 5, 2.5 or1.25 units of percentage.
3.4.8 Correction of NRR
Numerous factors have been shown to be able to influence the NRR according to the breeding situation. Some of the factors commonly used are: parity of the female (cow/heifer), technician, day of the week, herd, area of AI, year or season or month, semen price, Do It Yourself or not, herds on milk recording or not, milk production for cows, female breed if several.
As a minimum for correction, NRR should be adjusted for parity (cow/heifer).
In any case, it should be indicated if the NRR have been adjusted or not, and in case which factors have been used for correction.
As stated above, one should indicate:
a. The given period of time in which females have been inseminated.
b. The number of females.
c. The limits of the interval during which the returns have been observed after the date of each insemination (3-24, 18-24...).
d. Female breed(s).
e. If females with short returns were considered either pregnant or non-inseminated.
f. If nrr have been adjusted or not (and if yes, the source of variation taken into account).
The suggested expression of the NRR is as follow:
‘Given period’ (n=): ‘beginning of interval’-‘end of interval’ day NRR
e.g. for January 2000 (n=1,531): 18-24 day NRR = 68.4%
3.6 The 60 to 90 day NRR
60 to 90 day NRR has been a standard for AI organisations to work out breed receipts on a monthly rather than a daily basis. In that way the NRR of all the females bred in January is calculated at the end of March. The females bred on January first will have about 90 days in which to return. Those bred during the last days of January, however, would have had only about 60 days.
Pay careful attention that the common phrases “18-24 day NRR” and “60 to 90 day NRR” get things confused. “18-24 day” addresses to the two limits of the interval, whereas “60 to 90 day” only addresses to the end of the interval which has the particularity to vary according to the month’s day of the insemination.
The same information than for the previous NRR should be indicated.
The suggested expression of the NRR is as follow:
‘Given period’ (n=): ‘beginning of interval’-‘range of the end of interval’ day NRR
e.g. For the year 1999 (n=15,332): 3-60 to 90 day NRR = 58.9%
