Genetic Improvement in Deer
P Gatley, J Chardon
Abstract
The application of conventional genetic improvement principles, and the recent development of several enabling technologies, has created an opportunity to dramatically raise the genetic merit of New Zealand farmed deer by lifting the rate of genetic gain in elite animals and disseminating their genes to commercial herds.
The principles applied in genetic improvement are based on the following formula:
Rate of Genetic Variation x Accuracy x Selection Intensity
Genetic Gain = Generation Interval
The enabling technologies include DNA parentage identification, Breeding Value (BV) calculation, embryo transfer (ET), oestrous synchrony, cervical Artificial Insemination (AI), and fresh semen technology.
Introduction
The dairy farmer-owned Livestock Improvement Corporation has created a subsidiary, Deer Improvement, with the intention of harnessing modern technologies to improve the genetic merit of red deer farmed for venison production.
The principles of genetic improvement
1. Generation Interval
In deer, desired traits such as growth rate and velvet production can be evaluated in the male, obviating the need for progeny testing. In the case of venison growth rate the data is collected within the first year of the life of the animal. Small volumes of semen can be collected from exceptional spikers to advance genetic improvement programmes, and two-year-olds are capable of producing thousands of straws for commercial AI. Breeding from these comparatively young sires enables rapid turnover, shortening the generation interval and therefore increasing the rate of genetic gain. By comparison, a dairy sire is five years old by the time he is proven via progeny testing.
Likewise, proven females can be accessed at 16 months in deer compared to 24 months (part-lactation proof) or 36 months (full-lactation proof) in dairy.
2. Selection Intensity
Genetic gain is enhanced when the performance of a large number of animals is measured and few are chosen to breed from. Given that practical farming constraints place severe limits on the selection pressure that can be applied to the female line (as a large proportion are required as replacements), it is essential that stags be selected from large contemporary groups with a broad genetic base. For this reason any livestock industry will benefit from a central database providing objective evaluations and transparency which enables the truly elite genes to be identified by all participants. This is why Deer Improvement joined the Invermay Sire Reference scheme at the earliest opportunity and why the company strongly supports the establishment of an industry-wide database.
Deer Improvement is carrying out ET with elite hinds, and the generation of multiple offspring from top sire/dam combinations further enhances selection intensity. Outstanding females from ET and contract AI programmes will be brought together to form a nucleus herd. Numbers will be increased to a critical mass in order to provide optimal selection intensity, as well as protection from inbreeding.
The operation of a commercial AI service in deer will also increase selection intensity as elite sires are able to carry out 5,000-10,000 inseminations annually compared to 50-100 using natural mating.
3. Accuracy
The genetic gain equation assumes all data is accurate. In reality a major effort and investment is required to ensure this is the case.
The GIGO (garbage in, garbage out) principle applies strongly in genetic improvement programmes. For this reason Deer Improvement DNA profiles every stag, hind and calf in its programme, farm staff receive training in performance recording, and specialist staff oversee the establishment of systems such as the electronic identification (EID) of animals and the direct linkage between electronic scales and the database. Use of AI for progeny testing confers an additional advantage in that all matings can take place on the same day, minimising error associated with comparing animals born as a result of matings weeks apart. All progeny are managed in the same mobs from conception until the progeny test is complete.
Accuracy of evaluation can be further enhanced by increasing the volume or frequency of measurements. For example, the establishment and growth of a central database will dramatically lift the volume of data, and frequent performance measures such as weight recording will also contribute. This is why Deer Improvement takes seven weights from pre-weaning to the yearling stage.
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4. Genetic Variation
The variability in a trait as a result of genetics is a crucial factor in determining the rate of gain that can be achieved. For example, we know genetics is responsible for a large range of growth rate in red deer, so we know that rapid improvements in growth rate are achievable.
Technologies
1. DNA parentage testing
DNA analysis is now available to confirm relatedness between individual animals. DNA parentage testing is especially useful in deer due to factors such as the tendency of hinds to calve down in cover and hide their progeny, and the negative impact on fawn survival rates due to interference for purposes such as ear tagging.
2. Breeding Values and Economic Indices
Breeding Value (BV) calculations distil genetic influences from the impacts of management and environment. They utilise various sources of information such as performance data for the individual itself but also data pertaining to known relatives. This raw data is processed using sophisticated computer programmes that solve complex simultaneous equations to calculate the genetic contribution to a biological trait.
BVs for individual traits can be assigned economic weights and combined to form Breeding Indices for the purpose of measuring the commercial value of genes transmitted. A good example of this is the Breeding Worth (BW) index used in the dairy industry. This combines economic weights for the following BVs:
· Milkfat
· Protein
· Milk volume
· Liveweight
· Fertility
· Survival
· Somatic Cell Count
The units of the index are dollars and they represent net profit per annum after accounting for feed. For example, 600 cows at the upper decile (currently BW$114) would generate $26,400 more net profit per annum than 600 cows with an index at the lower decile (BW$70) farmed under identical conditions. This is why the herd BW has a major impact on herd value.
An economic index for venison production systems in deer could possibly include BVs relating to:
· Growth rate pre-weaning (male and female)
· Growth rate post-weaning (male and female)
· Six- or twelve-month weight
· Mature hind weight
· Temperament
· Fertility
Mature hind weight could be assigned a negative value just as cow liveweight is in dairy due to the energy requirement of maintenance. Such adjustments ensure the focus stays on efficient production (profit) rather than absolute production.
Deer Improvement is already working with AgResearch Invermay to identify the genetic component of Temperament with the intention of creating a Temperament BV.
3. Embryo Transfer
Some sire/dam combinations are so valuable that breeders will want to achieve multiple offspring from the pairing. There is also advantage to be gained by increase the probability of male offspring due to the fact that a stag has much greater capacity than a hind to disseminate its genes across a population. ET enables several embryos to be implanted in recipient hinds and this dramatically improves efficiency in capturing value from specific pairings. MOET (Multiple Ovulation and Embryo Transfer) has been used in deer since the mid-1980s and even greater benefits are expected from the development of IVP (In Vitro Production of embryos) which enables larger numbers of offspring to be generated from a donor (Berg et al, 2004).
ET effectively shortens the generation interval as a sire/dam combination can produce multiple offspring in one season. Natural mating or AI would take years to generate the same numbers.
4. Oestrous Synchrony
Hinds in oestrous do not show marked behavioural changes so identification of cycling animals is problematic. Even if hinds could be easily detected on heat it would not be efficient to provide an AI service on a daily basis given the geographic location of deer farms and the difficulty of repeatedly mustering and drafting the animals. The solution is to synchonise hinds using a CIDR (Controlled Internal Drug Release) device. This tool was originally developed in a three-way partnership by Ruakura, Carter Holt Plastics and Livestock Improvement for the purpose of synchronising dairy heifers on run-off properties in order to facilitate faster genetic gain (young stock generally have the highest genetic merit).
The CIDR B (bovine) and the smaller CIDR G (sheep and goat) are both used in deer as off-label recommendations depending on the size of the hinds. The most common programme for average red hinds involves two CIDR G devices inserted simultaneously.
Lack of clarity regarding the mode of use, the unsuitability of the applicators, and limited knowledge regarding the timing window for AI post-CIDR removal undermine confidence in the programme. For this reason Deer Improvement is currently co-ordinating an effort involving Pfizer and AgResearch Invermay to enable the production and registration of a dedicated “CIDR D” for deer. Obvious benefits would include the provision of a suitable applicator, the need to insert only one (suitably-sized) device per animal, and the potential to have greater flexibility in timing of CIDR removal and AI.
5. Cervical AI
Artificial Insemination has been carried out in deer since the 1970s and was originally based on laproscopic interventions which were relatively expensive and inefficient. Cervical AI was tried at least as far back as 1990 but early attempts failed to provide conception rates in line with the laproscopic approach (Bowen, 1990). As recently as 1997 the laproscopic technique was still “the method of choice” for red deer (Hunter, 1997).
More recently cervical AI has become the norm and has proven to be highly successful (Rhodes, 2003). Experienced bovine Technicians with small hands are found capable of delivering consistent results in their first season on deer, and with basic handling facilities hinds can be processed at around 20 per hour. In-calf rates range mostly between 60-80%, significantly higher than the level achieved in either beef or dairy cattle. This represents a comparative advantage to deer in terms of disseminating elite genes throughout the wider population.
6. Semen collection
Electro ejaculation has been used in the deer industry for many years but the equipment, technique and individual operator expertise has advanced considerably.
Operators such as veterinary surgeon Mike Bringans who is contracted to Deer Improvement are able to quickly and efficiently collect commercial quantities of high quality semen from stags without the use of drugs (Bringans, 2004).
Close examination of stag behaviour on a frequent collection regime has raised no animal welfare issues and the stags show no aversion to regular mustering into the facility during the collection season.
7. Fresh semen technology
Livestock Improvement is the world leader in the field of fresh semen technology. Over 90% of its 3m+ annual bovine inseminations are carried out using the exclusive Long Last LiquidTM formulation which enables a ten-fold increase in the number of straws generated from each collect. Conception rates are not compromised with inseminations carried out up to three days post-collection.
The use of a truly elite stag to mate only 50-100 hinds in one herd represents an enormous opportunity cost in terms of genetic wastage. A stag used for AI with conventional deep frozen semen may produce 100-200 straws per collect, and perhaps 2,000-3,000 for the season which runs for about four months. Fresh semen usage during the AI season could enable 10,000 or more inseminations to be generated from a single mature stag on an annual basis.
The combination of liquid semen and a nationwide network of Technicians have placed the genes of top stags within reach of any commercial herd.
Deer Improvement’s genetic improvement programme
Deer Improvement’s breeding goal is the genetic potential to achieve 100kg liveweight by winter, a concept developed by AgReseach Invermay. The genetic improvement programme required to achieve this was designed by Livestock Improvement geneticists in consultation with AgResearch Invermay.
The plan involves the establishment of a nucleus herd of a size calculated to provide optimal selection intensity as well as protection from the negative effects of inbreeding.
In Year One (2004) twenty stags were purchased at auction from seven studs with breeding programmes focussed on growth rate. In the absence of any across-herd sire reference data individual animals were identified by analysis of within-herd data. A concerted effort was made to sample most of the promising bloodlines including representatives of Hungarian, Romanian, Yugoslavian, and German strains.
The only way to directly compare the genetic merit of these mature stags was to progeny test. AI was carried out in March 2004 with each stag contributing around 50 matings randomised across hinds in four contracted herds. The sires, dams and progeny were all DNA tested to establish pedigrees. All calves carry EID and seven weighings are carried out from pre-weaning to the yearling stage.
The first BVs were calculated at weaning in February 2005 and showed a range of 11.8kg. The top ranked sire was Carl, a mature stag from the Doncaster stud which had participated in the Invermay Sire Referencing Scheme. The first results from the Invermay programme became available in December 2004 and confirmed Carl as an outstanding individual.
Deer Improvement continues to source promising genetics with ongoing purchases of stags and hinds, and is making a considerable investment in AI and ET on elite hinds with contracts to purchase offspring.
The stag team used to provide the commercial AI service in 2004 was a representative sample of the original purchases, each of them being a top performer in their stud of origin. In the 2005 mating season Deer Improvement supplied a selected group of these animals with a considerably higher team average genetic merit. In 2006 the availability of Yearling Weight BVs on the first crop, and Weaning Weight BVs on more recent acquisitions, will enable the team average to be further increased.
Capturing value in commercial deer herds
1. Intrinsic benefits of AI
There are potential benefits from the use of AI, irrespective of the genetic merit of the stags. Some farmers are happy to reduce the number of stags required for mating, and many will appreciate the reduced risk of disease transmission as AI stags are routinely disease tested, and AI further diminishes the risk of disease transmission. Sire stags bred on the property enable the convenience of natural mating in extensively farmed operations while limiting the potential for the introduction of disease.
2. Value of replacement hinds, sire stags, and terminal progeny
The benefits of genetic gain can accrue through the retention of replacement females as well as sire stags. There is clearly some additional benefit from the improved growth rates of animals slaughtered in their first year but this is not the focus of the programme.
An indication of the gains that can be made using currently available AI stags is provided by the BVs established through progeny testing. At weaning in February we know that Carl is twelve kilos (11.8 to be precise) better than Midnight. Midnight is a pure Eastern ranked highly in his stud of origin. It would be reasonable to assume that Midnight is more highly ranked for growth rate than the typical commercial hind carrying genes from feral ancestors and perhaps some English bloodlines selected for antler traits. If we assume that Midnight is say 6 kilos better than the average hind, it follows that Carl is (6+12) 18 kilos ahead. That is, by lifting the genetic merit of commercial hinds and stags to the level of Carl, a farmer could lift weaning weights in late February by 18 kilos.
While this is happening the Deer Improvement programme will be capitalising on the availability of objective evaluations and using all available technologies to make further gains. By using the top ranked stags to generate replacement hinds and sire stags farmers can expect to achieve the same rate of gain in their own animals (Garrick, 1997). The same situation is seen in dairy where the merit of commercial dairy cows is improved at the same rate as the elite sires, albeit with a lag in absolute values at any given time.
3. Use of AI in extensive deer farming
Given the extensive nature of many farming operations focussed on venison production, use of AI over all animals is not practical. However selection of a group of high performing females can provide a small nucleus herd to supply both replacement females and sire stags after being mated to proven elite sire stags through AI.
Running a nucleus group of hinds simply involves retention of performance data such as weaning and yearling weights on all animals in the contemporary group. Combined with pedigree data derived from DNA testing, this performance data can be used to generate BVs. Future mating with proven sires of high reliability then provides the farmer with excellent data to make ongoing selection and breeding decisions.
All replacement females can be generated by mating only a small proportion of the herd to AI because of the low replacement rates and high conception rates that apply in deer relative to cattle (Archer, 2004).
4. BYO (breed your own) sire stags
There are several reasons why farmers may choose to breed their sire stags on their own property.
· The genetic merit of a stag, sired by a truly elite proven stag, and out of a top hind, and having proved himself exceptional in direct comparison with his contemporary group, can be expected to exceed the merit of a typical stag sold at auction. If the herd, or nucleus within a herd, is recorded, the genetic merit of each individual will be known, so the farmer will know exactly what level of genetic merit is being achieved.
· It enables farmers to avoid the need to introduce any new animals into their herd. With genetics brought in via AI the risk of disease transmission is diminished.
· It may enable farmers to source stags representing bloodlines not otherwise available on the market.
· The cost of breeding sire stags is not prohibitive.
5. Red deer AI in a hybrid terminal system
Farmers who use Wapiti terminal sires have been advised to avoid introgression of Elk genes into their maternal line (Asher et al, 2005). This means they need to source replacement red hinds and it is recommended that they generate these using top AI sires to ensure ongoing improvements in genetic merit.
This approach can also create options for the future when the farmer may choose to use high genetic merit red terminal sires and achieve a growth rate similar to that of the hybrids.
6. Capital value
As the market comes to recognise the value of genetic merit, herds with a history of consistently infusing elite proven genetics can expect to command a premium.
Conclusions
Every business must continually seek incremental productivity improvements, and every livestock industry must capitalise on the potential for genetic gain.
The genetic merit of the typical commercial red deer hind has not been accurately measured but there is every reason to expect that it lags well behind the best AI sire stags. This is especially true in respect of venison growth rate as most hinds are not far removed from their feral heritage and introduced genes have been dominated by English bloodlines selected for velvet production.
The genetic merit of progeny will reflect the parent average so proportionately large gains can be made in the first few generations.
Continued use of top stags will result in commercial hinds achieving genetic gain at the same rate as the elite stags graduating from an intensive programme making use of all available technology. The same situation is seen in dairy where the average New Zealand dairy cow in 2005 has a Breeding Worth higher than the great sires of the past (President, Prefect, Shamrock, Dante, and so on). After decades of selection pressure the rate of gain in dairy is undiminished. A similar situation is expected in red deer growth rates.
Because genetic gain is permanent, the incremental annual gains have a cumulative impact that has a major impact on farm profitability.
The genetic potential to achieve killable weight before winter has already been achieved in some animals. Further gains are there to be made and the genetics are now available to any commercial deer farmer.
The use of Artificial Insemination is essential if rates of genetic gain are to be optimised. This is because of the need to establish strong across-herd genetic links in order to identify outstanding sires, and because genetic improvement in commercial herds depends on widespread distribution of elite genes.
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