6 Breeding your cows and heifers

Transcription

1 6 Breeding your cows and heifers 6 Breeding your cows and heifers Regardless of the bulls you use, breeding your herd replacements from your best cows and heifers is essential if you want to achieve the greatest herd improvement through breeding. Heifers have a particularly valuable role to play in replacement breeding. As well as being the highest genetic value animals in the herd, they also tend to have the highest fertility. You will achieve the greatest progress by breeding only your best cows and heifers to sires that best build on their specific strengths and overcome any weaknesses, whether on an individual or group basis. What s in this section? Selecting your cows for replacement breeding Breeding replacements from your heifers Planning your matings for the greatest herd progress. If you wish to make the most rapid overall progress through breeding, embryo transfer offers valuable, if rather costly, opportunities. Contents Summary Page 6:2 Cow selection Page 6:3 Breeding from heifers Page 6:7 Planned mating Page 6:8 Embryo transfer Page 6:12 The Breeding+ Five-step Improvement Plan provides at-a-glance guidelines to raising you herd profitability through breeding. Improving through breeding 6:1

2 A summary of the section Selecting the best cows and heifers for replacement breeding is as important for individual herds as selecting the best bulls With a typical 25% replacement rate and normal 50% bull calves, around 60 cows and heifers are likely to be needed for replacement breeding each year in a 100- cow herd Every herd has some animals that should not be used for breeding replacements The selection process should define two clear groups of animals within the herd ahead of the breeding season: - Cows to be bred for replacements to a selected dairy sire - Cows to be bred to a beef bull to maximize surplus calf income As many heifers as possible should be used for replacement breeding by AI Where the management system makes it difficult to breed heifers by AI, most herds would be better advised to use a beef bull, rather than risk a dairy stock bull of unknown merit compromising herd improvement Mating the selected cows and heifers to the chosen bulls that best build on their specific strengths, while overcoming any weaknesses, is the final crucial step in maximising progress through breeding To minimise insemination errors, it is always advisable to maintain a clear list of cows and heifers matched to service sires in a prominent place where it can be used as a cross-check at service time Embryo transfer remains too costly for all but breeders herds with a ready market for embryos and surplus stock from particularly valuable cow families. See also... Section 2: Section 3: Section 4: Section 5: Section 7: Section 10: Assessing the tools Planning your approach Selecting your sires Managing your bull semen Making the most of specialist strategies Worksheet 6: Assessing annual semen need Worksheet 7: Replacement breeding cow selection Worksheet 8: Group mating assessment Worksheet 9: Service sire listing 6:2 Improving through breeding

3 Cow selection The greatest improvement in any breed will always be achieved by ensuring the best animals contribute the largest number of offspring to the next generation. This relatively small contribution reflects the: Lower reliability of cow evaluations compared to bulls Lower selection intensity among cows, as a relatively large proportion of animals are needed to breed replacements in most herds. At a breed level, four distinct selection pathways are available for improvement: Selecting bulls to breed bulls Selecting cows to breed bulls Selecting bulls to breed cows Selecting cows to breed cows. Genetic studies have established the relative contribution of these pathways to overall breed improvement (Table 6.1). Table 6.1: Selection pathways and their importance in genetic improvement Pathway Contribution to breed Bulls to breed bulls 41% Cows to breed bulls 29% Bulls to breed cows 27% Cows to breed cows 3% Source: The Impact of Sire Selection in Genetic Improvement: Canadian Dairy Network The extent to which AI puts the onus on a relatively small number of bulls in dairy breeding makes the selection of bull parents by far the most important contributor to breed genetic gain. Despite this national position, on an individual herd basis, selecting the best cows and heifers for replacement breeding is as important as selecting the best bulls. Establishing replacement breeding numbers The lowest possible enforced culling rate is vital for the greatest possible breeding progress (Section 3). Specifically, it: Increases the number of the cows and heifers available as replacement breeders Reduces the number of cows and heifers needed for replacement breeding Allows only the best cows and heifers to be selected for replacement breeding Enables a greater proportion of cows to be culled for performance each year Can alter farm incomes if these rely specifically on surplus stock sales. Of the 30% of national genetic improvement progress that is in the hands of individual producers, only 3% has been calculated to result from the selection of cows and heifers for herd replacement breeding. Improving through breeding 6:3

4 Annual replacement rates may need to be higher to give sufficient potential for culling on performance where health or fertility problems mean high levels of enforced culling. The number of cows and heifers required for replacement breeding also depends on: The number of replacement breeders involuntarily culled before they calve The number of replacement breeders giving birth to live calves The proportion of heifer to bull calves The level of heifer calf losses during rearing If expansion is planned, will the extra animals be home-reared or purchased. If purchased then consider the potential health issues. With a typical 25% replacement rate and normal 50% bull calves, around 60 cows and heifers are likely to be needed for replacement breeding each year in a 100-cow herd (Section 5). Selecting cows for replacement breeding For block-calving herds where all the replacements have to be bred within a short period, selection for replacement breeding is likely to be based on a cow s ability to conceive early in the breeding season more than anything else. The requirement to maintain a tight calving pattern means that animals not seen bulling or not holding to service early in the breeding season tend to be put to a beef bull or culled. Cow selection for replacement breeding can be more robust in allyear-round calving herds. In most cases, the relatively large proportion of the herd needed to breed replacements makes it easier to start by selecting out those animals that will not be used. Every herd has some animals that should not be used for breeding replacements. Worksheet 6 provides a pro forma for calculating annual replacement breeding numbers. Sexed semen (Section 5) and embryo transfer both offer opportunities for increasing the selection intensity placed on cows and heifers for replacement breeding by reducing the numbers needed. The most obvious candidates are: Animals particularly prone to mastitis or lameness High cell count individuals Cows with temperament problems Slow milkers Difficult breeders Previous Caesarean section animals Other cows with health or disease problems, such as Johnes carriers. 6:4 Improving through breeding

5 Having removed these animals from consideration, the replacement breeders are best selected from: Production records Type records Genetic indexes. In the absence of individual production or type records, selection for replacement breeding will have to be undertaken on the basis of subjective assessments. A simple assessment system gives more structure to the selection process (Example 6.1). Example 6.1: Simple cow assessment for replacement breeding Cow Above average Production Legs and feet Udders General health Below average Above average Below average Above average Below average Above Average Below average Worksheet 7 provides a pro forma for simple cow selection for replacement breeding. A far more objective selection of cows is possible where individual production and/or type records are available, allowing animals to be ranked in order of the specific improvement priorities identified (Section 3). For example, many milk recording computer programmes will now rank the herd for you in terms of milk production ( ) per day of life which can be an initial screening process for selecting cows to breed from. Genetic indexes for production and fitness provide a better basis for cow selection than milk records as they indicate the proportion of the observed performance that is due to genetics and likely to be transmitted to the next generation as distinct from that brought about by feeding and management (Section 2). Genetic indexes are available to all milk-recorded herds through DairyCo Breeding+ in the form of Herd Genetic Reports (Section 3). In general high yielding cows tend to be those with high production indexes but by combining this with fitness traits, the most profitable animals to breed from as indicated by the cow s PLI may be very different. When selecting cows for replacement breeding, a trade-off may need to be made between production, type and health strengths. Improving through breeding 6:5

6 While the balance of this trade-off will depend on the specific herd improvement priorities, it is important to appreciate that: It is best to avoid breeding from cows that are difficult to manage in your system, due to either health or fertility related problems In general, good udders, legs and feet together with the ability to get back in-calf determine herd longevity Particularly high-producing animals can be forgiven some type faults, especially if they have already survived for longer than the average herd life Particularly desirable traits like high fat percentages are always worth preserving. The cow selection process should define two clear groups within the herd ahead of the breeding season: Cows to be bred for replacements to a selected dairy sire Cows to be bred to a beef bull to maximize surplus calf income. 6:6 Improving through breeding

7 Breeding from heifers As many heifers as possible should be used for replacement breeding by AI because they: Generally carry superior genetics to their older herd mates Tend to be some of the most fertile animals in the herd Reduce the number of cows required to breed replacements, allowing an increased intensity of selection among them. The maximum use of heifers for replacement breeding is especially valuable in block-calving herds, because it allows for greater cow selection opportunities. As a general rule, only heifers bred from poor quality dams by mistake or showing severe type faults at an early age should be rejected for replacement breeding. Oestrus synchronisation can be a particularly valuable management tool for breeding heifers purely by AI, especially in block-calving herds. Avoiding calving difficulties Calving difficulties are always a concern in breeding from heifers. Direct calving ease is primarily associated with the size of the calf but bulls can also affect the calving experience of their daughters later in life, (maternal calving ease) (Section 3). Younger heifers tend to be easier calving than older ones due to their greater elasticity and the fact that they have had less chance to lay down internal fat. As a general rule, avoiding calving difficulties with heifers is far more about management than genetics. Providing heifers are not allowed to get over-fit at calving, averagely easy calving bulls are unlikely to cause problems in most cases. Where the management system makes it difficult to breed heifers by AI, most herds would be better advised to use a beef bull, rather than risk a dairy stock bull of unknown merit compromising improvement (Section 7). The Pd+ Farm Improvement Programme provides practical advice on improving fertility through better heifer management. Improving through breeding 6:7

8 Planned mating Organising individual mating Mating the selected cows and heifers to the chosen bulls that best build on their specific strengths, while overcoming any weaknesses, is the final crucial step in maximising progress through breeding. The way in which this is achieved in practice depends on the mating policy adopted herd, individual or group (Section 4). Organising herd mating Herd mating is the simplest policy to organise in practice. As all cows and heifers are bred to one or two bulls each year, there is no need to evaluate individual cows for specific strengths and weaknesses. In addition to being far easier to manage, this policy also minimises the risk of errors in semen identification. Compared to other breeding approaches, however, it maximizes the damage done to the herd if a bull proves unsuitable for one reason or another (Section 4), making the decision on the sires even more crucial. Because of its complexity, individual mating either across the whole herd or with particularly valuable cow families may require computer mating programmes to match bulls to cows (Section 4). Developed as aids to corrective mating for type in the late 1980s, computer mating programmes come in a variety of forms with varying degrees of independence and value. When considering mating programmes, it is important to appreciate that: Not all mating programmes are the same Some commercial companies offer mating programmes primarily as semen selling tools Some programmes do not include all bulls from all sources Some programmes do not include production as well as type information Some programmes use cow and heifer sire information instead of actual linear scores Even the best programmes need a good operator to ensure the best results. The best mating programmes: Involve an experienced operator evaluating cows and heifers on-farm for all linear traits Include up-to-date proof information from all available bulls from all sources Provide lists of proposed mating options for each cow and heifer Take full account of in-breeding levels Allow recessive genetic defects like CVM and BLAD (Section 2) to be excluded Are run on-farm to allow personalised development with herd managers. 6:8 Improving through breeding

9 For the most accurate results, it is vital that all cows are scored for their own individual type pattern across all the linear traits. Pedigree matings, based on evaluations of cows sires rather than the individuals themselves, fail to account for any strengths and weaknesses inherited from the dam side. Pedigree mating may be suitable for heifers where some traits ie udders, cannot yet be measured but even here scored information on the dam should be used, if available. Programmes that produce corrective matings only on the basis of one or two specific faults in each individual are, in most cases, far less thorough than they need to be. For the best results with computer mating programmes: Choose a system that meets the best programme criteria Insist the programme is run on farm, avoiding systems where records are taken away and results returned Be actively involved in the process Ensure that all the bulls of interest are included and the programme forced to use semen still in the tank Make sure the results are fully explained in understandable terms. A full assessment of each cow and heifer for all linear traits may be time-consuming but each individual only needs to be scored and entered into the computer once to allow the program to be run each breeding season. However, it will be useful to analyse all individuals with each lactation they milk, thus identifying those that have matured and developed with age, as cows can change markedly from calving as a heifer to a mature fourth calf cow. Improving through breeding 6:9

10 Organising group mating Successful group mating, breeding replacements from a small team of 3-4 proven sires each season, requires a broad appraisal of the herd to identify the most important improvement priorities (Section 3). It also requires the individual cows and heifers to be used for replacement breeding to be sorted into groups for mating to the sires that best suit their characteristics. Cows are best grouped according to their most pronounced weaknesses. Individual milk and type records provide the most reliable basis for grouping cows. Modern farm computer and internet-based recording systems allow this grouping to be done automatically with minimal time and effort. They further enable grouping for the particular production and type traits identified as herd improvement priorities (Section 3) and for which specific improver sires have been selected (Section 4). Worksheet 8 provides a pro forma for the simple assessment of cows for group mating. Once the cows have been grouped according to their main weaknesses at whatever level of detail the herd records allow they can be matched to selected sires in the annual bull team with complementary strengths in the same traits. Heifers are best allocated to mating groups initially on the basis of sire calving ease and then to complement any weaknesses established through visual assessment. To minimise insemination errors, it is always advisable to maintain a clear list of cows and heifers matched to service sires in a prominent place where it can be referred to as a crosscheck at service time (Example 6.3). In the absence of individual records, a simple assessment system structured around the most important general herd improvement priorities established in the initial planning stage (Section 3) provides a reasonable basis for grouping (Example 6.2). Example 6.2: Simple cows assessment for group mating Main weakness Cow Feet and General Production Udders legs health :10 Improving through breeding

11 Example 6.3: Service sire listing for group mating Animals to be mated Service sires A B C Key strengths Fat % body depth locomotion 101 Milk yield calving ease locomotion Milk yield calving ease locomotion Worksheet 9 provides a pro forma for individual herd service sire listing. Improving through breeding 6:11

12 Embryo transfer The reliability of procedures for super-ovulation and embryo recovery, freezing and implantation has improved significantly over the past decade increasing the feasibility of Embryo Transfer for individual herds. However, in reality Embryo Transfer remains too costly for all but breeders herds with a ready market for embryos and surplus stock from particularly valuable cow families. Assessing embryo transfer value Multiple ovulation and embryo transfer (MOET) is a useful way of increasing the selection intensity on the female side, just as AI does on the male side. By increasing the number of offspring bred from the herd s best cows the number of individuals required to breed replacements can be reduced and the rate of genetic improvement increased. Alternatively, embryos can be purchased from superior cow families in other herds to give a performance lift, providing the feeding and management is sufficient to match the genetics. Buying-in embryos is generally only cost-effective if the family has a particular commercial worth that can be further exploited by the sale of embryos, bulls and family members. Buying-in embryos has the advantage of enabling closed herds to retain a high health status, while introducing new and different bloodlines, which is becoming more important in today s herds which face so many herd health challenges. This protocol would certainly be advocated by many farm vets as the safest way to introduce new blood into the herd. Beef embryos can further be implanted into otherwise very valuable individuals who have failed to hold to several services as a way of maintaining them in the herd. For most herds the cost of the Embryo Transfer is likely to far outweigh the benefit from any improved rate of genetic gain. 6:12 Improving through breeding

13 Managing embryo transfer Even in the best herds, where Embryo Transfer is used as routine, results can be variable. Some cows do not respond to super-ovulation, while others fail to produce viable embryos. There is also a chance that the procedure will upset the cows natural fertility. Under these circumstances, attention to detail in the management of both donor and recipient cows is of paramount importance. Guidance provided by Embryo Transfer specialists in the preparation of donors and recipients and the treatment of recipients after transfer needs to be followed religiously if results are not to be disappointing. Improvements in freezing have provided more flexibility, allowing embryos collected in excess of available recipients to be stored for future use. In addition, sexing technology enables male embryos to be discarded to maximise replacement heifer production. In general, sexed semen is not recommended for use with embryo transfer. Embryo transfer costs almost invariably need to be offset by producing embryos for sale so the procedure is best confined to highly marketable combinations of cow family and bull. Improving through breeding 6:13

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