5 Managing your bull semen

Transcription

1 5 Managing your bull semen To avoid the waste of holding excess stocks, you should make an accurate estimate of your semen needs based on current replacement rates and herd fertility. A disciplined approach to semen-buying is equally vital to ensure you only purchase semen from bulls that meet your specific herd improvement needs. Do not be swayed by pushy salesmen who have the next hot bull. Discipline is also important if you are to secure the best prices by shopping around and negotiation, while maintaining sufficient flexibility to adjust your semen order in the light of changing circumstances. What s in this section? Establishing your annual semen needs Achieving the best value-for-money in your semen buying Maximising your semen value through good storage and use. In addition, good practice in your semen storage and handling will minimise unnecessary semen wastage for the greatest overall value. Contents Summary Page 5:2 Semen requirements Page 5:3 Sexed dairy semen Page 5:6 Mixed beef semen Page 5:8 Semen buying Page 5:9 Semen handling Page 5:12 Improving through breeding The Breeding+ Five-step Improvement Plan provides at-a-glance guidelines to raising your herd profitability through breeding. 5:1 5 Managing your bull semen

2 A summary of the section Accurate estimates of annual semen requirements are essential for cost-effective breeding management With a typical 25% replacement rate and 60% heifer and 45% cow pregnancy rates to first service, around 125 straws of dairy semen are likely to be needed each year in a 100-cow herd Sexed dairy semen can be valuable in allowing replacements to be bred from fewer, better cows and heifers, providing pregnancy rates are similar to conventional semen Mixed beef semen may be a valuable way of improving conception rates in cows not good enough for replacement breeding or in problem-breeding individuals that might otherwise be lost from the herd Buying only the amount of semen really needed from sires that meet the herd s particular improvement needs is the key to success Dabbling with the latest hot bulls or special offers only ever represents good value for money if the sires in question fit the herd s identified requirements Shopping around by getting quotes for all short-listed sires from all their suppliers invariably leads to the best value-for-money As large orders attract bigger discounts, ordering a herd s total requirements, including beef semen, at one time will ensure the best prices As a general rule, holding no more than four months semen needs at any time minimises costs while maximising order flexibility The correct handling of semen by everyone involved is vital to minimise the damage that can easily waste stocks and/or compromise pregnancy rates Both DIY and technician AI performance should be constantly reviewed through honest appraisal and an open discussion of results. See also... Section 2: Section 3: Section 4: Section 6: Section 10: Assessing the tools Planning your approach Selecting your sires Breeding your cows and heifers Worksheet 6: Assessing annual semen needs The Pd+ Farm Improvement Programme provides practical advice on improving fertility through better recording and management. 5:2 Improving through breeding

3 Semen requirements Although semen can be stored successfully for many years, carrying significant semen stocks from one breeding season to another is a waste for most herds because: Replacement rates may need to be increased to give sufficient potential for culling on performance where health or fertility problems mean especially high levels of enforced culling. Excess semen in the tank is dead money Older semen frequently remains unused Herd improvements since its purchase can mean older semen compromises genetic progress. Accurate estimates of annual semen needs are essential to cost-effective breeding management. The amount of semen needed each year fundamentally depends upon: The herd replacement rate The pregnancy rate Surplus stock sale requirements, if any. Calculating annual semen needs Annual semen needs primarily depends on the herd replacement rate. This, in turn, depends on the enforced culling rate (Section 3) and the speed of improvement required. In the absence of serious health or fertility problems, replacing 20-25% of the herd each year will enable good progress. Allowing for the normal ratio of bull to heifer calves, means breeding 40-60% of the cows and heifers pure (dairy breeds) to meet the annual 20-30% replacement needs. Assuming equivalent pregnancy rates, this proportion could, of course, be reduced substantially by using sexed semen. The herd pregnancy rate is equally important in determining annual semen need. While cow pregnancy rates to first service commonly now average 40-50%, rates of 60% or more are not uncommon in heifers. Using heifers for replacement breeding is, consequently, a good way of reducing semen needs, as well as maximising genetic gains (Section 6). With a typical 25% replacement rate and 60% heifer and 45% cow pregnancy rates to first service, around 125 straws of dairy semen are likely to be needed each year in a 100-cow herd (Example 5.1). Improving through breeding 5:3

4 Example 5.1: Calculating annual semen need Rate (%) Number A Herd size 100 B Annual replacements* C Cows and heifers available for replacement breeding (A+B) 125 D Heifer to bull calf births 50 E Cows and heifers required for replacement breeding (B x A D) 50 F Extra animals for replacement breeding contingencies (20% of E) G Total animals required for replacement breeding (E + F) 60 H Heifers to be used for replacement breeding (B : 100 x G) 15 I Cows needed for replacement breeding (G-H) 45 J Heifer pregnancy rate 60 K Cow pregnancy rate 45 L Straws of semen required for heifer breeding (H x 100 J) 25 M Straws of semen required for cow breeding (I x 100 K) 100 N Straws of semen required for replacement breeding (L+M) 125 * The annual replacement rate varies greatly and research shows it ranges from 11.5% to 35%, for simplicity 25% is used in this example. Worksheet 6 provides a pro forma for calculating annual semen needs. It is advisable to build a contingency into the semen need calculation to account for the fact that: Some of the replacement breeders will be involuntarily culled before they calve Not all cows earmarked to produce replacements will actually give birth to live calves A 20% semen contingency is considered worthwhile insurance for most all-year round calving herds, although block-calving units which rely on producing the year s replacements from a short breeding season may wish to increase this. The proportion of heifer to bull calves will vary from year to year Some of the heifer calves won t make it into the herd. 5:4 Improving through breeding

5 Simple herd replacement and pregnancy rate calculations can, of course, be used to make less precise but perfectly acceptable estimates of annual semen needs (Table 5.1). Table 5.1 Calculating annual semen need Straws of dairy semen needed per 100 cows, assuming a normal heifer/bull calf ration and allowing 20% for all contingencies. Herd replacement rate Herd pregnancy rate 30% 35% 40% 45% 50% 55% 60% 15% % % % % % Some allowance should be made for any semen carry-over from previous years when calculating annual semen purchasing requirements to avoid an excessive build-up of semen stocks. Herds earning income from breeding stock as well as milk, will rear significantly more heifers than their own replacement needs to provide surplus cows and heifers for sale. This is only worth considering, however, where average sale returns from surplus stock are likely to comfortably exceed heifer rearing costs and a reasonable market can be foreseen for in-milk heifers three to four years on. Decisions on the number of replacements bred to dairy sires is again very farm and business specific. For many herds it is more sensible to maximise calf income from animals not required for replacement breeding by using a beef bull (Section 4). Selling calves frees-up buildings and manpower, as well as reducing associated livestock costs. Improving through breeding 5:5

6 Sexed dairy semen Amongst its well-publicised benefits, sexed dairy semen may help to maximise progress through breeding. Pioneered by a UK breeding company in 1999, sexed semen is now available from a number of AI companies; it involves separation ahead of freezing to produce semen containing 90% female-bearing sperm. There is also now a cheaper version available in the UK which offers 75% female sperm. With the potential to almost double the heifer calf crop from the same number of cows, sexed semen promises to enable: Herd replacements to be bred from only the best cows and heifers More cows to be bred to beef bulls to produce valuable cross-bred calves Fewer unwanted dairy bull calves to be produced Calving difficulties to be reduced by breeding dairy heifers from heifers. The extent to which these benefits are actually realised, of course, depends on the reliability of the sexed semen in commercial practice. Assessing sexed semen Sexed semen was launched commercially in 1999 by a UK breeding company and is now available from most AI companies operating in the UK. Some producers have found sexed semen highly successful and use it routinely to concentrate their replacement breeding on fewer, better cows while maximising the use of a beef bull across the rest of the herd. In contrast, others have found sexed semen far less successful, primarily as a result of disappointing pregnancy rates and have ceased using it. The evidence to date suggests that poor results could be due to: The selective use of sexed semen among higheryielding animals which lose more body condition in early lactation and are prone to lower pregnancy rates (although not a concern in maiden heifers) The reduction in the number of sperm/straw resulting from the sexing process which may not be significant when the insemination process is handled well but leaves less margin for error in semen handling, thawing and insemination A reduction in the longevity of sperm as a result of its processing in particular, the extra time taken from collection to freezing. 5:6 Improving through breeding

7 All the evidence shows that in maiden heifers sexed semen pregnancy rates are close to ordinary semen. Pregnancy rate differences may become more apparent in older and higher-yielding animals. Sexed semen is likely to prove most valuable where: A significant proportion of replacements are to be bred from maiden heifers High levels of fertility are generally achieved through good herd management Semen is thawed, handled and inseminated with sufficient care and attention. Sexed semen is not recommended for use with: Animals receiving fixed-time inseminations following oestrus synchronisation Cows experiencing retained cleansings, mastitis, lameness or other health problems. Sexed semen will, of course, only make a positive contribution to herd improvement if the bulls chosen meet the specific herd improvement priorities (Section 3). Heifers cost the same to rear whether they are good or bad, which should be borne in mind when making any breeding decision. Improving through breeding 5:7

8 Mixed beef semen Mixed semen claims to improve conception rates by exploiting biological differences in the semen of different beef bulls. Because the rate at which inseminated sperm matures varies between bulls, mixing the semen of three bulls with different rates of so-called capacitation may extend the period over which an insemination remains viable from 20 to 34 hours. Assessing mixed semen Mixed semen is claimed to improve conception rates by 6-9%. It sometimes uses semen from three different breeds, simplifying sire recognition. Mixed beef semen may be a valuable way of improving conception rates in cows not good enough for replacement breeding or in problem-breeders that might otherwise be lost from the herd. Double inseminations twelve hours apart with a selected bull are also a useful way of increasing the length of time semen is available for fertilisation. Mixed semen is also available from dairy sires, however, there are obvious issues of sire identification of the resulting calf, this may not be considered an issue in commercial herds but in pedigree herds there will be the associated cost of DNA identification of the parentage. 5:8 Improving through breeding

9 Semen buying Good semen buying can make all the difference to cost-effective herd improvement through breeding. Buying only the amount of semen really needed from sires that meet the herd s particular improvement needs is the key to success. This does, however, require the discipline to accept that all short-listed sires are of roughly equal improvement value. In semen buying, it is also important to appreciate that: Volume is discount Semen should only be invoiced on delivery Semen orders can always be cancelled or changed ahead of delivery. All semen purchases need to meet the defined herd improvement priorities (Section 3). For group mating, 3-4 sires from the original short-list (Section 4) will generally be sufficient to complement each cow with a bull that suits her own particular characteristics Buying semen on the basis of an overall budget or an average price per straw for all breeding needs is a valuable way of building extra flexibility as well as discipline into the process. Dabbling with the latest hot bulls or special offers only ever represents good value-for-money if the sires in question fit the herd s identified requirements. As well as slowing down improvement in the priority areas, special offer bulls can introduce undesirable traits, which may take considerable time and effort to eliminate. Shopping around by getting quotes for all short-listed sires from all their suppliers invariably leads to the best value for money. This avoids rejecting good bulls on semen price alone, allowing suppliers to be challenged to put together packages around bulls of interest within clear budgetary constraints. Including beef or young sire semen in this process often enables packages to include dairy sires which might otherwise have been rejected on individual semen price alone. Working out an average price based on a total budget figure will give scope to include a desired bull that is perceived too expensive as long as he is offset by a cheaper bull. The relative costs of beef and dairy semen mean that, within an annual budget, the fewer cows and heifers required for replacement breeding the more money can be made available for dairy sires. Alternatively, of course, the more potential there is for reducing overall expenditure on semen. Improving through breeding 5:9

10 As large orders attract bigger discounts, ordering a herd s total requirements, including beef semen, at one time will ensure the best prices. Free straws can often represent better deals than blanket percentage discounts, so it is important to evaluate all offers on a cost per straw basis (Example 5.2). Example 5.2: Discount offer evaluations Base price Offer Straws required Total cost Cost/straw 22 20% discount for orders over 20 straws x 150 = % free semen on order x 120 = Purchasing semen with like-minded producers can add useful bulk to orders, attracting greater discounts. Arranging semen delivery Semen-buying groups need to be organised carefully, however, to ensure the sires selected are appropriate for all the herds involved, generally buying semen within buying groups is harder to do than buying feed or fertilizer, for example, as there are so many different herd criteria and so many different companies and sires. The best value-for-money in semenbuying also comes from arranging sensible delivery dates to avoid wasteful stock-holding and give the greatest flexibility to adjust orders in the light of changing bull proofs. For block-calving herds using their annual semen supplies over a relatively short period a single delivery ahead of the breeding season is likely to be most appropriate. Where the calving pattern is more extended, though especially with all-year-round calving scheduling semen deliveries at intervals over the breeding season is generally the best option. Because small volumes can attract high delivery charges, it makes sense to divide the annual order into two or three separate deliveries. 5:10 Improving through breeding

11 As a general rule, holding no more than four months semen needs at any time minimizes costs while maximising order flexibility. Paying for semen Insisting that semen invoices are only raised following delivery preserves the flexibility to revise orders through the breeding season. Re-calculation three times yearly means the proofs of chosen bulls can change markedly over the year especially so where they are of lower reliability (Sections 2 and 4). In addition, selected bulls may be superseded by others with superior proofs. Relative semen pricing can also change. Making all semen orders subject to review and confirmation ahead of each delivery ensures the greatest flexibility to cater for such changes. Most semen suppliers will offer an interest-free payment option over 3 or 6 months on orders over a certain value. This can be extremely useful for cash flow. Payment by standing order further allows the semen cost to be spread more evenly over the year, although the payment date should always be set for maximum convenience, for example, at the end of the month, once the milk cheque has been received. Specifically, it allows: A semen order to be cancelled or substituted for something more suitable if the proof or standing of a bull changes markedly A semen order to be cancelled then placed again at a better rate if the price of a bull s semen is reduced below that originally negotiated. To continue getting the best value-for-money in this way may mean cancelling an order with one supplier and ordering elsewhere. The implications of this on future discounts through the original supplier will obviously need to be taken into account especially where it involves prices negotiated on a large number of straws of which only a few have been taken. Improving through breeding 5:11

12 Semen handling Semen thawing The correct handling of semen by everyone involved is vital to minimise the damage that can easily waste stocks and/or compromise pregnancy rates. The most important considerations in this respect involve: Semen removal from the tank Semen thawing Insemination. Semen removal Time spent removing semen from the liquid nitrogen tank should be kept to a minimum. Temperatures can reach 10 C in the neck of the tank and damage can be caused if the entire canister of semen is raised above the frost line. Straws should be removed with tweezers not fingers. If the correct semen cannot be located within 5 seconds, the canister should be lowered back into the flask again for seconds. To minimise removal time, the location of semen in the tank should be noted before removing the plug. Besides aiding location, a tank inventory on a wall chart or an inventory wheel also provides an ideal means of stock control, with straws marked-off after each withdrawal. Semen should be thawed in a water bath at C for at least 30 seconds, with thermometers calibrated regularly to ensure accuracy. To make this process easier, there are many preset constant water baths on the market but they must be kept topped up with water and they still need checking regularly with a thermometer for accuracy. Thawing in the pocket (or the cow) will reduce the number of viable sperm. Semen straws should be completely dried before use, as water kills semen. Straws should be removed with tweezers not fingers while flicking the straw will remove any trapped nitrogen. The number of straws of semen thawed should not exceed the quantity that can be used within minutes. Different thawing times and handling are recommended by some companies for conventional and sexed semen; please consult the company you buy from for their best practice recommendations. Insemination The insemination gun should be warmed and kept close to the body (under clothing) to avoid coldshocking the semen. Having cut the straw at the crimped end with a straw cutter or sharp scissors, a plastic sheath should be placed over the semen and gun to keep it dry and clean. The semen should be inseminated as soon as possible after thawing and once thawed straws can not be re-frozen. Good inseminators place the semen just through the 5:12 Improving through breeding

13 cervix into the uterus with a margin of error of less than 1cm. Straws should not be split, this reduces the chance of the animal conceiving even though it may be perceived as a cheap option. To consistently achieve this accuracy: Cows should be restrained from sideways movement The cow and inseminator should be at the same floor level There should be no restrictions on inseminator movement, such as adjacent walls The insemination facilities should be under cover, with unobstructed cow entry and exit. Both DIY and technician AI performance should be constantly reviewed through honest appraisal and an open discussion of results. It is unusual for AI semen to be infertile but occasionally problems do arise. Monitoring pregnancy rates to each bull and batch allows any specific problems to be pinpointed, as well as providing good evidence with which to negotiate replacement and compensation. DIY AI is a well-established technique, considered by many to offer significant advantages over traditional technician service. However, the following considerations must be borne in mind: Australian work indicates only a marginal improvement in pregnancy rates as a result of increased flexibility in insemination timing The level of DIY performance on some farms is unacceptable with a pregnancy rate difference of 20% being equivalent of a 1p/litre loss in profit Lack of time, insufficient practice, inadequate support and the absence of comparison with others may all contribute to relatively poor DIY insemination success Training and retraining are critical, especially in smaller units or seasonally-calving herds when there are long periods with little or no insemination practice With an increasing herd size and workload, DIY AI may put too much pressure on staff in some situations and this can be to the detriment of critical heat detection success. Improving through breeding 5:13

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