10 Managing heifer rearing

Transcription

1 10 Managing heifer rearing Objective: To rear heifers to enter the herd at the correct weight and age for the best production and fertility performance. Challenge: Establish clear targets for your heifer rearing and monitor performance closely over the rearing period Ensure your heifers are served effectively and introduced into the milking herd carefully. Target Calve heifers at two years of age with optimum fertility. Fertile heifers The economic value of rearing heifers to calve into the herd at two rather than the traditional three years of age has been well established. For Holstein-Friesian heifers weighing kg post-calving this requires challenging but perfectly achievable average liveweight gains of over 0.7kg/ day from birth to calving. Other breeds with lower mature body weights require lower rates of daily gain. What s in this section? Setting appropriate rearing targets for two-year calving Monitoring growth rates and body condition Managing the first service and herd entry. Contents Action plan Page 10:3 Rearing costs Page 10:4 Growth targets Page 10:6 Rearing practice Page 10:9 Service options Page 10:14 Herd introduction Page 10:15 10 Managing heifer rearing The way heifers are reared and managed to meet the two-year calving target and then introduced into the milking herd is clearly important in maximising fertility as well as production capacity. 10:1

2 A summary of the section Because heifer rearing can be a significant drain on resources, each herd needs to examine its current replacement policy and plan realistic alternatives carefully for best overall value Heifer weight rather than age determines when puberty occurs and oestrus cycling begins The key to successful heifer rearing for twoyear calving is to maximise weight gains without creating over-fat animals Frame size assessed by height at the withers is perhaps the most valuable measure of heifer growth Heifer growth rates should be planned and monitored throughout the rearing period to achieve the required targets Accelerated calf growth systems, feeding as high a level of high protein milk replacer as calves can safely utilise, have been shown to give much heavier heifers at weaning and better development of udder secretory tissue Where rapid calf growth is required, there may be a value in increasing the protein content in the calf starter concentrates above the 18% which has been shown to be optimal under conventional rearing systems Since fertility increases up to the third oestrus cycle after puberty, heifers need to be grown to reach puberty at least six weeks before the start of serving Growth rates of kg/day are recommended during the first pregnancy to achieve a Condition Score of at calving, the key being to avoid heifers getting over-fat A bull fertility check is an essential investment in view of numerous cases of infertile bulls running with heifers Oestrus manipulation programmes have a valuable role for heifers Introducing heifers into the herd needs careful handling to minimise production and fertility-compromising stresses. See also... Section 6: Section 7: Section 8: Managing heat detection Optimising herd nutrition Addressing herd management 10:2

3 Action plan To calve your heifers at two years of age with optimum fertility. 1. Review your rearing costs Assess your current heifer rearing costs and explore ways of reducing them by changing your herd replacement policy (Page 10:4). 5. Get your heifer feeding right Feed your heifers up to first service and through pregnancy to meet your particular growth targets without becoming too fat (Page 10:11). 2. Set clear rearing targets Establish realistic growth targets for your particular system and assess withers height regularly to monitor performance against them (Page 10:6). 6. Manage natural service Check the fertility of any natural service sire you use on heifers in advance and employ controlled breeding techniques if necessary (Page 10:14). 3. Feed sufficient colostrum Ensure all your heifer calves receive sufficient high quality colostrum soon enough after birth to give them the greatest immunity to infection (Page 10:9). 7. Manage herd introduction Minimise the stress you place on your heifers as they enter the herd, through careful stock management (Page 10:15). 4. Manage your calf rearing Manage your calves on an accelerated growth system to take full advantage of their superior feed conversion efficiency and early growth potential (Page 10:9). 10:3

4 Rearing costs Heifer rearing is a significant cost for most dairy herds. With replacement rates of up to 40% (2.5 lactations average herd life) in some herds it is taking as long to rear a heifer as she eventually spends in the herd. Age at calving and herd culling rate both have a large effect on the number of replacements needed and the cost being carried (Table 10.1). Table 10.1: Total number of heifers needed by a 100- cow herd at different Culling Rates and Ages at First Calving Age at First Calving (months) Herd Culling Rate (%) assuming 5% calf mortality A 100-cow herd with a culling rate of 23%, calving heifers at 24 months of age needs to carry 16 fewer replacements of all ages than one with a culling rate of 26% calving at 28 months. When the amount of milk produced to 33 months of age is taken into account, the net effect on cash flow of rearing a heifer to 33 months is much less for the heifers which calve earlier (Table 10.2). Source: Heifer Rearing in the 21st Century, DairyCo Desktop Review :4

5 Table 10.2: Cost of rearing heifers to calve at different ages (December 2011). Age at calving Cost of rearing to calving* Milk from calving to 30 months ** Margin over all feed and quota *** Net cost to 30 months (months) ( ) (litres) ( ) ( ) * Including variable costs, labour and finance but not machinery or building depreciation, electricity and water. ** at 25 litres/day. *** at 15p/litre margin. Even if an allowance is made for the lower yield for younger-calving heifers early, calving is still advantageous. Research has indicated that heifers calving at 22 to 24 months demonstrate higher subsequent fertility performance, a higher proportion of their lives spent producing milk and lower culling rates than heifers calving at 26 months or older. Equally, if a flying herd policy is followed, the calf sale (plus interest on the money less rearing costs to one week old) can be used to offset the purchase price of a replacement. This approach is very exposed to market price fluctuations for replacement stock and creates significant biosecurity problems. However, it does enable low or moderate genetic merit herds to improve faster than would be possible by breeding-up. Because heifer rearing can be a significant drain on resources, each herd needs to examine its current replacement policy and realistic alternatives carefully for best overall business value. In particular, the costs of the capital tied up in rearing heifers need to be appreciated. Information on assessing the different options for rearing herd replacement can be found on the DairyCo website. Earlier calving, of course, also lowers costs by reducing the number of heifers that have to be carried at any one time (Table 10.1). Alternatives to home rearing include contracting-out heifer rearing or maintaining a flying herd, with all replacements bought as close-to calving or calved heifers. The value of contract rearing will depend on the professionalism of the rearer and the charges levied. 10:5

6 Growth targets Research has established that heifer weight rather than age determines when puberty occurs and oestrus cycling begins. The first signs of heat usually appear when heifers have reached about 40% of their mature body weight. While sexual maturity occurs at just under 12 months of age in well fed heifers, under-feeding and other stress-inducing conditions can delay the onset of cycling. Poor growth rates in heifers below six months of age are shown to reduce or limit their ability to conceive at 15 months of age. Contrary to conventional wisdom, suggesting milk production may be reduced by growing heifers about kg/day, current work suggests no harm will be done by growing Holstein dairy replacements at up to 0.85kg/day. Provided the high rate of growth does not lead to excessive body condition which could do permanent damage persisting to calving there appears to be little need for a period of slow growth prior to puberty. The key to successful heifer rearing for two-year calving is to maximise weight gains without creating over-fat animals. Setting rearing targets Research and experience confirm that heifer growth targets are best set as a percentage of mature weight and size within both breed and herd (Table 10.3). Table 10.3: Heifer growth targets Age/stage Percentage of mature weight (%) 6 months 30 9 months 40 Mating Pre-calving 90 Post-calving 85 Second calving 92 Individual herd mature weights can be checked by weighing third and fourth calvers or by monitoring the weights of cull cows leaving the farm, provided they are around Body Condition Score 3.0. While heifer targets have traditionally been set in terms of liveweight, these can result in small fat animals being served too early. Frame size assessed by height at the withers is perhaps the most valuable measure of heifer growth. 10:6

7 Apart from being a more meaningful indicator of heifer development, height at the withers is very much easier to measure than liveweight. It can be done with a yardstick while animals are in the crush or estimated by walking heifers alongside a wall with the target line clearly marked. The measurement can then easily be taken when heifers are being handled for routine management tasks such as worming, in order to reduce stress and workload. Regular, planned measuring of body weight/frame size at birth and at four-six months of age means that time can be allowed for any correctional nutrition needed. It may be useful to compare measurements against those of previous years to highlight any important differences. Veterinary or nutritionist advice should be sought if growth targets at six months of age are not being met. Around 75% of frame growth typically occurs pre-puberty, with growth levelling off as animals approach two years of age (Figure 10.1). Figure 10.1: Typical Dairy Heifer Frame Growth Curve Withers height Puberty Age (months) Source: Heifer Rearing in the 21st Century, DairyCo Desktop Review Weight-for-age and frame growth curves can be used to set detailed rearing targets for the main dairy breeds (Table 10.4). 10:7

8 Table 10.4: Heifer rearing targets for the main dairy breeds Age (months) Weight (kg) Holstein Friesian Jersey Withers height (cm) Weight (kg) Withers height (cm) Weight (kg) Withers height (cm) (mating) (pre-calving) (post-calving) Source: Heifer Rearing in the 21st Century, DairyCo Desktop Review For other breeds or crosses target weight-for-age guidelines should be set on the basis of percentage of mature bodyweight (Table 10.3) or withers height-forage (Table 10.5). Table 10.5: Withers height-for-age targets for other breeds Age Target withers height (cm) (months) Ayrshire Brown Swiss Shorthorn Source: Heifer Rearing in the 21st Century, DairyCo Desktop Review :8

9 Rearing practice To achieve the most rapid growth without over-fatness for the optimum financial and reproductive efficiency requires careful heifer management from birth to first calving and beyond. It is important to monitor heifer performance regularly over the rearing period to achieve the required targets, using withers height as a good measure and undertaking Body Condition Scoring (Section 7). It is important to make the best use of the particularly strong suckling drive calves appear to have in the first hour or two of life. Calves that will not suck the cow or a bottle teat will require a stomach tube, if using this method it is important to ensure that at least 2.5 litres is given, as the first 500ml will be deposited in the rumen and will not be available for antibody absorption. While the gut is open to absorb antibodies, of course, it is highly susceptible to bacterial infection, making feeding hygiene in the first 24 hours especially important. Feeding colostrum The first essential in heifer rearing is to ensure all calves receive sufficient colostrum early enough to absorb the very high levels of antibodies it contains. While these antibodies can only be effectively absorbed by the young calf over the first 24 hours of life, they are also valuable after this time to protect against infections within the gut. As a general rule, calves should have at least 10% of their bodyweight as colostrum in the first 24 hours of life, ideally half of this within six hours of birth. If possible the colostrum should be sucked from a teat (cow or bottle) as this by-passes the rumen for more rapid absorption. Calves need to suckle for at least minutes continuously to take 2 litres of colostrum. Bacteria numbers in warm colostrum in a bucket can double every 20 minutes. To minimise the risk of spreading Johne s disease, if present in the herd: Feed calves only colostrum from their own mothers Feed fresh or frozen colostrum from a cow which has tested negative for the disease Consider artificial colostrum substitutes if dam or test negative colostrums from the farm are not available Use a milk replacer rather than feeding surplus whole milk. The use of pasteurisers for colostrum is worth considering on large units. Managing calf rearing Feeding a 10% solution of milk powder at 10% of the calf s bodyweight to standard UK practice will produce healthy calves. 10:9

10 However, it may also seriously restrict growth rates at the time of the highest potential feed conversion efficiency in the animal s life. Accelerated calf growth systems, feeding as high a level of high protein milk replacer as calves can safely utilise, have been shown in US practice to give much heavier udders at weaning and better development of udder secretory tissue. It is important to appreciate, however, that an accelerated calf growth system means heifers have to be calved at two years of age or younger to recoup the costs. High protein (26-28%) low fat (15-16%) milk powders are essential for accelerated calf growth systems. These contrast with normal 22-23% protein, 19-20% fat powders. Feed rates and mixing rates are also increased from the normal 10% to around 15%. With a feed conversion efficiency of 1.25:1 at best, powder intakes of 900g/day are needed for maximum growth rates (0.7kg/day+). Calves will be slightly looser on these high milk replacer intakes but any scouring will not be caused by the high feeding level. Providing calf health status is good the system of milk feeding has been shown to make very little difference to growth rates, the weight of milk solids consumed being the determining factor. It is important, however, to appreciate that very high growth rates (> 0.85kg/day) are negatively associated with fertility, possibly due to excess levels of body condition, as well as being expensive to achieve. Given that the labour needed for twice daily bucket feeding is almost six times more than that required for ad lib machine feeding or group feeding from a barrel, these alternatives offer valuable opportunities for time and cost saving. Concentrate feeding Good feeding and management must be maintained through weaning and beyond if excellent calves at eight weeks of age are not to end up at a similar weight and size to more traditionally grown animals at 12 weeks at a very much higher cost. Grain has been shown to be more effective than forage in the very early development of the rumen, leading to significant rumen lining development by four weeks of age and reduced nutritional stress at weaning. Concentrates should, consequently, be made available from a few days of age. Where rapid calf growth is required there may be a value in increasing the protein content in the calf starter concentrates above the 18% which has been shown to be optimal under conventional rearing systems. High digestible undegradable (by-pass) protein sources do not appear to offer any advantage, soya being quite suitable. On high input systems, higher protein concentrates may help in achieving bigger rather than just fatter calves. However, the first essential is to ensure the concentrate is sufficiently palatable so calves will 10:10

11 actually consume it at the right level to support their development. Ideally, smaller calves should be monitored and grouped to be fed separately. Weaning dates should be based on calf weight and concentrate/forage intakes and not solely on age. Dehorning and similar activities are best performed before weaning, to minimise any growth check caused by stress. Housing and ventilation The health status of heifers has to be high to ensure efficient feed conversion and fast growth rates. In particular, housing must be well-ventilated to avoid respiratory problems. If better accommodation is not available, forced ventilation should be considered where old poorly ventilated buildings are used. While air flow must be maximised, it is equally important to avoid draughts. Sharing air space with older cattle should also be avoided. It is important to review calf housing and remove or minimise any obvious risks from injuries or accidents caused by poor accommodation. Good hygiene is another important aspect of successful calf rearing. Calf hutches for individuals or small groups of calves provide an optimum environment but can be labour intensive. Feeding to first service From weaning to kg (for Holsteins) the rate of weight gain greatly influences the age at which heifers first come into oestrus. Puberty, related primarily to body weight, can be reached at any time from eight months to 16 months of age under commercial farm conditions. Since fertility increases up to the third oestrus cycle after puberty, heifers need to be grown to reach puberty at least six weeks before the start of serving. To ensure successful implantation of the embryo a generous level of feeding should continue for six weeks after service. Recent studies show that growing heifers faster does not lead to a reduction in the rate of daily development of secretory tissue in the udder. While milk yields may be lower when heifers calve younger, this is now considered to be due to age alone, not rate of growth. A high number of secretory cells does not guarantee higher milk yields but could increase potential yields. Likely yield reductions in the first lactation with age at first calving are difficult to predict with any accuracy but can be estimated (Table 10.6). 10:11

12 Table 10.6: Estimated first lactation yield by Age at First Calving Age at First Calving (months) First lactation yield compared to 24 month calving (%) Source: Heifer Rearing in the 21st Century, DairyCo Desktop Review Limited investigations with periods of restricted growth followed by periods of generous feeding have shown heifer lactation yields may be improved by 8-21% through a step-feeding approach. Since step-feeding is difficult to manage accurately in commercial practice, the main value of this work is in confirming that below target performance earlier in the rearing period can be overcome by increasing feeding in the later stages without damaging future performance. Care must, however, be taken in pushing heifer growth rates postpuberty because this tends to increase body condition rather than frame size. Growth rates of kg/day are recommended during the first pregnancy to achieve a Body Condition Score of at calving, the key being to avoid heifers getting over-fat. Over-fatness is unlikely to be a problem unless high levels of concentrates are fed or heifers will be calving at more than 2¼ years old. Step-feeding work suggests there may be a benefit in growing heifers at less than 0.8kg for part of the pregnancy and boosting this in the last three months. However, high weight gains from concentrate feeding in late pregnancy can result in excess condition at calving which must be avoided if fertility is not to be compromised (Section 7). Heifers will not suffer from milk fever and there is evidence that anionic salts like magnesium chloride will depress feed intake more in heifers than in cows. Udder oedema can be a problem in heifers, particularly if they calve on high protein, high potash pastures or are receiving diets containing a high proportion of grass silage. Feeding forages or diets high in whole crop or maize silage will reduce this danger. Feeding during first pregnancy Although there is little scope to increase frame size at this late stage in heifer development, severe underfeeding could still prevent animals achieving the small potential which does exist. Managing to reduce lameness It has been suggested that nutrition during the rearing period may have an important effect on claw development and the sole ulcers and white line lesions that cause the most damaging lameness. 10:12

13 Given the major impact on lameness on both heat expression and detection (Section 6) and Pregnancy Rates (Section 8), careful management of rearing rations may make a valuable additional contribution to fertility improvement. Figure 10.2: Heifer wastage Calf mortality born from cows/ first calving heifers Liveborn heifer calves failed to reach first lactation Animals culled in first lactation Heifers that enter herd To minimise lameness problems, heifers should be: Fed dry diets (over 30% DM silage) where possible Kept off straw beds in summer housing Trained to use cubicles when bulling or in-calf Allowed to remain in straw yards for eight weeks after calving. Reducing heifer wastage DairyCo has researched the actual levels of dairy heifer wastage between birth and the end of the first lactation (Figure 10.2). Source: DairyCo report Reducing Wastage in the Dairy Herd (2008). This research has also shown the principle reasons why heifers are lost or culled: Below the age of 15 months heifers are lost mainly due to infectious disease Between the ages of 15 to 24 months heifers are lost mainly due to infertility Over the age of 24 months heifers are lost due to infertility, problems associated with calving and mastitis. Poor juvenile growth rates are often associated with later cases of infertility, calving problems and mastitis in first lactation heifers. 10:13

14 Service options Running a bull with heifers offers well-recognised Heat Detection and Pregnancy Rate benefits, particularly in groups of animals reared away from the main unit and not handled or seen as regularly as the milking herd. The choice of bull should take into account size, calving issues, calf value and the housing, handling and grazing conditions under which the cattle are kept. A factsheet on Natural Service Management is included within this folder. A bull fertility check is an essential investment in view of the numerous cases of infertile bulls running with heifers and resulting in the late calving of a whole year s replacements, seriously compromising the calving pattern. Ideally, change bulls weekly giving each one week working followed by one week resting to avoid the danger of impairing fertility by overworking. Controlled breeding and synchronisation (Section 8) can bring particular benefits for heifers, most notably: Giving better control of their entry into the herd Tightening the calving pattern Allowing AI to be used more effectively and easy-calving bulls to be selected Speeding up the rate of genetic improvement by enabling dairy semen to be used. The use of prostaglandin treatment with heifers has no negative impact on Pregnancy Rates and may even have a positive effect. 10:14

15 Herd introduction Grouping dairy heifers with mature cows soon after calving often results in stress which can seriously affect fertility performance (Section 6). A DairyCo-supported project presented the following guidelines for heifer management to reduce this stress: Accustoming heifers to the milking parlour prior to calving has also been shown to encourage milk production by reducing their fear of the new surroundings. Although separating the calf within 24 hours of birth is less stressful and easier to manage, there is evidence that heifers which are allowed to suckle their calves for eight weeks experience a close-tocomplete milk let-down, improving whole lactation yields. Where possible, heifers should be kept as a separate milking group for at least the first four months of the lactation promoting fair competition at the feed trough and allowing them to continue growing, so they reach their peak yield and get back into calf before having to compete with older animals If they are to be managed as part of a cow group, heifers need to be well-grown and the facilities must provide adequate lying space for the whole herd Heifers should always be kept in a recentlycalved group and not mixed with the herd until at least five days after calving Initial introduction into the herd should take place after the afternoon or evening milking while cows are less socially active. 10:15