Department of Animal Science,University of Tennessee,
Knoxville, TN 37901-1071 USA
Take Home Message
Raising heifers from weaning to calving involves proper planning, nutrition, and management. Rates of body weight (BW) gain are important to ensure that heifers are large enough to breed by 13 to 14 months of age at 340 to 380 kg. However, excess rates of BW gain - especially prior to puberty - can permanently reduce milk production. Heifers should be managed and fed to maintain 0.77 to 0.82 kg of BW gain daily. Body condition near calving should be 3.5 to 4.0. Ration quality - especially forage quality - is key to ensuring adequate rates of BW gain and achieving calving goals.
The replacement enterprise is often overlooked as a critical component of a dairy farm. The economic importance of dairy replacements is twofold. By the time heifers are ready to enter the milking herd they constitute a considerable economic input - in many cases, exceeding $1,200 (U.S.) per heifer. Improvements in management to minimize costs without sacrificing future lifetime production can significantly impact farm profit. Further, dairy heifers constitute the future genetic base of the herd. Proper management during the rearing period will allow heifers to express their genetic potential for milk production, whereas improper management during the rearing period may inhibit this expression of genetic potential.
Powell (28) reported that average ages at first calving for Holsteins and Jersey heifers calving between 1960 and 1982 were 27.5 and 26.2 months, respectively. Recent reports (13) indicate that age at first calving is declining, but the rate of change is slow. It is not clear why recommended age at first calving of 22 to 24 months is not widely accepted. Some producers feel that young heifers will be too small to effectively compete with larger, older cows in the herd and will suffer more metabolic and reproductive disorders. However, recent developments affecting heifer management may further improve the way heifers are reared.
Raising dairy replacement heifers from weaning to calving involves management different from that of preweaned heifers. While risks of mortality are reduced (2.2% of calves die between weaning and calving; 22), risks of morbidity and impaired growth rates are considerable. James (18) suggested that because the management of replacement calves is not the most important component of overall dairy management, the use of efficient and well designed systems was critical. James (18) further suggested that the systems should include:
Current recommendations for growing dairy heifers are based on three basic assumptions:
1. Optimal age at first calving is approximately 24 months of age
2. Excessive rates of gain, especially prior to puberty, may result in reduced lifetime productivity.
3. Costs associated with raising heifers are significant and should be minimized.
Management of weaned heifers is centered on obtaining acceptable rates of BW gain while minimizing costs. Typical rates of BW gain and variation around the mean are in Figure 1. The average heifer in the sample measured by NAHMS was 355 kg at 14 months of age and 545 kg at 24 months of age. These data suggest that growth rates prior to breeding are probably adequate, but growth of bred heifers may be too slow.
Age At First Calving
esearchers have modelled costs and productivity of dairy cows calving at various ages. In most studies productivity, measured as milk production in one or more lactations, has generally been maximized when heifers calve at 22 to 24 months of age (8, 19). Gill and Allaire (9) found that optimal age at calving to maximize lifetime production was about 23 months, and age for optimal profit was 25 months (slightly older heifers remained in the herd longer than heifers calving earlier).
If optimal calving age is 22 to 24 months, then breeding must occur at 13 to 14 months, assuming 9 months of gestation and 1.5 services per conception (14). Overall goals for replacement heifers include establishing an acceptable rate of BW gain to allow heifers to reach puberty and breeding at 13 to 14 months; housing and management to minimize morbidity, especially caused by pneumonia; management and heat detection to allow breeding at an acceptable age; and maintenance of BW gain through to calving to allow heifers an acceptable body size when they enter the herd.
Age at first calving and culling rates affect the number of heifers required to maintain herd size (Table 1). When calving is delayed or culling rate increases, the number of heifers needed increases.
Table 1. Number of heifers needed to maintain a herd size of 100 cows.
Age at first calving (mo)
|Cull rate, %||Number of heifers needed to maintain herd size|
Prepubertal Rates of Gain
Research during the 1960's established that increasing the "plane of nutrition" resulted in reduced lactation after calving. Much of the growth of secretory tissue in the mammary gland is deposited between about three months of age and puberty, therefore, this time period is especially important to future milk production by the heifer. Swanson (39) reported that increased energy in the diet increased rates of BW gain and subsequent fat deposition in the mammary gland. Deposition of fat was in preference to deposition of secretory tissue, and it was concluded that increased rates of BW gain were associated with reduced lactation through substitution of mammary parenchyma with adipose tissue. Rates of BW gain associated with impaired mammary development vary, but when they exceed 0.82 kg/day (and certainly 1.0 kg/day), there is significant risk of influencing mammary development.
Sejrsen and coworkers (32, 34, 35, 36) further refined the effects of increased energy concentration in the ration and determined that ad libitum feeding prior to puberty reduced secretory tissue in the mammary gland by 23% and tissue DNA by 32% compared to restricted feeding. Accelerated rates of BW gain after puberty did not affect lactation to the same extent as prepubertal overfeeding. Others have argued persuasively that controlling rates of BW gain prior to puberty (1, 4) and after puberty (16) are important to maximize total lifetime milk production and reduce incidence of calving disorders.
Researchers have questioned whether increasing total nutrients rather than energy alone would influence mammary growth. In one study, Holstein heifers were fed 100 or 124% of NRC requirements for all nutrients from 3 to 6 months of age, then 100 or 115% of NRC requirements from 6 to 24 months of age (6). Calves fed the increased nutrient concentrations gained more BW and had greater height, length, and heart girth, but were not over conditioned. These heifers were seven weeks younger at first service and conception than those fed according to NRC requirements. These data suggest that it may be possible to reduce the age at first calving, although neither lactational performance nor mammary tissue samples were evaluated. Others (6, 17) have suggested that accelerated rates of BW gain as a consequence of increased energy alone may result in depressed lifetime production, but increased density of all nutrients may allow heifers to fully express their genetic potential for BW gain. However, data have not been critically evaluated and current recommendations are to maintain rates of BW gain at < 1 kg/day prior to puberty.
Minimizing Costs of Raising Heifers
Raising heifers can be divided into three separate growth periods: weaning to 180 kg, 180 kg to breeding, and breeding to calving. Major inputs for raising calves from weaning to calving include feed and labor (Table 2).
Table 2. Costs associated with raising calves from birth to calving. Adapted from Cady and Smith (3).
|Item||Cost (U.S. dollars)||% of total|
|Breeding, bedding, supplies||71.00||5.7|
|Interest on investment||107.74||8.7|
|Initial value of heifer||100.00||8.0|
|Death loss (12%)||44.00||3.5|
Other inputs (housing, veterinary, breeding) are relatively minor, but depend upon the particular situation such as facilities available and use of pasture. Total costs usually average about $1,200 (U.S.), but can vary markedly, depending upon the individual situation. Under most conditions, it is expensive to raise dairy heifers. Although actual costs will vary with the situation, most estimates of total costs for raising a heifer to calve at 24 months range from $1,100 (PA) to $1,300 (WA). Most estimates assume above average management with little expense associated with items such as veterinary expenses, repeat breeding, etc. On the other hand, few data are available to evaluate costs of low-input management - i.e., heifers raised on pasture with little or no concentrate feeding and calving at 28 to 30 months of age.
Management from Weaning to 180 kg
The primary goals for heifers from weaning to 180 kg are to minimize transitional stresses and establish an acceptable rate of BW gain, usually 0.77 to 1.0 kg/day. The period around weaning is a particularly stressful time for the young calf. Adjustments in rumen fermentation and digestion as well as changes in housing, feeding, and other management practices all promote stress. It is our job to minimize these stresses by managing the transitions in feeding and housing.
Nutrient requirements of calves from weaning (about 68 kg) to 180 kg are significant (Table 3). Energy requirements are approximately 2.6 Mcal of ME/kg of DM, so these calves still require high energy feeds such as a commercial calf grower with good quality legume or legume/grass mixes. Protein requirements are approximately 16% of DM, so again, a high quality forage source is necessary. Water must be available free choice and kept clean.
The question of when to offer fermented feeds to young heifers is often asked. Researchers (40) have suggested that calves from as early as three months of age can effectively utilize high quality corn or alfalfa silage and grow similarly to calves fed high quality alfalfa hay. In these controlled research trials, calves grow well - often in excess of 1 kg/day. However, it is important to note that calves 4 months of age are especially susceptible to forage quality (including CP, fiber, energy, and fermentation characteristics) and feed bunk management. When calves are forced to consume spoiled silage, whether corn silage or haylage, intakes and BW gains will usually be depressed. Thus, when the level of heifer management is not "top-notch", then it is usually better to delay offering silage to calves until after four months of age.
Calves from weaning to 180 kg should be housed in small groups to minimize competition and allow all calves access to grain and forage. Overcrowding is a common problem and can result in slow growth, increased morbidity, and poor quality heifers. About two weeks after weaning, calves may be moved into group housing of four to six calves. Too many calves in a group will result in dominance of smaller calves. As a result, small calves often do not consume sufficient grain which can reduce their growth. Housing types vary widely according to the facilities available - producers can do an excellent job in super hutches, calf barns, and many other facilities. Generally, housing should be economical, clean, dry, and labor efficient. Many producers are successfully housing calves in approximately 45 kg groups and moving calves into new groups every two months.
Table 3. Age, weight, height, and nutrient requirements for large breed weaned heifers gaining 0.77 kg/day. Adapted from: NRC (23), NAHMS (22), Heinrichs and Hargrove (12).
|CP, kg||CP, % of DM|
Calves are particularly susceptible to coccidiosis and respiratory diseases shortly after weaning. Ionophores (monensin, lasalocid) and decoquinate are effective in controlling disease caused by coccidial infection (7, 37). Thus, the use of coccidiostats in feed and proper ventilation are essential. Most mortality in weaned calves occurs due to respiratory infections (although scours are also significant; NAHMS, 22).
Pasture and ensiled forages (unless excellent quality) should be reserved for calves older than four months. When high quality, intensively managed pasture is available, it can be an excellent source of forage. Remember, however, that calves usually still require supplementation - pasture may contain too little energy and much of the protein will be highly degradable, so a source of undegradable intake protein is recommended in the supplement. Body weights of heifers on pasture should be determined monthly, using a scale or weigh tape. This is the only way to determine if pasture quality is sufficient to maintain growth.
Management from 180 kg to Breeding
This period is characterized by declining nutrient requirements (as a proportion of total DM intake), an increasing reliance on forages and pasture for nutrients, and preparation for breeding. Dry matter intake requirements increase from about 4.5 kg/day at 180 kg of BW (6 months of age) to 8.4 kg/day at 363 kg of BW (14 months of age). Requirements for ME and CP decline as a percent of total DM (ME from 2.56 to 2.31 Mcal/kg of DM; CP from 16.0 to 12.0% of DM) from 181 to 363 kg of BW. Heifers will grow in stature about 18 cm during this time also.
Heifers from 180 kg will consume significantly more dry matter than that predicted by NRC (23), particularly if they are housed in confinement (29, 30). Prediction of intakes based on experimental data indicates that heifers will consume up to 15% more DM than predicted. Thus, it may be necessary to reduce the concentration of energy and protein in the ration to control rates of BW gain.
Puberty occurs at approximately 11 to 12 months of age or 250 to 295 kg (4, 24, 40). Since the onset of puberty is more a function of size than age, it is possible to reduce the age at which calves are bred by increasing rate of BW gain (as described previously). Again, rates of BW gain of about 0.77 to 0.82 kg/day will allow heifers to reach puberty by 12 months of age. Body condition of heifers is an important criterion of acceptable BW gain. However, it is important to be sure that hair coat and other factors are taken into consideration when measuring body condition.
Hoffman (14) and Hoffman et al. (15) described the effects of environmental conditions on nutrient (particularly energy) requirements of growing replacement heifers. The topic can be summarized by the following quote from Hoffman (14) "NRC nutrient requirements for replacements assume perfect environmental conditions which seldom apply to a commercial dairy herd." Clearly, any deviation from optimal environmental conditions can affect growth rates. Some common deviations include weather and climate (heat, cold, wind chill, rain, snow, mud), level of worm infestation, distance heifers walk on pasture, body condition, water availability, animal density, and many other factors. It is important to take environmental conditions into consideration when formulating rations. The best method of determining adequate ration formulation is to have feeds analyzed regularly and to measure growth rates of heifers regularly.
Managing heifers near breeding should be centered around the need for heat detection and breeding. Hoffman (14) suggests that artificial breeding should be initiated at 13 to 14 months of age to ensure conception by 15 months of age. Many producers successfully use estrus synchronization programs to increase the success of heat detection and reduce services per conception. Others use natural service to minimize the time spent in heat detection. O'Connor (25) concluded that the primary reason that producers do not use artificial insemination is a lack of proper restraint facilities designed for the purpose. Housing breeding age heifers together can help to minimize the number of heifers to be observed and facilitate mounting activity which can improve heat detection rates. It is a good idea to manage these heifers to maximize the success of the breeding program - remember, open heifers can be a real drain on the overall enterprise. Not only do open heifers calve late, they often are fat, prone to calving difficulty, and more likely to have trouble in the next lactation. Culling decisions made before too much is invested in a heifer can save money in the long run.
Management from Breeding to Calving
Primary goals for bred heifers are to maintain 0.77 to 0.82 kg of BW gain per day while maximizing forage and/or pasture use and minimizing costs. Heifers gaining < 0.77 kg/day from breeding to calving will be too small, which may result in reduced milk yield, increased dystocia, and inability to compete with older, larger cows after parturition. Similarly, heifers gaining excess BW (>0.9 kg/day) from breeding to calving may be over conditioned at calving, which can lead to dystocia and metabolic disorders in the first lactation.
Nutritional inputs during the last stage of heifer growth are relatively low compared to those prior to breeding (Table 3). Requirements for CP and energy are lower than those before breeding and can generally be met with forage and/or pasture. Heifers should not be allowed to accumulate excess condition prior to calving, as fat heifers are generally more susceptible to reproductive and calving disorders than heifers calving in proper condition. Most heifers should have a body condition score of 3.5 to 4.0.
Since calving is such a stressful experience, proper preparation is essential. When heifers are about four weeks prepartum, they can be moved into a group to prepare them for calving. Often, this group is with older dry cows. Generally, there is a decline in DM intake from three to four weeks prepartum, with a dramatic decline in the last week. Thus, the transition diet should be very highly palatable and similar to the ration the heifer will consume after calving.
Higher intakes of undegradable intake protein during the last month of gestation may be beneficial to improving the metabolic state of the animal and reducing the incidence of ketosis (5). In addition, many producers use diets with a negative dietary cation-anion balance (DCAB) to minimize the incidence of milk fever. This is more of a problem in older cows, but close-up heifers are often housed with older dry cows, so they receive the same supplement. Using the same feeding system in the close up group allows heifers to adapt to the system after calving.
Alternative Management Systems
Ionophores are compounds that alter fermentation in the rumen. Currently, two ionophores are approved for use in rations of growing dairy heifers - monensin (Rumensin®, Elanco Products Co., Indianapolis, IN) and lasalocid (Bovatec®, Hoffman-La Roche, Nutley, NJ). These compounds have been used widely in diets of growing and finishing beef cattle for many years. Ionophores are classified as polyether antibiotics, which influence the transport of cations across cellular membranes.
Addition of ionophores to diets of beef cattle improves BW gain and/or feed efficiency (10). Baile et al. (2) reported that monensin added to diets of dairy heifers increased rates of BW gain with little or no reduction in intake of DM. Therefore, efficiency of feed utilization was increased by nearly 13% when heifers were fed 200 mg of monensin per day. The basal diet used in this study was typical of intensive managed heifers - haylage (62%), corn silage (24%), and corn (15%) in quantities to permit 0.68 kg BW gain/day. There was no effect on subsequent lactation after calving in this experiment (2).
In a more recent study, Meinert et al. (20) fed 40 Holstein heifers 0 or 200 mg of monensin daily. Diets were corn silage (2% of BW) or grass pasture for ad libitum consumption. A limited amount of grain was also offered. Although not statistically significant, BW gain in heifers beginning the study at 330 kg was increased by 12.5%, from 0.72 to 0.81 kg/day. Rates of BW gain in heifers that began the study at 217 kg were 0.76 and 0.78 kg/day for heifers fed 0 and 200 mg of monensin/day, respectively. In this study, intake of silage and pasture were not measured, so neither intake nor feed efficiency were determined. The authors reported no changes in estimates of body fat, protein, or body condition when monensin was fed (20).
Steen et al. (38) fed Holstein heifers (253 kg initial BW) 0 or 200 mg of lasalocid/day with or without added undegradable intake protein (UIP). Heifers were housed in a barn from 9 to 20 months of age. Concentrate (3.2 kg/day) was fed in addition to moderate quality fescue hay to maintain BW gain of 0.6 to 0.7 kg/day. Although not statistically significant, BW gain was increased by 4 and 6% (0.64 to 0.66 and 0.67 kg/day) and feed efficiency was increased by 7.5 and 9% when lasalocid or UIP were fed separately. The authors also reported slight increases in heart girth and fat and muscle depths when heifers were fed 200 mg of lasalocid/day or high UIP (42% of CP as UIP) separately. There were no effects when high UIP and lasalocid were fed in combination. The authors concluded that high UIP and ionophores may provide insufficient degradable protein to the rumen of growing animals, and production of microbial protein may be compromised when the combination is fed.
On the basis of two studies that have evaluated body composition when ionophores were fed (20, 38), it does not appear that either lasalocid or monensin will adversely affect the body composition of heifers raised to gain 0.6 to 0.8 kg of BW/day. However, further research is needed to determine if animals gaining more rapidly (0.8 to 1.0 kg/day) will be affected by ionophores particularly prior to puberty. Finally, ionophores may influence the age at which animals achieve puberty independent of rate of BW gain (20, 21, 38).
This system of raising heifers depends upon the phenomenon of compensatory growth. Compensatory or "catch-up" growth occurs when animals are limited-fed for a period of time. If the animals are later allowed full access to feed, they tend to become more efficient in growth, and tend to increase BW gain more rapidly than animals on a similar diet. The phenomenon has been reported in most species of animals, including beef and dairy cattle.
Table 4. Growth, intake, and BW gain in heifers fed control diet or by a stair-step method of growth (Source: Park et al., 26).
|BW gain, kg/d||0.68||0.98**||0.22|
*P < 0.10.
**P < 0.001.
Park et al. (22) fed heifers according to 100% of NRC requirements or according to a 5-2-5-2 month schedule in which nutrient density was either 15% below (5 months) or 40% above NRC requirements (2 months). Heifers on the compensatory growth regime gained more BW, consumed less feed, and had improved efficiency of growth over the entire trial (Table 4). Further, animals produced 2.1 kg/d more milk in the first lactation. This method of rearing has some inherent dangers - namely, delays in BW gain during the "maintenance" or slow growth periods increases the importance of BW gain during compensatory growth. Any upset in management during compensatory growth - disease, weather stress, change in quality of forage, etc., may have markedly detrimental effects on the animal. In fact, they may not be able to "catch up" to animals raised under normal conditions. Also, rates of gain during compensatory periods can exceed 2 kg/day. Effects of these rates of gain on body condition, mammary development, and long-term animal health are not known.
The use of BST in heifers around puberty increased the deposition of mammary parenchyma in Holstein heifers (33). Further, injection with BST increased BW gain of Holstein heifers (11) up to 0.18 kg/day during the injection period (2 months prior to breeding, injected for 5 months). However, by five months after completing injections, control animals were similar BW. There was no effect of BST on reproductive function or on milk production after calving. However, because animals on this study had reached puberty (they began the study at 13 to 16 months of age) it is likely that BST treatment would not affect parenchymal development. Heifers treated with BST had a greater hip height and pelvic size, indicating improved growth of frame in treated animals. However, research to date suggests that BST administered does not affect milk production after calving (31). Further research is needed to determine if BST does indeed influence milk production when administered prior to calving.
Although most recommendations for age at first calving range from 22 to 24 mo, in practice age at first calving is approximately 26 months of age (13, 28). A number of hypotheses have been proposed to explain this discrepancy: producers don't consider it economical to manage heifer nutrition programs for adequate growth, they use heifers to harvest forage from pasture that would otherwise be unusable, or the reproductive program is not managed to breed heifers by 14 months even if they are of sufficient size. It is possible that feeding and management programs to minimize inputs (particularly nutritional inputs such as concentrate) contribute to delayed age at first calving, but still are more economical than intensive rearing.
Pecsok et al. (27) evaluated heifer growth programs in relation to costs of forage and concentrate. The model included labor costs, housing prices, and prices of corn, soybean meal, and orchardgrass hay. Only when the price of orchardgrass hay was less than $28/ton (U.S.) was it profitable to reduce BW gain (by feeding less concentrate) to less than 0.82 kg/day. When the price of forage was greater than $28 per ton, it was more profitable to feed for BW gain of 0.82 kg/day. Therefore, the authors concluded that delaying the age at first calving by using low supplementation strategies would not be profitable if any type of harvested forage was fed. On the other hand, if prices of pasture (cost of establishment, fertilizer, maintenance, etc.) are sufficiently low, it may be economical to reduce rates of gain and delay age at first calving to maximize use of pasture.
There are many different strategies for managing dairy replacement heifers. Whatever the method used by producers, it must be economical, provide the animal with sufficient nutrients for growth without fattening, but with large body size and frame so that they can consume large amounts of feed and convert that feed to milk. Introduction of products such as ionophores can have a positive impact on animal BW gain and feed efficiency. Control of coccidiosis and improved reproductive status can further improve heifer management. When incorporated into a well-rounded management program, ionophores can improve the profitability of the heifer enterprise. Alternative rearing systems, including use of BST or stair-step growth patterns require further research prior to widespread adoption.