In most cases, intramammary infection is considered a disease of mature lactating and dry cows, and several mastitis control practices have been developed for this age group of animals. These include proper milking time hygiene, the use of functionally adequate milking machines, dipping of teats both before and after milking, use of dry cow therapy, prompt treatment of clinical cases of mastitis, and culling of those chronically infected cows that do not respond to repeated attempts at therapy. Management practices and disease control in heifers, however, emphasize proper housing, vaccination against calfhood diseases, adequate nutrition, and artificial insemination, without any regard to mastitis control. It must be emphasized that intramammary infections can develop in these young dairy animals, and mastitis-causing bacteria may be found in heifers with mammary secretions as early as 6 months of age.

Unfortunately, most dairymen regard young heifers as uninfected, and the presence of mastitis is not noticed until freshening or until the first clinical flare-up in early lactation. Thus, an animal may carry an intramammary infection for a year or more before it is diagnosed. The greatest development of milk-producing tissue in the udder occurs during the first pregnancy, so it is important to protect the mammary gland from pathogenic microorganisms to insure maximum milk production during the first and possibly the subsequent lactations. Research in New Zealand has shown that Staphylococcus aureus mastitis in heifers results in significant production losses during the first lactation, which carries over into the subsequent lactation even if the infected quarters are successfully treated.

Scientists at the Hill Farm Research Station became interested in heifer mastitis in the mid-1980s after several area dairymen complained that a large percentage of their heifers were freshening with clinical signs of mastitis. A subsequent study of postpubertal animals in the Hill Farm Research Station dairy herd revealed that intramammary infections were initially diagnosed at approximately 9 months of age, and infections persisted throughout pregnancy and into lactation. A follow-up study in four commercial dairies demonstrated that about 97% of breeding age and bred heifers (12 to 24 months of age) were infected. Most of the infections were caused by the coagulase-negative staphylococci (Staphylococcus chromogenes, Staphylococcus hyicus) followed by Staph. aureus (almost 20%) and the environmental streptococci (Figure 1); Streptococcus agalactiae were never isolated, and coliforms were only rarely found. Figure 1. Frequency of bacterial isolates from mammary secretions (%)

Somatic cell counts (SCC) are used to assess the udder health status of mature, lactating cows, and this parameter has been examined in heifer mammary secretions. In secretions from uninfected quarters, SCC were over 5 x 10⁶/ml; the volume of mammary secretion is very low in breeding-age animals, thus SCC become concentrated, resulting in high SCC. However, SCC were almost 20 x 10⁶/ml in quarters infected with Staph. aureus and over 12 x 10⁶/ml in those infected with the coagulase-negative staphylococci and environmental streps. Such elevated SCC over a long period of time suggests that the affected quarter would be in a state of chronic inflammation, which would adversely affect development of the milk-producing tissue. In fact, histological analysis of the mammary tissues obtained from several bred heifers chronically infected with Staph. aureus demonstrated that the potential for milk production was significantly reduced compared with tissues from uninfected quarters.

A product containing 1 million units of penicillin and 1 gram of streptomycin (Quartermaster, Pharmacia & Upjohn, Kalamazoo, MI) was used initially in several herds to treat both breeding-age heifers as well as those in various stages of pregnancy with confirmed infections caused by various bacterial species; several animals of all age groups served as untreated controls. Heifers were restrained in a squeeze chute equipped with a head gate, and teat ends were scrubbed with cotton balls soaked in 70% alcohol or with the pledgets accompanying mastitis tubes in order to sanitize the teat orifice prior to infusion. While administering the antibiotic, the partial insertion technique was used to avoid stretching the teat canal as well as to avoid the introduction of bacterial contaminants. Infected quarters of each animal were treated in an attempt to cure existing infections, and remaining uninfected quarters were treated prophylactically. After infusion, teats were immersed in a barrier teat dip to seal the teat orifice and prevent entrance of bacteria.

When the treated and untreated control animals freshened, milk samples were taken and processed to determine infection status. Results showed that the overall infection level in treated heifers was reduced almost 60% compared with controls, whereas the infection level did not change in untreated controls (Figure 2).
 

 

The percentage of quarters infected with Staph. aureus was reduced 91% in heifers that had received treatment compared with infected quarters not receiving treatment. This cure rate for Staph. aureus is far greater than the 25% cure rate observed after heifers are treated during lactation for this disease using conventional lactating cow therapy. Reasons for this high cure rate are unclear, but the relatively small secretory tissue area of heifer mammary glands compared with mature cows might allow for greater drug concentrations in the udder. Similarly, histological studies have demonstrated less scar tissue and abscess formation in the mammary glands of heifers compared with older cows, which would allow for better drug distribution and better contact with colonized bacteria. Detection of antibiotic residues demonstrated that on the day of calving, 2.9% of treated heifers were positive, which was attributed to two heifers whose expected calving dates were miscalculated that had been treated within 45 days of freshening.

In one of the Jersey herds evaluated, an economic analysis was performed to justify use of the heifer treatment program. Production data collected over the first two months of lactation demonstrated that mastitic heifers that had received nonlactating cow therapy during pregnancy produced an average of 5.4 lbs more milk per day than herdmates that did not receive treatment. At the milk price received at that time, this greater yield translated to a $42.12 increase for treated heifers, which was well worth the $5.00 cost of treatment.
 
Subsequent investigations using other nonlactating intramammary infusion products have been equally rewarding in treating heifers with Staph. aureus mastitis. For example, the treatment of animals 8 to 12 weeks prior to expected calving date with 300 mg cephapirin benzathine (Tomorrow®, Franklin Laboratories, Inc., Fort Dodge, IA) resulted in a 96% cure rate. An examination of SCC showed that at the time of treatment, SCC were 15 x 10⁶/ml, but decreased to 4 x 10⁶/ml 1 wk later and to 700,000/ml on the day of calving. If infected quarters were left untreated, heifers freshened with Staph. aureus-infected quarters with an average SCC of 5 x 10⁶/ml. When these later animals were treated with a lactating cow product containing 200 mg cephapirin sodium (Today®, Franklin Laboratories, Inc.) immediately after calving, cure rate was only 50%. Thus, cure rates were greater when a nonlactating cow product was administered several weeks prepartum than when a lactating cow product was given shortly after calving.
 
Lactating cow products have been used successfully in heifers when treating infections caused by the coagulase-negative staphylococci immediately prior to calving. In a Tennessee study, quarters of infected heifers were infused one time 1 week prepartum with either Today® (Franklin Laboratories, Inc.), 200 mg sodium cloxacillin (Dairyclox®, Smith Kline Beecham, West Chester, PA), or left untreated. At the time of infusion, approximately 90% of heifers were infected in one or more quarters, and if left untreated, 78% of animals remained infected at time of calving. However, only 18% of the heifers remained infected at calving if they were treated prepartum, regardless of the treatment used. By 3 days postpartum, antibiotic residues were not detected in milk from heifers infused with sodium cloxacillin, but about 39% of samples from those treated with cephapirin sodium were positive for residues; however, by 10 days, residues were not detected. This study also examined the influence of prepartum antibiotic treatment on subsequent lactational performance and found that heifers receiving treatment produced approximately 1000 lbs more milk per lactation than untreated controls.

Thus, prepartum treatment with lactating cow therapy was shown to be effective for quarters infected with the coagulase-negative staphylococci, but waiting until this time to treat chronic Staph. aureus mastitis might be too late. A mammary gland that has been infected with Staph. aureus for several months to a year will not develop normally, and treatment during the immediate prepartum period would most likely be of little, if any, benefit. At this point, the damage is already done, and affected quarters should have been treated earlier in gestation to cure the existing infections, reduce the chronic inflammation, and allow the mammary tissue to develop normally during the later stages of pregnancy.

The question arises as to when is the best time to treat bred heifers for optimizing cures against Staph. aureus mastitis. A 2-year study involving 175 Jersey heifers was designed to answer this question. In this trial, heifers were sampled shortly after they were confirmed pregnant and at 4-week intervals thereafter. After the initial sampling, animals were treated with a one-time infusion of one of four nonlactating cow infusion products (Cefa-Dri®, Bristol Laboratories, Syracuse, NY; Micotil® 300 @ 1 cc/infusion, Elanco Animal Health, Indianapolis, IN; Quartermaster®; or Albadry Plus®, Pharmacia & Upjohn) during the first (0 to 90 days), second (91 to 180 days), or third (181 to 270 days) trimester of pregnancy; a nontreated control group was also included. Treatment with Micotil® was purely experimental, as this product is not labeled for use as an intramammary infusion product.
 
Prior to treatment at the initial sampling, an average of 16.5% of quarters were infected with Staph. aureus, and the range among treatments was 12.9 to 21.3% (Figure 3).
 

 

In untreated control quarters, the percentage of quarters remaining infected with Staph. aureus remained above 20% through much of the prepartum period, then decreased to 13.3% at calving. Among the treated quarters, percentages of quarters infected with Staph. aureus decreased to less than 5% at the first sampling and remained low through calving. To date, an examination of cure rates among treatments indicates that all antibiotics used were equally effective in curing infections, and there was no apparent effect of the timing of therapy; treatment efficacy ranged from 83.3 to 100% (Figure 4).
 

 

Because therapy during the first, second, or third trimester of gestation had no effect on treatment efficacy, the timing of treatment, if deemed necessary, is probably best determined by what is most convenient for the management practices of a particular dairy or custom grower operation. For example, heifers could be treated during the first, second, or third AI service; during routine rectal palpation to determine pregnancy status; or when moved to a close-up pen, as long as treatment is administered no less than 45 days prior to expected calving date.

The treatment of heifers during pregnancy with a nonlactating cow product is advantageous because the cure rate is higher than during lactation, especially against Staph. aureus. In addition, there are no milk losses during therapy, the risk of antibiotic residues is minimal, SCC at calving is reduced, and milk production is increased in successfully treated cows. Treatment is indicated only in herds experiencing a high prevalence of heifers calving with clinical mastitis. The potential for residues at calving should be considered, especially in animals that calve early. Residue testing should be carried out before mixing milk from treated animals with herd milk.
 

A Staph. aureus vaccine formulated to stimulate pseudocapsule and alpha toxin antibodies was evaluated in heifers in New York. At 4 and 2 weeks prior to calving, heifers were given subcutaneous injections in the SMLN, and after calving, heifers were challenged with Staph. aureus. Vaccinates demonstrated a 52% reduction in new IMI; in addition, 64% of IMI in control cows became chronic compared with 12% in vaccinates.

A field study in Norway evaluated a Staph. aureus vaccine that contained 2 strains of whole, formalin-inactivated bacteria with pseudocapsule, alpha and beta toxoids, and mineral oil as an adjuvant. A total of 108 pregnant heifers on 16 farms with an average Staph. aureus prevalence of 19.2% was used. Vaccinates were injected sc. in the area of the SMLN with a dose of 2.5 ml at 8 and 2 weeks before calving, resulting in a 46% reduction in new IMI during the subsequent lactation. In a separate analysis, the antibody response to the above vaccine trial was evaluated. Antibody titers to Staph. aureus pseudocapsule and alpha toxin were markedly elevated in the serum of vaccinates, and these titers remained significantly higher in serum and milk during the entire lactation compared with those of controls.

The Australians developed an inactivated, cell-toxoid prepared from 2 strains of Staph. aureus that produced pseudocapsular material and beta and gamma hemolysins, and mixed this with an adjuvant consisting of mineral oil/dextran sulphate. They evaluated this vaccine using 1819 cows in 7 dairy herds. The vaccine was administered im. in the neck twice at 4- to 6-week intervals during the last 10 weeks of pregnancy. Over the subsequent lactation, the number of clinical cases of Staph. aureus mastitis across all herds was lower in vaccinates compared with controls (45 vs. 67), but the difference was not significant. However, in cows of the 1 herd with a history of Staph. aureus mastitis, the number of clinical cases in vaccinates was significantly lower than that in controls. Likewise, for both cows and heifers in this herd, vaccinated animals had a significantly lower prevalence of subclinical mastitis compared with controls.

In Argentina, a vaccine was developed based on an inactivated, highly encapsulated Staph. aureus strain, a crude extract of Staph. aureus strain exopolysaccharides, and inactivated unencapsulated Staph. aureus and Strep. species in an aluminum hydroxide adjuvant. This formulation was evaluated in 3 groups of 10 24- to 26-month-old heifers each in a 7-month trial. The first group received an intramuscular injection of the vaccine in the neck at 8 and 4 weeks prepartum, the second group was vaccinated similarly at 1 and 5 weeks postpartum, and a third group (control) received placebo injections at 8 and 4 weeks prepartum. The research herd from which the heifers were selected had bulk tank SCC ranging from 480 x 10³ to 730 x 10³/ml, and 19% of quarters were infected with Staph. aureus. This immunization program showed that the frequency of Staph. aureus IMI was reduced from 18.8% in controls to 6.7 and 6.0% for heifers vaccinated prepartum and postpartum, respectively, and this protective effect was maintained for at least 6 months.
 
In a subsequent study in Argentina, the vaccine used above was evaluated in 164 cows in 2 commercial dairy herds during a 4-month period. Initial SCC of the dairies ranged from 580 x 10³ to 600 x 10³/ml and the percentage of quarters infected ranged from 15 to 16%. Eighty-two lactating cows received the vaccine administered as above and the 2 doses were given within a 4-week period during lactation. Results demonstrated a 40.2% reduction in Staph. aureus mastitis in vaccinates.
 
In view of more recent studies showing success of vaccines in heifers, researchers in Louisiana evaluated a commercially available Staph. aureus vaccine in young dairy animals. The vaccine (Lysigin®) was a lysed culture of polyvalent somatic antigens in aluminum hydroxide. At 6 months of age, heifers were vaccinated using a 5-ml dose im., and 14 days later, vaccinates received a booster dose, which was repeated at 6-month intervals. Results demonstrated that the number of quarters exhibiting chronic IMI during pregnancy was reduced 43.1% in vaccinates compared with controls, rate of new IMI during pregnancy was reduced 44.8%, and rate of new IMI at freshening was reduced 44.7%.
 

Flies. Heifers with scabs and abrasions on the teat skin surface, presumably induced by flies, had a higher frequency of infection (70%) than heifers with normal teats (40%). Moreover, herds using some form of fly control had markedly fewer infections with environmental streptococci and Staph. aureus and somewhat fewer coagulase-negative staphylococcal infections than those without fly control (Figure 5).

Figure 5. Prevalence of mastitis in heifers in herds with and without fly control   Insecticide-impregnated tail tags have been developed in attempts to control flies as well as mastitis in dairy heifers. In North Carolina, heifers reaching puberty in the summer months were fitted with tags, and the presence or absence of abnormal milk was noted at calving. Results indicated a beneficial effect of this control measure. A subsequent study using beef animals conducted during the spring and summer in Louisiana demonstrated that the same tail tags were successful in reducing fly populations (60% decrease) and the incidence of new intramammary infections during the first 2 months after placement, but thereafter, there was little control of either parameter. In animals with tags, the incidence increased from 8.6 to 15% over 2 months, while in controls, incidence increased from 17.2 to 52.4% (Figure 6).     Figure 6. Incidence of mastitis in cows fitted with tail tags during the first 2 months after placement  
Clinical Mastitis. An examination of the frequency of clinical mastitis during pregnancy among bred heifers in four commercial dairies revealed a level of 7.5%. At the time of calving, frequency of clinical cases increased to 24%, indicating that either the presence of new infections during the prepartum period led to flare-ups of clinical mastitis at freshening or that chronically infected quarters in heifers should be controlled prepartum rather than at or following freshening. Somatic cell counts in uninfected quarters decreased from 7.6 x 10⁶/ml at the initial sampling during pregnancy to 1.5 x 10⁶/ml at time of calving. In infected quarters, SCC decreased from 23.1 x 10⁶/ml during pregnancy to 4.1 x 10⁶ at calving. This again indicates the need for infected heifers to be treated in order that they enter the milking herd with low SCC.

Secretion characteristics. The monitoring of mammary secretion characteristics demonstrated that quarters with a honey-like consistency exhibited low frequencies of infection (10%), whereas those with a thin, watery secretion with clots and flakes exhibited a high frequency of infection (78%).

Season. The effect of season on prevalence of infected quarters in breeding age heifers demonstrated that level of infection decreased through winter (55.6%), spring (42.3%), and summer (30.3%) and increased in the fall (49.6%). This trend is just the opposite of what was expected in view of the association of mastitis and the fly season in this region. However, at time of calving, prevalence of infection increased from winter (44.8%) to spring (49.6%) and summer (60.5%), and decreased in the fall (35.9%).
 

2. Nickerson, S. C., and R. L. Boddie. (1992) Prevalence of heifer mastitis in Northwest Louisiana. Louisiana Dairyman. pp. 2-3, April.

3. Oliver, S. P., M. J. Lewis, B. E. Gillespie, and H. H. Dowlen. (1992) Influence of prepartum antibiotic therapy on intramammary infections in primigravid heifers during early lactation. J. Dairy Sci. 75:406-414.

4. Owens, W. E., S. C. Nickerson, P. J. Washburn, and C. H. Ray. (1991) Efficacy of a cephapirin dry cow product for treatment of experimentally induced Staphylococcus aureus mastitis in heifers. J. Dairy Sci. 74:3376-3382.

5. Owens, W. E., S. C. Nickerson, P. J. Washburn, and C. H. Ray. (1993) Prepartum antibiotic therapy with a cephapirin dry cow product against naturally occurring intramammary infections in heifers. Vet. Med. B. 41:90-100.

6. Smith, K. L., H. R. Conrad, B. A. Amiet, and D. A. Todhunter. (1985) Incidence of environmental mastitis as influenced by dietary vitamin E and selenium. Kieler Milchwirtschaftliche Forschungsberichte. 37:482-486.

7. Trinidad, P., S. C. Nickerson, and R. W. Adkinson. (1990) Histopathology of staphylococcal mastitis in unbred dairy heifers. J. Dairy Sci. 73:639-647.

8. Trinidad, P., S. C. Nickerson, and T. K. Alley. (1990) Prevalence of intramammary infections and teat canal colonizations in unbred and primigravid dairy heifers. J. Dairy Sci. 73:107-114.

9. Trinidad, P., S. C. Nickerson, T. K. Alley, and R. W. Adkinson. (1990) Efficacy of intramammary treatment in unbred and primigravid dairy heifers. J.A.V.M.A. 197:465-470.

10. Trinidad, P., S. C. Nickerson, and D. G. Luther. (1990) Antimicrobial susceptibilities of staphylococcal species isolated from mammary glands of unbred and primigravid dairy heifers. J. Dairy Sci. 73:357-362.

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