**7. Efficacy of parenteral antibiotic treatment and an infusible teat seal in curing and preventing IMI**

In one study involving 1,067 pregnant heifers in 30 New Zealand herds (McDougal et al., 2005), mammary quarters were treated 1 month prepartum with 1) an infusible teat seal composed of bismuth subnitrate; 2) parenteral administration of antibiotic via injection of 5 gm of tylosin i.m. daily for 3 days; 3) teat seal plus tylosin; or 4) no treatment in order to determine if treatment reduced the prevalence of IMI and incidence of clinical mastitis postpartum. Results demonstrated that heifers treated prepartum with teat seal exhibited a reduced prevalence of IMI as well as reduced incidence of clinical mastitis. However, treatment with tylosin prepartum did not reduce prevalence of mastitis or incidence of clinical mastitis postpartum.

## **8. Efficacy of lactating cow products in curing IMI**

Lactating cow products have been used successfully in heifers when treating infections caused by the environmental streptococci and CNS immediately prior to calving. Studies on this subject are typically performed on heifers in late gestation 2 - 3 weeks before calving. In an initial study conducted at the University of Tennessee, quarters of 115 pregnant Jersey heifers were infused one time at approximately 1 week prepartum with either 200 mg

sodium cloxacillin, 200 mg cephapirin sodium, or left untreated (Oliver et al., 1992). At the time of infusion, approximately 90% of heifers were infected in one or more quarters. For heifers left untreated, 78% of animals (44.5% of quarters) remained infected at time of calving. However, only 17.6% of the heifers (4.5% of quarters) remained infected at calving if they were treated prepartum, regardless of the product used. Results demonstrated that significantly fewer antibiotic treated heifers and quarters were infected at calving compared with untreated controls. This study also examined the influence of prepartum antibiotic treatment on subsequent lactational performance, and demonstrated that heifers receiving treatment produced approximately 1,000 lb (455 kg) more milk per lactation than untreated controls.

Mastitis pathogens were isolated from 76% of untreated control quarters at 7 days before calving, from 47% of samples at 3 days after calving, and from 29% of samples at 10 days postpartum. Throughout the remainder of lactation, pathogens were isolated from 30% of control quarters. A similar percentage of samples (70%) was positive for mastitis pathogens at 7 days before calving in antibiotic-treated quarters; however, only 8% of samples obtained at 3 days after calving and 4% of samples obtained 10 days postpartum contained pathogens; throughout the remainder of lactation, mastitis pathogens were isolated from only 11% of quarters. *Strep. uberis, Strep. dysgalactiae,* and CNS species were isolated most frequently in both untreated controls and antibiotic-treated heifer mammary glands.

In a subsequent study reported by Oliver et al. (1997b), mastitis pathogens were isolated from 67% of samples obtained from control mammary glands (quarters to be left untreated) 14 days prior to expected calving, from 56% of samples obtained 3 days after calving, and from 36% of samples obtained 30 days postpartum; throughout the remainder of lactation, mastitis pathogens were isolated from 45% of quarters. In quarters to be treated with 200 mg cephapirin sodium, 64% were positive for mastitis pathogens prior to antibiotic treatment; however, only 16% of samples obtained at 3 days after calving and 8% of samples obtained 30 days postpartum contained pathogens. Throughout the remainder of lactation, mastitis pathogens were isolated from an average of 12% of quarters. Coagulase-negative staphylococci were isolated most frequently followed by environmental mastitis pathogens.

A follow-up study was conducted to determine if prepartum therapy with penicillinnovobiocin or pirlimycin hydrochloride was effective in reducing the percentage of infection with mastitis pathogens during early lactation (Oliver et al., 2004). Almost 73% of Holstein heifers (34.3% of quarters) were infected 14 days before expected calving. Of the quarters infected 14 days before parturition, 76% were uninfected following treatment with penicillin-novobiocin, 59% were uninfected following treatment with pirlimycin, and 26% were uninfected in the untreated control group. The majority of IMI were due to CNS (44%) and *Staph. aureus* (30%).

Among the Jersey heifers, 96% of animals and 71.3% of quarters were infected 14 days before calving. Of the quarters infected at 14 days before parturition, 75% were uninfected following treatment with penicillin-novobiocin, 87% were uninfected following treatment with pirlimycin, and 56% were uninfected in the untreated control group. The majority of IMI were due to CNS (61%), *Strep.* spp. (19%), and *Staph. aureus* (8%). Thus, prepartum therapy of heifer mammary glands with penicillin-novobiocin or pirlimycin hydrochloride was effective in reducing the percentage of heifers and quarters infected with mastitis pathogens during early lactation.

346 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

controls.

and *Staph. aureus* (30%).

sodium cloxacillin, 200 mg cephapirin sodium, or left untreated (Oliver et al., 1992). At the time of infusion, approximately 90% of heifers were infected in one or more quarters. For heifers left untreated, 78% of animals (44.5% of quarters) remained infected at time of calving. However, only 17.6% of the heifers (4.5% of quarters) remained infected at calving if they were treated prepartum, regardless of the product used. Results demonstrated that significantly fewer antibiotic treated heifers and quarters were infected at calving compared with untreated controls. This study also examined the influence of prepartum antibiotic treatment on subsequent lactational performance, and demonstrated that heifers receiving treatment produced approximately 1,000 lb (455 kg) more milk per lactation than untreated

Mastitis pathogens were isolated from 76% of untreated control quarters at 7 days before calving, from 47% of samples at 3 days after calving, and from 29% of samples at 10 days postpartum. Throughout the remainder of lactation, pathogens were isolated from 30% of control quarters. A similar percentage of samples (70%) was positive for mastitis pathogens at 7 days before calving in antibiotic-treated quarters; however, only 8% of samples obtained at 3 days after calving and 4% of samples obtained 10 days postpartum contained pathogens; throughout the remainder of lactation, mastitis pathogens were isolated from only 11% of quarters. *Strep. uberis, Strep. dysgalactiae,* and CNS species were isolated most

frequently in both untreated controls and antibiotic-treated heifer mammary glands.

In a subsequent study reported by Oliver et al. (1997b), mastitis pathogens were isolated from 67% of samples obtained from control mammary glands (quarters to be left untreated) 14 days prior to expected calving, from 56% of samples obtained 3 days after calving, and from 36% of samples obtained 30 days postpartum; throughout the remainder of lactation, mastitis pathogens were isolated from 45% of quarters. In quarters to be treated with 200 mg cephapirin sodium, 64% were positive for mastitis pathogens prior to antibiotic treatment; however, only 16% of samples obtained at 3 days after calving and 8% of samples obtained 30 days postpartum contained pathogens. Throughout the remainder of lactation, mastitis pathogens were isolated from an average of 12% of quarters. Coagulase-negative staphylococci were isolated most frequently followed by environmental mastitis pathogens. A follow-up study was conducted to determine if prepartum therapy with penicillinnovobiocin or pirlimycin hydrochloride was effective in reducing the percentage of infection with mastitis pathogens during early lactation (Oliver et al., 2004). Almost 73% of Holstein heifers (34.3% of quarters) were infected 14 days before expected calving. Of the quarters infected 14 days before parturition, 76% were uninfected following treatment with penicillin-novobiocin, 59% were uninfected following treatment with pirlimycin, and 26% were uninfected in the untreated control group. The majority of IMI were due to CNS (44%)

Among the Jersey heifers, 96% of animals and 71.3% of quarters were infected 14 days before calving. Of the quarters infected at 14 days before parturition, 75% were uninfected following treatment with penicillin-novobiocin, 87% were uninfected following treatment with pirlimycin, and 56% were uninfected in the untreated control group. The majority of As a part of the University of Tennessee studies, milk production and somatic cell score data from 82 control heifers and 111 heifers treated with antibiotics before calving were evaluated (Oliver et al., 2003). Milk production (actual and 305-day) was significantly higher in heifers treated prepartum with antibiotics. Additionally, treated heifers had a significantly lower somatic cell scores than control heifers (2.04 vs. 2.63). Thus, prepartum antibiotic treatment to reduce the rate of mastitis in heifers during early lactation was economically beneficial. Treated heifers produced 1,168 lb (531kg) more actual milk than the untreated controls. Based on a milk price of \$18.50/cwt this resulted in \$216.24 per heifer increase in gross revenue. Considering treatment costs of \$15.60 per heifer including teat hygiene (\$0.10), antibiotic (\$10.00), labor (\$2.50), and residue testing (\$3.00), the net revenue amounted to \$200.64 per heifer. The researchers concluded that it would be profitable to treat heifers before calving as long as the milk price was above \$0.013 per pound and as long as the increase in milk production was greater than 84 pounds (Oliver et al., 2003).

Middleton et al. (2005) also evaluated the prepartum treatment of heifers with pirlimycin hydrochloride at 10-14 days before parturition on the prevalence of IMI at calving in 2 dairy farms. Postpartum sampling revealed that heifers receiving treatment in herd A had a higher overall cure rate and higher cure rates for IMI caused by CNS and *Staph. aureus* as well as lower SCC and lower prevalence of chronic IMI compared with untreated controls. The cure rate for *Staph. aureus* of 78% was significantly greater than that for untreated controls (8%). Treated heifers in herd B had a higher overall cure rate and higher cure rate for IMI caused by CNS compared with untreated controls, but CMT (SCC) scores and prevalence of chronic IMI were not different. In contrast to previous results of using lactating cow therapy, (Oliver et al., 2003), milk production did not differ between treatment groups. Authors concluded that routine prepartum therapy of heifers may not benefit all herds.

Subsequently, Borm et al. (2006) evaluated the efficacy of lactating cow intramammary therapy (cephapirin) administered to heifers 10-21 days prior to expected calving date in a 9 herd study involving 561 animals. Results demonstrated a 59.5% cure rate among mammary quarters that were infected prepartum and treated with antibiotic vs. untreated controls (31.7%). However, treatment did not significantly affect SCC or milk yield during the first 200 days of lactation. This observation is similar to that found by Middleton et al. (2005) who observed that although successful, treatment did not necessary reduce SCC or result in greater milk production. Authors concluded that prepartum treatment of heifers with lactating cow antibiotics may not be warranted as a universal strategy for mastitis management.

The studies on prepartum treatment with lactating cow therapy administered 7 - 21 days before calving (Borm et al., 2006; Oliver et al., 1992, 1997b, 2003, 2004) have shown treatment to be effective for quarters infected with CNS 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 benefit in curing infections or salvaging mammary tissue. At this point, the tissue damage would have already been done, and affected quarters should have been treated earlier in gestation to: 1) cure existing infections; 2) reduce chronic inflammation; and 3) allow mammary tissue to develop normally during the later stages of pregnancy.

Results of these trials demonstrated that nonlactating and lactating cow antimicrobial treatment of heifers known to be at risk for developing IMI is advantageous because the cure rate is much higher than that obtained when treating infections during lactation. In addition, most studies showed that SCC are lower, there is no milk loss due to therapy , risk of antibiotic residue at calving is minimal, and future milk production is increased in heifers cured of IMI.
