Economic Benefit Associated With Antibiotic Treatment of Heifers Before Calving

E. C. Jaenicke, R. K. Roberts, H. H. Dowlen, and S. P. Oliver
The University of Tennessee
Knoxville, Tennessee


Intramammary infections (IMI) in breeding age and pregnant heifers occur frequently. Oliver et al. (1, 2, 3) demonstrated that prepartum antibiotic treatment was a simple and effective procedure for eliminating many IMI during late gestation and for reducing the prevalence of IMI during early lactation and throughout lactation. Furthermore, heifers treated with antibiotics prior to calving produced significantly more milk, milked significantly longer and had significantly lower somatic cell counts than untreated heifers (2). The objective of the present study was to quantify the economic consequences associated with prepartum antibiotic treatment of heifers.

Materials and Methods
Economic analysis was based on experimental results reported by Oliver et al. (1, 3). The initial study (1) was done in 115 pregnant Jersey heifers. Heifers were assigned alternately to three treatment groups: the 1st group received no intramammary antibiotic infusion, the 2nd group received intramammary infusion of all quarters with 200 mg of sodium cloxacillin 7 days before expected calving, and the 3rd group received intramammary infusion of all quarters with 200 mg of cephapirin sodium 7 days before expected calving. Concerns about antibiotic residues in milk from heifers that calved earlier than expected led to a second study (2) in which 82 Jersey heifers were divided into two groups. The 1st group of 42 heifers received no intramammary infusion while the 2nd group received intramammary infusion of 200 mg of cephapirin sodium 14 days prior to expected calving.

Economic Analysis: Milk production data from both studies were combined to determine the economic impact of prepartum antibiotic treatment on lactational performance of heifers. Actual milk production averaged 11,429 pounds for untreated heifers (n = 82) and 12,597 pounds for antibiotic-treated heifers (n = 111). The price of fluid milk used in the analysis was $15.80/cwt (Tennessee Agricultural Statistics Service, 1998). Treatment costs of $7.62 per heifer included the cost of a teat disinfectant and barrier teat dip, antibiotics, paper towels, and labor. Another cost that may arise is the cost of testing for antibiotic residues in milk of heifers that calve too soon after treatment. In this analysis, a cost of $2.00 was assigned to the antibiotic-treated group; however, actual costs will likely be less if only those heifers calving early require testing.

Actual heifer milk production data were used in our analysis. Using actual rather than marketable production implicitly assumes that the mean amount of milk discarded for 3 days after calving was the same for treated and untreated heifers and that the incidence of clinical mastitis later in lactation was the same for both groups. The per-heifer net revenue from treatment was calculated by the following formula: NR = p (QT - QU) - CT, where NR is the net revenue from treatment, p is the price of milk, QT - QU is the difference in milk production for treated and untreated groups, and CT is the cost of treatment. The per-heifer cost of treatment was specified to include teat hygiene, antibiotic, labor, and antibiotic residue testing costs. We calculated NR and examined how it varied as p, QT - QU, and wage changed.

Results and Discussion
Prepartum antibiotic treatment to reduce the rate of mastitis in heifers during early lactation was economically beneficial. Prepartum antibiotic-treated heifers produced 1,168-pounds more milk than the untreated control group. Multiplying this increase by a milk price of $15.80/cwt yielded a $184.54 per-heifer increase in gross revenue. Subtracting the cost of treatment from gross revenue, the net revenue from the actual production increase amounted to $174.92 per heifer. These net revenue figures included the cost of testing for antibiotic residues.

Net revenue analysis indicated that it would be profitable to treat heifers before calving as long as the milk price was above $0.008 per pound. This suggests that the milk price would not likely fall low enough to make treatment of prepartum heifers unprofitable. A similar relationship between the increase in net revenue and the hourly wage rate of labor was determined. Given a milk price of $0.158 per pound, net revenue is equal to zero where the hourly wage rate of labor equals $705.90 per hour. This suggests that treating heifers with antibiotics before calving would be profitable for wage rates below $705.90/hour. The relationship between net revenue increases and the increase in pounds of milk produced due to treatment, given a wage rate of $6.25/hr and a milk price of $0.158/lb was determined. Treatment would be profitable as long as the increase in milk production is greater than 60.9 pounds.

In conclusion, there is little question of the economic benefit associated with prepartum treatment of pregnant heifers based on experimental results of Oliver et al. (1, 2, 3). Results were quite robust for swings in the price of milk, the wage rate, and even the relative increase in milk production. Potential drawbacks of prepartum heifer treatment such as the potential for antibiotic residues in milk shortly after calving appear to be minor and controllable. As it becomes more widely known and understood that heifers have a high prevalence of intramammary infections near calving, it is likely that prepartum antibiotic treatment will become accepted as a general cost-effective procedure to reduce mastitis in heifers.

References
1. Oliver, S. P., M. J. Lewis, B. B. Gillespie, and H. H. Dowlen. 1992. Influence of prepartum antibiotic therapy on intramammary infections in primigravid heifers during early lactation. J. Dairy Sci. 75:406-4 14.

2. Oliver, S. P., M. J. Lewis, B. B. Gillespie, and H. H. Dowlen. 1997a. Antibiotic residues and prevalence of mastitis pathogen isolation in heifers during early lactation following prepartum antibiotic therapy. J. Vet. Med B. 44:213-220.

3. Oliver, S. P., M. J. Lewis, B. B. Gillespie, and H. H. Dowlen. 1997b. Prevalence of mastitis in heifers and strategies for control. Tennessee Agri-Science 181:22-27.

Presented at the National Mastitis Council 38th Annual Meeting, February 14-17, 1999. Published in the 1999 National Mastitis Council Annual Meeting Proceedings, pg. 229.
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