Influence of Clinical Mastitis During Early Lactation
on Reproductive Performance of Jersey Cows
A. R. Barker, F. N. Schrick, M. J. Lewis, H. H. Dowlen, A. M. Saxton, and S. P. Oliver
The University of Tennessee
Knoxville, Tennessee
Intramammary infections due to environmental pathogens such as Escherichia coli and Streptococcus uberis occur frequently during early lactation. Many of these infections originate in the nonlactating period, and result in clinical mastitis during the first 30 to 60 days after calving. Clinical mastitis during early lactation results in obvious losses such as decreased milk yield and alterations in milk composition. However, the influence of clinical mastitis on reproductive performance of dairy cows during early lactation is essentially unknown. Cullor (1990) indicated that endotoxin, a component of the cell wall of Gram-negative bacteria, induced luteolysis and influenced conception and early embryonic survival apparently via release of inflammatory mediators. Moore et al. (1991) indicated that cows from a herd with mastitis due to predominantly Gram-negative mastitis pathogens were almost twice as likely to have an altered interestrus interval following clinical mastitis compared with herdmates without clinical mastitis. However, in another herd with mastitis caused predominately by Staphylococcus aureus, no significant changes in estrous cycle length were detected. Based on the limited information reported thus far, it would appear that clinical mastitis during early lactation, particularly mastitis due to Gram-negative pathogens, can affect reproductive performance of lactating dairy cows.The purpose of the present study was to determine the influence of clinical mastitis during early lactation caused primarily by environmental pathogens on parameters of reproductive performance in a herd of high producing Jersey cows.
Materials and Methods
Jersey cows from The University of Tennessee Dairy Experiment Station dairy research herd at Lewisburg were used. General reproductive management of the herd included estrus detection at least three times daily for 15 to 30 min. In addition, milkers observed cows at milking time and all farm personnel regularly participated in estrus detection throughout the day. Following calving, cows were generally subjected to a voluntary waiting period of 60 days before first insemination. Routine postpartum reproductive exams were not performed. Only cows with retained fetal membranes, abnormal discharges, and/or cows with an anestrus period exceeding 45 days after calving were examined. Pregnancy exams were performed on all cows which did not exhibit a subsequent estrus 50 to 65 days after insemination.
Cows (n=102) experiencing clinical mastitis at some point during the first 150 days of lactation were evaluated. Samples of foremilk from quarter(s) of cows with clinical mastitis were collected aseptically upon diagnosis. Identification of mastitis pathogens to the species level was as described previously by Oliver et al. (1994). The majority of infections were due to environmental mastitis pathogens, primarily Escherichia coli, Streptococcus dysgalactiae, Streptococcus equinus and Streptococcus uberis. A group of control cows (n=103) with no clinical mastitis were evaluated also. The two groups of cows were balanced as closely as possible by lactation number and days in milk. Cows were further subdivided into the following groups: group 1- clinical mastitis before first insemination (n=48), group 2- clinical mastitis between first insemination and pregnancy (n=14), group 3 -clinical mastitis after confirmed pregnancy (n=40), and group 4 -cows with no clinical mastitis (n=103). Clinical mastitis status was based on Gram stain reaction (Gram-positive vs Gram-negative) due to the limited number of mastitis pathogens within any particular pathogen group. Distribution of clinical mastitis by Gram stain status was as follows: group 1 -31 Gram-positive and 17 Gram-negative mastitis pathogens, group 2 -5 Gram-positive and 9 Gram-negative mastitis pathogens, and group 3 -23 Gram-positive and 17 Gram-negative mastitis pathogens. Parameters of reproductive performance including services per conception, days to conception, breeding period, and days to first service were obtained from DHIA records. The influence of clinical mastitis on parameters of reproductive performance was evaluated and data were analyzed by least squares analysis of variance.
Results and Discussion
No differences in parameters of reproductive performance were detected due to milk production or between Gram-positive and Gram-negative mastitis pathogens. However, days to first service were significantly higher in cows with clinical mastitis before first insemination (93.6 days) than in all other groups of cows (71.0 days). Services per conception were higher (P<0.01) in cows with clinical mastitis after their first service (2.9) than in cows with clinical mastitis before first service (1.6) and in cows with no clinical mastitis or cows with clinical mastitis after confirmed pregnancy (1.7). Regardless of clinical mastitis status, cows with > 5 lactations required significantly more services per conception than all other parity groups. Days to conception in cows with clinical mastitis before first insemination (113.7 days), and in cows with clinical mastitis after first insemination (136.6 days) were higher (P<0.01) than in control cows and cows that developed clinical mastitis after confirmed pregnancy (92.1 days). The breeding period for cows with clinical mastitis between first insemination and pregnancy was higher (P<0.01) than in all other groups of cows. Collectively, results of this study suggest that clinical mastitis during early lactation can have a profound effect on reproductive performance of dairy cows. This phenomenon was not restricted only to Gram-negative mastitis pathogens as observed previously since similar responses were seen in cows with clinical mastitis due to Gram-positive and Gram-negative mastitis pathogens. Further studies delineating mechanisms by which intramammary infections influence reproductive performance are currently underway.
References
Cullor, J. S. 1990. Mastitis and its influence on reproductive performance in dairy cattle. pp. 176-180 In: Proc. International Symposium on Bovine Mastitis, Indianapolis, IN.
Moore, D. A., J. S. Cullor, R. H. BonDurant, and W. M. Sischo. 1991. Preliminary field evidence for the association of clinical mastitis with altered interestrus intervals in dairy cattle. Theriogenology 36:257-265.
Oliver, S. P., B. E. Gillespie, M. J. Lewis, T. L. Ingle, and H. H. Dowlen. 1994. Evaluation of chlorhexidine as a premilking teat disinfectant for the prevention of intramammary infections during lactation. J. Food Prot. 57:614-618.
Published in the 1997 National Mastitis Council Annual Meeting Proceedings, pg. 274
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