title: Experimental model of toxin-induced subclinical mastitis and its effect on disruption of follicular function in cows.
abstract: This study establishes an experimental model for subclinical mastitis induced by Gram-positive (G+) exosecretions of Staphylococcus aureus origin or Gram-negative (G-) endotoxin of Escherichia coli origin to examine its effects on follicular growth and steroid concentrations in Holstein dairy cows. Cows were synchronized with the Ovsynch protocol followed by a series of follicular cycles that included GnRH and PGF2α doses administered every 8 days. Cows received small intramammary doses of either G+ (10 μg, n = 10) or G- (0.5 μg, n = 6) toxin, or saline (n = 6; uninfected control) every 48 hours for 20 days. Follicular fluids were aspirated from preovulatory follicles before (aspiration one: control), at the end of (aspiration two: immediate effect), and 16 days after the end of (aspiration three: carryover effect) toxin exposure. During the 3 weeks of subclinical mastitis induced by G+ or G-, no local inflammatory signs were detected in the mammary gland and no systemic symptoms were noted: body temperatures of the treated cows did not differ from controls; plasma cortisol and haptoglobin concentrations were not elevated and did not differ among groups. Somatic cell count was higher in the treated groups than in controls, and higher in the G- versus G+ group. For analysis of reproductive responses, cows were further classified as nonaffected or affected based on an more than 20% decline in follicular androstenedione concentration in aspiration two or three relative to the first, control aspiration. Most G- (5/6) and 40% of G+ (4/10) cows were defined as affected by induced mastitis. An immediate decrease in the number of medium-size follicles was recorded on Day 4 of the induced cycle, toward the end of the 20-day mastitis induction, in the affected G+ compared with uninfected control group (1.0 ± 0.5 vs. 3.0 ± 0.4 follicles; P < 0.05); the affected G- and nonaffected G+ subgroups exhibited a similar numerical decline in the number of follicles. A carryover (but not immediate) decrease to 51% and 62% in follicular estradiol concentrations in G- affected group and G+ affected group was detected relative to controls (P < 0.05). The nonaffected G+ subgroup did not differ from its control counterparts. Based on the current experimental model, subclinical IMI induced by G+ or G- toxin disrupts follicular functions, and it seems that the ovarian pool of early antral follicles is susceptible to subclinical mastitis.
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel.
authors.forename: Ori
authors.initials: O
authors.lastname: Furman
authors.affiliation: Mastitis Reference Center, The Veterinary Institute, Bet Dagan, Israel.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Leitner
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel.
authors.forename: Zvi
authors.initials: Z
authors.lastname: Roth
authors.affiliation: Cattle Breeders Association, Caesarea, Israel.
authors.forename: Yaniv
authors.initials: Y
authors.lastname: Lavon
authors.affiliation: Institute of Animal Science, Agricultural Research Organization, Bet-Dagan, Israel.
authors.forename: Shamay
authors.initials: S
authors.lastname: Jacoby
authors.affiliation: Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University, Rehovot, Israel. Electronic address: david.wolfenson@mail.huji.ac.il.
authors.forename: David
authors.initials: D
authors.lastname: Wolfenson
mesh_terms: D000735:Androstenedione / Q000032:analysis; D000818:Animals; D001427:Bacterial Toxins; D002417:Cattle; D004731:Endotoxins / Q000008:administration & dosage; D004926:Escherichia coli; D004958:Estradiol / Q000032:analysis; D004973:Estrus Synchronization; D005098:Exotoxins / Q000008:administration & dosage; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry; D008414:Mastitis, Bovine / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology*; D006080:Ovarian Follicle / Q000473:pathology / Q000503:physiopathology*; D010053:Ovary / Q000503:physiopathology; D013211:Staphylococcus aureus
chemical_list: D001427:Bacterial Toxins; D004731:Endotoxins; D005098:Exotoxins; D000735:Androstenedione; D004958:Estradiol
keywords: Follicular development; Steroid; Subclinical mastitis