Naturally occurring mastitis effects on timing of ovulation, steroid and gonadotrophic hormone concentrations, and follicular and luteal growth in cows

Estrus to ovulation (E-O) intervals in uninfected cows (n=22) and in cows with clinical (n=9) or subclinical (n=37) mastitis. a) Percentage of cows exhibiting an extended E-O interval and cows that did not ovulate during the 96-h experimental period after onset of estrus. An asterisk indicates the difference between uninfected cows and subclinical or total mastitic cows that exhibited an extended E-O interval or those that did not ovulate (P<0.05). b) The E-O interval in uninfected cows exhibiting a normal interval and in clinical or subclinical mastitic cows exhibiting a normal or extended interval. One uninfected cow with extended E-O interval (76 DIM; fourth lactation; 54kg of milk/d; SCC 43 × 10³ cells/mL) that had postpartum disease was not included. Four of 12 cows did not ovulate during the experimental period. An asterisk indicates the difference in E-O interval between mastitic cows exhibiting an extended interval and uninfected or mastitic cows exhibiting a normal interval (P<0.01).

Mean (±SE) concentrations of cortisol in plasma from 3 representative days around estrus (d 19, 0, and 1) in uninfected cows (n=9) exhibiting a normal estrus to ovulation (E-O) interval and in subclinical or clinical mastitic cows exhibiting normal (n=14 or 5, respectively) or extended (n=5 or 2, respectively) E-O intervals.

Mean (±SE) concentrations of estradiol in plasma at onset of estrus in uninfected cows (n=11) exhibiting a normal estrus to ovulation (E-O) interval and in subclinical or clinical mastitic cows exhibiting normal (n=14 or 6, respectively) or extended (n=6 or 2, respectively) E-O intervals. An asterisk indicates the difference between uninfected, clinical mastitic, and subclinical mastitic cows exhibiting a normal E-O interval and subclinical and clinical cows exhibiting an extended E-O interval (P<0.05).

Pulsatile LH concentrations in representative uninfected, subclinical mastitic, and clinical mastitic cows. Samples were taken in the follicular phase over 6h at 15-min intervals.

Concentrations of LH in plasma around the preovulatory surge. a) Means of uninfected (n=10), subclinical mastitic (n=10), or clinical mastitic (n=5) cows exhibiting a normal estrus to ovulation interval. Pooled SEM are 1.1, 1.8, and 1.6 ng/mL, respectively. b) Individual LH concentrations of 3 mastitic cows exhibiting low LH surges, which subsequently manifested delayed ovulation. c) Individual LH concentrations of 2 mastitic cows exhibiting normal but delayed LH surges, which subsequently manifested delayed ovulation. d) Individual LH concentrations of 2 mastitic cows that did not exhibit or exhibited a minimal LH surge and subsequently did not ovulate during the 96-h experimental period.

a) Mean concentrations of progesterone in plasma of uninfected cows (n=14), cows with clinical mastitis (n=7), and cows with subclinical mastitis (n=27) exhibiting a normal estrus to ovulation (E-O) interval, and cows with subclinical mastitis (n=5) exhibiting an extended E-O interval. Data from 1 uninfected cow and 1 clinical mastitic cow, which had exhibited an extended E-O interval, are not shown. Pooled SEM are 0.19, 0.3, 0.13, and 0.37 ng/mL, respectively. b) Mean volume of the corpus luteum in uninfected cows (n=18), cows with clinical mastitis (n=7), and cows with subclinical mastitis (n=32) exhibiting a normal E-O interval, and cows with subclinical mastitis (n=6) exhibiting an extended E-O interval. Pooled SEM are 524, 841, 393, and 447mm³, respectively. Progesterone in plasma and the corpus luteum volume did not differ among groups, and there were no interactions between group and day.

Growth patterns of the first- and second-wave dominant follicles during the estrus cycle following ovulation of uninfected (n=17), clinical mastitic (n=7), and subclinical mastitic (n=32) cows exhibiting a normal estrus to ovulation (E-O) interval, and subclinical mastitic cows (n=6) exhibiting an extended E-O interval. Pooled SEM for the respective groups during the first follicular wave were 0.6, 0.8, 0.3, and 0.8mm, and during the second follicular wave were 0.5, 1.0, 0.4, and 0.9mm. The second-wave dominant follicle (d 14–20) was smaller in subclinical cows with an extended E-O interval compared with uninfected and subclinical-normal groups (P<0.05).

Numbers of a) medium follicles (5–9mm) and b) large follicles (>10mm) of uninfected (n=17), clinical mastitic (n=7), and subclinical mastitic (n=32) cows exhibiting a normal estrus to ovulation (E-O) interval, and subclinical mastitic cows (n=6) exhibiting an extended E-O interval. Pooled SEM for the respective groups for the number of medium follicles were 0.25, 0.21, 0.19, and 0.46 and for large follicles were 0.08, 0.09, 0.07, and 0.17, respectively. The number of medium follicles was greater in subclinical cows with an extended E-O interval compared with the other groups (P<0.05). The number of large follicles did not differ among groups, and there was no interaction of group by day.