Chronic mastitis is associated with altered ovarian follicle development in dairy cattle

Abstract

Connection between mastitis and fertility is multifaceted; therefore, several aspects need more elucidation. In particular, the aim was to investigate if naturally occurring chronic mastitis has an effect on ovarian function. At the time of slaughter, a milk sample and both ovaries were collected from 68 cows. The presence and intensity of chronic mastitis was diagnosed by the combined evaluation of bacteriological examination and somatic cell count of the milk of each individual quarter according to the measures of the National Mastitis Council. Animals were divided into 4 groups characterized by a low (n=15), mild (n=14), intense (n=19), or severe (n=16) degree of infection. A count of visible follicles on each ovary was followed by a quantitative analysis of microscopic traits on a selected group of animals (n=16). The latter included the classification and count of the entire preantral follicle population, and the morphometric analysis of the vascular bed extension and connective stroma in the cortical region. Finally, the expression of growth and differentiation factor-9 (GDF-9) was studied. The number of follicles with diameters ranging from 1 to 3 mm and 4 to 7 mm was not affected by the degree of infection. A significant effect of the degree of udder infection was observed on the number of follicles with a diameter larger than 8 mm. Furthermore, the intensity of mastitis had no effect on the number of primordial and primary follicles, but severely affected cows showed a lower number of secondary follicles (0.5±0.1 vs. 0.2±0.03). Quantitative analysis demonstrated a decrease in the density of blood vessels (6.30±1.08 vs. 4.68±0.28) expressed as ratio of vascular bed/total area) and a higher incidence of fibrous stroma (1.60±0.99 vs. 6.04±3.08 expressed as ratio of connective tissue/total area) in the cortical area of the most affected animals. Finally, the level of GDF-9 protein within the oocytes of different follicle size was lower in the animals with the severe form of chronic mastitis (1.34±0.05 vs. 0.78±0.21 expressed as arbitrary units). In conclusion, decreased fertility of cows with chronic mastitis takes place through an effect on the ovary altering the dynamics of folliculogenesis. Within the ovary, this implies a reduction of the vascular bed and an increase in the fibrotic tissue together with a direct effect on oocyte-specific factors as GDF-9, all of which are essential regulatory elements of folliculogenesis.

Effects of Escherichia coli- and Staphylococcus aureus-induced mastitis in lactating cows on oocyte developmental competence

“…GDF9 is involved in oocyte maturation via regulation of cumulus cell function in the preovulatory follicle (Gui & Joyce 2005). A recent study reported lower GDF9 expression in primordial, primary, and secondary follicles in cows with subclinical mastitis (Rahman et al 2012). It is therefore possible that the effect on GDF9 expression is associated with subclinical mastitis, rather than the acute mastitis examined here.…”

Comparing the effects of heat stress and mastitis on ovarian function in lactating cows: basic and applied aspects

“…Lower GDF9 expression in primordial, primary, and secondary follicles of cows with subclinical mastitis was reported [53]. Oocyte maturation in follicular fluid aspirated from subclinical mastitic cows (induced by GÀ toxin) resulted in low GDF9 transcription level in MII-stage oocytes and 4-cell-stage embryos [18].…”

“…Subclinical, chronic mastitis attenuates growth of secondary and preantral follicles as well as medium-sized follicles [53]. This is associated with low expression of GDF-9, a germ-cell marker and member of the transforming growth factor b superfamily which plays a central role in folliculogenesis and oocyte maturation.…”

Intramammary administration of platelet concentrate as an unconventional therapy in bovine mastitis: First clinical application

“…Chronic mastitis is described as repeated cases of mastitis where the cow fails to respond successfully to treatment, although clinical symptoms may disappear temporarily (Akers, 2002). In our study, cows were considered affected by chronic mastitis when the SCC was >500,000 cells/mL for 3 consecutive months (Rahman et al, 2012) in a quarter-milk sample. Cows needing general antibiotic treatments were excluded from this study.…”