The Effect of Different Storage Temperatures over Time on the pH of Mammary Gland Secretions in Periparturient Mares

TL;DR

This study examines how storage temperature affects the pH of mare mammary gland secretions around foaling and finds minimal variation except at pH ~7.5.

Contribution

The study is the first to evaluate storage temperature effects on MGS pH and confirm sodium-potassium inversion in all mares at parturition.

Findings

All mares exhibited sodium-potassium inversion and acidic pH at foaling.

Milk pH is neutral in the first week postpartum and becomes slightly alkaline afterward.

Storage temperature minimally affects MGS pH except for pH ~7.5, which rises to ~8 post-storage.

Abstract

Mammary gland secretions (MGS), electrolytes, and pH are used to detect impending parturition in mares. Questions remain about whether all mares present sodium potassium inversion at labor. This study demonstrated that all mares had sodium potassium inversion and acidic pH at the time of parturition. Milk pH is neutral in the first seven days postpartum; the clinical significance of this remains to be determined. The pH of MGS can be measured with minimal variation stored at three different temperatures, except when the pH is ~7.5, which went up to ~8 immediately after the storage; however, the clinical significance of this variation can likely be negligible. This present study is the first to address these two physiological and practical questions about the pH of MGS in periparturient mares.

The objectives of this study were (i) to determine pH and electrolyte concentrations in MGS collected prepartum and at parturition, (ii) to characterize mare milk pH during the first week postpartum, and (iii) to evaluate pre-foaling MGS pH at three storage temperatures. This study outlined two hypotheses: (i) all mares exhibit acidic pH, increased calcium, magnesium, and potassium, and reduced sodium concentrations regardless of prepartum pH and electrolytes; (ii) pre-foaling MGS pH varies with storage temperature and time in an initial value-dependent manner. Twenty-three multiparous mares were monitored daily from 320 days of gestation until parturition. Pre-foaling MGS was collected, and pH was immediately measured using a hand-held pH meter. Aliquots were preserved for further electrolyte analysis. Postpartum, samples from day −7 to 0 (day of foaling) were thawed, and electrolyte concentrations (calcium, magnesium, sodium, potassium) were determined. For the three storage temperatures, pH was measured at 0, 15, 30, 45, and 60 min after storage, and hourly for 10 h post-collection. A range of pH 8 to 6.5 was included to avoid bias towards a specific pH value. The chosen pH groups were 8 (range 7.8–8.2), 7.5 (range 7.3–7.7), 7 (6.7–7.2), and 6.5 (6.2–6.6). Overall, storage temperature affects pH (p < 0.05). In conclusion, this study demonstrated that the majority of the mares had sodium–potassium inversion and acidic pH at foaling. Milk pH is neutral up to four days after foaling, becoming slightly alkaline afterwards, with undetermined clinical significance. The pH of MGS showed minimal variation across storage temperatures, except for pH ~7.5, which increased to ~8 post-storage. This study is the first to address these physiological and practical questions about MGS pH in periparturient mares.

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