The effect of dietary protein on reproduction in the mare. V. Endocrine changes and conception during the early post partum period.

This research investigates how varying dietary protein in pregnant Anglo-Arab and Thoroughbred mares affects hormonal changes and conception during the immediate period after giving birth, including aspects such as serum progestagen, FSH, LH concentrations, ovulation and the timing of oestrous cycles.

Research Method

• The study involved 24 pregnant mares of Anglo-Arab and Thoroughbred breeds.
• The mares were divided randomly into four groups of six according to their age and breed. This was done approximately six weeks before their expected foaling date.
• The four groups were given different diets that varied in their essential amino-acid and total protein contents.
• The researchers monitored and determined the levels of serum progestagen, FSH (Follicle-stimulating hormone) and LH (Luteinizing hormone) from the day the mares gave birth until foal heat, and during the first oestrous cycle following foal heat.

Findings

• The levels of serum progestagen, FSH, and LH did not significantly vary between the groups despite the different diets.
• Progestagen levels were notably high (averagely 7.0: 5.2-16.4 ng/ml) at the time of birth, but quickly decreased within 48 hours. As progestagen levels decreased, LH levels increased from days 3-6 postpartum and reached a peak at or the day after ovulation.
• FSH concentrations declined 3-4 days postpartum and increased 2-3 days before ovulation at foal heat.
• The study found that the duration of high progestagen concentrations during the luteal phase of the following oestrous cycle had an effect on the period between ovulations (interovulatory period). Furthermore, a 12-14 day FSH cyclical release pattern was observed.
• The resumption of normal oestrous cyclicity during the postpartum period was impacted by the season and photoperiod.
• The mares that were fed a low-quality protein diet showed a larger range in the duration of the first oestrous cycle after foal heat (13-30 days) compared to mares that were fed a high-quality protein diet (18-26 days).

Conclusions and Implications

• These findings indicate that while the protein content of a mare’s diet might not significantly affect hormone levels, it could potentially influence the length and variance of oestrous cycles postpartum.
• The study provides valuable insights that can help in managing the diets of pregnant horses to ensure better reproductive outcomes after giving birth.