THE EFFECT OF DIETARY-PROTEIN ON REPRODUCTION IN THE MARE - V - ENDOCRINE CHANGES AND CONCEPTION DURING THE EARLY POST-PARTUM PERIOD

Pregnant Anglo-Arab and Thoroughbred mares (n = 24) were divided rando mly according to age and breed into 4 groups of 6 mares each from appr oximately 6 weeks before their expected foaling date. Diets received b y the 4 groups varied in essential amino-acid and total protein conten ts. Serum progestagen, FSH and LH concentrations were determined from the day of parturition until foal heat and during the Ist oestrous cyc le following foal heat. Serum progestagen, FSH and LH concentrations d id not differ between the treatment groups. Progestagen concentrations were high ((x) over bar = 7.0: 5.2-16.4 ng/ml) at parturition but dec reased rapidly within 48 h. As progestagen concentrations decreased LH concentrations increased from Days 3-6 post partum to reach maximum v alues at, or the day after ovulation. FSH concentrations declined 3-4 d after parturition and increased 2-3 d before ovulation at foal heat. The duration of elevated progestagen concentrations during the luteal phase of the subsequent oestrous cycle affected the interovulatory pe riod. A 12-14 d FSH cyclical releasing pattern occurred. Season/photop eriod affected the resumption of normal oestrous cyclicity during the post partum period. The duration of the Ist oestrous cycle after foal heat in mates fed a low-quality protein diet showed a greater range (1 3-30 d) compared to mates fed a high-quality protein diet (18-26 d).