Abstract: The purpose of this experiment was to study the effects of diets with different calcium (Ca) and phosphorus (P) levels on colostrum composition, fatty acid composition of colostrum fat, the plasma physiological and biochemical indexes including plasma Ca and P and hormones related with Ca and P metabolism, growth and reproduction in Yili mares after delivery, and to provide reference for defining the appropriate Ca and P requirement of Yili mares during the late gestation period. Twenty-five healthy Yili mares without kinship, and with the age of 12-13 years old, body weight of (380±32) kg, parity of 4-5 births and about in the 10 th gestational month were selected and randomly divided into 5 groups with 5 replicates in each group. Ca feeding levels of the 5 groups were 36.00, 39.00, 42.00, 45.00 and 48.00 g·d^-1, respectively and P feeding levels were 26.30, 28.30, 30.30, 32.30 and 34.30 g·d^-1, respectively. The pre-test period was 10 days, and the experimental period lasted from the 11th day of the trial to the 2nd day after delivery. Samples of colostrum and fasting blood were collected within 12 hours after delivery to determine the milk composition, fatty acids content in milk fat, and plasma concentration of Ca, P, parathyroid hormone (PTH), calcitonin (CT), osteocalcin (OC), placental prolactin (PL), pituitary prolactin (PRL), estrone (E₁), estradiol (E₂), progesterone (PROG), thyroxine (T₄), triiodothyronine (T₃), growth hormone (GH), and insulin-like growth factor-Ⅰ (IGF-1). The results showed that:1) Dietary Ca and P levels had no significant effect on the Ca, P, milk fat percentage and lactose percentage in colostrum, but there were significant differences in milk protein percentage, total solids, somatic cell counts, total saturated fatty acids (SFA) and unsaturated fatty acids (UFA) percentages in milk fat among groups (P<0.05). With the increase of dietary Ca and P levels, the concentration of P, milk protein percentage and UFA percentage in colostrum significantly increased linearly (P<0.05), total solids significantly increased quadraticly (P<0.05), and lactose, SFA and myristic acid percentage significantly decreased linearly (P<0.05). 2) Plasma concentrations of OC and PROG were significantly affected by dietary Ca and P levels (P<0.05). With the increase of dietary Ca and P levels, the concentration of plasma ionic Ca, CT and OC significantly decreased linearly (P<0.05), while the concentration of PTH and PROG significantly increased linearly (P<0.05). Dietary Ca and P levels had no significant effect on the concentration of reproduction hormones such as PL, PRL, E₁, E₂, and growth and metabolism hormones such as T₃, T₄, GH and IGF-1. In this experiment, it can be concluded that dietary Ca and P levels affect colostrum compositions by increasing the milk protein percentage and total solids content, changing the saturated fatty acid and unsaturated fatty acid content in milk fat, affect Ca and P metabolism by reducing OC concentration, and affect fertility status by increasing PROG concentration.

Key words: Yili mares, late gestation period, calcium, phosphorus, postpartum, colostrum, fatty acid, osteocalcin, progesterone