Requirements Of Dietary Digestible Energy And Crude Protein Of Yili Mares During Late Pregnancy Period

This test was conducted to study the effects of feeding different digestible energy and crude protein levels in diets to Yili mares during late pregnancy period on apparent digestibility of nutrients, body weight(BW), blood biochemical indexs, colostrum ingredients and BW after delivery and blood biochemical indexs, neonatal foals body sizes and weight, to explore the appropriate requirement of digestible energy and crude protein of Yili mares during late pregnancy period.Twenty-five Yili mares aged 12-13 years with BW of 380±48 kg, parity of 5-6 in late pregnancy were selected, and were randomly divided into five groups, each group with five repeats. Five diets with different DE and CP levels were designed based on mare’s BW of 400kg. The DE and CP of each group were 8.61 MJ/kg/8.68%(91.28 MJ/d,0.920 kg/d),9.12 MJ/kg/9.35%(96.72 MJ/d,0.990 kg/d),9.39 MJ/kg/9.75%(102.16 MJ/d,1.060 kg/d),10.16 MJ/kg/10.68%(107.61 MJ/d,1.130 kg/d)and 11.06 MJ/kg/11.75%(113.05 MJ/d,1200 kg/d)(dry matter basis) respectively. The results showed that there were no significant differences of initial weight, final weight, average daily gain and BW after delivery(P>0.05), but when Yili mares fed with different DE/CP levels diets during late pregnancy period the ADG showed a linear decreasing trend(P=0.060). With increasing of dietary DE/CP levels the apparent digestibility of nutrients had no significant effect(P>0.05), but the CP apparent digestibility had increasing trend (P= 0.059),and group I digestible Ca utilization rate was significantly lower than that of the other groups(P< 0.05), and showed significant linear and quadratic increased (P< 0.05), digestible energy utilization was linear increasing trend (P=0.073). There were no significant differences of placental lactogen(PL), prolactin(PRL) and triglyceride(TG)(P>0.05). As compared with group Ⅲ, the insulin-like growth factor (IGF-I) and creatinine(CREA) contents of the group Ⅰ increased by 30.17% and 15.4%(P<0.05). The blood urea nitrogen (BUN) contents of the group Ⅰ decreased by 25.06%,26.62%and 26.11%(P<0.01), respectively, as compared with group Ⅲ, Ⅳ and Ⅴ. As compared with late pregnancy, concentrations of serum blood estradiol(E2), progesterone(PROG), estrone(E1), phosphorus(P), calcitonin(Ca) and thyroxine(T4) at postpartum decreased significantly (P<0.01), and triiodothyronine(T3), growth hormone(GH) and IGF-I decreased significantly (P<0.05) and parathyroid hormone(PTH) increased (P<0.01)significantly. The diets and physiological stage showed a significant interaction on serum contents of Ca and CREA (P<0.05).There were no significant differences of fat, protein, total solids content and somatic cell number in milk when Yili mares fed with different DE/CP levels diets during late pregnancy period(P>0.05), but the milk lactose contents of group Ⅲ was higher than group Ⅱ (P<0.05),and with different DE/CP levels diets showed a linear increasing trend(P=0.065). From the perspective of fatty acids profile in colostrum, the main saturated fatty acid (SFA) in the colostrum was the palm acid, and the main unsaturated fatty acids (USFA) were oleic acid and linoleic acid. The contents of SFA, total USFA and monounsaturated fatty acid (MUFA) were not significantly affected by the dietary DE/CP levels, but with the increase of dietary DE/CP level, the contents of the polyunsaturated fatty acids (PUFA) increased obviously.and showed a highly significant linear increasing trend(P<0.01). As compared with group Ⅰ, the PUFA contents of the group Ⅳ and Ⅴ increased by 28.17%and 31.07%(P<0.05),and showed highly significant linear increased (P<0.01).In late pregnancy period, Yili mares fed with diets with different levels of DE/CP, there were no significant differences of body weight and body size indexes of newborn foals, but the birth length, circumference of cannon, heart girth and birth weight of the newborn foals in group Ⅰ were the highest among the groups.As the results, the dietary DE and CP suitable requirements of Yili mares during the late pregnancy were 8.61 MJ/kg(91.28 MJ/d) and 8.68%(0.920 kg/d), respectively. It’s 1.27 and 1.29 times of the NRC(2007). With the increasing of dietary DE and CP level, the contents of PUFA in colostrum of Yili mares were increased, and decreasing concentrations of plasma IGF-I and FFA, and increasing contents of CREA and BUN.