Effects Of Different Levels Of Calcium And Phosphorus Diets On Nutrient Digestion And Metabolism,Milk Performance And Plasma Biochemical Parameters Of Yili Mares During Lactation Period

The objective of this study was to evaluate the effects of feeding different levels of calcium（Ca）and phosphorus（P）diets to Yili mares during lactation period on body weight,heart girth,nutrient apparent digestibility and metabolism,milk yield,milk composition and plasma biochemical parameters and growth development and blood biochemical parameters of foals,in order to provide references for confirming requirement of Ca and P for Yili mares during lactation period.Twenty-five Yili mares in their end of second lactation month with similar age（11-14 years old）,body weight（BW）（371±21）kg and four to six parity were selected,and divided into five groups randomly according to the BW of mares and foals,each group with 5 replicates.In the beginning of the trial（the 3rd lactation month）,dietary Ca and P levels of the five groups were（dietⅠ）45.0,30.0 g/d;（dietⅡ）48.5,32.0 g/d;（dietⅢ）52.0 and 34.0 g/d;（dietⅣ）55.5,36.0 g/d;（dietⅤ）59.0 38.0 g/d,respectively.During the 4th and 5th lactation month,dietary Ca and P levels were reduced to（dietⅠ）43.60 g/d、27.63 g/d;（dietⅡ）46.42 g/d、29.24 g/d;（dietⅢ）49.25 g/d、30.86 g/d;（dietⅣ）52.07 g/d、32.47 g/d;（dietⅤ）54.92 g/d、34.12 g/d,respectively.The trial lasted for 90 days,and every 30 days for a test cycle.The results showed as follows:（1）dietary Ca and P levels had no significant effect on body weight,heart girth of mares and growth development of foals in the 3rd,4th,5th month of lactation（P>0.05）.（2）Compared with dietⅠ,ⅡandⅢ,CP apparent digestibility of dietⅤwas significantly higher（P<0.05）.The Ca digestibility of dietⅠ,Ⅱ,Ⅲwas higher than that of dietⅣ,Ⅴ（P<0.05）.P apparent digestibility of dietⅢ,Ⅴwas higher than that of dietⅡ（P<0.05）.DietⅠhad higher apparent digestibility of DM,OM,CP,GE,NDF in the 5th month of lactation（P<0.05）.（3）The 3rd month of lactation:Utilization of DE of dietⅠ,Ⅴwas higher than that of dietⅢandⅣ（P<0.05）.The Ca utilization rate was higher in dietⅡ（P<0.05）.The4th month of lactation:DietⅢCa retention was higher than that of dietⅣandⅤ（P<0.05）.P retention of dietⅢandⅤwas higher than that of dietⅠandⅡ（P<0.05）and P retention rate was higher than that of dietⅡ（P<0.05）.The 5th month of lactation:The energy metabolism of dietⅠwas the highest in each group（P<0.05）.The Ca utilization rate of dietⅠ,Ⅲ,ⅣandⅤwas significantly higher than that of dietⅡ（P<0.05）.（4）Dietary Ca,P levels had no significant effect on milk yield and milk composition of Yili mares in the 3rd month of lactation（P>0.05）.DietⅠmilk Ca content was higher than that in other groups in the 4th month of lactation（P<0.05）.Milk Ca content of dietⅤwas higher than that of dietⅡ,ⅢandⅣin the 5th month of lactation（P<0.05）.（5）Twenty-seven kinds of fatty acids were detected in the horse milk fat,and contents of decanoate,laurate,myristate,palmitoleate andα-linolenic acid were more than 5%,and palmitate,cis-9-oleic acid and linoleate acid were more than 10%.（6）The PTH level of dietⅠandⅢin the 3rd lactation month was higher than that in other groups（P<0.05）.The levels of Ca,P,PTH,CT and BGP were not significantly affected by dietary Ca and P levels in the 4th lactation month（P>0.05）.The plasma Ca²⁺level of dietⅤwas higher than that of dietⅠandⅢin the 5th lactation month（P<0.05）.（7）The progesterone level in dietⅡ,ⅣandⅤwas higher in the 3rd month of lactation（P<0.05）.DietⅢPRL levels and dietⅡprogesterone levels compared with the other group were higher in the 5th month of lactation（P<0.05）.Compared with dietⅣandⅤ,the level of PL of dietⅠandⅢwas significantly higher（P<0.05）.（8）The levels of plasma Ca,P,PTH and BGP of foals showed no significant differences when mares fed different levels of dietary Ca and P levels in the 3rd month of lactation（P>0.05）.Plasma Ca²⁺level of dietⅤwas higher than that of other groups in the 4th month of lactation（P<0.05）.Compared with dietⅢandⅣ,the level of PTH of dietⅠandⅡwas significantly higher（P<0.05）,and the level of CT in dietⅠwas higher than that of other groups in the 5th month of lactation（P<0.05）.In conclusion,under the experimental conditions,suitable dietary Ca and P are beneficial to improve the digestibility and utilization of nutrients,and maintain a high level of energy metabolism.The increase of dietary calcium and phosphorus can increase the milk yield linearly,which suggested different levels of calcium and phosphorus diets can be selected according to production needs.The recommended feeding amount of calcium and phosphorus of Yili mares during lactation period is 45.03 g/d,30.05 g/d in the 3rd month of lactation,and 43.60 g/d,27.63 g/d in the 4th,5th month of lactation,respectively.