Study On Appropriate Supplemental Level Of RPMet And RPLys In Lactating Cows And Effects Of Lys Deficiency On Mammary AA Metabolism In Lactating Goat

Met and Lys were principal limiting amino acids of lactating dairy cows, when they werefed corn-alfalfa diets. NRC (2001) recommended the requirements of them.Studies haveshown that lactating ruminants can increase limiting amino acid supply for mammary byincreasing blood flow of the breast and increasing the extraction rate of udder. It meant thatlactating ruminants were a certain ability to adapt to the lack of the essential amino acids. Thepurposes of this study are:(1) On the basis of the amount of NRC recommended, theappropriate additive amount of Met and Lys were researched under the conditions of a typicaldairy cow diets in the north of China;(2) Represented by Lys, it was researched to affect ofthe lack of essential amino acids on amino acids metabolism of mammary gland and milkcomposition.1.Study on Appropriate Additive Amount of RPMet and RPLys in Lactating cowsRandomized grouping design was used in this trial. Experimental was designed fourgradients. Met and Lys were respectively accounted for2.4%and7.2%of the diet MPbenchmark, recommended by the NRC (2001). RPMet and RPLys were added to the surfaceof diets.Treatments on the basis of a basal diet (control group) were supplemented RPMet andRPLys per cow per day. the group I: Met13g+Lys6g; the group II: Met43g+Lys98g; thegroup III: Met74g+Lys190g. The results show that:(1)Supplementation of RPMet andRPLys is no significant effect on feed intake(P>0.05),when the cows were normallyfed;(2)the group III milk yield was significantly higher than that in the control group andgroup I (P <0.05); Impact on milk composition was not significant(P>0.05)；milk protein,milk fat and the lactose production were increased with RPMet and RPLys added, milkprotein of the group II and III were significantly (P <0.05) than the group I; milk fat andlactose yield of III group was significantly higher than the group I. Milk urea nitrogen of III group was significantly lower than the control group and the group I.(3)The Metconcentration was increased with increasing of the addition of dietary RPMet and RPLys, theplasma Met of group II and III was significantly (P <0.01) higher than the control; Lys ofgroup III was very significantly higher than that of the control group, group I and group II;plasma urea nitrogen was lower with the increasing of the addition of RPMet and RPLys, buttriglycerides are elevated; PUN of group III was significantly lower than the control group;the triglycerides of group II and III were significantly higher than that of the control group;(4)The conversion efficiency of lactation was increased with the supplementation of RPMet andRPLys.2. Effect of Lack of Lys on AA Metabolism in the Mammary Gland of Lactating Goat.In3×3Latin Square design, lactating goats were fed the basal diet to meet metabolizableprotein and energy requirements for maintain. The protein and energy of milk productionwere met by infusing glucose (GLU) and an AA mixture into the abomasums for24h. Theexperimental treatments were: an AA mixture (F)(full AA), an AA mixture excluding Lys(-L) and without amino acid (O). The results showed that (1) milk yield of group F wassignificantly (P <0.05) higher than the group of O; There was a trend of above the group of-L;milk fat and lactose content of the group-L was significantly higher than Group F; milkprotein yield of the group F was significantly higher than group-L and group O; milk protein/milk fat of group F was significantly higher than group-L.(2) Concentration of the aminoacid in the milk had no significant effect.(3) The amino acid concentration in artery and invein, amino acid concentration difference of arteriovenous, the amount of amino acidsabsorbed by mammary tissue and the ratio of amino acid uptaken by mammary tissue andoutput in milk, the group O was generally lower than group F and group-L;Lys concentrationof group–L in artery and in vein, Lys concentration difference of arteriovenous the amount ofLys absorbed by mammary tissue and the ratio of Lys uptaken by mammary tissue and outputin milk were all lower than group F; the extraction rate of Lys in mammary glands increasedbut not significantly.