Effects Of Rumen Lysine And Methionine On Growth Performance And Carcass Quality Of Holstein Milk Bull

The present study was conducted to determined the impacts of adding of different levels ofrumen protected lysine (RPLys) and methionine (RPMet), on growth performance andcarcassquality in Holstein bulls. The experimental design for this study was single-factorrandomized design.Twenty five healthy Holstein bulls with similar13months of age, bodyweight and body size were divided into five groups, each group contain five bulls. The controlgroup was fed the basal diet, the other three groups were fed the basal diet with addedRPMet15g/d, RPLys30g/d, and RPMet15g+RPLys30g/d, respectively. The group5wasadded RPMet15g+RPLys30g/d in the low-protein diet, which was abbreviated RPLys+RPMet (L). Adaptation periodand experimental period lasted10days and150days,respectively. The results show that:(1) The experimental group had higher (P <0.05) bodyweight, average daily gain, and feed conversion ratio compared to the control. The end weightand feed conversion ratio of RPLys+RPMet and RPLys+RPMet (L) were, higher than controlRPLys group, and RPMet group (P <0.05), but the difference between them was not significant(P>0.05)(2) Rumen protected lysine and methioninehada significant influence (P <0.05) onchest widthof Holstein bulls and no significant effect body on heightand body length (P>0.05).The Chest widthof RPLys+RPMet (L) group and RPLys+RPMet group were increased (P<0.05) by9.16cm and9.14cm, respectively.(3) Rumen protected lysine and methioninehadsignificant effects on meat weight, meat percentage, carcass, and meat to bone rate (P <0.05) ofHolstein bull compared with the control. RPLys group RPLys+RPMet group RPMet hadhigher (P <0.05) meat weight than control group, meat weight of RPLys+RPMet (L) groupwas higher (P <0.05) thancontrol group. RPLys hadthe highest slaughter rate (50.33%) andwere higher (P <0.05) than RPLys+RPMet (L) group and the control group. The control grouphadthe lowestmeaty to bones rato (3.98%) and was significantly lower (P>0.05) than the otherfour groups,(4)Rumen protected lysine and methioninehad no significant effect (P>0.05) oneye muscle area, shear force, cooking loss, marbling, pH, and flesh of Holstein bull.(5)Rumenprotected lysine and methionine had a significant effect (P <0.05) on muscle protein contentofHolstein bull. RPLys+RPMet group and RPLys+RPMet (L) group had the highest crudeprotein content but there was no significant difference between them (P>0.05).(6)Rumen protected lysine and methionine had a significant effect(P <0.05)on threonine, leucine, asparticacid, serine, glutamic acid, glycine, alanine, cystine, tyrosine, proline content,and total aminoacid content of Holstein bull beef. The threonine, leucine, arginine of ofRPLys+RPMet groupand RPLys+RPMet (L) group in essential amino acids were significantly higher (P <0.05) thanother groups, the isoleucine of RPLys+RPMet group was significantly higher than the othergroups (P <0.05). The aspartic acid, glycine and glutamic acid of RPLys+RPMet group andRPLys+RPMet (L) group were significantly higher (P <0.05) than the other groups. Inaddition, RPLys+RPMet group and RPLys+RPMet (L) group werealso significantly higherthan the other groups (P <0.05) except for tyrosinein non-essential amino acid,. The tyrosine ofRPLys+RPMet group and RPMet group was significantly higher (P>0.05) than the othergroups. The total amino acid content of RPLys+RPMet group and RPLys+RPMet (L) wassignificantly higher than the other groups (P <0.05).(7)Rumen protected lysine andmethioninehad no significant effect(P>0.05) onfatty acid compositionin beefof Holsteinbulls.(8) The costof basal diet was11.55yuan/day, The cost basal diets added RPLys+RPMetwas14.25yuan/day. While the costoflow-protein diets added RPLys+RPMet was12.97yuan/day, it decreased1.28yuan compared with RPLys+RPMet group. The current beef pricewas16yuan/kg。economic efficiency of the control group，RPLys+RPMet group, and RPLys+RPMet (L) groupwas5.09,7.35, and7.67yuan/dayper head, respectively. The economicefficiency of RPLys+RPMet group and RPLys+RPMet (L) group were higher than thecontrol group, while the economic efficiency of RPLys+RPMet (L) group washigher (0.32yuan/day·per head)than RPLys+RPMet group.These results show that the addition of rumen protected lysine and methionine in Holsteinbulls effectively improved the growth performance, carcass index, and amino acid compositionof beef, but had no significant effect on beef quality and fatty acid content. In conclusion,rumenprotected lysine and methionine can improve growth performance and carcass qualityofHolstein bull. In addition,it can also reduce the cost of feeding and increase economicefficiencyat a certain extent.