RESPONSES OF LAYING HENS TO DIETS CONTAINING UP TO 2-PERCENT DL-METHIONINE OR EQUIMOLAR (2.25-PERCENT) 2-HYDROXY-4-(METHYLTHIO)BUTANOIC ACID

Diets supplemented with up to .6% DL-Met (DLM) or .68% 2-hydroxy-4-(me thylthio)butanoic acid (HMB, Alimet(R)) acidify the urine and reduce t he incidence of urolithiasis in pullets and laying hens. Excessive aci dification potentially may reduce eggshell quality and bone mineraliza tion by interfering with Ca metabolism and may severely challenge the liver and kidneys, which are the primary organs responsible for attenu ating metabolic acidosis. To evaluate these possibilities, 30-wk-old S ingle Comb White Leghorn hens in full production (five hens per replic ate, six replicates per diet treatment) were fed for 30 d a 15.7% CP c orn and soybean meal-based control layer ration alone or supplemented with DLM (.5, 1, 1.5, or 2%) or equimolar HMB (.56, 1.13, 1.69, or 2.2 5%). None of the diets caused mortality or gross hepatic or renal ; da mage. Hens fed diets supplemented with the highest levels of DLM and H MB exhibited significant reductions in feed intake,hen-day egg product ion, and liver mass and had lower plasma concentrations of alanine ami no-transferase and isocitrate dehydrogenase when compared with hens fe d the control diet. Kidney mass was not significantly affected by high levels of DLM or HMB,but plasma uric acid was significantly higher in hens fed 2% DLM compared with hens fed the control diet. The highest levels of DLM and HMB did not significantly alter total plasma Ca or i norganic phosphate concentrations, nor were percentage eggshell or fem ur mineralization (femur ash mass:defatted bone mass, femur ash mass:b one volume) significantly reduced. These results indicate that very hi gh dietary levels of both DLM (2%) and HMB (2.25%) cause feed avoidanc e and a corresponding reduction in egg production. Cessation of egg pr oduction probably accounted for the decrease in liver mass and for red uced plasma concentrations of hepatic enzymes. Feed avoidance may amel iorate the potential impact of very high levels of DLM and HMB on Ca m etabolism and hepato-renal function.