Responses of Laying Hens to Diets Containing up to 2% DL-Methionine or Equimolar (2.25%) 2-Hydroxy-4-(Methylthio)Butanoic Acid

Abstract

Diets supplemented with up to .6% DL-Met DLM) or .68% 2-hydroxy-4-(methylthio)butanoic acid (HMB, Alimet®) acidify the urine and reduce the incidence of urolithiasis in pullets and laying hens. Excessive acidification potentially may reduce eggshell quality and bone mineralization by interfering with Ca metabolism and may severely challenge the liver and kidneys, which are the primary organs responsible for attenuating metabolic acidosis. To evaluate these possibilities, 30-wk-old Single Comb White Leghorn hens in full production (five hens per replicate, six replicates per diet treatment) were fed for 30 d a 15.7% CP corn 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 2.25%). None of the diets caused mortality or gross hepatic or renal damage. Hens fed diets supplemented with the highest levels of DLM and HMB exhibited significant reductions in feed intake, hen-day egg production, and liver mass and had lower plasma concentrations of alanine amino-transferase and isocitrate dehydrogenase when compared with hens fed 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 inorganic phosphate concentrations, nor were percentage eggshell or femur mineralization (femur ash mass:defatted bone mass, femur ash mass:bone volume) significantly reduced. These results indicate that very high dietary levels of both DLM (2%) and HMB (2.25%) cause feed avoidance and a corresponding reduction in egg production. Cessation of egg production probably accounted for the decrease in liver mass and for reduced plasma concentrations of hepatic enzymes. Feed avoidance may ameliorate the potential impact of very high levels of DLM and HMB on Ca metabolism and hepato-renal function.