Effect of Monensin on Milk Production Parameters, Feed Intake, Body Weight, Body Condition, and Efficiency of Milk Production When Fed to Holsteins

Abstract

Holstein cows (primiparous n=305 and multiparous n=553) from nine locations were used in a study to measure the effect of monensin sodium on milk yield, milk composition, feed intake, body weight, body condition, and efficiency of milk production. Cows were assigned to study using a randomized complete block design. Cows were blocked on parity, days in gestation, and body weight (BW). Previous-lactation milk yield and genetic potential of multiparous and primiparous cows, respectively, were also considered for blocking. The cows were fed diets containing 0, 8, 16, or 24ppm monensin on a dry matter basis in total mixed rations (TMR). Monensin was added via a dry corn supplement which represented 5% of the dry matter of the TMR. The rations were formulated to meet National Research Council requirements and were fed ad libitum beginning 21 ± 3 days prior to anticipated calving and continued through the subsequent lactation and dry period (if applicable). Trial site personnel were blinded to assignment of animals to treatment groups. Milk production was measured daily and milk composition was determined from samples collected weekly. Feed intake was measured daily. Body weights and body condition scores (BCS, 1 to 5 scale)1 were determined periodically throughout the study. Data were analysed with mixed models which included location, treatment by location, and block as random factors, and parity, treatment, and parity by treatment as fixed factors. Previous lactation, genetic potential, BW, and BCS were considered for pre-treatment covariates. Data collected longitudinally were analyzed with repeated measures techniques.