Estimating the benefit:cost ratio of monensin supplementation

Abstract Text: The economic benefits of monensin supplementation have not been well documented.  The objective of this study was to estimate the benefit:cost ratio of monensin supplementation.  A deterministic, partial-budget model was used to estimate the effect of monensin supplementation in the lactating and dry cow rations of a dairy herd.  Feed costs for lactating, far-off dry, and close-up dry rations were set at $227 per ton dry matter, $2.50 per cow per day, and $3.50 per cow per day, respectively.  The non-supplemented herd level incidence rate of clinical mastitis, displaced abomasum, and clinical ketosis were set at 19.7%, 3.6%, and 6.3%, respectively.  Milk price was determined using 5-year (2011 to 2015) means of Federal Milk Marking Order product prices for butterfat ($4.50/kg), protein ($6.76/kg), and other solids ($0.73/kg).  Monensin supplementation costs per cow per day were set at $0.050 and $0.035 in lactating and dry rations, respectively.  The average response to monensin supplementation across lactation was established by a 2008 meta-analysis (2% decrease in dry matter intake, 2% increase in milk yield, 3% decrease in milk fat percentage, 1% decrease in milk protein percentage, decreased risk of ketosis (risk ratio = 0.75), decreased risk of displaced abomasum (risk ratio = 0.75), and decreased risk of mastitis (risk ratio = 0.91)).  The model was run under three scenarios to estimate the sensitivity of monensin supplementation to pre-supplemented herd milk yield, milk fat percentage, and milk protein percentage.  In scenario 1, milk yield was 31.8 kg/cow/d with 4.1% milk fat and 3.2% milk protein.  In scenario 2, milk yield was 36.3 kg/cow/d with 3.8% milk fat and 3.1% milk protein.  In scenario 3, milk yield was 40.8 kg/cow/d with 3.5% milk fat and 3.0% milk protein.  All scenarios increased income over feed cost per cow per day ($0.29, $0.35, and $0.42, respectively) and resulted in a positive benefit:cost ratio (5.6:1, 6.8:1, and 8.0:1, respectively).  The biggest factor influencing returns from monensin supplementation in all scenarios was increased income from milk sales ($5.63, $7.11, and $8.69 per cow per month, respectively).  Other factors contributing to the positive benefit:cost ratio of monensin supplementation were reduced total feed costs (-$1.53, -$1.70, and -$1.85 per cow per month, respectively) and reduced losses from disease (-$0.95, -$0.99, and -$1.02 per cow per month, respectively).  Future stochastic models should consider how variation in other factors affect the monensin supplementation benefit:cost ratio. 

Keywords: monensin, benefit:cost, economic model