David T. Galligan

Optimizing replacement of dairy cows: modeling the effects of diseases

We modified an existing dairy management decision model by including economically important dairy cattle diseases, and illustrated how their inclusion changed culling recommendations. Nine common diseases having treatment and veterinary costs, and affecting milk yield, fertility and survival, were considered important in the culling decision process. A sequence of stages was established during which diseases were considered significant: mastitis and lameness, any time during lactation; dystocia, milk fever and retained placenta, 0-4 days of lactation; displaced abomasum, 5-30 days; ketosis and metritis, 5-60 days; and cystic ovaries, 61-120 days. Some diseases were risk factors for others. Baseline incidences and disease effects were obtained from the literature. The effects of various disease combinations on milk yield, fertility, survival and economics were estimated. Adding diseases into the model did not increase voluntary or total culling rate. However, diseased animals were recommended for culling much more than healthy cows, regardless of parity or production level. Cows in the highest production level were not recommended for culling even if they contracted a disease. The annuity per cow decreased and herdlife increased when diseases were in the model. Higher replacement cost also increased herdlife and decreased when diseases were in the model. Higher replacement cost also increased herdlife and decreased the annuity and voluntary culling rate.

Economic optimization of dairy heifer management decisions

Abstract A farmer exercises control over the heifer rearing unit in two main areas: a nutritional plane of growth and the moment of insemination. The two management controls interact with biological aspects of growth thereby influencing future profitability of the dairy heifer. A dynamic programming model was developed to optimize these decisions for individual heifers, using the hierarchic Markov process (HMP) technique. HMP provides a method to model a wide variety of heifer calves, differing in age, season, body weight, reproductive status and prepubertal growth level. Under Dutch conditions the optimal rearing strategy resulted in an average calving age of 22.6 months at a calving weight of 564 kg. Faced with the scarcity of exact information on the interrelationships of rearing strategies with the productivity of the dairy replacement, the strength of this heifer model lies in the field of the sensitivity analyses by providing valuable information regarding the critical components of heifer rearing.

Mathematical models of the population biology of Ostertagia ostertagi and Teladorsagia circumcincta, and the economic evaluation of disease control strategies

The construction and use of mathematical models of the population biology of Ostertagia ostertagi and Teladorsagia circumcincta is discussed. Simulated field trials implemented by deterministic mathematical models currently share with actual field trials the disadvantage that they convey no information concerning the risk associated with the net return demonstrated by the trial. This has important implications when it is necessary to rank disease control strategies in order of usefulness.

Application of Portfolio Theory for the optimal choice of dairy veterinary management programs

Abstract Portfolio theory, an established technique in the selection of stocks and financial instruments for investment purposes, was used as a means of selecting an economic mix of veterinary interventions in a dairy herd. The expected return on investment in six veterinary services and the associated standard deviations (as measures of risk) were calculated using computer simulation modeling techniques. Mathematical programming techniques were applied to identify the optimal combinations of veterinary interventions which maximize expected financial returns while minimizing risk. Parametric analysis was used to show how risk (standard deviation) increases as the required expected return is increased along the efficient risk-return frontier of these optimal combinations. This exercise emphasizes the importance of regarding risk in addition to expected return when considering investment in veterinary services.

Animal nutrition and management in the 21st century: dairy cattle

Dairy producers strive to increase production and efficiency. Consumers want products that contain less fat and more protein. Negative impacts of pollutants from animal agriculture on the environment must be controlled. The foregoing can be accomplished by regulating metabolic processes of the dairy cow through nutrition and biotechnology. The application of genetic engineering techniques can increase production and its efficiency, change the composition of milk and improve prevention, diagnosis and treatment of disease. Competent nutrition, reproduction and health programs and improved information systems for managing and utilizing information will be required.

Economic decision making in veterinary practice: Expected value and risk as dual utility scales

Abstract Measurement of variance or standard deviation of return values provides a method of quantifying the riskiness of a particular course of action. The quantified risk can be used together with expected return value as dual criteria for ranking alternatives in decision analysis. Furthermore, when choosing between interventions, a risk and return break-even point can be determined. Depending on the decision-makers attitude to risk, risk consideration may modify a decision made by comparison of expected values alone.

Evidence for transmission of bovine leukemia virus by rectal palpation in a commercial dairy herd

Abstract The risk of Bovine Leukemia Virus (BLV) transmission by rectal examination was determined over 22 months in a commercial dairy herd. All 167 BLV seronegative cattle, of breeding age or greater, were divided randomly into two groups and identified by neck-chain color. In the treatment group, routine rectal palpation occurred after a BLV infected animal and without a change of sleeve, while in the other group, palpation occurred in a similar manner with the exception that sleeves were changed between animals. When BLV seronegative cattle in either group were palpated after BLV infected cattle, the event and identification of the cattle involved were recorded. Serologic testing was performed eight times during the 22 month study to determine the number of animals that became infected following a palpation (an event). Thirty-one animals seroconverted during the study; 24 in the treatment (no sleeve change) group and seven in the sleeve change group. Sixteen of the animals in the treatment group that seroconverted had been palpated prior to their seroconversion. A hazard ratio (relative risk) for BLV seroconversion was determined between the two groups. Cows palpated with no sleeve change had a 2.8-fold increase in risk (confidence interval 1.1–6.8) of BLV infection. The increased risk of BLV infection associated with rectal palpation may have been affected by the presence of some highly infectious cows in the herd. This study confirms that rectal palpation without a change of sleeve may be a significant risk factor in some herds, and if efforts are made to decrease the spread of BLV in a herd, the potential for rectal sleeve transmission must be considered.

Optimal heifer management decisions and the influence of price and production variables

Abstract A dynamic programming model was developed to optimize the rearing strategy of individual heifers. The model optimized management decisions with respect to growth rate, insemination and replacement by maximizing the present value of net returns per heifer place. Faced with the scarcity of exact information on the fundamental elements of heifer rearing, sensitivity analyses were carried out to evaluate the technical and economic consequences of various price and production variables. Results for Dutch conditions showed that it was most profitable to rear heifers at the highest achievable growth rates without fattening. Based on a critical prepubertal average daily gain (ADG) of 900 g/day and a maximum achievable postpubertal ADG of 700 g/day, optimum policy resulted in an average age of first calving of 21.2 months at a body weight of 541 kg. The sensitivity analyses demonstrated a considerable impact of the critical prepubertal growth rate on both the optimal rearing policy and expected net returns. Technical and economical results were also very sensitive to seasonal influences on price and production variables. Heifer calves born in winter were the most profitable calves to rear.

Economics of porcine parvovirus vaccination assessed by decision analysis

Abstract Porcine parvovirus (PPV) is ubiquitous in swine herds throughout the U.S.A. and has an established role in reproductive failure. Infection of pregnant swine prior to development of fetal immunocompetence can result in embryonic and fetal death with serious financial consequences for the producer. Although an effective vaccine is available, many farms still rely on natural infection of gilts for developing immunity prior to breeding. A decision tree model was used to assess the economic benefits of a vaccination program against PPV. The model predicts substantial economic benefits for a breeding herd PPV vaccination program.

Use of a repeated-measures logistic regression model to predict chronic mastitis in dairy cows

Abstract The use of a repeated-measures logistic regression model is shown by evaluating the use of somatic cell counts to identify cows with chronic mastitis as determined by bacteriologic culture. The most important variable to predict wether a cow had chronic mastitis was the average linear score of all of the previous Dairy Herd Improvement Association (DHIA) test dates. The model did not accurately classify cows with chronic mastitis. Results from this study suggest that DHIA centers should be cautious using algorithms of the somatic cell count type to report cows with chronic mastitis to dairy farmers.