R.W. Blake

An optimization model of the dual-purpose cattle production system in the humid lowlands of Venezuela

Abstract We developed a deterministic, multi-period linear programming (LP) model of the dual-purpose (milk-beef) cattle production system in the Sur del Lago region of Venezuela. The LP model selected animal, forage, and purchased feed activities subject to nutritional, land, and herd composition constraints to maximize discounted herd net margin. A cattle nutrition model provided original coefficients for feeds and animal nutrient requirements. Revised coefficients resulted from an iterative procedure to avoid errors from the interaction between diet and requirements. Model applications demonstrated that alternatives to traditional feeding practices are profitable and nutritionally feasible. However, the benefits of alternative nutritional management depend on labor availability. Our simulation of price policy changes in the late 1980s indicated that dual-purpose producers may experience increased relative incentives for milk production under the new input and output prices. The model is adaptable to dual-purpose production systems elsewhere in Latin America.

Environmental Impacts of Livestock in the Developing World

(2001). Environmental Impacts of Livestock in the Developing World. Environment: Science and Policy for Sustainable Development: Vol. 43, No. 2, pp. 7-17.

Economic analysis of alternative nutritional management of dual-purpose cow herds in central coastal Veracruz, Mexico.

Market information was combined with predicted input–output relationships in an economic analysis of alternative nutritional management for dual-purpose member herds of the Genesis farmer organization of central coastal Veracruz, Mexico. Cow productivity outcomes for typical management and alternative feeding scenarios were obtained from structured sets of simulations in a companion study of productivity limitations and potentials using the Cornell Net Carbohydrate and Protein System model (Version 6.0). Partial budgeting methods and sensitivity analysis were used to identify economically viable alternatives based on expected change in milk income over feed cost (change in revenues from milk sales less change in feed costs). Herd owners in coastal Veracruz have large economic incentives, from

Limitations and potentials of dual-purpose cow herds in Central Coastal Veracruz, Mexico

584 to

Profit-Maximizing Dairy Sire Selection Package

1,131 in predicted net margin, to increase milk sales by up to 74% across a three-lactation cow lifetime by improving diets based on good quality grass and legume forages. This increment is equal to, or exceeds, in value the total yield from at least one additional lactation per cow lifetime. Furthermore, marginal rates of return (change in milk income over feed costs divided by change in variable costs when alternative practices are used) of 3.3 ± 0.8 indicate clear economic incentives to remove fundamental productivity vulnerabilities due to chronic energy deficits and impeded growth of immature cows under typical management. Sensitivity analyses indicate that the economic outcomes are robust for a variety of market conditions.

Modelling the economics of animal health control programs using dynamic programming

Feed chemical and kinetic composition and animal performance information was used to evaluate productivity limitations and potentials of dual-purpose member herds of the Genesis farmer organization of central coastal Veracruz, Mexico. The Cornell Net Carbohydrate and Protein System model (Version 6.0) was systematically applied to specific groups of cows in structured simulations to establish probable input–output relationships for typical management, and to estimate probable outcomes from alternative management based on forage-based dietary improvements. Key herd vulnerabilities were pinpointed: chronic energy deficits among dry cows of all ages in late gestation and impeded growth for immature cows. Regardless of the forage season of calving, most cows, if not all, incur energy deficits in the final trimester of gestation; thus reducing the pool of tissue energy and constraining milking performance. Under typical management, cows are smaller and underweight for their age, which limits feed intake capacity, milk production and the probability of early postpartum return to ovarian cyclicity. The substitution of good-quality harvested forage for grazing increased predicted yields by about one-third over typical scenarios for underweight cows. When diets from first parturition properly supported growth and tissue repletion, milk production in second and third lactations was predicted to improve about 60%. Judiciously supplemented diets based on good quality grass and legume forages from first calving were predicted to further increase productivity by about 80% across a three-lactation cow lifetime. These dual-purpose herd owners have large incentives to increase sales income by implementing nutritional strategies like those considered in this study.

Estimating the effectiveness of extension information systems using farm trials and subjective probabilities

The Net Present Value Sire Summary Professional Package (NPVSS) is a microcomputer program designed for technical personnel to help dairy producers better manage investments in genetic improvement. NPVSS is written in C language, utilizes the MS-DOS operating system, and requires 256K of RAM. It is menu driven and includes parameter screens to define herd management characteristics of individual producers. Profit rankings of bulls can be generated to evaluate alternative: a) objective functions (selection policies for genetic merit in milk income and type scores), b) herd management performance factors (conception rate, calving interval, age at first calving), and c) economic factors (milk price, semen price, discount rate, planning horizon).

Effects of weed control and manure application on nutrient fluxes in the shifting cultivation milpa system of Yucatán

Abstract A new application of an optimization tool, dynamic programming (DP), is described to model the economics of animal health control programs. To demonstrate the value of this technique, a model is applied to determine optimal net benefits of controlling East Coast fever (ECF) in Malawi Zebu cattle in the Lilongwe plateau. The objective function was the present value of net benefits due to treatment, defined as mortality savings minus treatment costs. Mortality savings were based on decreased mortality from ECF following treatment. Model constraints included herd size, animal (herd) nutritional requirements, and program budget. Treatment options were tank dipping in acaricide, and vaccination. Secondary data from a dipping trial of 1800 Malawi Zebu cattle conducted from 1991 to 1994 were used to determine probabilities of mortality. Total optimal net benefits of long-term treatment (25 years, i = 10%) from vaccination (Malawi Kwacha (MK) 21 069) exceeded benefits for treatment with chlorfenvinphos acaricide (MK15 203).

Effect of Herd Environment on the Genetic and Phenotypic Relationships Among Milk Yield, Conception Rate, and Somatic Cell Score in Holstein Cattle

A method of combining survey data and Dairy Herd Improvement Association (DHIA) records to achieve low cost farm trials is presented. Farm trials and surveys of current practices and production responses are useful to identify yield gaps between expectations predicted from experimental findings and actual field results. Different management schemes can be ranked using subjective probabilities and stochastic dominance to enhance successful implementation of research findings and to increase the feedback between researchers, extension workers, and producers. A survey of current masitis control practices and expected milk yield response is the example. Combining survey results with DHIA records allowed estimating the relationship between somatic cell counts (SCC) and milk yield. Eliciting beliefs about the relationship between sec and milk yield showed that producers agreed with predictions from the statistical model. Subjective probabilities about SCC and mastitis control practices showed that our sample of experts and producers consistently ranked the different practices but extension agents had no consensus about the the most or least effective ones.

Interaction Between Milk Yield of Holstein Cows in Mexico and the United States

Maize (Zea mays L.) cultivation under the shifting cultivation system of Yucatán, Mexico, is normally limited to 2–3 years due to nutrient depletion and weed pressure. This study was undertaken to evaluate the effect of manure application and weed control on partial nutrient budgets for maize, and assess the effect of grain-only or whole-plant harvest on nutrient removal. Two farms were selected near Mérida, Mexico, each including two cultivation years. Maize grain, stem, and leaf fractions were harvested and analyzed for N, P, and K concentrations, and compared to quantities added through manure, to generate partial nutrient budgets. Multiple years of cultivation did not change soil organic matter content while extractable P was reduced (53–62%) at both farms and extractable K was lower (22%) for farm 1. Plant fractions contained similar amounts of N, while P accumulated in grain, and stem and leaf contained the largest K pools. Applied treatments affected crop nutrient removal predominantly through crop yield. Partial nutrient budgets suggested that with stover removal, the lower rate of manure may be sufficient to maintain P, but not N or K; whereas with the higher rate of manure all partial budgets were positive, suggesting nutrient accumulation over time.