Whole-farm systems modelling of livestock production systems should include appropriate consideration of the grazing animal. This raises challenges with modelling nutrients in dung and urine, grazing behaviour, dry matter intake and enteric methane loss, as examples. This paper discusses these challenges and opportunities when integrating animal models into grazing system models for evaluating productivity and environmental impact.

The data available are increasing, but diversity makes it difficult to obtain meaningful information because current research approaches are not specifically designed for complex systems. It is possible to develop new applied animal science approaches if researchers integrate modern approaches specifically designed for dealing with high quantities of diverse data, system complexity and significant abstraction. This approach implies a more efficient resource and data use, deeper system understanding, and therefore a more relevant and faster response to the society.

A biochemical, mechanistic, dynamic model of adipose tissue metabolism was developed and integrated with an existing metabolic model. The model of metabolism (Molly, UCDavis) was integrated with a model of estrous cyclicity explicitly through IGFI and steroid degradation in the liver. The model demonstrates the effects of changes in adipose tissue and liver metabolism during lactation on reproductive cyclicity.

Urinary and fecal nitrogen excretions and milk nitrogen secretions are correlated to each other and are more accurately described by a multivariate model to predict the trivariate response. By incorporating mass-balance relationships between the three dependent variables, the Bayesian model presented facilitates independent, and simultaneous estimation of both digestion and post-absorption efficiency of nitrogen use.

Ammonia and methane emissions from dairy farms could be accurately predicted if volume and nutrient composition of manure are known. A set of empirical equations was developed for predicting nutrient excretions in faeces and urine from lactating Holstein cows. The equations could predict the nutrient excretions with appreciable accuracy, when evaluated with an independent set of observations.

Variability of bodyweight among pigs complicates management decisions related to feeding and slaughter; growth models that account for variability can be used to test and to propose feeding strategies to control this variability. This study demonstrates this concept and confirms its applicability in an in vivo experiment. Decision support tools based on such a modelling approach can be developed to propose feeding strategies allowing reaching target levels of performance in many fields (growth rate, economy and environmental impact).

It is necessary to characterise the Redbro genotype to define the amino acid requirements of the lineage. The digestible lysine intake for Periods I, II and III, based on 60% of the maximum potential for nitrogen retention, was 711, 989 and 1272 mg/day, respectively. The comparisons of these studies demonstrate that Redbro birds should be fed with specific levels based on their genetic potential.

Modelling nitrogen deposition based on a bird’s weight rather than age allows the estimation of amino acid requirements to achieve a specific weight that is desirable to poultry producers. In this study, we developed a dynamic model to predict nitrogen deposition that provides consistent estimates of lysine requirements to design nutritional strategies. This dynamic model opens an alternative way to study the bird’s potential for nitrogen deposition and amino acid requirements without the need to apply destructive methods.

Modelling two options to improve the nitrogen use efficiency (NUE) to subsequently reduce nitrous oxide (N₂O) emissions for three southern Australian dairy regions found that reducing the N concentration of supplementary feed, to better balance the overall diet N concentration, reduced N₂O emissions by an order of magnitude greater than increasing the amount of N exported in milk.

We used models in an attempt to scale the results from component studies up to farm and over a full season to evaluate the potential of diverse pastures (mixtures of ryegrass, herbs and legumes) to reducing nitrogen leaching. The combined reduction in urinary nitrogen load and concentration in farm systems with 20% or 50% of the land in diverse pastures has the potential to reduce nitrogen leaching by 11% or 19%.

Understanding the rate and variation in growth of beef cattle in extensive tropical regions is needed to improve management and monitor environmental impacts including methane emissions. This study combined frequent liveweight measurements, collected remotely, with novel data-model techniques to estimate feed intake and methane emissions for individual animals. The approach provides information with potential for increasing productivity and decreasing methane emissions in extensive grazing operations.

The northern Australian beef industry emits significant quantities of livestock greenhouse gas emissions and impacts other stocks and fluxes in the carbon cycle. Sixteen years of data from the Wambiana grazing trial was used to contrast two grazing management strategies, moderate and heavy stocking rates. The moderate stocking rate treatment had a better net carbon position than the heavy stocking rate supporting previously identified benefits on land condition, financial return and reduced risk.

This research evaluated whether the Sustainable Grazing Systems (SGS) pasture and animal model could be used in northern Australian beef systems. While SGS has been used to simulate farms in southern Australia, this research demonstrated that SGS is also capable of representing tropical rangeland systems well. Recommendations for further model development were also made, such as incorporating fire, tree growth and the use of urea supplementation in the model.

The BeefSpecs fat calculator is a decision support system underpinned by a research model run in conjunction with a translation process that converts inputs recorded in live animal and carcass assessment language into research model parameters. The outputs produced by BeefSpecs include final live weight, final subcutaneous fat depth and hot standard carcass weight which are traits used to determine carcass value in the domestic and international markets.

This study evaluated the BeefSpecs fat calculator, a decision support system developed to assist the beef industry increase compliance rates with carcass specifications. BeefSpecs fat calculator accurately predicted final P8 fat in two datasets (Bos taurus and Bos taurus × Bos indicus steers). Sensitivity analysis indicated that increasing the accuracy of estimating frame score and P8 fat has the potential to significantly improve the profitability of the beef industry.

Prima facie evidence suggests that both increasing agricultural food production and reducing greenhouse gas emissions is a polarised goal. We used a whole-farm modelling approach to investigate management and genetic interventions to prime lamb enterprises that might increase production and reduce or maintain net farm emissions. Strategies satisfying this aim were those that increased the proportion of juveniles to adults but did not alter annual average stocking rate. Such interventions hold promise for sustainably intensifying agricultural productivity.

Whole-farm simulation analyses across southern Australia show that local characteristics of the soils and farming systems are as important as broad climatic factors in determining how substituting perennial for annual pastures alters the trade-off between profitability, financial risk and wind erosion risk on mixed farms. Permanent perennial grass pastures separated from continuous cropping may both increase profit and reduce business and erosion risk at low-rainfall locations with Mediterranean climates.

The intensification of livestock-farming systems is noted for its negative impact on the environment through the production of ammonia (NH₃) and greenhouse gases (N₂O, CH₄). This paper presents the development of a model simulating the flows (feed intake, manure, gas emissions) of nitrogen and phosphorus in a rabbit production farm. This model could be used to design more sustainable rabbit production systems by identifying best practices that minimise environmental impacts.

A database of milk production information from 37 published studies from six regions of the world, totalling 173 data points, was used to test four ruminant nutrition models. We conclude that not all models were suitable for predicting milk production and that simpler systems might be more resilient to variations in studies and production conditions around the world.

Maintenance requirements and efficiencies of utilising dietary energy for maintenance and tissue gain were estimated with a large database of indirect calorimetry from growing cattle. Prior knowledge was introduced into the analysis through Bayesian methods, which were used to implement parametric and non-parametric models. Biological principles and underlying assumptions of various modelling strategies were discussed to examine differences among energy retention and heat production models.

Volatile fatty acids (VFA) produced in the rumen, e.g. acetic acid, are the major sources of energy for ruminants. We describe a modelling procedure that enables data obtained when tracer VFA are infused intraruminally to be used to quantify VFA production rates (and their interconversions) in the rumen. The results enhance our understanding of how resident microorganisms digest feeds in the rumen.

The beef industry uses animal models to formulate animal rations and predict animal performance. We evaluated the precision and accuracy of two models in predicting the feed intake and liveweight gain of Ongole (Bos indicus) cattle kept under Indonesian conditions. The Large Ruminant Nutrition System provided better predictions of animal performance, and it appears suitable for use in Indonesian production systems.

This mechanistic model of grazing cattle in a tropical environment is promising and original by focusing on herbage–animal relationships and on the prehension. This model is targeted to predict the diet of animals, considering the growth of the sward and starting from measurements carried out at the level of the vegetative tillers. It completes previous approaches by integrating various spatial and temporal scales, while stressing the individual variability.

The challenge of measuring intake of individual grazing animals may be overcome using wireless sensor networks (WSN). However, there is need for benchmark data to underpin the necessary algorithm development. Pasture disappearance and chemical marker-based techniques may be used to provide such data. This study showed the need for further refinement of these techniques, and studies over a wide range of pasture conditions, in order to understand the limits within which they will produce reliable results.

This publication, based on meta-analyses of the literature, showed how some characteristics linked with dietary parameters are causes of limitation of intake in cattle. This is particularly the case of the daily total mastication time and of the level of intake of the neutral detergent fibre part of the long forage. The maximum values for these two parameters are 1000 min/day and 1.35% of liveweight.

This paper presents methane modelling results and tests the hypothesis that individual animal-controlled feeding of the supplement would result in higher enteric methane abatement than uncontrolled feeding or voluntary intake. Controlled feeding, with all animals either having the same average supplement intake or having a controlled maximum intake, resulted in higher herd- or flock-scale methane abatement than did voluntary intake feeding. Thus, supplementation aimed at reducing enteric methane is more effectively administered through some form of controlled feeding which will also be less likely to lead to excessive intake, wastage and adverse animal impacts.