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The first paper in this series described the development of procedures for predicting the effect of management changes on wool growth rate and fleece characteristics. A model of a self-replacing flock of Merino ewes was modified to provide weekly predictions of wool growth rate, fibre diameter, staple length and staple strength. This paper presents the results of a comparison of biological predictions of the model with field observations collected under a range of seasonal conditions and stocking rates. The results of the comparisons demonstrated the ability of the model to mimic the seasonal pattern of events and the trends in pasture and sheep performance generated by a wide range of stocking rates. The model successfully predicted the direct effects of stocking rate and changing seasonal conditions, as well as the interactions between them. For most of the fleece data, the model predictions were well within one standard deviation of the field observations. No major biases in the predictions of the model were evident.

At least 25% of lambs born in Australia die before marking. Research across southern Australia has demonstrated that reducing mob size at lambing by 100 ewes will, on average, increase the survival of single-born lambs by 0.8% and twin-born lambs by 2.2%. In this paper we assessed the economic value of lambing ewes in smaller mobs to improve lamb survival. The analysis considered scenarios for Merino and non-Merino flocks where producers subdivided lambing paddocks using temporary or permanent fencing, or where ewes were reallocated within existing paddocks based on ewe pregnancy status. Optimum mob sizes were most sensitive to the type of fencing used for subdivision, whether ewes were single- or twin-bearing, whether the effect of paddock size on potential stocking rate was included and the target return on investment. Breed, ewe stocking rate, scanning percentage and lamb price also impacted optimum mob size but had a smaller effect. The optimum mob size for twin-bearing Merino and non-Merino ewes was between 34% and 60% that of single-bearing ewes and this was similar for scenarios where paddocks were subdivided or ewes were reallocated within existing paddocks. Permanent subdivision of paddocks also presents an opportunity to increase stocking rate by capitalising on the benefits of improved pasture utilisation in smaller paddocks. The relationship between paddock size and pasture utilisation is not well quantified but it has an important effect on optimum mob and paddock size. The value of reallocating ewes within existing paddocks was greatest at a scanning percentage of 150% as this presents the greatest opportunity to alter mob sizes for single- and twin-bearing ewes. The economic return from adjusting the relative mob size of twin-bearing ewes from 100% to 50% that of single-bearing ewes was up to $0.27/Merino ewe/yr and $0.44/non-Merino ewe/yr with lamb at $6/kg carcass weight. Overall, these analyses demonstrate that reducing mob size at lambing can be a profitable strategy for improving lamb survival depending on the current size of lambing mobs. However, it is difficult to provide generic recommendations to producers for the optimum mob size of ewes and value of paddock subdivision because these are dependent on enterprise-specific factors.

In the tropics, milk production systems present high diversity and distinct ability to adapt to the demands of consumers and market conditions. Knowledge of the factors that affect the quality of milk and agglomerate of production systems into fewer groups can facilitate analysis and the decisions needed to improve them. The objective of this paper was to characterize, classify and analyze dairy production systems in the Brazilian southern region, and relate their productive aspects to the physical–chemical attributes of the milk produced. A multivariate analysis was conducted with 26 indicators obtained from a survey covering 328 dairy farms. Variance was fully explained by the first three principal factors. The first factor included feeding strategies, the second included the farm’s structure traits and the third included milk composition. Canonical analysis revealed distribution of farmers into three clusters. All feeding strategies, except salt supplementation, as well as monthly milk production, herd size, number of lactating cows in farm and unstable milk frequency were important discriminant variables to determinate cluster formation. The clusters were differentiated by feeding strategies used and the high standard deviation in some of these strategies demonstrated the adoption of specific strategies in different seasons. Cluster 3 had the largest monthly milk production and larger number of lactating cows, but the productivity of cows in the different clusters was not significantly different. The lower unstable milk frequency in cluster 3 is associated with more intensive use of silage, mineral-vitamin premix and commercial concentrate in the diet of animals. The physical–chemical composition of milk and the somatic cell count did not differ between clusters.

The average dressed weight for barrows and gilts slaughtered in the United States has increased 23% since 1977, from an annual average of 163 lbs to 201 lbs in 2010. This measure of pork production includes pork produced from US born and raised hogs as well as hogs imported from Canada. This paper addresses technological change in US born and raised pork production. Since pork produced from Canadian hogs could distort estimates of technological improvement and other variables describing changes in US born and raised pork production, a method of adjusting production data series for the portion of US pork production that comes from foreign-born hogs is developed. The resulting data are used to estimate the rate of change in average dressed weight, assumed to be due to technical change in the US swine herd.

Intensive dairy farming results in significant phosphorus (P) emission to the environment. Field data indicates that farm-gate P surplus is highly positive in Finland and strategies to mitigate the surplus are needed. The objectives of this study were to build a P cycle model for dairy farms (1) and to validate the model with independent field data (2). The dairy farm nutrient management model (“Lypsikki”) described in this paper includes three sub-models: (1) soil and crop, (2) dairy herd and (3) manure management. The model is based on empirical regression equations allowing estimations of crop and milk yields in response to increased fertilisation and nutrient supply, respectively. In addition, the model includes a dynamic simulation model of the dairy herd structure and calculation of the farm-gate nutrient surplus. The model was validated with independent annual (average for 1–4 years) farm-gate P surplus data from 21 dairy farms. Model simulations were conducted using two levels of soil productivity, mean (M) and low (L). The model validation indicated a strong relationships between model-predicted and observed farm-gate P surplus: (M: R2 = 0.77 and L: R2 = 0.80). The line bias between the model-predicted and observed data was negligible and insignificant (P > 0.6) suggesting a robustness of the model. The mean biases were relatively high and significant (M: 4.7 and L: 1.8 kg/ha, P

To reduce (P) surpluses on dairy farms and thereby the risk of P losses to natural waters we studied different management alternatives by a nutrient balance model described in the companion paper. The strategies evaluated mitigating the P surpluses were: mineral P fertilisation, dietary mineral P supplementation, replacement rate, animal density, production level, feeding intensity, dietary P concentration and nutrient efficiency in crop production. Responses to several interventions (e.g. mineral P fertilisation, purchased feed P, replacement rate) were similar to those observed in Finnish field studies. Reducing or completely giving up the use of purchased mineral P fertilisers was the most efficient measure to reduce P surplus. The slope between the amount of mineral fertilisers and P surplus was 0.98–0.99 (in the field data 1.0). Increased animal density resulted in a greater P surplus, but the slope between P input from purchased feed and surplus was considerably smaller (0.65) than that of P fertilisation. Increasing milk yield with improved genetic potential of the cows would have minimal effects on P surplus per unit of product, but it would increase P surplus per hectare. When the intensity of energy and protein feeding was increased, P surplus rose markedly both per unit of product and hectare. This is (1) due to increased dietary P concentration and (2) due to smaller marginal production responses than those calculated from feeding standards. Reducing dietary P concentration by constraining P excess per kg milk in least-cost ration formulation improved P efficiency in milk production and dairy farming system. However, feed cost increased as low P energy (sugar-beet pulp) and protein (soybean meal) supplements are more expensive than cereal grains or rapeseed feeds. Improving the nutrient use efficiency in crop production had a strong influence in the whole-farm efficiency and P surplus. The modelling results showed that Finnish dairy farms have a great potential to improve P efficiency and reduce P losses to the environment, even by increasing production intensity (milk/ha). It is concluded that the most cost-effective scenario to mitigate P surpluses at a dairy farm would be to reduce or give up the use of mineral P as fertilisers and supplements, and to improve the use of present soil P reserves.

Biological productivity of grazing livestock under semi-arid conditions in northern Kenya is limited by marked seasonal fluctuations in the availability and quality of rangeland resources. With the increasing trend towards sedentarization of pastoral herds and households, the search for an alternative to herd mobility as the most effective adaptive management strategy to attenuate the effects of seasonality in production resources is an issue of growing concern. Using data collected during an experimental study conducted in pastoral goats in northern Kenya, this paper is concerned with the assessment of the effects of controlled seasonal breeding on biological herd productivity. The experiment was conducted over a period of 4 years (1984–1988) in Isiolo District, northern Kenya. The experimental treatment consisted of six different mating seasons per year, which were replicated three times over the course of the experiment. Assessment of biological productivity was done with a previously developed procedure for steady-state productivity assessments in livestock herds. The criterion used to evaluate biological herd productivity was an energetic efficiency ratio, defined as the total gross energy output of the herd divided by its total metabolizable feed energy requirements at the stationary state. The first hypothesis for testing was that there is an optimal period in a year to which breeding can be restricted to improve overall biological productivity of pastoral goat flocks. Second, a simulated, aseasonally reproducing herd was used as a reference in testing whether controlled breeding is superior to uncontrolled breeding. The general conclusion that emerged from this study is that restricted breeding can effectively be used as a management control to manipulate overall biological herd productivity primarily because of its positive effect on youngstock mortality rates. For achieving maximum energetic efficiency in pastoral goat flocks, breeding should be constrained to the long dry season (June to October). However, when compared to this breeding regime simulated aseasonal breeding performed remarkably well, and more field research is required to ascertain the superiority of controlled over aseasonal breeding.

This paper presents studies on feed utilization in two Indonesian villages (Putukrejo and Kedungsalam) with large seasonal variation in availability of feeds. The model used calculates the effect of varying degrees of feed selection on the number of animals that can be fed ad libitum, the corresponding mean liveweight gain (MLWG) per animal and total liveweight production (TLWP) of the herd. Calculations assume that, if only part of the feed is used, the feeds giving the highest intake of metabolizable energy are selected first. When feeds were pooled for the whole year, 2976 AU (animal units) could be fed ad libitum in Putukrejo and 4443 in Kedungsalam, but maximum TLWP was obtained with a smaller herd size (HS; 2300 and 3800 AU, respectively), not using the poorest feeds. Without transfer of feeds from one month to another, the maximum number of AU that could be fed ad libitum each month varied from 583 to 4130 AU in Putukrejo and from 1446 to 11080 in Kedungsalam. The optimum constant HS, giving maximum TLWP for the whole year, varied with assumptions regarding transfer of feeds between seasons. With assumptions most closely reflecting farmers' practices, optimal HS was 1200 AU for Putukrejo and between 1900 and 3200 for Kedungsalam, with MLWGs of 199 and 131-159 g AU(-1) d(-1), respectively. This corresponded well with actual HS (1320 and 2985 AU, respectively) and actual MLWG (182 g animal(-1) d(-1)). (C) 2003 Elsevier Science Ltd. All rights reserved.

This paper examines the potential to use multiple objective programming to reduce nutrient excretion from dairy cows through incorporation of nutrient excretion functions into a ration formulation framework. In a typical ration formulation model, a ration is formulated to minimize cost while providing sufficient nutrients to meet the needs of the animal type being fed. To reduce the nutrient loading, rations can be formulated to minimize cost, and nitrogen and phosphorus excretion using multiple objective programming. Rations were initially formulated to minimize cost, nitrogen excretion and phosphorus excretion. Compromise programming was then utilized to examine the impacts on ration formulation of combining the three individual objectives. The multiple objective ration formulation reduced phosphorus excretion by 5% and marginally reduced nitrogen excretion with a small increase in ration cost compared to the single objective minimum cost ration. Multiple objective programming does have the potential to reduce nutrient excretion.

Due to public concerns over food quality and animal welfare, beef producers are under increasing pressure to produce a high-quality product while still maintaining economic efficiency. Hence the need for a model for the accurate prediction of growth and carcass composition of beef cattle that is flexible enough to deal with the wide range of breeds of cattle and feeding regimes, either silage only or supplemented with concentrates, encountered on UK farms. This paper describes a model that has been developed based on a substantial database of experimental observations from a series of trials carried out by the Department of Agriculture for Northern Ireland. If animal and feed costs are provided, the model can provide information on the most economic level of concentrate feeding to achieve the animal growth and quality of carcass composition required.

This paper is the first in a series that presents the development and use of a quantitative model of a sheep grazing system. The animal growth model presented here draws from a range of sources reported in the literature, and accounts for interactions between an animal's physiological state and herbage quality on diet selection and levels of feed intake. The model estimates partition of energy between maintenance, pregnancy, lactation, wool growth and fat and protein accretion. The model was tested against a range of published data and was found to be acceptable for its intended use as a research tool to evaluate animal performance and the physical and economic consequences of alternative technologies and management strategies.

A simulation model of a breeding ewe flock was extended to facilitate the evaluation of management strategies for improving the quality of Merino wool. The model extensions described in this paper were designed to improve the prediction of wool growth rate and to provide procedures for predicting the four most important clean wool characteristics of Merino sheep, namely fibre diameter, staple length, stample strength and vegetable matter level.

Management alternatives for beef herds that varied in level of reproductive efficiency were studied by computer modelling. This paper describes the stochastic dynamic model developed to describe reproductive processes in beef cattle. The model is compared with other stochastic models of reproduction in cattle. Results from modelling different management alternatives (length of breeding season and breeding heifers 21 days ahead of cows in spring-calving herds) are discussed. Proportion of females in the breeding herd that became pregnant increased with length of breeding season and by breeding heifers ahead of cows. Proportion of females in the breeding herd that weaned a calf was mostly affected by the pregnancy rate but also by survival of calves to weaning. Average age of calves at weaning increased with increasing first-service conception rate and decreased length of breeding season. With high first-service conception rate, length of breeding season had relatively little effect on age and weight at weaning.

This paper describes the experiences of the authors with the Texas A&M University model when used to simulate the production of beef cattle in a grazing system. Problems associated with the lack of interaction between pasture and animals, including the monthly time interval, supplementation and an input parameter (weight at maturity), are discussed.

A simulation model was constructed to compare the profitability of feeding high- and low-protein diets when rearing pullets for egg production. Low-protein diets were found to be more profitable if laying adult birds were subsequently retained beyond 58 weeks of age, although predictions of the model were shown to be very sensitive to some of the inputs and production parameters incorporated in the model. The optimum length of lay for the data being analysed extended beyond 84 weeks of age. This model may be simply modified to study other genotypes and diets than those considered in this paper.

Part I demonstrated a method for deriving from standard meteorological data a ‘green season’ and a ‘dry season’ which correspond to the main periods of liveweight gain and loss respectively of cattle on native grass pastures. This paper describes (a) the geographic variation in the incidence and duration of the green season utilising a network of 77 stations in tropical Australia, and (b) the year-to-year variability for eight of these stations. Variability in the date of commencement of the green season (the termination of the dry season) differed among stations, with ranges as low as 11 weeks and as high as 20. Differences of up to 16 weeks in the median duration of the green season between stations occurred within the study area, while the range of variation from year to year at a station was as low as 13 weeks and as high as 34. Results are compared with those of previous descriptions. Difficulties imposed on management by climatic variability are discussed.

A simulation model was developed to study voluntary forage intake, energy requirements for maintenance, liveweight change and calving rate of grade Zebu cows in the Llanos of Colombia. Multiplicative correction factors were fitted to intake and maintenance requirement prediction equations researched from the literature to account for reduced intake due to sparse regrowth of recently burned native savanna and to conditions of mineral deficiency, increased intake and decreased maintenance requirement during periods of high compensatory gain during the rainy season, and increased intake and maintenance requirement due to the effects of lactation and gestation. A frequency distribution was constructed relating liveweight at time of mating to subsequent calving rate, and this was used to simulate the calving rates of cow herds in the Llanos. Use of the model would allow prediction of the amount of improved pasture or supplemental feed that would be necessary to raise calving rates in a particular herd to an acceptable level, defined as at least three calves per cow every four years. The model was fitted by computer and was then run on programmable calculators. This type of simulation is suited to regions of the world in which computer time is expensive or unavailable. Verifications, validations and experimentation with the model are presented in a companion paper.

The evaluation of wool by objective measurement means that decreases in fleece weight, such as those caused by higher stocking rates, may be wholly or partly compensated for in value by increased prices for wool of reduced fibre diameter. This paper examines the effect of such compensations on the marginal returns to increased stocking rates. Two approaches were used. First, the effect of stocking rate on gross margins was examined over a given distribution of seasons so as to determine the most profitable stocking rate. Secondly, the cash flow of a wool-producing enterprise was examined over a random sequence of years. The most profitable stocking rate was increased by objective evaluation by about 12% if a decrease in fibre diameter of one micron were associated with an increase in wool price of 10 cents per kilogramme, using fleece weight-stocking rate relationships derived from field experiments. Inventory analyses were used to examine the long-term relationships between stocking rate, financial stability and profitability. For each stocking rate studied, the cash flow and mean and minimum bank balances of a farmer were simulated over a set number of years. The stocking rate at which the highest minimum bank balance was recorded was about 15% (one to two wethers per hectare) lower than that at which the standard of living and the mean bank balance were at a maximum. That is, a risk-avoidance policy would not differ greatly from a profit-maximisation policy with respect to stocking rate.

The paper describes a package of computer programs known as ‘CAMDAIRY’, which is written for CP/M80 and MS-DOS operating systems. The core program is a bio-mathematical model of a lactating cow, which incorporates functions to predict nutrient requirements, feed intake, substitution effects when feeding concentrates, tissue mobilisation and partition of nutrient utilisation between milk production and growth. Nutrient partitioning is described by a series of asymptotic curves relating energy intake to milk production, such that energy requirements per litre increase progressively with level of milk production. This model is incorporated into an econometric model, ‘Maximum Profit’, which uses linear programming procedures to formulate rations for up to two groups of cows in a herd in a way which maximises income above feed costs, whilst meeting nutrient requirements and satisfying constraints on feed supply and milk production requirements. Other programs in the CAMDAIRY package are ‘Least Cost’, a program which calculates a leastcost ration using fixed energy requirements for milk production, and ‘Analysis’, a program which predicts likely milk production given characteristics of the cows, feed intake and feed composition.

The paper presents the results of on-station research into the potential for winter fattening of steers and follows up the results with testing by communal area farmers. The on-station diets were based on bran fed at two levels in conjunction with stover only or stover treated with ammonia. Ammoniation produced no significant response on any of the parameters measured, whereas level of bran produced significant responses in all cases. Significant relationships were found between age and all parameters except liveweight gain. Ad libitum stover supplemented with a high level of bran produced the best results. On-farm testing was carried out in the following year with a group of farmers belonging to a borehole syndicate. Farmers assumed responsibility for the day to day running of the trial with advice provided by project staff. Animals used in the trial varied considerably in age and weight. Even so, results indicated that farmers were able to obtain a higher return than that from other possible marketing options.

This paper presents a review of the calculation of herbage intake by grazing sheep. A number of different simulation models and feeding recommendation sources are compared, both as to form and as to numerical results for a series of examples. In addition to the overall approach, the following aspects of the calculation of intake are considered; the effects of animal and plant characteristics on intake, the differences between lactating or gestating ewes and dry ewes, the treatment of intake from heterogeneous pastures, and herbage intake when milk, or supplements, are also available. The general conclusion is that the models presented are each likely to have only a limited range of applicability. The main use of this review, then, is to provide guidance in developing empirical models of intake for other situations, rather than to suggest a generally valid model.