Application of a simple ecological sustainability simulator (SESS) as a management tool in the semi-arid rangelands of northeastern Mexico

We use a simple ecological sustainability simulator (SESS) [Diaz-Solis, H., Kothmann, M.M., Hamilton, W.T., Grant, W.E., 2003. A simple ecological sustainability simulator (SESS) for stocking rate management on semi-arid grazinglands, 76, 655] for rangelands with mean annual precipitation of 500 mm to evaluate tendencies in range productivity and cattle production under four management options: (1) supplemental feeding, (2) short-term reduction of stocking rate, (3) early weaning, and (4) adjustment of breeding seasons. We have made five modifications to SESS for the present paper. (1) Cattle mortality now occurs each month as a function of body condition. (2) Cows that are not pregnant 2 months after the end of the breeding season are sold. (3) Forage intake is calculated separately for each cohort of cows. (4) Cows that have been sold or have died are replaced just before the beginning of each breeding season (except for the short-term reduction of stocking rate strategy). (5) The calculation of stocking rate now includes cows, bulls, nursing calves, weaned heifers less than 20 months of age, and pre-reproductive heifers aged 20 months or older.Simulation results suggest the four management options might be ranked from best to worst, in terms of increasing cattle production while maintaining range productivity, as: (1) short-term reduction of stocking rate, (2) adjustment of breeding seasons, (3) early weaning, and (4) supplementation. Short-term reduction of high stocking rates reduces the deterioration of range productivity because of the reduction in the number of stock. Adjustment of breeding seasons such that periods of highest energy requirements of cows and calves coincide with periods of highest forage production increases percentage pregnancy. Early weaning of calves improves the body condition of cows and increases annual production of weaned calves, but does not reduce the stocking rate and thus does not improve range productivity. Supplemental feeding, and other management practices that artificially sustain herbivores, break the negative feedback that promotes good range productivity and maintains long-term system stability. In general, strategies to increase cattle production in semi-arid rangelands should be based on the improvement of natural forage production.     

Simulation of beef cattle production systems in the Llanos of Colombia: Part 2—Results of the modelling

Verifications and validations were conducted of a simulation model of beef cattle production on tropical ranges of the Colombian Llanos. Liveweight changes were simulated for individual cows sampled at random, for cow herds alternately grazing native savanna and molasses grass (Melinis minutiflora) and for steers grazing native savanna. Correlation coefficients between observed and simulated liveweight change were high. Simulations of the calving rates of cow herds from two experiments at Carimagua Research Station were also conducted and there was reasonably good agreement between observed and simulated data. Shortcomings of the model included an inability to simulate the heavy weight losses of grazing animals on molasses grass during the dry season and under-estimates of calving rates for the most productive herds. An experiment was conducted with the validated model from which it was concluded that grazing molasses grass and weaning of calves at 84 days of age would do little to increase calving rate.     

Simulated comparisons of breeding plans for beef production: Part 3—systems for producing feeder-calves involving intensive culling and additional breeds of sire

A dynamic model of a beef-cow herd producing feeder-calves was used to evaluate nine mating plans and an intensive culling policy in combination with management options of producing replacement heifers or purchasing them. The nine mating plans were: straightbred Angus, two-breed static crosses using Angus dams mated to Hereford, Charolais, Simmental, Jersey, Limousin and South Devon sires, a Hereford-Angus criss-cross and a three-breed static cross using Charolais sires mated to Hereford-Angus dams. All of these crosses were simulated under a culling policy of culling a cow as soon as she failed to produce a calf.Kilogrammes of calf weaned per cow was the criterion of herd productivity. The Hereford-Angus criss-cross and the Charolais Hereford-Angus three-breed static cross were the most productive crosses. The high productivity of the three-breed cross was due to the heavy calves weaned and the high productivity of the criss-cross was due to a high ranking for the number of calves weaned per cow bred.The intensity of culling which was practised on the cow herd had diverse effects on herd productivity. The heavy culling option increased the proportion of cows in the herd of three years of age or less by 72·6 to 86·4%, resulted in a higher incidence of calving difficulty and decreased the number of calves produced per cow by up to 17·5%. Structure and productivity were altered the most by a change in culling policy when large breeds of sire were used in the mating plans.     

Simulated comparisons of breeding plans for beef production—Part 2: Hereford,angus and Charolais sires bred to Hereford,Angus and Hereford-Angus dams to produce feeder calves

Breeding plans using Hereford, Angus and Charolais sires mated to Hereford, Angus and Hereford-Angus dams were simulated. All breeding plans were considered in combination with a culling policy of culling a cow only if she failed to produce a calf for two consecutive years. The criterion of productivity was kilogrammes of calf produced per cow bred. Productivity of a herd was influenced by the age structure of the herd, since cow fertility, cow and calf mortality and preweaning growth of the calf were determined by the age of the cow, as well as by the genotypes of the cow and calf.For herds with purchased replacement heifers, the three-breed static crosses using Charolais sires were the most productive. The Hereford-Angus criss-cross ranked second, followed by the two-breed static crosses. The two-breed static crosses using Hereford or Angus sires were more productive than the two-breed crosses using Charolais sires. The straightbreds were the least productive. For herds producing their own replacement heifers, producing the replacements from the younger cows increased the kilogrammes of calf produced per cow bred by 2·7% in the Charolais-Angus static cross and 2·8% in the Charolais-Hereford cross.     

Simulated comparisons of breeding plans for beef production—Part 1: A dynamic model to evaluate the effect of mating plan on herd age structure and productivity

A computer program to simulate beef production is described. The model is based on the principles of industrial dynamics and constructed in the simulation language DYNAMO. This dynamic model is composed of subroutines that simulate herd structure for a cow herd and a production herd composed of calves from the cow herd. Additional subroutines model pre-weaning and post-weaning growth of the calves.The portion of the model that simulates the herd structure includes ten age classes of cow. The subroutine which models the portion of the herd between 2 and 9 years of age utilises twelve variables to describe the events that occur in the herd during the passage of a year. The age structure of the herd is influenced by the breeding system and the way in which the herd is managed.The production herd is modelled by sequential subroutines. These subroutines follow the number and growth of calves weaned from the cow herd until they are sold at 32, 52, 67 or 85 weeks of age. Mating plans utilising different breeds can be simulated in combination with various management options.     

Comparative economics of Holstein/Gir F1 dairy female production and conventional beef cattle suckler herds – A simulation study

Three cow–calf production systems were compared using simulation: N (straightbred Nelore), AN (Nelore cows producing Angus by Nelore calves) and HG (Gir cows producing Holstein by Gir calves). All three systems produced their own straightbred replacement females. Male calves were sold at weaning and female calves in excess of those required to keep the herd size constant were sold at one year of age. In the base situation, F₁ HG females were priced at twice as much as the price per kg of the beef male calves, according to present market values. Typical 1000 ha beef cattle farms were simulated for each system, based on Brachiaria brizantha pastures managed according to recommended practices. Herd dynamics were controlled by reproduction and survival. Literature figures on monthly pasture nutrient production, live weights and milk yield were used to estimate nutrient requirements to match stocking rate to nutrient availability in each system. For calving rate set to 0.8 in all three systems, the total numbers of cows for the N, AN and HG systems were, respectively, 803, 795 and 885 and the total live weight sold annually was 129,070, 133,120 and 127,680 kg. The annual economic return on investment was 5.21%, 5.81% and 10.84%, respectively, for the N, AN and HG systems. Reducing the relative price of the HG heifers diminished the economic superiority of this system over N and AN. The difference was zero when the price of HG heifers was reduced to approximately 1.2 times the beef calf price. This also happened when the calving rate of the Gir cows was set to 0.6 keeping N cows at 0.8 or higher.     

Computer assisted management decisions for beef production systems

A linear programming model was developed to determine management policy for a yearly planning horizon on a typical 1320 acre (535 ha) Southern Colorado mountain ranch. Income producing activities (selling cattle and hay and leasing land) and cost activities (buying cattle, borrowing capital, feeding supplements, purchasing fertiliser and fuel, hiring labour and leasing land) were defined for three land types through four seasons.The purpose of the modelling effort was to determine the level of each activity (cow herd size, yearling herd size and area of meadow to be harvested for hay) that resulted in maximum net return for the ranch subject to resource limitation on land, labour and capital. In addition, sensitivity and shadow price analyses revealed expansion options that would be profitable during existing economic conditions.The optimal management plan, using 3 April, 1975 prices, called for grazing 199 head of 450 lb (204 kg) steers and 52 head of 530 lb (240 kg) steers. The plan also called for purchasing and spreading 42 tons (38 MT) of nitrogen and 10 tons (9 MT) of phosphorus on Land I and for growing, harvesting and selling 742 tons (674 MT) of hay. This optimal management plan produced a net return of $27,642. In addition, the optimal plan showed that hay production began replacing beef production when the price of hay was $35·48/ton (39·08/MT) and that the maximum amount of hay was produced with the price increased to $50·00/ton ($55·00/MT).     

Kleingrass growth and utilization by growing steers

A model of kleingrass (Panicum coloratum L.) growth and utilization by steers is presented. The model included stochastic inputs of climatological characteristics, water retention at different soil depths, rainfall runoff, potential evapotranspiration, forage growth, forage intake and steer performance. The model was used in a 2 × 3 × 4 factorial experiment where the factors were energy systems (ARC, 1965 versus NRC, 1976), stocking rates (2·47 head per hectare, 4·32 head per hectare and 6·18 head per hectare), and four management options. Individual steer weights by months were not significantly affected by the use of either energy system. Steer weights at the end of the grazing season were affected (F = 0·06) by energy system, the NRC system predicting 7·2 kg per head more liveweight gain than the ARC system. The light stocking rate had greater (P = 0·01?0·13) daily gains over months than the heavier stocking rates. The heavy stocking rate resulted, however, in greater (P < 0·05) production per hectare per year than the lighter stocking rates. Season-long production per hectare favored (P < 0·1) management options that removed steers immediately after forage was consumed rather than anticipating rainfall and new forage growth. The light stocking rate had the least mean seasonal production per hectare (P < 0.·05) but also had the least year-to-year variability. The heavy stocking rater yielded the greater (P < 0·05) mean seasonal production per hectare but the year-to-year variation was much greater. It was emphasized that the use of such probabilities of production could aid the grazier in making stocking rate and related decisions.     

Effect of Formic Acid with Formalin or Barley Incorporation into Grass Silage on Silage Fermentation and the Performance of Dairy Cows

Perennial ryegrass was ensiled in three different ways: (1) with a formic acid with formalin silage additive at 4·0 l/t; (2) with an addition of 50 kg/t ground barley; and (3) no-additive. Formic acid with formalin produced well-fermented silage, which, when subsequently given to lactating dairy cows significantly enhanced daily dry matter (DM) intake and butterfat, protein and butterfat plus protein output and reduced the liveweight decrease experienced with the other treatments. The addition of ground barley at ensilage provided less benefit in terms of fermentation, but had a more pronounced effect upon daily silage DM intake and milk yield than formic acid with formalin treatment. The daily liveweight losses of cows given the non-additive-treated and ground-barley-treated silages were significantly higher than those given formic acid with formalin treated silage. Silage treatment had no significant effect upon cow fertility.     

Simulation of beef cattle production systems in the Llanos of Colombia—part I. Methodology: An alternative technology for the tropics

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.     

Replacement policy in dairy herds on farms where heifers compete with cows for grassland: Part 2-Experimentation

Replacement policy is not easy to determine on dairy farms where heifers compete with cows for grassland. Using a computer simulation model of this farm situation, two factorial experiments were conducted to evaluate quantitatively the effect of different replacement rates on profitability and herd improvement.The variables changed in herds of average health and very good health were replacement rate (0·14, 0·22, 0·30), age at first calving (36, 24 months), calving index (13, 12 months) and AI sire merit (standard, premium). Initially, the experimental herd had average health, a replacement rate of 0·22, a calving index of 13 months, calved its heifers at 36 months and had been using standard bulls for many years.After 15 years, the increase in the level of a sinking fund when the age at first calving was reduced was between three and five times greater than when premium bulls were used, calving index was reduced or herd health was improved. There was a major interaction between replacement rate and age at first calving.Yield per cow was significantly reduced (P≤0·001) by reducing the age at first calving and significantly increased when premium bulls (P≤0·001) were used or when herd health was improved (P≤0·05).Some treatments were not tested as expected due to the restraining effect of a 13-month calving interval on the availability of cows for breeding pure in a seasonally calving herd.     

Prediction of herbage intake and liveweight gain of cattle grazing tropical pastures from the composition of the diet

As a basis for calculating growth rates of cattle within a model of a beef herd, three experiments were carried out. Their purpose was to (i) develop equations to predict organic matter, digestible organic matter and metabolisable energy intakes of cattle, (ii) establish the conversion of metabolisable energy to live weight of tropical cattle, and (iii) establish the validity of these relationships for predicting the liveweight change of grazing animals.In the first experiment, Brahman × Shorthorn crossbred cattle were held either indoors in pens or in long laneways outdoors where they walked approximately 5 km per day. Organic matter intake was measured in both situations and was found to be not significantly different between the situations. Regression equations were calculated relating intake of organic matter and digestible organic matter by cattle indoors to the chemical composition of their diet. The conversion of digestible organic matter to metabolisable energy intake and finally to liveweight gain was confirmed in a second experiment. The liveweight gain of outdoor animals was predicted accurately provided the metabolism of crossbred animals was considered and an allowance made for the energy required for walking.The diet selected by oesophageally fistulated animals at pasture was chemically analysed over a four-month period following these measurements. Feed intake and liveweight gain of non-fistulated animals grazing native and improved pastures were predicted from the chemical composition of the diet selected. There was good prediction of liveweight gain in both pasture situations.     

奶牛智能饲喂关键技术研究

随着现代规模化养殖新格局的初步形成,奶牛智能养殖装置的不断涌现,奶牛饲喂技术发展呈现出信息化、精细化、智能化的趋势。通过分析奶牛全混合日粮饲喂技术与奶牛自动饲喂装备系统的特点和应用情况,对国内外奶牛养殖技术装备进行总结,国内中小型养殖场仍存在自动化水平较低、饲喂技术与装备结合不完善、饲喂效率较低等问题;大规模养殖场面临核心技术需进口、养殖成本与装备研制成本较高的问题;国外的智能养殖装备技术相对成熟,相关装备系统已经大范围使用。此外结合国内外研究现状提出我国饲喂技术装备的改进方向,针对实际养殖情况对装备技术进行研发,促进我国自主装备及核心技术的推广应用,推进奶牛养殖装备技术向精细化、智能化发展,切实提升我国奶牛养殖水平。     

Profit in a pig herd from performance testing and selection of breeding stock. The effect of variation in the accuracy and cost of testing

Computer modelling was used to compare a variety of performance testing and selection programmes whose objective was to increase the monetary value of pigs as determined by their rate and efficiency of growth and the leanness of their carcases.Factors varied over feasible ranges were the cost and accuracy of performance testing, the culling rates of breeding stock and the degree of subdivision of the herd into a nucleus supplying breeder replacements for the whole herd and a production unit producing slaughter stock.Net returns per sow, evaluated over 10 years of selection, increased, by 120 times, the standard deviation (sd) of the breeding objective for each improvement of 0·1 in the correlation between the selection criterion and the breeding objective (test accuracy).A unit of the cost of testing each pig equalled 0·4 sd of the breeding objective and net returns in the unsubdivided herd declined by 0·6 for each unit increase in cost. Herd subdivision increased net returns by reducing the number of pigs tested—and hence the cost of testing. The optimum ratios of production unit to breeding nucleus sizes which maximised net returns were found. When herds were subdivided in an optimum way, the decline in net returns with increasing testing costs was reduced sixfold.Returns were highest when boars were worked for only one breeding cycle (approximately 6 months) in both the nucleus and the production unit. Depending on the accuracy and cost of testing, maximum net returns occurred when nucleus sows were culled after one or two farrowings. Sows in the production unit were an optimum combination of culled ‘old’ sows and selected ‘young’ gilts from the nucleus. There were a number of other replacement schemes which were almost equally profitable.     

The climatic potential for beef cattle production in tropical Australia: Part I—Simulating the annual cycle of liveweight change

This is the first of a series of papers dealing with a survey of the agricultural climate as it pertains to the beef cattle industry in northern Australia. Beef cattle production here, as in most of the tropics, is characterised by an annual periodicity of weight gain and loss in train with seasonal water supply and temperatures. Trends in a weekly growth index derived from a simulated water budget and mean daily temperatures were found to correlate with trends in liveweight changes. Criteria for estimating the start and cessation of a ‘green season’ and a ‘dry season’, corresponding to the main liveweight gain and loss periods respectively, are derived and validated using cattle liveweight data from seven locations and both native and improved pastures. Linkage between cattle liveweight change and climate was close on native grass pastures but not on legume-improved pastures.     

Long-term stochastic simulation of mountain beef cattle herds under diverse management strategies

A stochastic simulation model was used to assess the effects of diverse management strategies on beef herds under mountain conditions in the Spanish Pyrenees. Animals grazed on different seasonal resources (valley meadows, forest pastures and mountain pastures) and were fed with forages and concentrates during winter. The simulated management strategies were winter calving (WC, weaning at 180 days), autumn calving (AC, weaning at 160 days), 8-month calving (8MC, weaning at 180 days), and two calvings in 3 years, with weaning taking place at either 170 days of age (2C3Y) or at 9 months (2C3Y9 M). Each strategy was tested for two types of production systems: (i) cow-calf farms that market calves just after weaning; and (ii) cow-calf/finishing farms that fatten the animals by means of an intensive feeding system until achieving a suitable weight for slaughter. A herd of 100 cows was simulated over 15 years, but only data obtained after reaching the steady state (year 6) was used in the analysis. The strategies were evaluated by considering reproductive, productive and economic performance. The percentages of pregnant cows at the end of the mating season were highest for 8MC, 2C3Y and 2C3Y9M (between 92% and 94%). The percentage was intermediate for AC (88%) and lowest for WC (78%), which also showed greater variability between years. The two strategies that extensified management (2C3Y, 2C3Y9M) produced, as expected, a lower number of calves weaned per year (59 and 60), whereas this figure was the highest for 8MC (90). Although AC and 8MC resulted in higher productive performances, the increased labour requirements and winter feeding costs resulted in low economic margins for these strategies, which also meant poorer utilization of natural resources. In economic terms, WC was the best strategy for cow-calf/finishing farms, whereas 2C3Y was the worst of the two types of production systems, although it resulted in the most intense utilization of grazing resources. The long lactating period of 2C3Y9M did not affect the reproductive performance of cows, so this strategy yielded the highest economic margin at weaning. The extensification strategies (2C3Y and 2C3Y9M) were less sensitive to changes in the price of feedstuffs. The information obtained from the simulation of the different strategies is useful for evaluating the possible trade-offs between production, economics, use of natural resources and labour requirements.     

农用柴油机在肉牛养殖中的应用

柴油机是我国农业生产中不可或缺的动力源,农用柴油机种类繁多、经济性好、适应性强。近年来,伴随我国饮食结构调整实施“粮改饲”、“粮改畜”,以肉牛养殖等为主的畜牧养殖业得到大力发展,机械化养殖是现代化肉牛养殖的重要支撑,养殖各环节以柴油机为动力的农业机械得到了大量应用。本文以肉牛养殖为例,阐述农用柴油机在牧草生产、收获、加工、饲喂、废弃物处理环节的配套应用,分析农用柴油机发展中存在的工作稳定性较差、噪声和排放较大问题,进一步提出应用电控高压喷射等先进技术提升农用柴油机性能、做好农用柴油机与专业机具的配套适应性以及加强农用柴油机制造工艺和强化生产过程管理的发展策略。     

Adaptive management of stocking rates to reduce effects of drought on cow-calf production systems in semi-arid rangelands

We used simple ecological sustainability simulator (SESS) [Díaz-Solís, H., Kothmann, M.M., Hamilton, W.T., Grant, W.E., 2003. A simple ecological sustainability simulator (SESS) for stocking rate management on semi-arid grazinglands. Agric. Syst. 76, 655–680. <http://dx.doi.org/10.1016/j.agsy.2005.07.008>], modified to represent each of five management strategies (sets of decision rules) for adjusting stocking rates, to identify strategies that could reduce effects of drought on cow-calf production systems in semi-arid rangelands. We parameterized the model to represent a region of extensive cow-calf production in the northeastern portion of the Mexican state of Coahuila, and evaluated animal performance (animal body condition, cow mortality, and calf production) and range condition resulting from each strategy under random precipitation conditions typical of the region. To evaluate the validity of the randomly generated precipitation, we conducted the simulations under an historical (1950–1994) precipitation regime.The five management strategies included one with no adjustments to stocking rate (CONTROL, most common current practice), one with stocking rate adjustment rules based on changes in animal body condition (BCS), and three with different stocking rate adjustment rules based on various comparisons of recent-year precipitation with long-term mean precipitation during the growing season (March–November) (REPLA, PPT 1Y, PPT 2Y). Each strategy was evaluated at each of three initial base-level stock cow stocking rates (125, 250 and 500 AUY · 5000 ha⁻¹). Stocking rate adjustments consisted of partial or total de-stocking, with the re-establishment, or not, of the initial number of stock cows before the beginning of the subsequent breeding season.Results of 45-year simulations under both random and historical precipitation suggest CONTROL and PPT 2Y (based on comparison of current year and previous year precipitation with the long-term mean) strategies, combined with the high base-level stocking rate, are the worst and best, respectively. Under the historical precipitation regime, in the last period of time simulated (1980–1994) these two strategies resulted, respectively, in poor (0.5) versus good range condition (1.0), animal body condition scores of 2.6 versus 5.2, annual cow mortalities of 76 versus 5%, and calf production rates of 0.9 versus 10.6 kg ha⁻¹ year⁻¹ at weaning. The PPT 1Y strategy (based on comparison of current year precipitation with the long-term mean) produced results fairly similar to PPT 2Y, with BCS and REPLA strategies producing results intermediate between CONTROL and PPT 2Y. Our results suggest it is advantageous to adjust stocking rates based on precipitation during the current growing season since it improves cattle production without damaging range condition. Considering the practical feasibility of the strategies, we recommend the PPT 1Y strategy because it maintains range condition at moderate stocking rates, results in good animal performance and does not require total de-stocking of the ranch.The simple method we developed to stochastically generate monthly precipitation produces a time series of precipitation values that were representative of general historical precipitation patterns and provided realistic levels of uncertainty in simulated forage production to evaluate alternative management strategies.     

基于卧式厌氧装置的稻秸高固态消化与甲烷菌变化研究

针对单一稻秸高固态厌氧消化长期运行不稳的问题,接种瘤胃内含物和厌氧污泥,在卧式反应装置中研究3个有机负荷(OLR)下消化特性。结果表明,体系最高容积产气率达到了1.04 L/(L·d)。当OLR为2.26 g/(L·d)时,甲烷体积分数均值为54.39%,甲烷产率为280.90 m L/g,达到了稻秸理论产值的80.29%。卧式装置中半纤维素和纤维素最高降解率分别达到了49.71%和31.25%;纤维素酶活性显著提高,有利于纤维素的降解。当OLR升高到2.47 g/(L·d)时,氨氮质量浓度均值达到了1 082.63 mg/L。固体样品中嗜氢型Methanobacteriales数量从1.70×10~9拷贝数/g下降至1.04×10~6拷贝数/g;而嗜乙酸型Methanosarcinales数量从7.89×10~6拷贝数/g增加至9.44×10~6拷贝数/g,甲烷产率下降为256.54 m L/g。此时厌氧装置中丙酸质量浓度均值达到了253.32 mg/L。从而明确了稻秸高固态体系中产甲烷菌结构的变化。     

The climatic potential for beef cattle production in tropical Australia: Part IV— variation in seasonal and annual productivity

In Part II liveweight loss in the dry season was found in most years to be closely related to cumulative ‘dry weeks’; extraordinary weight loss occurred in the dry season in years in which there were a low number of ‘growth weeks’ in the previous green season. Annual liveweight gain was related to the total number of ‘green weeks’. In this paper the geographic variation in these three agro-climatic parameters is described using a network of 77 stations across northern Australia, and the year-to-year variability is examined for eight representative stations.Variation in dry season severity was greater than variation in green season productivity (growth weeks). Median ‘dry weeks’ in the dry season varied from 29 to nil over the area. ‘Green weeks’ in the dry season as a result of winter rain is an important phenomenon in a relatively small part of the area, but in this area year-to-year variability is extremely high.It is concluded that the objectives of the study, to extend existing agro-climatic methodology to interface with cattle production and to use this in surveying the climatic potential for this form of land use over the entire tropical region of Australia, were achieved to the extent that the existing animal production data allow.