Sheep Enterprises Research Articles

Comparison of productive and reproductive efficiency of Afrino, Dorper and Merino sheep in the False Upper Karoo

The productive and reproductive performance of, as well as income generated by Afrino, Dorper and Merino sheep at two localities in the False Upper Karoo region were evaluated. A total of 1242 ewe reproductive records was available, while data of respectively 772 and 405 lambs were analysed for the growth traits and slaughter traits. Percentage of lambs weaned per ewe in the flock was 132.0%, 100.0% and 93.7% for Afrino, Dorper and Merino ewes at Grootvlei, respectively. Corresponding values for Twistkraal were 153.3%, 114.7% and 96.4%, respectively. Body weights of 52.3 ± 1.4 kg, 56.6 ± 1.4 kg and 43.4 ± 1.4 kg were recorded for Afrino, Dorper and Merino ewes, respectively. Merino ewes produced on average 1.3 kg more clean wool, of a 0.6 μm stronger diameter than Afrino ewes. At each locality Dorper lambs were the heaviest at weaning, followed by Afrino and then by the Merino lambs. Dorper lambs were slaughtered earlier than Afrino lambs, with Merino lambs taking the longest interval to reach slaughter weight. A definite seasonal effect was also evident, where the autumn-born lambs reached slaughter weight earlier than spring-born lambs in all breeds. With the current wool and mutton prices, Afrino sheep had the highest gross income per ewe, followed by Merino and Dorper ewes respectively. However, Merino sheep had the highest gross income per hectare at both localities, followed by Afrino and then Dorper sheep. The combination of low ewe body weights, high wool production and a relatively high reproductive rate, resulted in Merino sheep generating the highest income per hectare, compared to Afrino and Dorper sheep. Reproductive rate, mature body weight and fibre production are the primary factors determining profitability of a specific sheep enterprise. These parameters should thus be considered when changing from one breed or commodity to another. Keywords : Body weight; wool production; slaughter traits; income South African Journal of Animal Sciences Vol. 35 (2) 2005: pp.98-108

A bioeconomic approach to derive economic values for pasture-based sheep genetic improvement programs.

Economic values for a range of different maternal and carcass sheep performance traits were derived for hill sheep in the United Kingdom. A bioeconomic model that includes estimates of available energy supply and herbage intake for sheep from hill and mountain pastures, together with that from improved grassland, has provided a base from which to define the economic limitations to genetic improvement in harsh environments. The degree to which different farm systems can accommodate changes in animal performance as a result of genetic improvement was explored. Results showed that genetic improvement in harsh environments is likely to be of greater benefit to farms with fewer constraints to improvements in production, such as better quality pasture or a higher ratio of improved grassland to hill pasture. For farm types in the harshest locations, the economic value of improving litter size was only positive within defined production limits. Increasing litter size beyond these limits resulted in diminishing marginal returns because the costs of additional inputs outweighed the benefits of extra returns. Results also showed that relative improvements in maternal characteristics are at least as economically important as improvements in lamb carcass quality. The effects of variation in market prices on economic values for the major costs and returns of the sheep enterprises showed that, in general, economic values are robust. The methodology described could be adapted and applied to other extensive sheep systems worldwide.

Limitations to pasture and sheep enterprises and options for improvement in the Victorian Mallee

A survey of 29 sheep producers was conducted to benchmark current sheep production practices and producer attitudes to sheep and pasture management in the Victorian Mallee. This report describes the farming systems, defines current sheep management practices and identifies management issues that are limiting production. It also highlights limitations of adoption, suggests potential adoption rates of specific practices by producers, and estimates increases in productivity achievable. Sheep producers could achieve small gains in farm productivity (an estimated average 0.3% annually) by adopting sheep management practices including using superior genetics, reducing ram numbers and introducing supplementary feeding. Possible reasons why recommended practices have not been adopted are discussed. The difficulty of integrating sheep into current short cropping systems was considered to be a key limitation to the adoption of management that could substantially increase productivity, such as higher stocking rates and winter–spring lambing. Important benefits to both productivity and environmental sustainability may be achieved through the replacement of fallowed land with improved pastures. However, a lack of data on the feed base and sheep production in relation to a changing feed base made it impossible to estimate the size of these benefits. It was concluded that further research is needed to collect data and benchmark pasture and livestock enterprises to allow quantification of the potential impact on farm profit of changes to pasture and sheep management in this region.

A review of the biology linking fibre diameter with fleece weight, liveweight, and reproduction in Merino sheep

There is increasing economic pressure on the Merino industry to grow finer wool and at the same time to turn off more sheep meat. Fleece weight generally decreases with finer fibre diameters, so theoretically, finer wool sheep should be able to partition more nutrients to reproduction and muscle growth. However, complex and often indirect mechanisms appear to prevent this in practice. This review summarises the available data on genetic and phenotypic relationships between wool fibre diameter and fleece weight, liveweight, fatness, and reproductive performance, and develops mechanistic hypotheses for these relationships that could be tested experimentally.Selection for reduced fibre diameter may decrease liveweight, fatness, and reproductive performance. These characteristics are also affected by the availability of nutrients, and finer fibre diameter may affect nutrient metabolism through 2 adaptations that tend to maintain fleece weight: an increase in follicle density and/or an increase in relative fibre length. These act in different ways. Follicle density may affect final body size through linkages established during fetal development. Increased fibre growth rate requires an increase in protein synthesis rate in the skin, which in turn may affect whole-body protein turnover rate and the sensitivity of tissues to insulin. Other pathways potentially affected by fibre diameter include the control of feed intake, prenatal programming of insulin sensitivity, and a reduced responsiveness of tissues to nutrient supply. However, none of these mechanisms accounts for the reports of an increased proportion of dry ewes in fine wool sheep, particularly if run in environments that experience periods of low quality pasture.Although associations between fibre diameter and growth rate, fatness, and reproduction rate are repeatable, there are not yet enough data for such associations to be realistically accounted for in breeding goals. More experimentation and a better knowledge of the causative relationships will facilitate development of finer wool sheep for environments where sheep turnoff normally provides a significant proportion of income from the sheep enterprise. Such mechanistic understanding will facilitate the development of molecular techniques for targetted selection, and the identification of more useful attributes for a quantitative genetics approach to improving simultaneously the profitability from both wool and meat.

Nitrate leaching losses and their control in a mixed farm system in the Cotswold Hills, England

Abstract. Nitrate leaching was measured for four years at the Royal Agricultural College ‘s Coates Farm in the Cotswolds, England. Coates is a typical Cotswold mixed farm with thin, well‐drained calcareous soils especially prone to leaching. Over the duration of this study there were dairy, sheep and arable enterprises on the farm. A ‘Farm Gate’ nitrogen (N) budget was constructed. Small 120 m × 20 m ‘farmlets’ were sited in ten fields across the farm, covering all parts of the rotation, as the sites for detailed measurements. Each farmlet received the same management as the rest of the field in which they were situated. Using ceramic probes inserted to 60 cm, soil water was sampled every two weeks throughout the winter drainage season. The annual drainage varied from 135 mm under grassland in 1996/7 to 600 mm under cereals in 1998/9. Average N losses by leaching were determined mostly by rainfall and were 65 kg N ha–1 yr–1, accounting for 25% of the N inputs. Especially leaky parts of the rotation were the ploughing out of a lucerne ley and the grazing of stubble turnips with sheep, both typical Cotswold farm practices. The research highlights some of the difficulties in developing practicable, profitable management practices to decrease nitrate losses.

Economic Analysis of Using Sheep to Control Leafy Spurge

Leafy spurge (Euphorbia esula L.), a widely established exotic, noxious, perennial weed, is a major threat to rangeland and wildland in the Upper Great Plains. A deterministic, bioeconomic model, incorporating relationships between sheep grazing and leafy spurge control, grass recovery, and forage consumption by cattle, and expected costs and returns from sheep enterprises was developed to evaluate the economic viability of using sheep to control leafy spurge. Various scenarios were developed depicting likely situations facing cattle ranches adding a sheep enterprise for leafy spurge control. Two levels of flock profitability, one based on a level of proficiency achieved by established sheep ranches and one substantially lower than typically achieved in the sheep industry, were combined with debt and no-debt to represent best- and worst-case scenarios, respectively. In the best-case situations, using sheep to control leafy spurge was economical in all of the scenarios examined. In the worst-case situations, the economics of using sheep to control leafy spurge were mixed across the scenarios examined. Leafy spurge control with poor flock proficiency, high fence expense, and unproductive rangeland generally was not economical. Situations with low fencing costs, moderately productive rangeland, and poor flock proficiency resulted in less economic loss than no treatment. Actual returns from leafy spurge control for most ranchers will likely fall between the extremes examined. DOI:10.2458/azu_jrm_v54i4_bangsund

Livestock sustaining intensive smallholder crop production through traditional feeding practices for generating high quality manure-compost in upland Java

Information is needed on the biophysical and economic rationale for labour-demanding (and therefore, expensive) backyard animal rearing systems on smallholdings in the uplands of Java where livestock have been an integral part of highly intensive agriculture for centuries. The occurrence of high densities of ruminant livestock is counter-intuitive considering the extent and continuous nature of cropping on densely populated islands such as Java where little land remains suitable for grazing. As a consequence, livestock are permanently housed in backyards and fed indigenous forages cut from field margins and roadsides. Although cut-and-carry feeding is labour-intensive, it is surprising that farmers collect quantities of forage greatly in excess of the requirements of their livestock. In an experiment, indigenous forage was fed to sheep at increasing rates: 25, 50 or 75 g DM kg −1 liveweight daily. The results showed that although DM intake and liveweight gain rose with increasing offer-rate, the incremental improvements from 50 to 75 were non-significant ( p<0.05) and <25 to 50. It is unlikely that farmers justify their excess-feeding strategies on the basis of these marginal gains in animal productivity alone. The rationale for excess-feeding also lies in the production of manure-composts. Group-interviews, involving preference-ranking and matrix scoring exercises, indicated that in upland areas, farmers have an extensive knowledge regarding organic fertiliser quality and use. Farmers place value on the inclusion of animal wastes, particularly urine, into composts. In rain-fed areas, manure production ranked similar to meat production in importance as outputs from the sheep enterprise. The research demonstrates how livestock are traditionally used to produce high quality compost and provides evidence to support the hypothesis that integration of livestock into Javanese agriculture is essential to sustaining some of the world’s most intensive smallholder farming systems.

Economic analysis of using sheep to control leafy spurge

Leafy spurge (Euphorbia esula L.), a widely established exotic, noxious, perennial weed, is a major threat to rangeland and wildland in the Upper Great Plains. A deterministic, bioeconomic model, incorporating relationships between sheep grazing and leafy spurge control, grass recovery, and forage consumption by cattle, and expected costs and returns from sheep enterprises was developed to evaluate the economic viability of using sheep to control leafy spurge. Various scenarios were developed depicting likely situations facing cattle ranches adding a sheep enterprise for leafy spurge control. Two levels of flock profitability, one based on a level of proficiency achieved by established sheep ranches and one substantially lower than typically achieved in the sheep industry, were combined with debt and no-debt to represent best- and worst-case scenarios, respectively. In the best-case situations, using sheep to control leafy spurge was economical in all of the scenarios examined. In the worst-case situations, the economics of using sheep to control leafy spurge were mixed across the scenarios examined. Leafy spurge control with poor flock proficiency, high fence expense, and unproductive rangeland generally was not economical. Situations with low fencing costs, moderately productive rangeland, and poor flock proficiency resulted in less economic loss than no treatment. Actual returns from leafy spurge control for most ranchers will likely fall between the extremes examined.

Wild dogs and their manipulation to prevent livestock predation in Australia

Author(s): Fleming, Peter J. S. | Abstract: Dingoes and other wild dogs cause substantial damage and control expense in many Australian environments. The main methods of control are exclusion fencing, poisoning with 1080, and trapping. Strategies to mitigate livestock predation by wild dogs include; enterprise substitution, the reduction of wild dog populations, and baited buffer zones between wild dog country and sheep country. Damage functions show significant positive relationships between density indices and the losses caused by predation for both sheep and cattle enterprises. However, descriptive and explanatory models fitted the data poorly. A strategic approach to the management of wild dogs that aims to reduce predation on livestock while allowing the conservation of wild living dingoes is also outlined.

The Rural Environment Protection Scheme of the Republic of Ireland

Agricultural modernisation has had an impact on the Irish environment but official policy to address this developed only slowly. The reform of the EU CAP provided the incentive for the formulation of the Rural Environment Protection Scheme (REPS). This is a wide-ranging scheme to promote environmentally friendly farming through application of 11 measures and six supplementary measures. Significant characteristics of the REPS include its: universal availability, voluntary nature, comprehensiveness, payment limitation, tailoring to individual farms and inclusion of training. There has been a high level of adoption, with participation being greatest in the small-farm west with its cattle and sheep enterprises.

Farmer experience of perennial ryegrass endophyte on a Manawatu dairy farm

Case studies of two Manawatu properties currently experiencing ryegrass staggers (RGS) are presented; a dairy farm and a run-off grazing both dairy heifers and intensive bull beef. Before its conversion from a sheep and cattle enterprise to dairying an outbreak of RGS was experienced in 1987. Tall fescue-based pastures were established to minimise the potential threat of RGS. In the intervening 12 years high endophyte ryegrass cultivars have been established and hotter, drier summers are being experienced in this region. Severe cases of RGS have been observed in the last three years. On the dairy farm in 1998/99, 21 cows were dried off in January due to severe RGS. The loss in production is impossible to measure. Sixteen heifers and weaner bulls died during that summer due to RGS and those alive were 35 kg LWT below target. Management options to reduce the effects of endophyte-related disorders include establishing non-toxic pastures such as tall fescue or forage crops to utilise during periods of the year when RGS can be experienced. While limited in cultivar choice at present, the use of novel endophytes provides long-term options for farmers wishing to reduce RGS yet still maintaining ryegrass pastures. Including herbaceous species such as chicory or plantain in pasture mixes will provide high quality summer forage and can dilute the effects of endophyte in the total daily intake. Keywords: bull beef, dairy cows, endophyte, heifers, perennial ryegrass, ryegrass staggers

The long-term influence of superphosphate and stocking rate on the production of spring-lambing Merino sheep in the high rainfall zone of southern Australia

The productivity of spring-lambing fine wool Merino sheep grazing pastures sown in 1977 to perennial ryegrass and subterranean clover was assessed from 1989 to 1998. The pastures were fertilised each autumn with single superphosphate at 6 levels, and were stocked at a low, medium, or high stocking rate (SR) at each level of fertiliser. The average phosphorus (P) applied annually since sowing (P ) ranged from 1.6 to 32.9 kg/ha. The SRs used varied with fertiliser level in that they were higher where more fertiliser had been applied, so that the highest SR at each level of fertiliser ensured that the pastures were well utilised. Each ewe raised 1 lamb, which was removed at weaning. The influence of fertiliser on the productivity of the sheep at 4 classes (1–4) of SR (mean SR = 7.1, 10.1, 12.6, and 18.2 ewes/ha for classes 1–4, respectively) was described by: y = A−BCP, where y represents production per sheep (kg), and A, B, and C are constants. For greasy fleece weight, estimates of B and C were 1.59 and 0.84; and for SR classes 1–4, the estimates of A were 5.06, 4.89, 4.78, and 4.46, respectively. For weaning weight of lambs, estimates of B and C were 8.4 and 0.82, and estimates of A were 23.5, 22.7, 21.5, and 20.9 for SR classes 1–4. The mean fibre diameter (µm) of the wool was described by: D = 14.18+1.48 GW, where GW is the mean greasy wool produced annually per sheep (kg) averaged over all sheep and years for each of the 18 treatments. The price (cents/kg) of wool with a fibre diameter D (P D) was given by: P D = 12197+4.94P2 + 688D−0.1945P20D − 5810√D, where 20 µm wool is P20 cents/kg. Supplements were fed if the body condition of ewes fell to a predetermined level. The supplement fed per ewe each year (S), expressed as metabolisable energy (in MJ) was described by: S = −602 − 44.1S R + 178.5P + 8.71S R P +539 √SR− 338.5√P−70.8P√SR, where S R and P represent the mean stocking rate (ewes/ha) and mean P applied annually. When a current set of costs and prices was applied to these equations, the maximum gross margin for a SR of 7.1 ewes/ha was $AU119/ha with 8.6 kg P/ha applied annually, and $AU262/ha for SR of 18.2 ewes/ha with 17.6 kg P/ha applied annually. If income derived from sheep is maintained constant, intensifying the sheep enterprise from the low to the high SR system would involve increasing sheep numbers by about 17%, but would release about 55% of the farm’s area for another purpose.

Responses of productive and unproductive kikuyu pastures to top‐dressed nitrogen and phosphorus fertiliser

In South Africa there is widespread reliance on kikuyu grass as a source of summer forage for intensive dairy, beef and sheep enterprises. There is, however, a dearth of reliable information on the fertility requirements of kikuyu pastures. Responses of previously productive and unproductive kikuyu pastures in the Mistbelt and Highland Sourveld of KwaZulu‐Natal to top‐dressed nitrogen (N) and phosphorus (P) fertilizers were studied infield cutting trials conducted during two consecutive seasons. Significant dry matter (DM) yield responses accompanied incremental N applications of up to 500 kg ha−1. First‐season DM yields of previously productive pastures at zero applied N were in the range 6 to 9 t ha−1, while yields of previously unproductive pastures at zero N were 0 to 2 t ha−1. By the second season, yields at zero N were uniformly low on the various pastures, reflecting the limited extent of plant‐available N reserves in soils under productive kikuyu. In both the Mistbelt and Highland Sourveld, efficiency of response to applied N in seasons when rainfall was similar to the long‐term mean was approximately 30 kg DM per kg N over the N application range of 0 to 250 kg N ha−1. When rainfall was substantially below average, N efficiencies decreased markedly. Application of N in six rather than three dressings during the growing season resulted in the N efficiency increasing by 3.5 kg DM per kg N. In contrast to the enormous responses to N, there was little or no response to P in the various trials. An optimum P test (NH4 HCO3 / NH4F / EDTA) for high clay content (>50% clay) Mistbelt soils of approximately 10 mg L−1 is suggested from yield‐soil test calibrations. Data highlighting the impact of soil sampling depth on P test values are presented, and this information serves to underline the importance of standardizing sampling procedures in the soil testing of pastures for fertility purposes.

Economic Feasibility of Grazing Sheep on Leafy Spurge-Infested Rangeland in Montana

Leafy spurge (Euphorbia esula L.) is a noxious weed on rangelands throughout the Northern Great Plains. Most of these ranges are grazed by cattle which do not use leafy spurge as forage. Although sheep graze leafy spurge, most land managers are reluctant to use sheep to control this noxious weed, which may be related to economic uncertainties regarding their profitability. The purpose of this study was to evaluate the economic feasibility of implementing a sheep enterprise to control leafy spurge on cattle ranches. The physical characteristics of a typical Northern Great Plains ranch, recommended stocking rates for cattle and sheep on native and leafy spurge-infested rangelands, and a sheep enterprise budget were developed using information from the literature. A LOTUS spreadsheet was developed to calculate returns over total costs of implementing various sheep enterprises. Annual returns from implementing sheep grazing on 520 ha of leafy spurge on a 4,905 ha ranch exceeded total costs by $4,675. Given the ownership costs and returns of our ranch, the breakeven lamb price would be $1.16 kg-1. Returns per head and per unit of land will vary with the distribution and size of a leafy spurge infestation, and sheep production costs and returns. Returns from sheep grazing were higher when leafy spurge was concentrated in fewer rather than in many pastures. Returns were positive when as little as 4% of the ranch was infested with leafy spurge. The availability and utility of our model will allow land managers to assess the feasibility of developing sheep enterprises to control leafy spurge.

Sheep and Goat Production in Hot Climates

This paper discusses the reasons for keeping small ruminants and investigates the areas in which technological improvements are likely to have most impact in increasing the output from sheep and goat enterprises in hot climates. The most important areas in which biological manipulation can raise productivity lie in the areas of improved nutrition and increased survival of young animals. Nutritional studies of animals receiving diets of natural tropical grazing and browse may not reflect the rations actually consumed due to the ability of animals to select high quality forage from what is on offer. One suggestion is made as to how this selection can be exploited to increase the productivity of the herd as a whole. Improved health care offers the largest potential for increases in productivity by reducing the large mortality of young animals seen in many tropical production schemes. Much of this mortality has its roots in parasite infection. Anthelmatics have proved valuable for short term therapy but the speed at which parasites become resistant to drugs indicates that selective breeding of animals with resistance to parasites is a more valuable long term solution.

Measuring Financial Performance: An Overview of Financial Statements

Financial management has emerged as a critical component in the long-term viability of today's ranches and farms. Proper and timely financial reporting and analysis of financial statements are valuable tools that agricultural producers can use to monitor, coordinate, and plan their operational production and marketing schemes and strategies. A side note to preparation of financial statements. With the concerns over lender liability issues associated with statements either assisted with or prepared by a lending officer, agricultural producers will be responsible for preparing their own statements. The lending institutions may prepare their own statements in their assessment of the financial condition of a business and or individual, but, ultimately, the responsibility of financial statements is the borrower's. Some of the material presented in this article provides important input for use in such analytical programs as the National Cattlemen's Association, Integrated Resource Committees, and Standard Performance Analysis (SPA). SPA techniques and associated software have been or currently are under development for cow-calf, stocker, seedstock, and sheep enterprises. Critical to the analysis is having complete and correct financial statements. These analytical programs build on the financial statements. These analytical programs build on the financial statements as recommended by the FFSTF. Proper financial reporting is critical not only to a SPA assessment but also to the overall financial management of today's farms and ranches. Recognizing the importance of financial management in production agriculture is not enough, taking a proactive stance in one's financial plan is paramount to success. Failure to do so will only enhance the exit rates of producers from production agriculture.

Farm Financial Standards

The Farm Financial Standards were developed by a national effort to encourage standardization. Standardization includes financial statement formats, terminology, and calculations for measuring financial position and format. Comparative analysis and education efforts are enhanced greatly by standardization. The Standardization Performance Analysis (SPA) system was developed on the basis of the performance standards for beef cattle and sheep enterprises. This article summarizes the Farm Financial Standards and illustrates the calculations with a worksheet.

A model-farm approach to research on crop-livestock integration — II. Experimental results

Abstract A six-year project was conducted to show how better crop-livestock integration and improved management increase the outputs of crops and sheep products. Three farm types were compared, consisting of different crop and sheep enterprise mixes, together with natural pastures. The conceptual framework and experimental methods used were reported in a previous paper. This paper reports the crop and sheep enterprise results. Higher yields of grain and straw from wheat and barley crops resulted from improved crop management and better varieties although the contribution of these two factors could not be ascertained. Harvest losses from all crops were substantial and represented a significant economic loss. Input of feeds harvested from the farms or purchased doubled from the poorly managed to the well-managed flock and most of them were offered during late pregnancy and early lactation. Substantial responses in ewe fertility, and offtake of cull ewes, lambs and milk were associated with improvements in feeding level.

A model-farm approach to research on crop-livestock integration — I. Conceptual framework and methods

Abstract For several decades better crop-livestock integration of farming systems in West Asia and North Africa has been promoted as a way to improve crop and livestock output. To achieve this integration, pasture or forage legumes are usually introduced into rotations or grown on fallow land. This paper reports the conceptual framework and methods used in a six-year on-station project which used model farms to investigate the benefits of closer crop-livestock integration and improved husbandry practices. Three farm types were compared. One consisted of a model farm, experimental sheep flock and natural pasture managed using traditional (T) practices. The second had the same enterprise combination but rotations that allowed better integration (I) of the crop and sheep enterprises which were subjected to improved management practices. The third farm type consisted of a sheep flock and natural pasture, with poor (C, control) management practices being applied to the sheep flock. The model farms and experimental flocks were managed by researchers.

Reproductive research on farm animals for Australia--some long-distance goals.

In Australia, much of the research on the reproduction of farm animals has emphasised the technological manipulation of the reproductive tract, gametes and embryos. However, most of the animal production in Australia is still based on sheep and beef cattle enterprises that are managed on an extensive scale; the managers need technologies that can be easily and cheaply implemented on a large scale, and that are aimed at extensive control rather than intensive manipulation. For example, for synchronizing oestrus in the wool flocks the "ram effect' has, and probably always will have, far more impact on extensive grazing systems than technologies based on exogenous prostaglandins or progestagens. This can also apply to the newer animal industries (such as emu farming), to human problems (such as population control), and to environmental problems (such as control of feral animals). Moreover, under the pressure of public opinion, the industries that are currently intensive are going 'free range'. In addition, surgical managerial tools (such as castration) will probably have to be abandoned or replaced. To cope with such profound influences, new types of reproductive management systems will be needed. This paper is an attempt to broaden our research horizons by developing the concept of 'control systems technologies', aimed at controlling reproductive performance rather than simply improving it. Ideas for such technologies already exist and are evident in the responses to environmental factors that our farm animals developed under the pressure of natural selection (before domestication). Stress, nutrition, photoperiod, lactation, and socio-sexual cues (e.g. pheromones) can all exert profound effects on reproductive activity. We already have a good grasp of the final common pathway through which the brain responses to these factors affect gonadal activity, namely the hypothalamic system that generates pulses of gonadotrophin-releasing hormone. All we need to do is learn how the major environmental cues exert their impact on the systems that control the final common pathway. When we understand them, we shall be able to manipulate them. This is not too speculative; we already have several technologies that take advantage of this approach, including steroid-based contraceptives, the "ram effect', a vaccine-based antifertility treatment for rangeland cattle and the melatonin formulation used to control seasonal breeding in sheep. These and the other pathways linking environmental inputs to reproductive output are waiting to be explored, explained and exploited.