Environmental trade-offs of pig production systems under varied operational efficiencies.

Production of pork, the most consumed meat globally, is estimated to emit 668 m tonnes CO2-eq of greenhouse gases each year. Amongst various production systems that comprise the pig industry, grain-based intensive production is widely regarded as the largest polluter of the environment, and thus it is imperative to develop alternative systems that can provide the right balance between sustainability and food security. Using an original dataset from the Republic of Ireland, this paper examines the life-cycle environmental impacts of representative pig farms operating under varying production efficiencies. For the baseline farm with an average production efficiency, global warming potential (GWP), acidification potential (AP) and eutrophication potential (EP) per kg carcass weight departing the slaughterhouse were estimated to be 3.5 kg CO2-eq, 43.8 g SO2-eq and 32.1 g PO4-eq, respectively. For herds with a higher production efficiency, a 9% improvement in feed conversion ratio was met by 6%, 15% and 12% decreases in GWP, EP, AP, respectively. Scenario and sensitivity analyses also revealed that (a) a switch to high-protein diets results in lower GWP and higher AP and EP, and (b) reducing transportation distances by sourcing domestically produced wheat and barley does not lower environmental impacts in any notable manner. To improve cross-study comparability of these findings, results based on an auxiliary functional unit, kg liveweight departing the farm gate, are also reported.

Foraging behaviour, nutrient intake from pasture and performance of free-range growing pigs in relation to feed CP level in two organic cropping systems.

In organic pig production one of the major challenges is to be able to fulfil amino acid requirements based on organic and locally grown protein feed crops. The pig is an opportunistic omnivore with a unique capacity for foraging above and below the soil surface. It is hypothesized that direct foraging in the range area can pose an important contribution in terms of fulfilling nutrient requirements of growing pigs. Foraging activity, lucerne nutrient intake and pig performance were investigated in 36 growing pigs, foraging on lucerne or grass and fed either a standard organic pelleted feed mixture (HP: high protein) or a grain mixture containing 48% less CP (LP: low protein) compared with the high protein feed mixture, from an average live weight of 58 kg to 90 kg in a complete block design in three replicates. The pigs were fed 80% of energy recommendations and had access to 4 m2 of pasture/pig per day during the 40 days experimental period from September to October 2013. Behavioural observations were carried out 12 times over the entire experimental period. For both crops, LP pigs rooted significantly more compared with HP pigs but the effect of CP level was more pronounced in grass (44% v. 19% of all observations) compared with lucerne (28% v. 16% of all observations). Feed protein level turned out not to have any significant effect on grazing behaviour but pigs foraging on lucerne grazed significantly more than pigs foraging on grass (10% v. 4% of all observations). Daily weight gain and feed conversion ratio were significantly affected by feed protein and forage crop interactions. Compared to HP pigs, LP treated pigs had 33% lower daily weight gain (589 v. 878 g) and 31% poorer feed conversion ratio (3.75 v. 2.59 kg feed/kg weight gain) in grass paddocks, whereas in lucerne paddocks LP pigs only had 18% lower daily weight gain (741 v. 900 g) and a 14% poorer feed conversion ratio (2.95 v. 2.54 kg feed/kg weight gain) compared with HP pigs. LP pigs foraging on lucerne used 169 g less concentrate CP/kg weight gain, compared with HP pigs, indicating the nitrogen efficiency of the system. The results indicate that direct foraging of lucerne may be a valuable strategy in terms of accommodating CP and lysine requirements of organic growing pigs.

Feed intake and activity level of two broiler genotypes foraging different types of vegetation in the finishing period.

A study was performed with 2 broiler genotypes (slow and medium growth) restricted in supplementary feed and foraging 2 different mixed vegetations (grass/clover or chicory) to identify possible benefits of herbage on nutrition during the finishing period (80 to 113 d of age). Three hundred birds were included in a 2 × 2 factorial design with groups of 25 birds replicated 3 times. The use of outdoor areas, performance, and forage intake were investigated. To identify possible differences in foraging activity, the use of the range was monitored one day per week at 4 different times of the day. Feed intake from foraging was estimated by killing 4 birds per plot (2 males and 2 females) in the morning and in the evening on 3 d during the experiment and measuring crop content. Vegetation type did not influence broiler use of the free-range area, feed intake, or performance. Differences in the use of the range area, activity level, and feed content in the crops were observed in relation to genotype, sex, age of broilers, and also the time of day. Foraging activity was positively correlated with age. Medium-growth broilers spent more time inside and closer to the broiler houses during the day with increased foraging activity during evenings, in contrast to the slow-growing broilers that showed a more uniform activity during the day. Based on the measurement of crop content it was estimated that the slow-growing genotype had a daily intake of 5 to 8 g of forage per day, whereas the medium-growing genotype had an intake of 9 g for females and 20 g for males. In conclusion, limitation of supplemented protein feed in the finishing period may be acceptable for broilers that have access to highly nutritious vegetation.

Developments in greenhouse gas emissions and net energy use in Danish agriculture - how to achieve substantial CO(2) reductions?

Greenhouse gas (GHG) emissions from agriculture are a significant contributor to total Danish emissions. Consequently, much effort is currently given to the exploration of potential strategies to reduce agricultural emissions. This paper presents results from a study estimating agricultural GHG emissions in the form of methane, nitrous oxide and carbon dioxide (including carbon sources and sinks, and the impact of energy consumption/bioenergy production) from Danish agriculture in the years 1990-2010. An analysis of possible measures to reduce the GHG emissions indicated that a 50-70% reduction of agricultural emissions by 2050 relative to 1990 is achievable, including mitigation measures in relation to the handling of manure and fertilisers, optimization of animal feeding, cropping practices, and land use changes with more organic farming, afforestation and energy crops. In addition, the bioenergy production may be increased significantly without reducing the food production, whereby Danish agriculture could achieve a positive energy balance.

The effect of breed and feed-type on the sensory profile of breast meat in male broilers reared in an organic free-range system.

1. Studies on the sensory profiling of male broiler breast meat were carried out to evaluate the effect of two very different broiler breeds (JA757 and New Hampshire), two different feed types (broiler and grower feed) and age at slaughter (82 and 110 d). 2. The sensory profiling consisted of a pilot study, 4 training sessions, and finally the assessment. During the training session a panel of 9 assessors defined 17 attributes, which were used to describe the smell, texture and flavour of the breast fillets. Each attribute was evaluated on a 15-cm unstructured line scale. 3. The breast meat became significantly less hard, and more juicy and tender in the New Hampshire at 110 d of age, whereas the opposite was found in JA757, which also acquired a more "sourish" flavour with age. The smell of "sweet/maize" and "bouillon" became weaker with age in JA757, but not in New Hampshire. 4. Several significant differences in relation to the main factors of breed and age were found. The traditional broiler hybrid JA757 did best for most smell and flavour attributes, whereas New Hampshire did best for the texture attributes. Age had a negative effect on the flavours and smell attributes "fresh chicken", "neck of pork" and "sweet maize", but a positive effect on the texture attribute "crumbly". In addition meat was more "stringy" at 110 d of age. 5. The flavours "neck of pork" and "umami" were significantly improved when JA757 was fed on the broiler feed and when New Hampshire was given the grower feed. The meat smelt more "sourish" at 82 d of age and less "sourish" at 110 d of age when the grower feed was consumed. Meat was significantly harder and stringier when JA757 was fed on the grower feed. This was not the case for New Hampshire. In general, the meat was significantly less crumbly and stringier with the grower feed. 6. Overall a very distinct difference in sensory profile was found between the two breeds. In addition different slaughter ages and feeding strategies should be taken into consideration in a niche production based on alternative genotypes.

Induction of lactational estrus in organic piglet production.

The longer lactation period required in organic piglet producing herds reduces the potential number of produced litters per sow per year compared with that of conventional production. Induction and use of lactational estrus may be a way to increase the productivity in organic production. However, if lactational estrus is to be beneficial under practical husbandry conditions, it is crucial that the majority of sows are successfully mated within a few days to make batch farrowing procedures possible. The objective of this study was to investigate the occurrence and timing of lactational estrus in an organic outdoor system based on ad libitum feeding, individual housing until Day 35 in lactation, followed by grouping and introduction of a boar and weaning of piglets after 8 wk. Five groups with four sows ((Danish Yorkshire x Danish Landrace) x Danish Duroc) in each were observed, and rank was determined by a food competition test. All sows showed lactational estrus, and 84% of these sows showed estrus within 1 wk, on average 43.5 d and 7.3 d after farrowing and boar introduction, respectively. The number of days from boar introduction to estrus increased significantly with increasing feed competition rank (the lowest number being the top rank position). Eighty-four percent of all sows were diagnosed pregnant 5 wk after estrus. Behavioral observations revealed that the average total number of copulations per estrus sow was 2.3 with a range of 0 to 5 copulations. The findings of the current study indicate that it is possible to combine lactational estrus and batch farrowing procedures to increase the number of weaned piglets per year per sow in organic piglet production based on 8 wk of lactation or more.

The mating behavior and reproduction performance in a multi-sire mating system for pigs.

An important aim of organic animal production is to allow natural animal behaviour. Regarding reproduction techniques, artificial insemination is permitted but natural mating is preferred. The outdoor multi-sire system, where the sows are placed in large paddocks with a group of boars, is one example of a service system, which complies well with the organic ideals of facilitating natural animal behavior. However, very little knowledge is available about such system. Seven groups of in total of 47 sows and 31 boars were observed to study the mating behavior in an outdoor multi-sire mating system and the subsequent reproduction results. The time of start of courtship, behavior and the cause of disruption if the courtship was terminated, were recorded each time a boar courted a sow. All aggressive interactions between the boars were also recorded to estimate the boar ranking order. The observations revealed numerous poor quality matings, a huge variation in the number of times sows are mated, and overworked boars. Only 35% of all copulations lasted 2min or more and 63% of all copulations were disrupted, mainly by competitor boars. The higher social status of the boar, the more copulations did it disrupt (p<0.05). The outcome was an unacceptable variation in reproduction results. Only 71% of all estrus sows conceived, corresponding to a pregnancy rate of 77% of all mated sows. A large inter-group variation in reproduction performance was observed, indicating scope for improvements. In some groups all sows showed estrus and all sows conceived. Recommendations for improvement of the system are proposed.

Crop content in nutrient-restricted versus non-restricted organic laying hens with access to different forage vegetations.

1. The purpose of this study was to evaluate how feed intake of organic layers varies according to type of forage vegetation available when hens are fed a normal concentrate for organic layers or a nutrient-restricted diet with whole wheat and oyster shells, assuming that the nutrient-restricted diet would reflect the capacity of the hens to forage. 2. Two 23-d experiments were arranged with chicken runs in a 2 x 2 factorial design with two types of complementary feed (concentrate with 184 g/kg dry matter (DM) crude protein vs whole wheat with 120 g/kg DM crude protein) and two types of forage vegetation (grass/clover vs a mixture of forbs in experiment 1 and grass/clover vs chicory in experiment 2): each experiment was carried out in three replications. 3. Twice during each experiment two hens from each run were slaughtered - two in the evening and two the following morning. Subsequently, the birds' crops were removed. Crop content was separated into 8 fractions. 4. For most feed items crop content was found to be significantly higher in the evening than in the morning. 5. Complementary feed significantly influenced the content of several feed items in the crop. In both experiments wheat-fed hens had a significantly higher amount of soil in the crops and a significantly lower amount of weed seeds compared to the concentrate-fed hens. Plant material and grit stone were significantly more abundant in wheat-fed hens only in experiment 2 and numerically more abundant in experiment 1, whereas the amount of oyster shells was significantly higher in wheat-fed hens in experiment 1 and numerically higher in experiment 2. 6. Type of forage itself only significantly influenced the amount of soil in the crops in experiment 1 and amount of seeds in experiment 2, since more soil was found in hens foraging on the mixed forbs and more seeds were found in the hens foraging on the chicory plots, respectively.

Whole wheat versus mixed layer diet as supplementary feed to layers foraging a sequence of different forage crops.

In many cases health and welfare problems are observed in organic egg production systems, as are high environmental risks related to nutrient leaching. These disadvantages might be reduced if the layers are allowed to utilise their ability to forage to a higher degree thereby reducing the import of nutrients into the system and stimulating the hens to perform a natural behaviour. However, very little is known about the ability of modern high-producing layers to take advantage of foraging to cover their nutritional needs, and the aim of the present work was to clarify this subject. Six flocks, each of 26 hens and one cock, were moved regularly in a rotation between different forage crops for a period of 130 days. Half of the flocks were fed typical layer feed for organic layers and half were fed whole wheat. The forage crops consisted of grass/clover, pea/vetch/oats, lupin and quinoa. At the beginning of the experiment, wheat-fed hens had a lower intake of supplementary feed (wheat) and a lower laying rate, egg weight and body weight. However, after a period of 6 to 7 weeks, the intake of wheat increased to approximately 100 g per hen per day and the laying rate increased to the same level as for the hens fed layer feed. For both groups of hens egg weight and body weight increased during the remaining part of the experiment. Crop analysis revealed different food preferences for hens fed layer feed and wheat-fed hens. Wheat-fed hens ate less of the cultivated seeds, whereas the amounts of plant material, oyster shells, insoluble grit stone and soil were larger in the crops from wheat-fed hens. Floor eggs were significantly more frequent in the hens fed layer feed, whereas wheat-fed hens only rarely laid floor eggs. Irrespective of treatment, hens were found to have excellent health and welfare. We conclude that nutrient-restricted, high-producing organic layers are capable of finding and utilising considerable amounts of different feed items from a cultivated foraging area without negative effects on their health and welfare.

Comparison of descriptive sensory analysis and chemical analysis for oxidative changes in milk.

Oxidation in 3 types of bovine milk with different fatty acid profiles obtained through manipulation of feed was evaluated by analytical methods quantifying the content of potential antioxidants, the tendency of formation of free radicals, and the accumulation of primary and secondary oxidation products. The milk samples were evaluated in parallel by descriptive sensory analysis by a trained panel, and the correlation between the chemical analysis and the descriptive sensory analysis was evaluated. The fatty acid composition of the 3 types of milk was found to influence the oxidative and lipolytic changes occurring in the milk during chill storage for 4 d. Sensory analysis and chemical analysis showed high correlation between the typical descriptors for oxidation such as cardboard, metallic taste, and boiled milk and specific chemical markers for oxidation such as hexanal. Notably, primary oxidation products (i.e., lipid hydroperoxides) and even the tendency of formation of radicals as measured by electron spin resonance spectroscopy were also highly correlated to the sensory descriptors for oxidation. Electron spin resonance spectroscopy should accordingly be further explored as a routine method for detection of early events in lipid oxidation in milk to predict shelf-life.

Quantitative secretion and maximal secretion capacity of retinol, beta-carotene and alpha-tocopherol into cows' milk.

Changes in the contents of retinol, alpha-tocopherol and beta-carotene in plasma, milk and milk fat from 38 Holstein-Friesian cows were followed during their first lactation, and the quantitative and kinetic relationships for secretion of alpha-tocopherol and beta-carotene from blood into milk were determined. The cows were assigned to three groups such that all cows in the same group had the same sire. Milk yield and milk fat content differed with stage of lactation, but not according to sire. The plasma concentrations of retinol, alpha-tocopherol and beta-carotene differed with stage of lactation; in addition, retinol and beta-carotene concentration also differed according to sire. The concentrations of all three vitamins in milk and milk fat differed according to sire and stage of lactation. Furthermore, the total secretion of retinol, alpha-tocopherol and beta-carotene into milk (expressed as mg/d) differed with sire and stage of lactation. The quantitative secretion of alpha-tocopherol and beta-carotene from blood into milk followed Michaelis-Menten kinetics for active transport across membranes. Values of maximum secretory capacity Vmax and the half-rate constant K(m) for both alpha-tocopherol and beta-carotene varied according to sire. Overall means for Vmax for alpha-tocopherol and beta-carotene were 32.4 and 2.5 mg/d. Thus, the daily secretion of alpha-tocopherol and beta-carotene is limited in quantity, and is independent of the yields of milk and milk fat. It follows that continuing breeding and management systems that focus solely on increasing milk and milk fat yield will result in a steady dilution in the milk fat of these vitamins and antioxidants important for the immune defence of the cows and oxidative stability of milk products. The genetic variation found offers the possibility of utilizing these variations in breeding systems.

Effects of dietary protein supply on caseins, whey proteins, proteolysis and renneting properties in milk from cows grazing clover or N fertilized grass.

The objective of this work was to examine whether variation in the amino acid supply to cows could be a reason for the reduced casein content and poorer renneting properties of milk that often occur in late summer, or whether these effects are related to proteolysis in the raw milk. In a 2 x 2 x 2 factorial design, we investigated the effects of sward (clover v. rye-grass) and supplementary feed with a high or low level of rumen-soluble N or of rumen undegradable protein on milk protein composition during the grazing season. A total of 32 Danish Holstein cows were included in the experiment. Milk protein and casein contents and the ratios casein N:total N and casein:true protein were at a minimum in late summer, whereas the contents of urea, non-protein N and whey protein were higher during this period. These seasonal effects were unrelated to either the type of supplementary feed or the type of sward; neither were they clearly related to proteolysis, although casein: true protein was related to the proteose peptone content. The results indicated that whey proteins other than alpha-lactalbumin or beta-lactoglobulin accounted for the higher proportion or concentration of whey protein in late summer. Based on a principal component analysis including variables such as citric acid, lactose and non-protein N, we suggest that the cows' energy supply during this period may be a critical factor in determining the milk protein composition, although our results were not conclusive. There was an interaction between the supplement of rumen undegradable protein and type of sward. When clover was grazed, a high supplement increased the concentrations of protein and casein in milk and the kappa-casein: total casein ratio. When rye-grass was grazed, the opposite response was found, and overall milk protein yield was not affected. The very low N content of clover in early summer reduced milk protein and casein protein during this period.

Effect of modified dairy fat on postprandial and fasting plasma lipids and lipoproteins in healthy young men.

Fatty acid profile of milk fat can be modified by cow feeding strategies. Our aim was postprandially and after 4 wk to compare the effect of a modified milk fat (M diet) [with 16% of the cholesterolemic saturated fatty acid (C12-16) replaced by mainly oleic and stearic acids] with the effect of D diet, including a conventional Danish milk fat on plasma lipids and lipoproteins. A side effect of the cow feeding regime was a 5% (w/w) increase in trans fatty acid in M diet. Eighteen subjects were fed for two periods of 4 wk strictly controlled isoenergetic test diets with 40% of energy from total fat and the same content of dietary cholesterol in a randomized study with cross-over design. Contrary to expectations, fasting low density lipoprotein (LDL) cholesterol concentration did not differ after the experimental periods. However, M diet resulted in a higher fasting total triacylglycerol concentration compared to D diet (P = 0.009). Postprandial samples were taken at two different occasions (i) at day 21, after breakfast and lunch and (ii) on the last day of the study 2, 4, 6, and 8 h after a fat load. Postprandial plasma triacylglycerol and chylomicron triacylglycerol showed higher peak values after D diet than M diet (interaction effect, diet x times P < 0.05). In conclusion, M diet did not lower LDL cholesterol compared to D diet. Thus any cholesterol-lowering effect of oleic and stearic acids may have been obscured by the high content of cholesterol-raising saturated fatty acids in milk fat. A higher content of the trans fatty acids in M diet might have counteracted the cholesterol neutral/decreasing effect and increased plasma triacylglycerol.

Effects of stage of lactation, milk protein genotype and body condition at calving on protein composition and renneting properties of bovine milk.

The lactational variation in milk protein composition and renneting properties and their relationship to the cow's body condition at calving were investigated in 39 Danish Holstein first lactation cows fed on a well balanced standard diet. All milk characteristics measured were significantly affected by stage of lactation (P < 0.01). Casein as a proportion of total milk nitrogen reached a maximum in mid lactation. The proportion of alpha s- and kappa-casein in total casein decreased and the proportion of beta-casein increased systematically during lactation while the proportion of gamma-casein was lowest in mid lactation. The alpha-lactalbumin content of milk and its proportion of total whey proteins decreased during lactation. Renneting time was highest and curd firmness lowest in mid lactation. These results appeared to reflect a low degree of proteolysis in late-lactation milks compared with several other investigations, probably because of the good nutritional state of the cows. The body condition at calving affected proteolysis and the renneting properties of milk. A good body condition increased the content of whey protein in total milk nitrogen and of gamma-casein in total caseins (P < 0.05); in addition, curd firmness was improved (P < 0.01) and aggregation time was reduced (P < 0.05). We suggest that these effects were related to the fat metabolism and energy status of the cows during lactation. The interrelationships between the milk characteristics were evaluated by factor analysis to support the interpretation.

Prediction of milk fatty acid profile in dairy cows fed dietary fat differing in fatty acid composition.

The objective of this work was to predict changes in milk fat composition caused by differences in dietary fat. Twenty-two references describing 35 experiments and 108 treatments were used in the analysis. For lauric, myristic, and palmitic acids in milk, proportions in the dietary fat and the total dietary fat concentration were important predictors for their concentrations in milk as well as for stearic and oleic acids in milk. Using a model that included these four parameters, the residual standard deviation around the observed versus predicted line within experiments was approximately 10% of the mean for short-chain fatty acids (< C12); for lauric, myristic, palmitic, and oleic acid; and for total C18 fatty acids in milk. The model also effectively predicted milk fatty acid profile with respect to lauric, myristic, palmitic, and oleic acid and total C18 fatty acids across experiments despite differences in breed, basal diet, and milk yield among experiments. The content of short-chain acids, stearic acid, and poly-unsaturated fatty acids were less effectively predicted across experiments. Possible explanations for the differing predictabilities for different milk fatty acids are discussed.

Effect of the levels of N fertilizer, grass and supplementary feeds on nitrogen composition and renneting properties of milk from cows at pasture.

In a 2 x 2 x 3 factorial design grazing experiment we investigated the effect of fertilizer (none or 240 kg N/ha), amounts of clover grass available (low or high) and type and level of daily supplementary feed for each cow (3.5 kg barley, 3.5 kg concentrate mixture rich in protein and fat, or both, 7 kg) on the protein composition and renneting properties of their milk. The experiment was carried out in two successive grazing seasons (years) and included a total of 79 Danish Holstein cows. The effect on milk protein composition was determined in both years whereas the effect on renneting properties was determined only in the second year. Fertilization of the clover grass significantly decreased total milk protein concentration (-1.4 g/kg; P < 0.01) and tended also to decrease the relative proportion of whey protein N. Fertilization had no effect on renneting properties. Increased availability of clover grass significantly increased milk protein concentration (1 g/kg; P < 0.05) and resulted in significantly poorer renneting properties, that is increased clotting time (P < 0.01) and decreased coagulum development. These effects seemed to be mediated through an effect on the pH of the milk (+0.05; P < 0.05) as the effect was markedly reduced when statistical correction was made for the actual pH. Use of the protein- and fat-rich concentrate mix (3.5 kg) significantly reduced the total protein content of the milk (P < 0.05) and increased the proportion of non-protein N (NPN) in total N compared with use of the other supplementary feeds (P < 0.05). We found no effect on renneting properties of the different supplementary feeds. Throughout the grazing season and independent of the main treatments, the NPN proportion of milk N increased at the expense of casein N. At the same time, renneting properties became poorer, especially with high clover grass availability.

The effect of supplementary formalin treated soya-bean meal on feed intake, milk yield and live-weight gain of dairy cows fed ensiled fodder beets.

The present experiment compared formalin treated soya-bean meal (2 kg DM) with barley and urea (2.4 kg DM) as supplements for a mixture of ensiled beets and ammonium-treated straw given ad libitum in a cross over experiment with two periods of 6 weeks. Furthermore, these diets were compared to a traditional diet with fodder beets and ad libitum feeding with grass silage for a period of 12 weeks. The soya-bean meal increased the daily intake of beet-straw silage significantly from 13.1 to 14.1 kg DM (P < 0.01), the yield of milk protein (from 775 to 803 g; P < 0.05) and the live-weight gain (from 138 to 400 g; P < 0.05). Compared to the traditional diet, in which the total energy intake was close to that of the beet-straw silage diets, milk and protein yield (but not milk fat yield) were lower by the beet-straw silage feeding, although not significantly. However, this response seems to be typical and may indicate that not only the amino acid supply of the cows but also the supply of other glucogenic nutrients may be adversely affected when feeding ensiled beets.

Apparatus for EEG recording and electrical stimulation of discrete brain areas in an unrestrained small animal.

An apparatus that permits the observation of behavior, recording of EEG and electrical stimulation of the brain can be built from readily available and inexpensive components. This type of apparatus has a variety of uses in biomedical research.

An electrode-cannula unit for intracerebral electrical stimulation, EEG recording and drug administration in small animals.

An inexpensive and reliable method for administering chemicals into the brain substance while simultaneously monitoring EEG activity and/or electrically stimulating the brain has many applications. Such an electrode-cannula unit can be easily made from readily available components.