3. Why is Water Important for Livestock?
3.1 Why is water so important?
Water is often overlooked as an important component in diets of livestock (Adams and Sharpe 1995). For example, these authors claim that livestock need a plentiful supply of good, clean water for normal rumen fermentation and metabolism, proper flow of feed through the digestive tract, good nutrient absorption, normal blood volume and tissue requirements. Notably, however, a broad consensus based on scientific evidence for this statement is lacking. For example, the water component of the diet may be adequate to support normal animal production in many situations. Growing pasture has a high water content (82-85%) while dried grains and concentrates have very low water contents (around 15%). Additional water is only needed to supplement the water that animals consume in their diet, although this in itself is misleading. Livestock species differ widely in their ability to conserve water. Key to this is the animals ability to recover water by producing concentrated urine in the kidneys. If an animal is given ad libitum access to water, it may well drink in excess of its 'requirements' and thereby reduce the amount of water recovered from urine by the kidneys.
To give some examples, sheep are well able to concentrate urine in times when water is in short supply, especially breeds such as the Merino. The ancestors to the Merino derive from the hot arid environments of Spain and North Africa, and as such are well adapted to conserving water by producing highly concentrated urine to a much greater degree than strains which evolved in cooler North European climates (McFarlane 1968). Clark and Jay (1975) ran a small trial at Lincoln College comparing production of ewes with or without access to drinking water for a period of 4 years; their data are not conclusive, but there was little if any impact on overall productivity, except perhaps in one year. Interestingly, the non-water group grazed more at night.
Unlike sheep, deer in general are not well adapted to water restriction and do not have the ability to produce highly concentrated urine. They have evolved, and are well distributed in the wild, in the moist temperate and cooler regions of the world (Harrington 1985). The structure of the kidney in Reindeer is such that they do not have the ability to concentrate urine to any degree (Valtonen and Eriksson 1977). This means that deer are heavily reliant on the supply of supplemental water to meet their water requirements.
Despite the importance of water to livestock, limited research has examined the water requirements of livestock, the variability of water composition, the effect of contamination and the overall impact on animal performance. In most cases, nutrition advisors must rely upon their own anecdotal experiences to assess whether water is limiting performance of livestock (Socha et al. 2003). Many publications note that there is a lack of good data on effects of water quality problems and further research is required, although the Canadian work of Willms et al. (2002) is very useful in this respect. However, there are numerous advisory documents, especially in the United States and Canada, which make statements about the need for dairy cows to be supplied with ample, good quality water to maintain production, growth and health. The particular sensitivity of dairy cows is noted due to their large requirement (average figures of 70 litres/head/day for lactating cows, Lincoln University 2003), unique rumen and digestive tract, and their losses through milk, urine, faeces and evaporation (Adams and Sharpe 1995; Murphy 1992).
The ANZECC (2000) water quality guidelines state that: "Good water quality is essential for successful livestock production. Poor quality water may reduce animal production and impair fertility. In extreme cases, stock may die. Contaminants in drinking water can produce residues in animal products (e.g. meat, milk and eggs), adversely affecting their saleability and/or creating human health risks." However, in reference to ruminants, the scientific basis for such statements is often obscure. From a regulatory and welfare perspective (the New Zealand Animal Welfare Act 1999), the managers of livestock in New Zealand are required to provide "proper and sufficient food and water", and, "protection from, and rapid diagnosis of, any significant injury or disease, appropriate to the species, environment and circumstances and in accordance with both: (a) Good practice; and (b) Scientific knowledge".
While farmers are required to supply proper and sufficient water to their animals, the definition of what is 'proper and sufficient' for livestock, is disputed, due to the scientific evidence being scarce and frequently conflicting. In addition, this evidence does not provide any guidelines for water quality and quantity that could maximise livestock productivity. Hence it is possible that there is a real opportunity to enhance livestock productivity through the provision of better quality water in sufficient quantity to animals. This would require New Zealand farm system-based research to define the 'optimum to minimum' quality and quantity ranges for livestock.
3.2 How much water do livestock need or use?
Investigations in New Zealand and overseas have resulted in data on water consumption by livestock. Because of the nature of the factors influencing consumption, there is quite a divergence of opinion on this matter. The data in Table 1 are from ANZECC (2000). Lincoln University (2003) has published similar figures as a basis for the design of stock watering systems. These authors suggest that peak demands are determined on the basis that the average daily consumption is used within a period three to four hours in the case of set-stocking in large area paddocks and 10 to 12 hours for intensive stocking on small paddocks. Unpublished data from AgResearch Invermay indicate that, given ad libitum access to water, deer on dry feeds such as hay or pelleted diets will consume around 4 times (w/w) their dry matter intake as water (4.5 times when feed moisture is taken into account), while sheep consumed slightly less water. However in the grazing situation, sheep and cattle will often be consuming pasture with dry matter contents of 15 to 20%, which given the data presented here would be similar to their actual water intake on dry feeds.
3.2.1 Influence of water intake on feed consumption
There is good evidence for a relationship between water intake and feed intake in cattle. For example, Utley et al. (1969) reported a reduction in feed intake from 6.2 to 4.8 kg/day when water was restricted to 60% of free choice, while the ratios of water to feed intake decreased from 2.9 to 2.2 litre/kg of feed. Similarly Murphy et al. (1983) showed that energy intake/dry matter intake (DMI), is a major determinant of milk production and that DMI was highly correlated with water consumption. It has long been suspected that water intake and turnover rate are related to milk production, given the fact that milk contains around 87% water. However, data supporting such a relationship will remain equivocal until the interactions of production level, along with dietary and environmental effects can be resolved (Murphy 1992). Woodford et al. (1984) attempted to separate these effects by measuring the half-life of water in four cows in various physiological states (during the dry period at 24 d prepartum, 24 d postpartum with the cows restricted to their prepartum feed consumption, and 42 d postpartum when they were allowed at least one week of ad libitum feeding). The estimates of the half-life of water were 7.5, 3.7 and 2.9 d respectively.
Table 1: Estimates of water requirements for livestock (water quality varies widely among the different classes of livestock and is also influenced by factors such as climate and the type of feed being consumed; Source: ANZECC (2000), derived from Burton (1965)).
|
Type of livestock |
Average daily consumption |
Peak daily |
|
|
Sheep
|
Lactating ewes on dry feed |
(litres/head) 9 |
(litres/head) 11.5 |
|
Cattle
|
Dairy cows in milk |
70 |
85 |
|
Horses |
Working |
55 |
70 |
|
Pigs
|
Brood sows |
22-25 |
30 |
|
Poultry
|
Laying hens |
(litres/100 birds) 32 |
litres/100 birds) 40 |
In particular respect to dairy cattle, Looper and Waldner (2002) commented that providing the opportunity for livestock to consume a relatively large amount of clean fresh water is essential, especially considering that water is consumed several times per day and is generally associated with milking. They stated that cows may consume 30 to 50 percent of their daily water intake within 1 hour of milking and reported rates of water intake varying from about 4 to 16 litres per minute. They also stated that the amount of water a cow drinks depends on her size and milk yield, quantity of dry matter consumed, temperature and relative humidity of the environment, temperature of the water, quality and availability of the water, and amount of moisture in her feed. They produced the data presented in the following tables (with the data for sub-zero temperatures deleted). The data indicate that increases in both the water temperature and the ambient air temperature lead to significant increases in water consumption, as did increasing milk production, dry matter intake (DMI) and live weight. Interestingly, the data in Table 2 for cows at 0o C are around 4.5 times the actual DMI, a value similar to that noted earlier.
Table 2: Estimated daily water consumption (litres/day) for a 750 kg lactating cow producing 20 to 50 kg of milk dailya (from Looper and Waldner 2002)
|
Milk production |
Estimated DM intake (kg/day) |
Mean minimum temperatureb |
||
|
0°C |
7°C |
12°C |
||
|
18 |
19 |
84 |
90 |
97 |
|
27 |
22 |
96 |
103 |
110 |
|
36 |
25 |
109 |
115 |
122 |
|
45 |
27 |
122 |
128 |
135 |
|
aSodium intake of 0.18% of DMI bMean minimum is typically is 5 to 8°C lower than the mean daytime temperature. |
||||
Table 3: Estimated water intake (litres/day) for dairy heifers dailya (Looper and Waldner 2002)
|
Liveweight (kg) |
Air temperature |
|||
|
1.5°C |
12.5°C |
|||
|
100 |
9.1 |
12.5 |
||
|
200 |
17.4 |
23.1 |
||
|
300 |
24.6 |
33.0 |
||
|
400 |
31.1 |
41.7 |
||
|
500 |
36.4 |
48.0 |
||
|
600 |
40.9 |
55.0 |
||
|
aSodium intake = 0.18% of DMI |
||||
3.3 Implications of water quality and guidelines for livestock
The five key properties in assessing water quality for both humans and livestock are regarded in general terms as the organoleptic properties, physiochemical properties, the presence of toxic compounds, excess minerals or compounds, and microbial contamination (bacteria and algae).
3.3.1 Salinity, total dissolved solids (TDS) or total soluble salts (TSS)
Total dissolved solids (TDS) provide a measure of the total inorganic salts dissolved in water and is a guide to water quality; the measurement also includes substances such as organic compounds, if present (ANZECC 2000). Salinity (TDS) is used in Australia as a convenient guide to the suitability of water for livestock watering. Salinity, TDS and total soluble salts (TSS) are all measures of water-soluble constituents commonly used in North America. Sodium chloride is the first consideration, but other components associated with salinity are bicarbonate, sulfate, calcium, magnesium and silica, and, a secondary group (lower concentrations) of constituents including iron, nitrate, strontium, potassium, carbonate, phosphorus, boron and fluoride (Looper and Walder 2002).
High salinity is of little concern for New Zealand farmers, but is often an issue with water supplies in Australia and in other arid climates. However salinity does impact on animal productivity, and this may be significant for some situations. Interestingly, there have even been positive responses to sodium supplementation in inland areas of New Zealand (O'Connor 2000).
The ANZECC guidelines (2000) state that "Highly mineralised waters can cause physiological upset and sometimes death in terrestrial animals, including humans. Animals under physiological stress, for example due to pregnancy, lactation or rapid growth, are particularly susceptible to mineral imbalances. Livestock generally find water of high salinity unpalatable. Water of marginal quality can cause gastrointestinal symptoms and a reduction in weight gain and milk or egg production. However, livestock can acclimatise physiologically to some extent to water of higher salinity when the level is adjusted over several weeks."
The US National Academy of Sciences (NAS 1974) noted that water with up to 5000 ppm TDS can safely be given to dairy cattle, and in some cases water containing 7000 to 10000 ppm TDS has been used without any effect on milk production (Frens 1946). Generally water with over 10,000 ppm TDS is considered highly saline and the risks are such that its use cannot be recommended. Having said this, Heller (1933) found that dairy cows were able to adapt to survive on water containing 15000 ppm (1.5%) sodium chloride.
Subsequent to the NAS review, reductions in milk production in dairy cows and in liveweight gain of cattle were reported at TDS levels of 2700 to 4400 mg/litre (Jaster et al. 1978, Solomon et al. 1995, Challis et al. 1987). Also Saul and Flinn (1985) reported reductions in performance when Hereford heifers were introduced to water containing TDS levels of 5000-11000 mg/litre.
The ANZECC guidelines (2000) classified levels for different livestock species as shown in Table 4 and stated that "Salinity is used as a convenient guide to the suitability of water for livestock watering. If water has purgative or toxic effects, especially if the TDS concentration is above 2400 mg/litre, the water should be analysed to determine the concentrations of specific ions."
The tolerance of sheep to saline drinking water may depend on the type of forage consumed. For example, pen-fed sheep were shown to tolerate up to 13000 mg/litre TDS (Peirce 1966, 1968a). However, with sheep at pasture, lambs showed increased diarrhoea, higher mortality and lower body weight gains at levels of 13000 mg/litre TDS or reduced body weight gains and wool production at 10000 mg/litre TDS (Peirce 1968b). Looper and Waldner (2002), in defining water quality requirements for dairy cattle presented the information in Table 5. These guidelines are more stringent than the ANZECC (2000) guidelines but the two sources are generally in agreement. Further information is presented in Appendix Table 1.1.
Table 4: Estimated tolerances of livestock to TDS in drinking water (ANZECC 2000)
| Livestock |
Salinity or Total dissolved solids (TDS, mg/litre) |
||
| No adverse effects on animals expected | Animals may have initial reluctance to drink or there may be some scouring, but stock should adapt without loss of production | Loss of production and a decline in animal condition and health; stock may tolerate these levels for short periods if introduced gradually | |
| Beef cattle | 0-4000 | 4000-5000 | 5000-10000 |
| Dairy cattle | 0-2500 | 2500-4000 | 4000-7000 |
| Sheep | 0-5000 | 5000-10000 | 10000-13000 |
| Horses | 0-4000 | 4000-6000 | 6000-7000 |
| Pigs | 0-4000 | 4000-6000 | 6000-8000 |
| Poultry | 0-2000 | 2000-3000 | 3000-4000 |
Table 5: Guidelines for use of saline waters for dairy cattle (Looper and Waldner 2002, based on National Research Council 2001).
| Total Dissolved Solids (ppm) | Comments |
| Less than 1,000 | Presents no serious burden to livestock. |
| 1000 to 3000 | Should not affect health or performance, but may cause temporary mild diarrhoea. |
| 3000 to 5000 | Generally satisfactory, but may cause diarrhoea especially upon initial consumption. |
| 5000 to 7000 | Can be used with reasonable safety for adult ruminants; should be avoided for pregnant animals and baby calves. |
| 7000 to 10000 | Should be avoided if possible: pregnant, lactating, stressed or young animals can be affected negatively. |
| Over 10000 | Unsafe: should not be used under any conditions. |
The response of non-ruminant species to saline drinking water may also be instructive. For example, the incidence of eggshell defects (thin and cracked shells) in laying hens was increased by an increased intake of mineral salts (Balnave and Scott 1986). Municipal water supplemented with 250 mg/litre NaCl increased shell defects two fold, while 2000 mg NaCl/litre added to drinking water resulted in defects in up to 50% of all eggs (Balnave and Yoselwitz 1987, Brackpool et al. 1996). The adverse effect of the saline water, even for short periods of time during early lay, was not overcome when the water supply was replaced with lower salinity water; notably equivalent levels of sodium chloride in feed did not adversely affect egg shell quality (Balnave and Zhang 1998). This again raises the important issue of considering both feed and water as sources of such components. An increase in water consumption and some initial diarrhoea are common observations when pigs are introduced to water containing more than 4000 mg/litre TDS, but concentrations as high as 6000 mg/litre TDS are unlikely to adversely affect pigs that have become accustomed to the water (Robards and Radcliffe 1987). In experiments in Queensland, pigs reared from 20 to 80 kg showed no reduction in performance and no adverse effects on health when given water containing up to 8000 mg/litre TDS, although water consumption did increase with increasing salinity, particularly in summer (McIntosh 1982).
3.3.2 Hardness of water
Hardness is generally expressed as the sum of calcium and magnesium (the major factors) expressed as the equivalent amount of calcium carbonate. However other cations, such as iron, zinc, and aluminium also contribute but are usually at very low concentrations compared with calcium and magnesium. While Looper and Waldner (2002) stated that water hardness has no effect on animal performance or water intake, there is very limited research on the impact of hardness. For example, there are three studies (at around 120, 200 and 300 mg/litre in dairy cows, Blosser and Soni 1957, Allen et al. 1958, Graf and Holdaway 1952), all of which apparently show no effect on milk production, weight gain, or water consumption. From these studies, it can be concluded that milk production was not compromised by water sources with up to say 300mg/litre hardness. Such water would be classified as hard to very hard, given the NRC (1980) categories of hardness (in mg/litre: soft less than 60; moderate 60 to 120; hard 120 to 180; very hard, greater than 180 mg/litre). However the actual cations involved, the composition of the diet and the physiological state of the animal may also affect the specific response to the 'hardness' of the water. This is particularly so with cations such as calcium and magnesium in late pregnancy/early lactation in dairy cows, being two minerals that are associated with metabolic upsets during these periods (hypocalcaemia and hypomagnesaemia). As such, more specific research is indicated.
3.3.3 Acidity or pH
Looper and Waldner (2002) stated that "The preferred pH of drinking water for dairy animals is 6.0 to 8.0. Waters with a pH outside of the preferred range may cause non-specific effects related to digestive upset, diarrhoea, poor feed conversion and reduced water and feed intake." In this respect, there are several studies that indicate the benefits of considering acid-base balance in ruminant nutrition and animal performance and productivity may be relevant and worthy of serious consideration (Riond 2001).
Specifically the acidity of the water supply or pH may become a more important issue in New Zealand. For example, a recent report from Environment Waikato (2004) found that many of the rivers in the region have shown a decline in pH over the last 10 years (decreases of 0.1-0.4). In another study, Scarsbrook et al. (2003) found a median decrease in pH of 0.004 per year (compared with 0.02/yr in the Waikato rivers) in a 10-year survey of 77 New Zealand rivers. This acidification is regarded as evidence of deterioration in water quality, but the cause is unclear. Although the declines were not correlated with catchment use, the rivers of the Waikato region are frequently used to water livestock.
3.3.4 Microbiological quality
Water supplies for livestock in New Zealand are seldom treated for microbial contamination, and hence livestock will be exposed to bacterial loadings in the water supply. There is evidence that livestock can tolerate relatively high bacterial loadings in drinking water (Jemison and Jones 2002) although there are actually very little data available. Table 6 presents a summary of guidelines for bacterial limits, although the primary sources are relatively obscure. As the Table shows, the microbiological limits given for livestock water supplies vary considerably.
The level of faecal (thermo-tolerant) coliforms provides an indication of faecal contamination, but does not directly relate to the number of known harmful bacteria (i.e. those that may affect production or health) present in the water. However, as a test, it is more accessible than the alternative of a full range of specific tests (such as species-specific tests) that would be required to encompass all of the water-borne microbial pathogens and parasites that could be present. The other alternative 'single test' is one for total bacterial counts but this includes a greater number of non-infectious or non-pathogenic bacteria, and so has the potential to be misleading. For this reason, a faecal coliform count is the most cost-effective and practical test for on-farm use. However it may not be as directly relevant to animal productivity as the detailed suite of tests, or reveal the most appropriate improvement measure for a particular poor water quality situation.
Table 6: Guidelines for bacterial limits
| Reference | Animal |
Bacterial limit (faecal coliforms per 100ml water) |
| MUE 1995 | Adult animals | 1,000 |
| Young animals | 1 | |
| Grant 1996 | Adult cattle | <10 |
| Calves | 0 | |
| Looper and Walder 2002 |
Adult animals Young animals (especially calves) |
<10 <1 |
| ANZECC 2000 | All livestock | <100 (median) |
| Smith et al. 1993 | All stock water | <1000 (geometric mean) |
| (NZ research) | >5000 (< 20% of samples) |
ANZECC (2000) guidelines recommend "that a median value of thermo tolerant coliforms is used" [to monitor bacterial presence], based on a number of readings generated over time from a regular monitoring program. Investigations of likely causes are warranted when 20% of results exceed four times the median trigger value".
With regards to specific bacterial limits, only Looper and Waldner (2002) provide any guidelines recommending that faecal streptococci counts not exceed 30 or 300 per litre for calves and adult cattle, respectively, although the basis for this statement is unclear.
3.3.5 Algae
Algal growth in troughs is a common occurrence and an occasional problem in freestanding water, such as farm ponds, although apart from the issue of cyanobacteria, no studies were located concerning the influence of algae on the health and performance of livestock.
Cyanobacteria (also known as blue-green algae as they are similar to algae in habitat, morphology and photosynthetic activity) are a component of the natural plankton population in healthy and balanced surface water supplies. They are found as single cells or in clumped or filamentous colonies. Cyanobacteria only become a potential hazard when they are present in large numbers (blooms). Thus the cyanobacteria of concern are generally freshwater or brackish water species and are commonly found as 'blooms' in slow-flowing, nutrient-rich waters, usually in the warmer months (Carmichael 1994; Anna Crowe, Cawthron Institute, pers. comm.). Often, there may be more than one species of cyanobacteria associated with a bloom (Ressom et al. 1994). Highly toxic "scum" material can form on the water surface, creating a potential danger for livestock and humans. Some species can also grow on the bottom sediments, sometimes forming coherent mats. These benthic (attached) taxa can be a problem especially during periods of low flow when the mats become accessible to livestock. For example, such benthic cyanobacteria mats (Oscillatoria-like species) have been linked to dog deaths in New Zealand (Hamill 2001). The toxins associated with cyanobacteria are mostly intracellular in healthy blooms and only affect animals following direct ingestion of cells (either in the water or as dried mats left on the shore), or from drinking water where the death of cells has caused a release of toxins into the water supply.
Such water quality issues are real issues for New Zealand. For example, in the summer of 2003, health warnings were issued at four of New Zealand's recreational lakes and along 400 km of the Waikato River, which is widely used as a farm water supply. Despite the fact that bloom-forming cyanobacteria have become increasingly prevalent, records of actual stock poisoning by cyanobacteria in New Zealand are rare. The first reports of suspected animal poisonings from ingestion of toxic cyanobacteria in freshwater ponds in New Zealand were reported by Flint (1966). Stock deaths from the cyanotoxin, nodularin have also been reported around Lakes Ellesmere and Forsyth (Anna Crowe, pers. comm.). Although there have almost certainly been other cases in New Zealand, particularly sub-clinical ones, they have not been reported.
As a guide, ANZECC (2000) indicated that an increasing risk to livestock health is likely when cell counts of cyanobacteria exceed 11,500 cells/ml and/or the concentrations of microcystins (a common cyanbacterial hepatotoxin produced by several cyanobacteria taxa including Microcystis) exceed certain levels. The ANZECC guidelines are based mainly on Australian and other data from outside New Zealand, as there has been very little research within the country. However New Zealand shares many of the toxic cyanobacteria found in Australia and other countries (e.g. Microcystis, Anabaena, Nodularia, Oscillatoria, Cylindrospermopsis, Anna Crowe pers. comm.) and also has the same types of cyanotoxins, such as microcystin, although cyanobacteria also produce neurotoxins. Some general information (e.g. Pridmore and Etheredge 1987) is available around the types of cyanobacteria and the cyanotoxins found in New Zealand freshwaters and hence likely to be present in troughs and other water sources. ANZECC advises that algal blooms should be treated as possibly toxic and the water source withdrawn until the algae are identified and the level of toxin defined. However shading of water troughs and frequent sanitation will also minimize algae growth.
3.3.6 Guidelines for specific substances in drinking water for livestock
The intake of minerals and other chemical compounds from drinking water is a potential concern for livestock producers. However it is important to consider the total intake from all dietary sources (and possibly including soil where animals are grazing pasture or consuming root crops, such as brassicas). Thus consideration of all sources of nutrients, including bioavailability, is important when assessing the potential impact on the nutrition of the animals in question, and the potential impact of normal dietary constituents in the water supply. Most of the literature relating to mineral toxicity or deficiencies refers to amounts of components in feedstuffs. In some cases mineral toxicities or deficiencies lead to clinical signs that are specific to the disease, but often the signs are not specific to one mineral and may be apparent only as a failure to thrive or produce optimally.
High dietary intakes of some minerals can be important as they can either depress the absorption of essential minerals, or prove toxic. For example, the depression of copper uptake in ruminants resulting from high intakes of molybdenum and sulfur together, or from interference by iron are well established, while lead, fluorine and arsenic are well-known poisons. In a more general sense, elevated concentrations of nitrate, sulfate, zinc and total dissolved solids have been implicated in negatively impacting milk production (see review by Beede and Myers 2000, this review and Appendix 1).
There are several published guidelines for water quality with little information as to how the guidelines were formulated and how they definitions of "acceptable" levels of water components and contaminants were derived. However, as noted previously, the ANZECC (2000) guidelines appear to be based on the most rigorous review of the data available, albeit acknowledging that "most trigger values ... need further validation … should be considered interim guidelines". Therefore Table 7 presents a summary of guidelines for specific components of water quality derived from the three main sources.
The Socha et al. (2003) guidelines are derived from several sources (Bergsrud and Linn 1990; Hutcheson 1996; NAS 1974, 1980; Puls 1994). For most substances, the upper level for livestock is from the U.S. Environmental Protection Agency (USEPA) or the U.S. Public Service Guidelines recommended limits for livestock and/or humans. However, it should be noted that values published as the upper desired levels vary considerably, highlighting the level of uncertainty around the area. For instance, the NAS lists the safe upper limit for nitrates at 440 ppm, while the USEPA lists the safe upper limit for livestock at 100 ppm. As noted previously, part of the variation in standards is due to the limited amount of data available on the impact of varying substance concentrations in water on animal performance. Furthermore, there may be additive or interactive effects of increasing levels of multiple substances in the water on animal performance.
Table 7: Guidelines and generally considered safe concentrations of some potentially toxic nutrients and contaminants for livestock drinking water
| Looper and Waldner, 2002 (generally considered as safe for cattle) | Socha et al. (2003) | ANZECC (2000) | |||
|
Substance (ppm = mg/litre ) |
Upper Limit, Guideline1 | Upper Level | Maximum Upper Level |
Trigger value (low risk)a |
|
| pH | 6.0-8.0 | 6-8.5 | 8.5 | ||
| Element or compound | |||||
| Aluminium, ppm | 0.50 | 5 | 10 | 5 | |
| Arsenic, ppm | 0.05 | 0.2 | 0.2 | 0.5 up to 5b | |
| Barium, ppm | 10 | 1 | 1 | ||
| Bicarbonate, ppm | 1000 | 1000 | |||
| Boron, ppm | 5 | 30 | 5 | ||
| Cadmium, ppm | 5 | 0.005 | 0.05 | 0.01 | |
| Calcium, ppm | 100 | 150 | 1000 | ||
| Chloride, ppm | 100 | 300 | |||
| Chromium, ppm | 0.10 | 0.1 | 1.0 | 1 | |
| Cobalt, ppm | 1 | 1 | |||
| Copper, ppm | 1 | 0.2 | 0.5 | 0.4, 1, 5c | |
| Fluoride, ppm | 2 | 2 | 2 | 2 | |
| Iron, ppm | 2.0 | 0.2 | 0.4 | Not sufficiently toxic | |
| Lead, ppm | 0.015 | 0.05 | 0.1 | 0.1 | |
| Magnesium, ppm | 50 | 100 | 2000 | ||
| Manganese, ppm | 0.05 | 0.05 | 0.5 | Not sufficiently toxic | |
| Mercury, ppm | 0.01 | 0.01 | 0.01 | 0.002 | |
| Molybdenum, ppm | 0.03 | 0.06 | 0.15 | ||
| Nickel, ppm | 0.25 | 0.25 | 1.0 | 1 | |
| Nitrate-Nitrogen, ppm | 10 | 20 | 100 | 400 | |
| Phosphorus, ppm | 0.7 | 0.7 | |||
| Potassium, ppm | 20 | 20 | |||
| Selenium, ppm | 0.05 | 0.05 | 0.1 | 0.02 | |
| Silver, ppm | 0.05 | 0.05 | |||
| Sodium, ppm | 50 | 300 | |||
| Sulfates, ppm | 500 | 50 | 300 | 1000 | |
| Uranium, ppm | 0.2 | ||||
| Vanadium, ppm | 0.10 | 0.1 | 0.1 | ND d | |
| Zinc, ppm | 5.0 | 5 | 25 | 20 | |
| Microbial | |||||
| Total coliforms, n/litre | 150 | 5 | 5 | ||
| Faecal coliforms, n/litre | 100 | 1 | 1 | 1000 | |
| Total bacteria, n/litre | 5000 | 10000 | 10000 | ||
| Microcystise, cells/litre | 11.5 x 106 | ||||
| Cyanotoxinf, μg/litre | 2.3 | ||||
| a) Higher
concentrations may be tolerated in some situations; b) May be tolerated if not provided as a food additive and natural levels in the diet are low; c) Respectively, levels for sheep, cattle, and, pigs and poultry; d) ND = not determined, insufficient background data to calculate; e) Microcystis = Cyanobacteria; f) Microcystin-LR toxicity equivalents (Cyanotoxin) |
|||||
A survey carried out in the U.S. by Socha et al. (2001) and a summary of data from water samples collected from 1957 to 1969 from 140 locations (NAS 1974) both indicated that surface water can vary substantially in mineral content and that some sources of water can contribute a significant amount of mineral towards meeting the mineral requirements of animals. In some cases, nutritionists have not recognized minerals supplied by water during diet formulations, due to concerns that minerals in water may have a low bioavailability. Socha et al. (2003) cautioned that the merits of this practice need to be reconsidered. While it may be true in general, there are well-known examples where bioavailability is greatly influenced by the chemical form such as the well-defined differences in availability between the common salts and the chelate/proteinate (organic) forms (Baker et al. 2003) of the transition metals such as copper, manganese and zinc. Thus it is likely that the presence of minerals that have been metabolised by microbes in the water may have markedly different impact to those that are in solution. Thus a high level of organic matter or a high bacterial loading in the water supply may provide a highly available source of micronutrients.
Further information is presented in Appendix 1.
3.3.7 Nitrate and nitrite
The nitrate situation is a specific issue that merits considerable discussion, given the potential problems associated with nitrate toxicity, and the widespread presence of nitrate in both plants and water. Thus the contribution from feed may well have a significant impact on the toxicity of the water supply. This factor is likely to account in part for the differences between various guidelines or references.
Nitrate and nitrite are oxidised forms of nitrogen, both of which can occur naturally in waters, although nitrate generally predominates. Nitrate is usually present in unpolluted streams at concentrations below 1 mg/litre (Meybeck 1982). Higher concentrations are often associated with over-use of nitrogen fertilisers and manures, intensive livestock operations, and/or leakage from septic systems and municipal wastes. Elevated concentrations of nitrite typically are found only under anoxic conditions.
Nitrite is absorbed into the bloodstream, where it converts haemoglobin to methaemoglobin, thus reducing the oxygen-carrying capacity of the blood. Symptoms of acute poisoning include increased urination, restlessness and cyanosis, leading to vomiting, convulsions and death. Ruminants exhibit adaptation to high nitrate diets developing a rumen flora with a higher capacity for reduction of nitrate/nitrite. Despite this, non-ruminants such as pigs and chickens, are less susceptible as they rapidly eliminate nitrate in the urine (ANZECC 2000). Interactions with other dietary constituents may also be important; for example, a high dietary nitrate intake may inhibit iodine uptake by the thyroid (Puls 1994).
High rates of application of nitrogen fertilisers, and the application of poultry litter or animal manures can lead to excessive nitrate accumulation in plants. Plants under stress (e.g. from drought, or a lack of adequate nutrition or sunlight) may also accumulate nitrate. Rapidly growing plants in N-rich environments have been known to accumulate nitrate at toxic levels in New Zealand. A good example is the recorded instance of nitrate poisoning in cattle grazing special purpose ryegrass or oats crops in late winter (Low 1974). In the general sense, animals are likely to be at higher risk of nitrate/nitrite poisoning through consumption of pastures, forages and feeds containing high levels of nitrate than from their water supplies.
Groundwaters may contain elevated nitrate concentrations due to natural processes (Lawrence 1983) but more typically, high nitrate concentrations in groundwaters are associated with contamination. For example, nitrate concentrations above 20 mg/litre have been reported in many Australian groundwaters, with a small proportion showing concentrations of more than 100 mg nitrate/litre (Lawrence 1983, Keating et al. 1996). Nitrate is a potential contaminant of livestock water in New Zealand, as highlighted by the recent discovery that nitrate levels in the Ashburton-Rakaia Plains groundwater have exceeded Ministry of Health human drinking standards (nitrate concentration of over 11.3 mg/litre) in the north-east Ashburton, Fairton, Seafield and Chertsey-Dorie areas (Environment Canterbury 2004). In the first three areas it appears likely that this was due to discharge of meat processing waste coupled with elevated background levels of nitrate, but in the other, it appears to be solely due to cumulative result of agricultural land use; however subsequent testing has found that the levels have apparently dropped back below 11.3 mg/litre. Such levels are well below those that are likely to cause problems in ruminants, although given that there is a considerable delay (years from a land activity to the resultant nitrate contamination of the groundwater), it is possible these levels could continue to rise, and hence potentially impact on the sheep and dairy cattle farmed in this area.
The ANZECC Guidelines (2000) note that "Nitrate concentrations less than 400 mg/litre in livestock drinking water should not be harmful to animal health. Water containing more than 1500 mg/litre nitrate is likely to be toxic to animals and should be avoided. Concentrations of nitrite exceeding 30 mg/litre may be hazardous to animal health. Both nitrate and nitrite can cause toxicity to animals, with nitrite being far more toxic than nitrate."
Table 8 has been derived from several published sources (Beede and Myers 2000; NRC 1974; Looper and Waldner 2002; Jemison and Jones 2002; Socha et al. 2003), and further information is presented in Appendix 1.
Table 8: The expected response from the consumption of drinking water containing various levels of nitrate
|
Nitrate (g/litre or ppm) |
Comments |
| 0-44 | No harmful effects. |
| 45-132 | Safe, if diet is low in nitrates and nutritionally balanced. |
| 133-220 | Could be harmful if consumed over a long period of time. |
| 221-660 | Dairy cattle at risk; possible death losses. |
| 661-800 | High probability of death losses; unsafe. |
| Over 800 | Do not use; unsafe. |
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