Water Requirements

Total water requirement is determined by body weight, physiologic state, level of activity, production level, dietary composition, and environmental conditions. Animals maintained on pasture have nearly twice the water turnover rate compared with indoor housed animals. The numerous factors influencing a given animal’s water needs confound our ability to generate specific requirement models (see NRC for review).⁷ Using isotope dilution methods, water turnover rate can be measured, and this value is assumed to be equivalent to the animal’s total water intake or loss assuming a steady state balance. Only one study measured water turnover rate in llamas. Under confinement in a temperature-neutral environment, adult llamas had higher water turnover rate (62.1 ± 8.8 milliliters per kilogram of body weight [mL/kg BW^0.82]) compared with goats (59.0 ± 10.9 mL/kg BW^0.82).⁹ In this same study, llamas maintained on pasture had a water turnover rate nearly twice (122.2 ± 29.8 mL/kg BW^0.82) that of confined animals. A similar water turnover rate (116 ± 5 mL/kg BW^0.82) was determined in free-ranging llamas, whereas a higher rate (151.8 ± 28 mL/kg BW^0.82) was reported for free-ranging alpacas.^13,14 These higher values are consistent with water turnover rates in grazing sheep and goats. Water requirement can be estimated relative to energy expenditure or DM intake.⁷ Estimates for water requirements for SAC maintenance in a thermoneutral environment have been related to energy intake (1 milliliter per kilocalorie [mL/kcal] of metabolizable energy intake) or energetic requirement based on metabolic body weight (122 mL/kg BW^0.75).^6,16 The former estimate is essentially equivalent to the observed water turnover rate for confined animals, whereas the latter model predicts slightly lower water requirements than the water turnover rate measured in pastured llamas (Table 9-1).

Few reports have documented additional water requirements for physiologic states beyond maintenance for SACs, so some extrapolation from other species is necessary. Water requirement is increased between 30% and 70% above maintenance in the final 2 months of pregnancy in goats and sheep, respectively.⁷ Given that sheep seemingly have a much higher pregnancy water requirement compared with other small ruminants, a suggested increase of 30% to 50% above maintenance should be reasonable for SACs. Water loss in support of milk production in goats was estimated at 1.43 kg/kg of milk yield. Other studies have shown a water requirement for lactating small ruminants to range between 412 and 433 mL/kg BW^0.75 housed on pasture in warmer weather.⁷ One study reported the water turnover rate in free ranging lactating llamas as 396 ± 9 mL/kg BW^0.82 (equivalent to 552.5 mL/kg BW^0.75) under pastoral conditions.¹⁴ This higher requirement relative to other small ruminants may reflect lower body fat composition during lactation in llamas and higher metabolic rate associated with extensive pasture management. Additional required water in support of growth has been evaluated in various small ruminant species. Suggested water requirements for nursing and weaned animals are 8 to 13 mL/g BW gain and 7 to 8 mL/g BW gain, respectively.⁷ Incorporating these suggested water requirements for gain with maintenance, nursing animals gaining between 100 and 400 g/day have an estimated water requirement of 255 to 316 mL/kg BW^0.75, whereas weaned animals gaining 200 to 400 g/day would have a water requirement of 244 to 348 mL/kg BW^0.75.⁷ The range in daily gain for nursing animals is consistent with observations in growing llamas and alpacas; however, this rate of gain for weaned animals would be higher than that observed in llamas and alpacas.

The goal for a water program is to provide water in amounts that would exceed voluntary consumption under given environmental conditions to ensure adequate water availability. Although water consumption is highly associated with DM intake (see Figure 9-1), accurate intake determination for llamas and alpacas is difficult under typical group feeding systems; thus, water requirements might be best predicted relative to energy requirements. A comparison of various maintenance water requirement models and suggested models using metabolic body size to estimate SAC water requirements over various physiologic states are shown in Table 9-1. These models are assuming an isothermic ambient temperature (50°F) and will need to be adjusted for differing ambient temperatures (see Figure 9-1). In comparing maintenance water requirements (Figure 9-2), the confined model is the minimal water requirement and could be used to estimate water needs for sick or strictly confined animals. Animals that are confined or managed in dry lots would have a water requirement estimated by the 122 mL/kg BW^0.75 model, whereas pasture-based animals have a higher requirement (182.1 mL/kg BW^0.75). For the final 3 months of pregnancy, water requirements should be increased by 50% above either confinement or pasture maintenance requirements, depending on the management system. The lactating water requirement (552.5 mL/kg BW^0.75) was based on a single reported study, but adjusted to a metabolic body weight basis. With no camelid data for a basis, recommended water requirements are based on described NRC models for nursing animals with a range of growth from 100 to 400 g/day.

Fresh clean, high-quality water should be accessible for free-choice intake at all times. At least two watering stations should be provided for each pen of animals to prevent water access to socially inferior animals being restricted by the socially superior animals within a group. Minimal documented information is available regarding water space requirements for SACs. At least 12 inches of water trough space per ewe or goat has been recommended; however, this greatly exceeds water station size recommendations for dairy cattle (36 inch per 10–15 cows).¹⁷ If two watering stations are present in a pen, then 2.5 to 3.5 inches of water space per animal should be sufficient. SACs suck water with a slightly opened mouth and generally adapt to most open surface watering units.

Water Quality Assessment

Water is the most essential, although often the most neglected, nutrient. A short time frame exists between inadequate water intake and clinical manifestations of water deficiency. Required amounts and availability of water, as in the case of other essential nutrients, are not the only issues to be addressed; water quality must also be addressed. Water quality can be evaluated subjectively by its color, taste, and smell. High-quality water should be colorless and have no offensive odor or taste. A “rotten egg” smell to water is the result of high sulfate (odorless) content, in which sulfate ion is reduced to produce hydrogen sulfide (H₂S) gas, which gives out the obnoxious smell. Determinations of pH, total dissolved substances (TDSs), mineral content and hardness, contaminants (herbicides, pesticides, organic compounds, etc.), and microbiologic culture provide objective measures of water quality. Water that meets current standards for human consumption obviously is equally satisfactory for animal consumption. The question is the tolerance level of animals relative to their willingness to consume adequate amounts of water that does not meet current human standards and not experience adverse consequences. Definitive evidence is minimal regarding the lower tolerance level of water quality for animals, especially for microbial contamination. A number of publications addressing livestock water quality generally describe experiential assessment of water quality for livestock.18–20

Beyond the initial subjective evaluation of a water source, measures of pH and TDSs provide a preliminary water quality assessment and may suggest the need for further evaluation. Ideal water pH is approximately 7.0, but most animals will tolerate water with a pH range between 6.0 and 9.0. Water pH can be easily measured with litmus paper or commercially available battery-operated pH meters, some of which may also measure TDSs. Salinity is a measure of total dissolved substances (or solids) most of which are mineral compounds, which accounts for electrical conductivity being another potential measure for salinity. Other measures of water quality will require a certified laboratory to complete desired analyses. Contact a chosen laboratory to determine appropriate methods for sample collection.

Increasing salinity of water sources, irrespective of mineral sources, results in decreased water intake, transient diarrhea, and reduced performance because of lower feed intake (Table 9-2). Younger animals and lactating animals are most sensitive to water salinity. Most animals can acclimate to moderately saline water. High levels of TDSs in a water sample would suggest that further evaluation of mineral content is warranted, although low levels of TDSs water could contain inappropriate mineral content. The most common dissolved minerals include calcium, magnesium, sodium, sulfate, and bicarbonate. Water hardness, a measure of calcium and magnesium content, is not a significant health or water intake issue. Hard water may contribute additional calcium or magnesium to the diet but does not increase urolithiasis risk. Beside potential toxic minerals that may contaminate water (Table 9-3), dissolved substances may affect aesthetic quality, which may lead to decreased intake; provide an additional mineral source to the diet potentially altering available mineral balance; or interfere with other minerals thus altering dietary mineral availability. Iron, manganese, and sulfate content of water are of primary concern, as they have an adverse impact on aesthetic qualities and also interfere with other minerals. Excessive iron and sulfate intake may adversely affect dietary copper availability, although by separate mechanisms. High sulfate intake may induce polioencephalomalacia that is nonresponsive to thiamin supplementation. Nitrates are another potential water contaminant of concern, especially in ruminant animals, in which nitrate is converted to more toxic nitrite by ruminal microbes. Absorbed nitrites will bind to hemoglobin reducing the blood’s oxygen carrying capacity, which results in varying stages of anoxia in affected animals. Although water nitrate content generally is not solely responsible for animal intoxication, it can significantly contribute to dietary nitrate content in predisposing to potential intoxication (Table 9-4).

A zero tolerance level is expected for microbiologic contamination of human water sources. Animals, however, seemingly tolerate low to moderate bacterial loads in their water supply. Younger animals are perceived to be less tolerant than older animals to coliform contamination of water. Although no definitive criteria have been established, total bacteria, fecal coliform, and concentrations of fecal streptococcal organisms exceeding 1 million—less than 10, and less than 30 organisms per 100 mL, respectively—are considered potential problem levels.¹⁹ Water poses a risk for transmission of various pathogenic organisms (i.e., cryptosporidia, coccidia, leptospira, and fecal coliforms) if contaminated by the urine or feces of infected animals. During summer months, surface water sources may become contaminated with blue-green algae, which, if consumed, may produce hepatotoxins capable of causing severe liver disease and death.

Energy Partitioning

During digestion, energy stored within chemical bonds of carbohydrate, fat, and protein molecules is released in varying degrees and made available to the animal. Gross energy (GE) is the total amount of energy in a feed measured as heat released during total combustion. GE is categorized into definable components, namely, digestible, metabolizable, and net energy, based on the proportion of GE available to the animal at different phases of the digestion and utilization process.²¹ Digestible energy (DE) is that portion of GE that is not excreted in feces. Metabolizable energy (ME) is the portion of DE that is not lost in urine or as fermentation gases. ME is available to the animal’s tissues and is used for various productive functions. Although ME would be a more descriptive measure of animal performance based on energy availability, combustible gas production is fairly consistent (approximately 18% of DE) in nonruminant animals and ruminants at maintenance. Therefore, ME is often approximated as 0.82 × DE; however, this relationship may vary considerably, depending on diet composition and level of feeding. Finally, net energy (NE) is the proportion of ME used to maintain body physiologic functions (maintenance) or productive condition (e.g., tissue growth, pregnancy, lactation, fiber growth). The difference between ME and NE is heat production following heat losses during digestion and metabolism of a given nutrient (heat increment) and heat losses from fermentation. Efficiency of conversion of ME to NE also depends on the productive purpose. Pregnancy is the least efficient process (approximately 12%–15% ME energy conversion to fetal energy deposition), whereas maintenance and lactation are relatively efficient (67%–72% conversion). Conversion efficiency for growth will depend on tissue composition (fat versus protein) that is being deposited.

Use of GE to define an animal’s energy requirement is of no value, since it does not account for any difference in digestibility among feed sources. With regard to GE, corn cobs have the same energy value as corn grain. On the other extreme, NE most precisely defines feed energy truly available to the animal. However, measurement of feed NE content is tedious, complicated in ruminant species, and requires highly specialized metabolic chamber equipment. Most energy determinations are obtained through simple digestion trials to quantify DE. However, DE determination overestimates feed energy for forages and fibrous byproduct feeds because of the variable production of fermentation gases, which supports direct determination of ME as the preferred measure of energy needs. Both DE and ME determinations are further confounded by loss of energy from nondietary feed sources from endogenous cellular debris and enteric bacteria. Apparent digestibility or availability does not account for the energy contribution from these nondietary sources in feces or urine, thus underestimating the true digestibility or availability of energy from the given feed source. Methods to assess endogenous or bacterial contributions are not feasible in ruminants, as they require severe feed restriction to measure endogenous body losses and because enteric bacterial populations would need to be eliminated. Thus, the limitations to the ability to measure or describe energy requirements of SACs need to be considered.

Another commonly used energy term is total digestible nutrients (TDNs). TDNs are defined as the sum of digestible protein, sugar and starch carbohydrates, fiber, and fats. Digestible fat is multiplied by 2.25 to account for its greater energy density compared with carbohydrates. TDN content of forages is overestimated in comparison with cereal grains as a result of inherent assumptions of protein digestion made in the TDN calculation and different carbohydrate to protein ratios in these two feed types. Although TDN is often mistakenly equated with DE, it fits into the energy scale somewhere between DE and ME. Traditionally, feed TDN content was determined from digestibility trials performed on sheep, which accounts for our largest database of feed composition information. Currently, feed TDN is predicted from regression models using some combination of acid detergent fiber, neutral detergent fiber, and crude protein (CP) and is expressed as a percent of DM. Since feed TDN content is based on digestibility, the TDN value for any given feed will be dependent on the species consuming that feed. Ruminant animals are more efficient fiber digesters; therefore, TDN values for fiber-based feeds will be greater for ruminant animals compared with those for other nonruminant herbivores. Regression models to predict feed TDN content for dairy cattle are considered applicable to other ruminant animals. A slightly higher TDN value compared with that for ruminants would be expected for lower-quality forages based on evidence of greater fiber digestion in SACs. A challenge in using feed TDN values is that digestibility is reduced with increasing feed intake, so the current NRC recommendations apply a discount factor to adjust TDN value for animals with higher feed consumption. Required TDN is expressed as a percent of diet (typically 45%–65%) or amount (grams [g] or pounds [lb]) per day. Total digestible nutrients content of feeds or a diet can be interconverted with DE using the defined value of 1 kg TDN = 4.409 Mcal of DE (1 lb = 2 Mcal DE).

Dietary Energy Sources

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