Abstract
The experiment was conducted to assess the effects of an intermittent watering regime on physiological indicators of lactating Shami goats. Twelve does in late lactation were equally distributed to two treatments: control and watered once every four days. Several serum and milk variables were assessed at the beginning of the experiment and on four subsequent days. The does' body weight was assessed at the beginning and at the end of the experiment while milk production was recorded daily. The intermittently watered animals showed increased serum osmolarity, urea, protein and albumin concentrations, denoting dehydration. Milk production and body weight were not affected by the treatment. In addition, milk composition was similar between the control and the intermittently watered animals. It was concluded that the Shami goats could tolerate the intermittent watering regime during late lactation with minimal physiological disturbances. However, the long-term consequences of the treatment on production and health warrant further research.
1. Introduction
The Shami (Damascus) breed, native to arid countries, is well known for its dairy potential and it has been exported to different regions (Mavrogenis et al. Citation2006), where high temperature and water shortage are common constraints.
The first response to water stress reported in different animals is the reduction in feed intake (Alamer Citation2006); still others have observed no effect of water deprivation on dry matter intake (Al-Ramamneh et al. Citation2012). The decrease in feed intake could be an adaptive measure to prevent feed accumulation and secure proper digestive function (Ahmed Muna & El Shafei Ammar Citation2001). Consequently, body weight loss is observed. Furthermore, body water loss leads to haemoconcentration demonstrated by increased haemoglobin, proteins, and packed cell volume (PCV) due to the smaller blood volume (Alamer Citation2006; Mengistu et al. Citation2007a; Abdelatif et al. Citation2010). Goats also respond to dehydration by modifying their fluid regulatory mechanisms leading to an increase in plasma osmolarity and Na+ concentration (Mengistu et al. Citation2007a, Citation2007b). Similarly, plasma urea and creatinine are reported to increase following dehydration, denoting higher retention at the level of the kidneys in order to reduce water loss through urine (Silanikove Citation2000; Alamer Citation2006; Abdelatif et al. Citation2010). Increased urea retention may also be used as a source for nitrogen recycling and utilisation (Silanikove Citation2000). The effect of water stress on serum cortisol concentration is not consistently reported in literature. Increases in cortisol were reported in water-restricted lactating goats (Olsson & Dahlborn Citation1989) and whether sheep (Li et al. Citation2000), while others reported no significant effects in Awassi sheep (Jaber et al. Citation2004; Ghanem et al. Citation2008).
One of the most important products of goats is milk. Water deprivation led to a drop in milk production in lactating black Moroccan (Hossaini-Hilali et al. Citation1994) and Ethiopian Somali goats (Mengistu et al. Citation2007b). On the contrary, Maltz and Shkolnik (Citation1984) reported that lactating black Bedouin goats sustained their milk yield even after two days of water deprivation. The drop in milk production following dehydration resulted in an increase in milk osmolality that mirrored plasma osmolarity; in fact, Hossaini-Hilali et al. (Citation1994) observed an increase in milk lactose and dry matter contents with no change in milk protein and fat.
The current project proposes to assess the effect of intermittent watering, a common practice in arid and semiarid regions, on various physiological variables of lactating Shami does.
2. Materials and methods
The experiment took place at the Agricultural Research and Education Center of the American University of Beirut, Lebanon, with temperatures ranging between 14.3 and 35.8°C and relative humidity between 23.1% and 52.4%. Twelve does, aged 3–4 years in their third lactation (average weight 48.7 ± 2.39 kg), were selected. The animals were in their fifth month of lactation (five months postpartum). The month of May was selected since it is when the temperatures start to rise above the comfort zone and water shortages are likely to be experienced in extensively raised goats. They were assigned to two groups, control and water restricted (watered ad libitum once every four days), six animals in each, in a way to achieve homogeneous body weight distribution. The water restriction was repeated over eight cycles between 30 April 2009 and 31 May 2009. They were housed in a shaded barn with access to an outdoor enclosure. The two groups were separated by a partition at all times. They were offered feed (50:50 concentrate and silage mixture) and water once in the morning (8:00 am) and once in the afternoon (16:00 pm), in common feeders and water troughs accessible to all animals in the group. Water of the restricted group was removed at 8:00 am 24 hours after watering. The left over feed was measured daily, before replenishing with fresh feed, and the quantities consumed by the group were calculated accordingly. The same was applied for measuring water consumption, on daily basis for the control group and at the time of water removal for the restricted one. Hand milking was performed by an experienced person once in the morning and daily milk production was recorded for each animal.
Feeding was according to the NRC (Citation2007) requirements. The daily water intake from feed was estimated based on the moisture content of the mixed feed (silage and concentrate) and the daily total feed consumption. The feed composition is presented in .
Table 1. Composition of feed offered to lactating Shami goats subjected to daily or intermittent watering regime.
All the does were weighed at the beginning and at the end of the experiment. Blood and milk samples were taken early in the morning, at 7:00 am at the beginning of the experiment, and on days 4, 8, 16, 24, and 32, right before offering water to the restricted group. Additional blood samples were taken after one hour, right before offering water, for cortisol analysis. The double samples for cortisol analysis (one-hour apart) were taken to minimise the effect of animal handling that could create variation in cortisol levels between the different animals, especially upon the first exposure to the handler in the morning. Blood collected in heparinized vacutainers was analysed for PCV and haemoglobin concentration. PCV was measured by the microhematocrit method (microcapillary/centrifuge method) while haemoglobin concentration was determined using the cyanmethaemoglobin method (Cork & Halliwell Citation2002).
Milk was frozen at −40°C until it was analysed on an ultrasonic milk analyzer (Ekomilk total ultrasonic milk analyzer, Stara Zagora, Bulgaria), previously calibrated for goat milk, for fat, protein, lactose, pH, solid-non-fat (SNF) and density. The samples were brought to a temperature of 40°C to solubilize the fat, mixed manually and then were analysed after cooling to room temperature.
Serum from non-heparinized blood was also analysed for cholesterol, total serum protein, albumin, globulin, urea and creatinine using a Roche/Hitachi 912 Analyzer (Roche Diagnostics GmbH Laboratory systems, D-68298 Mannheim, Germany). Osmolarity was assessed by freezing point depression on a Slamed osmometer (Slamed Ing GmbH, Frankfurt, Germany) and insulin was measured by Immulite Insulin Kit radioimmunoassay using Immulite Analyser (Diagnostic Products Corporation, Los Angeles, CA, USA). Furthermore, serum samples were analysed for cortisol concentration by a solid-phase single antibody procedure, using radioimmunoassay kits (CORT-CT2, Cisbio, Bagnols-sur-Cèze, France).
At the end of the experiment, the animals were returned to their original flock where they were offered daily feed and water.
The experiment was approved by the Institutional Animal Care and Use Committee of the American University of Beirut.
2.1. Statistical analysis
The data were analysed using the General Linear Model Repeated Measures application including a random effect for the animal and a fixed effect for the treatment. The data from the first collection (at the beginning of the experiment) were used as a covariate. This approach is recommended for experiments involving the use of the same animals over time (Morris Citation1999). The model tests for the treatment effect while taking into consideration the fact that the repeated samples are not independent of each other. Since there were only two treatments, only two means could be directly compared for each variable, one for the control and one for the water-restricted group, based on the significance. The mean daily feed and water consumption per group were compared by one-way analysis of variance (ANOVA). All the statistical analyses were run on IBM-SPSS software (Version 19, SPSS. Inc.).
In order to understand the relationships between the variables and the effects of the dehydration principal, component analyses (PCAs) were also performed. As there were some data missing, we chose the variables observed during the first day of each experiment (used as a basal value) and the data after two weeks of dehydration. The objective of a PCA is to synthesise the overall information contained in a set of observed variables into a smaller number of linear combinations of orthogonal variables called Principal Components (PCs). The PCs sequentially minimise the remaining variation in the multivariate data space. Thus, the PCA condenses the information into loadings which show the relative importance (weighing) of the original variables in accounting for the variability in the observed data. The distribution of the observed data across the PCs is shown by the scores.
3. Results
Overall feed and water consumption were similar in the two groups (). No differences were observed in body weight changes or in total milk production throughout the experimental period (). However, differences were observed in protein, albumin, urea and osmolarity, whereby all these variables were higher in the water-restricted group (). On the other hand, pH, haemoglobin, cholesterol, insulin, globulin, creatinine and cholesterol showed no significant differences. Milk composition in terms of % SNF, protein, lactose, fat, pH and density was not affected by water restriction (). The PCA showed that the first two components explained a little less than half of the total variance (). The first component was explained by the variation in milk composition, and the second one, by the variation in blood components. Neither the treatment nor the sampling day had an effect on the results.
Table 2. Body weight change and milk production in lactating Shami goats subjected to daily versus once every four days watering regime during 32 days.
Table 3. Blood chemistry parameters in lactating Shami goats subjected to daily versus once every four days watering regime during 32 days.
Table 4. Milk composition of lactating Shami goats subjected to daily versus once every four days watering regime during 32 days.
The quality of the water used in this experiment, as reflected by water pH (6.7) and electric conductivity (0.47 dS/m), fell within the acceptable range for safe drinking water to all livestock at different physiological stages (de Araújo et al. Citation2010).
4. Discussion
The water-restricted and control animals maintained similar feed consumption that is comparable to reported intake levels in other breeds based on animal weights and treatments (Hossaini-Hilali et al. Citation1994; Al-Ramamneh et al. Citation2012). In contrast, a decrease in feed intake was one of the first observations reported under water restriction in many sheep (Jaber et al. Citation2004) and goat breeds (Alamer Citation2006).
The capacity of goats, indigenous to arid and semiarid regions, to replenish their water shortage in a very short time is well documented (Silanikove Citation2000; Abdelatif et al. Citation2010). This was demonstrated in this experiment whereby the water-restricted animals drank on the day of rehydration 3.2 times more than the daily consumption of the control group. This capacity to ingest large water quantities without disruption of the homeostasis denotes the adaptation of these goats to partial dehydration. Furthermore, the provision of shade and daily temperature fluctuations were reported to greatly help animals adapt to the high heat load experienced at peak temperatures (Silanikove Citation2000). Seen under this light, the results of our experiment seem to indicate that all animals were consuming water above their maintenance requirement. The maintenance requirement was reported to be 107 ml/kg BW0.75 (Giger-Reverdin & Gihad Citation1991). The same authors reported the requirement for milk production as 165 ml/kg BW0.75 for a milk production level of 148 g milk/kg BW0.75, while in our study the milk production was in the range of 29.8 g milk/kg BW0.75. Therefore, the water consumption seems to reflect the combined needs of low milk production, at this advanced stage of lactation, and the requirements for coping with the hot ambient temperature.
The weight change of lactating animals was not different between the two groups although the water-restricted animals lost weight while their daily watered counterparts gained weight. This could be partially attributed to the individual variation that was observed in both groups with respect to weight changes. Furthermore, as previously mentioned, the goats in both groups showed similar feed consumption under the two treatments which probably contributed to maintaining body weight. Previous research on lactating goats (Hossaini-Hilali et al. Citation1994; Mengistu et al. Citation2007b) and sheep (Hamadeh et al. Citation2006) indicated that weight loss in lactating animals subjected to water restriction was usually greater than in non-lactating animals under the same treatment.
The blood chemistry reflected a state of dehydration mostly through the observed increase in osmolarity. Increased osmolarity is consistently reported in water-restricted lactating and non-lactating goats (Dahlborn Citation1987; Hossaini-Hilali et al. Citation1994; Mengistu et al. Citation2007b). Similarly, an increase in serum urea is also reported under water restriction in lactating goats. This increase is a reflection of urea reabsorption at the level of the kidney which plays an important role in water retention and prevention of excessive water loss (Hamadeh et al. Citation2006). Other physiological changes were also observed in the water-restricted lactating animals, namely, increase in protein and albumin. These responses further denote dehydration and the decrease in blood volume. Similar changes have been observed in lactating ewes (Hamadeh et al. Citation2006) and goats (Dahlborn Citation1987; Hossaini-Hilali et al. Citation1994; Megistu et al. Citation2007b). The increase in protein, particularly albumin, reflects its important role in maintaining the osmotic tension of the blood under dehydration (Hamadeh et al. Citation2006; Mengistu et al. Citation2007b). Serum cholesterol and insulin concentrations were similar between the two groups probably indicating that body stores were not highly mobilised (Jaber et al. Citation2011). This is in agreement with the weight change observations, leading to the suggestion that the observed variations in body weight are probably a reflection of body water loss and not body mass loss in the form of fat depot utilisation. Damascus goats in Cyprus could tolerate a temperature between 25–30°C as the upper limit of their thermal comfort zone (Giger-Reverdin & Gihad Citation1991). In this experiment the average of maximum temperatures recorded was 35.8°C. Furthermore, blood was sampled on the last day of water restriction, in each cycle, therefore reflecting the maximum, rather than the average, effect of the treatment throughout the experiment. This suggests that the overall effect of the treatment could be milder than reported which leads to the proposition that these goats can tolerate the imposed watering regime. In fact, adapted ruminants are reported to respond to cycles of dehydration and rehydration through various mechanisms including water retention in the rumen upon rehydration and delayed diuresis to avoid haemolysis and preserve the water for use in the coming dehydration cycles (Olsson Citation2005).
The cortisol concentrations showed great variations, even before the start of the treatment. However, all values fell within previously reported results in goats (Marsico et al. Citation2009) and other small ruminants (Jaber et al. Citation2004; Ghanem et al. Citation2008). Other researchers reported lower baseline values (Komara et al. Citation2010). However, the interpretation of cortisol concentration results should be made carefully due to the fact that this variable is affected by different factors such as: handling, circadian rhythm, short-term versus long-term stressors, etc. (Möstl & Palme Citation2002). In our experiments, serum sampling was done by the same trained person from the jugular vein; nevertheless close human handling could have contributed to the observed variations especially since the animals were housed in groups. With these limitations in mind it can be concluded that: (1) the animals probably did not experience high stress level due to the treatment since their cortisol serum concentrations remained within reported normal ranges (Marsico et al. Citation2009) and (2) other indicators such as behavioural observations (Mazurek et al. Citation2007) or neutrophil to lymphocyte ratio (Davis et al. Citation2008), or other non-invasive cortisol sampling methods such as faecal cortisol (Möstl & Palme Citation2002) may be more useful in similar experiments to assess animal welfare.
The physiological stress of milk production varies greatly throughout lactation with the first month postpartum being the most demanding (Dunshea et al. Citation1990). In the current study, the animals of both groups showed a declining milk production over time. This is probably why overall milk production was similar between the two groups, since the physiological requirements for milk production were naturally decreasing irrespective of the imposed water restriction. Furthermore, the capacity of different goat breeds to sustain milk production under water shortage varies greatly. While the Ethiopian Somali and the black Moroccan goats reduced their milk production immediately at the start of water deprivation (Hossaini-Hilali et al. Citation1994; Mengistu et al. Citation2007b), the Bedouin goats could maintain their milk production when watered every second day (Maltz & Shkolnik Citation1984). The desert-adapted Aardi goats reduced their milk production by 20% and 18% when subjected to 50% and 25% water restriction, respectively (Alamer Citation2009). Milk flow was increased in goats given intravenous vasopressin to mimic dehydration levels although the mammary blood flow was decreased thus proving that milk production could be sustained (Olsson Citation2005). Long-term studies over a full lactation would be interesting to reveal the adaptability of the Shami goats to an intermittent watering regime, such as commonly practised in the field.
The intermittent watering treatment had little effect on milk composition. This is another indication that milk production, in late lactation, could be maintained under the imposed watering regime. Previous studies have showed an increase in milk osmolality, lactose and density following water deprivation for 48 hours (Dahlborn Citation1987; Hossaini-Hilali et al. Citation1994). In contrast, lactating Aardi goats subjected to 50% or 25% water restriction showed slight alterations in milk composition most notably in the form of reduction in milk fat content in the 25% restriction group and an increase in osmolality in the 50% restriction group (Alamer Citation2009). The author concluded that this reflected the adaptability of this breed to the harsh arid environment. Milk osmolality is strictly controlled to keep it isotonic with plasma; the increase in lactose under water restriction, being the major osmotic component of milk, is probably a response to the increase in serum osmolarity under water restriction (Dahlborn Citation1987). The same trend was observed in the current study but differences between the two groups were not statistically significant.
5. Conclusion
This study provided a preliminary insight into the adaptability of the Shami breed to an intermittent watering regime under lactation, a physiologically demanding condition. Intermittently watered does experienced dehydration as indicated by key physiological variables, however, overall milk production and composition were not affected over the one-month study period. These findings warrant larger scale research on this economically important breed to assess its adaptability to long-term water shortage at the different stages of its reproductive cycle and under different environmental conditions.
Funding
The authors are grateful for the Lebanese National Council for Scientific Research and The American University of Beirut Research Board for financially supporting this project.
Additional information
Funding
References
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