|dcterms.abstract||Water is the main challenge facing animal husbandry in arid and semi-arid regions of the globe. These areas are characterized by a long dry season lasting between 6 and 8 months. At certain times during the long dry period, water can be so scarce that animals may face severe water shortages. Many studies have been conducted to highlight how ruminants cope during these times of severe water deprivation. Yet, livestock are much more often exposed to mild water shortages for several months in a year. Only a few studies have been conducted to investigate mild water restriction in ruminants, highlighting the effects on feed intake and blood parameters. However, the effects of mild water restriction on other physiological processes are yet to be studied. Therefore, the present study aimed at bridging this knowledge gap by investigating whether mild water restriction affects (a) the digestibility, digesta passage and faecal microbial biomass, (b) alters rumen fermentation, microbial yield and turnover, and (c) enhances nitrogen retention and shifts nitrogen excretion towards the faeces.
Two feeding trials were conducted at Sultan Qaboos University, Muscat, Oman, during the dry summer months (August-October) in 2013 and 2014. In each trial, three watering regimes (100%, 85% and 70% of individual ad libitum consumption) were imposed to nine adult male Batinah goats in a 3 x 3 Latin Square design. Water intake, feed offered and refused, rumen fluid and solids, urine and faeces were quantified and their respective quality determined using standard procedures.
The results revealed that mild water restriction does not affect feed intake and digesta passage of goats. However, there was an increase in apparent feed digestibility during water restriction but this was not associated with altered digesta kinetics. While the total faecal microbial mass was not affected by water restriction, the microbial community structure shifted towards fungal C when water was restricted to 70% of ad libitum intake. Moreover, ammonium-N in the rumen fluid substantially increased when water was restricted to 70% of ad libitum intake. Also, the proportion of butyrate increased when water was restricted to 70% of ad libitum intake. These phenomena were associated with increases in protozoal counts when water intake decreased. Mild water restriction did neither affect the goats’ nitrogen balance nor the partitioning of nitrogen excretion between urine and faeces. Therefore, a restriction of the ad libitum water intake to 70%, which is expected to occur more frequently with current climate change phenomena observed in the semi-arid tropics and subtropics, may be anticipated with serenity because it improves feed utilization in agro-pastoral farming systems without compromising the performance of regionally adapted goat breeds, and this observation may also pertain to other adapted breeds of domestic ruminants.||eng