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Oklahoma State University (2019)

Resilience of Sheep to Limited Water Availability

Hussein, Ali Hussein

Titre : Resilience of Sheep to Limited Water Availability

Auteur : Hussein, Ali Hussein

Université de soutenance : Oklahoma State University

Grade : Doctor of Philosophy (PhD) 2019

Résumé
In 2 experiments, the objective was to establish performance, physiological, and nutritional assessments of hair sheep resilience to drinking water shortage. A total of 130 Dorper, Katahdin, and St. Croix female sheep with initial body weight of 60, 63, and 45 kg, respectively, were used. They were derived from the Midwest, Northwest, Southeast, and central Texas with all breeds representing the 4 climatic regions. In 4 separate 9-wk trials using different sheep over 2 yr, animals were housed individually, were fed a pelleted diet at 160% of the metabolizable energy requirement for maintenance, and were offered water ad libitum for 2 wk, 75% of ad libitum intake for 2 wk, and 50% of ad libitum intake for 5 wk in 3 consecutive periods. All animals were weighed 3 times and blood samples were collected 2 times each week. Data from the 4 trials were pooled and analyzed for effects of and interactions involving breed, region, period, week within period, and time of blood sampling within a week using different statistical models for different response variables. Across breeds and regions, the sheep decreased dry matter intake with advancing water restriction, gained weight when switched to 75% water restriction, suffered minor weight losses in wk 1 of 50% restriction, and gained weight in the remaining 4 wk of that restriction. Assessment of blood measurements and metabolites sensitive to water shortage revealed that across breeds and regions, all sheep exhibited minor changes in packed cell volume, hemoglobin concentration, plasma osmolality, and serum concentrations of albumin, cholesterol, creatinine, glucose, lactate, total protein, triglycerides, and urea under 75% water restriction. All sheep needed 1 wk to adapt to the severe water shortage of 50% and maintained levels of blood measurements and metabolites that were slightly higher than baseline values thereafter. In Experiment 2, nutrient digestibility and energy utilization of the diet fed in Experiment 1 were determined in a crossover design in which 11 St. Croix ewes were offered water at 50 or 100% of ad libitum intake. Water restriction increased apparent digestibility of dry matter, organic matter, neutral determent fiber, and crude protein, but did not affect energy utilization. It was concluded that the 3 hair sheep breeds had high resilience to limited water availability in the absence of heat stress and that improved digestibility of dietary nutrients was an adaptation mechanism that enabled them to gain weight under severe water shortage.

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