Effect of Water Restriction on Hair Sheep Breeds from Different Regions of the United States

Twenty-four Dorper (DOR; initial BW = 60 ± 2.8 kg), 23 Katahdin (KAT; BW = 63 ± 2.6 kg), and 21 St. Croix (STC; BW = 40 ± 2.7 kg) female sheep (0.9-8.9 yr) from 45 commercial farms in the Midwest, Northwest, Southeast, and central Texas were used to evaluate resilience to water restriction. Animals were housed individually and fed a 15% CP, 50% concentrate pelleted diet at 160% of the ME requirement for maintenance. In period 1, 2 wk in duration, ad libitum water intake was determined, followed by 25 and 50% decreases in water availability in periods 2 and 3 that were 2 and 5 wk in duration, respectively. Water was offered at 0700 h and blood was sampled at 0800 and 1400 h on the last 2 d of each week. Data presented are means of values within periods, with breed and region means separated by least significant difference and linear and quadratic contrasts addressing period effects. There were no effects of or interactions involving region for the variables analyzed. During the baseline period, water intake was 3.59, 3.79, and 3.00 kg/d for DOR, KAT, and STC, respectively (SEM = 0.140) and DMI averaged 58.6 ± 0.98 g/kg BW^0.75. There were linear decreases (P < 0.01) in DMI from period 1 to 3 of similar magnitude for DOR and KAT (134 and 153 g/d, respectively), whereas there was no change for STC (P = 0.52; 27 g/d; pooled SEM = 41.5). Plasma osmolality (mOsmol/kg) was 301, 307, and 303 for DOR, 302, 307, and 305 for KAT, and 306, 308, and 307 for STC in periods 1, 2, and 3, respectively (SEM = 1.4), with a quadratic effect of advancing period for DOR (P < 0.01) and linear and quadratic effects (P < 0.05) for KAT. There were no effects on packed cell volume (P > 0.05). Serum protein concentration changed quadratically (P < 0.001) as period advanced for each breed (7.1, 6.0, and 7.2 g/dL in periods 1, 2, and 3, respectively; SEM = 0.11). In conclusion, there were no indications of influences of region on resilience to water restriction based on period means, and the lack of change in DMI by STC with limited water availability suggests relatively high resilience for this breed.