Immunobiochemical status of sheep exposed to periods of experimental protein deficit and realimentation

Abstract

Immunobiochemical status of sheep exposed to periods of experimental protein deficit and realimentation was studied in 12 sheep (15 mo) randomly distributed into 2 equal groups and fed individually 2 different concentrate supplements along with wheat straw to provide 100% (normal protein, NP) or 50% (low protein, LP) of CP requirements. The study was comprised of 3 periods; during period 1 (0 to 13 wk) and 2 (14 to 26 wk) animals in the 2 groups were fed NP and LP diets, respectively; during period 3 (27 to 44 wk), animals in the LP group were switched over to NP diet to allow realimentation, whereas animals in the NP group remained on the same NP diet. Blood was collected from all groups at end of each period, and serum glucose, total protein, albumin (sAlb), globulin (sGlb), urea (sU), creatinine (sCr), cholesterol, triiodothyronine, and thyroxine concentrations were determined. During the same periods, the cell-mediated immune (CMI) response was measured by a delayed type hypersensitivity (DTH) assay and in vitro nitrite production by lymphocytes. At the end of periods 2 and 3, humoral immune response (HIR) was measured by sensitizing the sheep with Brucella abortus S99 antigen and measuring antibody titers on 0, 7, 14, 21, and 28 d postinoculation by ELISA. Feed intake decreased with prolonged protein deficit and showed recovery during period 3. Blood chemistry revealed reduced sAlb concentration in the LP group resulting in narrow sAlb:sGlb ratio, increased sCr concentrations (P = 0.008) accompanying a decreased (P = 0.004) sU:sCr ratio, and decreased glucose concentrations (P = 0.05). Other variables did not change significantly between the NP and LP groups. The DTH response at the end of period 1 and 2 showed marked (P = 0.008) effect of protein restriction on CMI. Nitrite production, basal and after lipopolysaccharide stimulation, was greater (P = 0.04) in the NP group. The HIR was less (P = 0.04) in the LP group during period 3. Realimentation of protein in the LP group during period 3 showed recovery in CMI and HIR. In conclusion, protein deprivation induced a decline in CMI and HIR in sheep accompanying alterations in related metabolic profile. However, a marked recovery was observed after realimentation.