Abstract

Thirty two Afshari lambs were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments to evaluate a nutritional supplement designed to provide multiple gluconeogenic precursors during heat stress (HS).  Lambs were housed in thermal neutral (TN) conditions and fed ad libitum for 8 d to obtain covariate data (period 1: P1) for the subsequent experimental period (P2).  During P2, which lasted 9 d, half of the lambs were subjected to HS and the other 16 lambs were maintained in TN but pair-fed (PFTN) to the HS lambs.  Half of the lambs in each thermal regime were fed (top-dressed) 100 g/d of a feed supplement designed to provide gluconeogenic precursors (8 lambs in HS [HSG] and 8 lambs in PFTN [PFTNG]) and the other lambs in both thermal regimes were fed only the basal control diet (HSC and PFTNC).  Heat stress decreased DMI (14%) and by design there were no differences between the thermal treatments, but HSG lambs had increased DMI (7.5%; P < 0.05) compared to the HSC.  Compared to PFTN lambs, rectal temperature and skin temperature at the rump, shoulder and legs of HS lambs were increased (P < 0.05) at 0700 and 1400 h.  Rectal temperature at 1400 h decreased for HSG (0.15 ± 0.03°C; P < 0.05) compared to HSC.  Despite similar DMI between thermal treatments, ADG for HS and PFTN lambs in P2 was decreased 55 and 85%, respectively, compared to P1 (P < 0.05).  Although the pre-feeding glucose concentration was not affected by thermal treatment or diet, HSG had increased post-feeding glucose concentration compared to HSC (P < 0.05).  In contrast to the glucose responses, circulating insulin was only influenced by thermal treatment; HS lambs had increased insulin concentration (P < 0.01) pre-feeding and decreased concentration (P < 0.05) post-feeding compared to PFTN lambs.  Heat-stressed lambs had decreased NEFA concentration pre-feeding (P < 0.01), but not post-feeding, relative to PFTN lambs.  Although this nutritional strategy did not affect ADG, the lower rectal temperature in HSG lambs indicates that dietary inclusion of a mixture of glucogenic precursors can potentially benefit animal health during HS.