Dose-dependent effects of rumen-protected betaine on growth performance, thermoregulation, antioxidant status, and metabolic parameters in heat-stressed lambs.

Abstract

This study evaluated the effects of rumen-protected betaine (RPB) supplementation on growth performance, physiological responses, hematological parameters, immune status, and oxidative stress in crossbred lambs under heat stress conditions. Forty Île-de-France × (Dalagh × Romanov) lambs (33.3 ± 2.67 kg) were assigned to four dietary treatments in a completely randomized design (n = 10): a control group (CTRL) and three RPB-supplemented groups receiving 2 g (RPBL), 4 g (RPBM), or 6 g (RPBH) of RPB per lamb per day. The study lasted 67 days, including a 7-day adaptation period. Feed intake, body weight, and feed conversion ratio were recorded biweekly. Physiological parameters such as rectal and skin temperatures, respiration, and pulse rates, were measured at different times of the day. Blood samples were collected for hematological, biochemical, immunological, and oxidative stress marker analyses. Growth and physiological parameters recorded over time were analyzed using a repeated measures model (PROC MIXED in SAS), while blood variables were assessed using one-way ANOVA (PROC GLM), followed by Tukey's test for multiple comparisons. Linear and quadratic trends were evaluated using polynomial contrasts, with significance set at p < 0.05. Results indicated that RPB supplementation significantly improved average daily gain and feed efficiency (P < 0.05). Physiological responses, particularly respiration and pulse rates, were lower in RPB-fed lambs, suggesting improved heat stress resilience. Serum immunoglobulin concentrations (IgA, IgG, IgM) increased (P < 0.05), while oxidative stress markers, including malondialdehyde, decreased with RPB supplementation. These findings suggest that RPB enhances performance, mitigates heat stress, and improves immune function and oxidative balance in lambs under high-temperature conditions. Further research is warranted to elucidate the underlying mechanisms.