Lactational Responses of Heat-Stressed Dairy Goats to Dietary L-Carnitine Supplementation.

Abstract

Simple SummaryEndogenous carnitine synthesis is reduced by heat stress, and we hypothesized that carnitine supplementation would improve lipid metabolism and performance of dairy goats when exposed to high ambient temperature. In the current study, goats were exposed to thermal-neutral (15 to 20 °C) or heat stress (28 to 35 °C) conditions. In each environmental condition, goats were supplemented or not with rumen-protected carnitine in their diets. Goats exposed to heat stress experienced high body temperatures and respiratory rates, and reduced feed intake and milk production. Carnitine supplementation was transferred efficiently to blood, but had no effect on physiological or productive parameters in goats. We conclude that extra carnitine has no beneficial effects on goats’ performance and is not needed in thermal-neutral or heat stress conditions. Heat stress causes significant losses in milk production, and nutritional strategies are needed to alleviate its effects. Endogenous carnitine synthesis is also reduced by heat stress (HS). Carnitine plays a central role in fatty acid oxidation and buffers the toxic effects of acyl groups. We hypothesized that carnitine supplementation would make up for any carnitine deficiencies during HS and improve lipid metabolism. The objective was to evaluate rumen-protected L-carnitine (CAR) supplementation in dairy goats under thermo-neutral (TN) or HS conditions. Four Murciano-Granadina dairy goats were used in a four × four Latin square design. Goats were allocated to one of four treatments in a two × two factorial arrangement. Factors were 1) diet: control (CON) or supplementation with CAR (1 g/d); and 2) ambient conditions: TN (15 to 20 °C) or HS (0900 to 2100 h at 35 °C, 2100 to 0900 h at 28 °C). Blood free-, acetyl-, and total-carnitine concentrations increased almost three times by supplementation. Despite this efficient absorption, CAR had no effect on feed intake, milk production or blood metabolites in TN or HS conditions. Heat stress increased rectal temperature and respiratory rate. Additionally, HS goats experienced 26% loss in feed intake, but they tended to eat longer particle sizes. Compared to TN, heat-stressed goats lost more subcutaneous fat (difference in fat thickness measured before and after each period = −0.72 vs. +0.64 mm). In conclusion, supplemented L-carnitine was efficiently absorbed, but it had no lactational effects on performance of goats under thermo-neutral or heat stress conditions.