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

Abstract

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.

Milk Production and Energetic Metabolism of Heat-Stressed Dairy Goats Supplemented with Propylene Glycol

“…For TN goats, average rectal temperature and respiratory rate values increased ( p < 0.05) from 38.74 °C and 28 breaths/min at 08:00 h to 39.00 °C and 33 breaths/min at 12:00 h. No additional increase was observed at 17:00 h for TN goats (39.10 °C and 35 breaths/min). These results agree with the findings of Hamzaoui et al [ 1 ], Mehaba et al [ 6 ], and Contreras-Jodar et al [ 9 ], where goats exposed to HS experienced high rectal temperatures and respiratory rates. The increment in respiratory rate under HS conditions was for dissipating the heat load by pulmonary water evaporation as indicated by the greater consumption of water by HS goats (see hereafter).…”

“…The BW change, DM intake, water consumption, and calculated energy balance data of TN and HS goats with or without PG supplementation are shown in Table 2 . The decrease ( p < 0.01) in DM intake by the effect of HS was 34% on average, which is similar to DM intake losses in heat-stressed goats at mid lactation (–26%; [ 6 ]), but greater than losses observed during late lactation (–19%; [ 1 ]). Heat-stressed animals decrease their DM intake to reduce the production of metabolic heat given the fact that heat increment of feeding is an important source of heat production in ruminants [ 23 ].…”

“…Under HS conditions, DM intake decreases by 25 to 40% in dairy goats, causing a negative energy balance and body weight (BW) loss [ 1 , 6 ]. Paradoxically, this significant reduction in DM intake is not accompanied by body fat mobilization, as blood non-esterified fatty acids (NEFA) levels did not vary between HS and TN cows [ 3 ] or goats [ 1 , 6 ]. Heat-stressed dairy goats are also able to keep similar blood glucose [ 2 , 6 ] despite the reduced feed intake and the apparent blockage of using fatty acids as compensatory energy source.…”

“…Paradoxically, this significant reduction in DM intake is not accompanied by body fat mobilization, as blood non-esterified fatty acids (NEFA) levels did not vary between HS and TN cows [ 3 ] or goats [ 1 , 6 ]. Heat-stressed dairy goats are also able to keep similar blood glucose [ 2 , 6 ] despite the reduced feed intake and the apparent blockage of using fatty acids as compensatory energy source. Alternatively, it seems that HS-goats catabolize their muscles (protein mobilization) and use glucogenic AA to keep blood glucose levels [ 2 , 4 ].…”

Effects of Cold Exposure on Some Physiological, Productive, and Metabolic Variables in Lactating Dairy Goats

“…Throughout the experiment, goats were individually kept in sawdust-bedded pens (1.0 × 1.5 m) equipped with individual feeders and drinkers. Since there are no studies reported in the literature examining the impact of cold temperatures in Murciano-Granadina goats, power analysis was performed based on data reported in heat-stressed goats of the same breed and use the same experimental design and facilities [ 21 , 22 ]. The fat-corrected milk data recorded for control and heat stress goats (2.10 vs. 1.78, SD = 0.22, respectively) were used to calculate the anticipated number of goats needed to provide sufficient statistical power.…”