Abstract
Heat stress is a serious threat to dairy cow health worldwide. N-carbamylglutamate (NCG), a novel feed additive, has been applied in dairy cow industry. However, the effects and mechanisms of NCG on dairy cows under heat stress are still unknown. A total of 48 Holstein dairy cows with similar days in milk (154 ± 13.6 d), parity (1-3), and body condition score were randomly divided into 4 groups of 12 animals each. Under heat stress, the cows were fed a TMR diet supplemented with 0 (control), 15, 20, 25 g of NCG/d per cow for 60 days. Milk production performance was recorded and serum parameters were examined. Meanwhile, metabolomics study of plasma based on liquid chromatography-mass spectrometry was also applied to investigate metabolites and pathways in response to NCG supplementation. Milk yield was increased but milk urea nitrogen was reduced by the NCG treatment. Addition of 15 g of NCG/d increased the milk protein percentage compared with the control. No effect of NCG was observed on dry matter intake, lactose percentage, milk fat percentage and somatic cell count. Serum glucose concentrations in cows fed with 15, 20, 25 g of NCG/d were 5.34 ± 0.312, 5.78 ± 0.473 and 5.54 ± 0.711 mmol/L, which were greater than those in the control (4.87 ± 0.367 mmol/L, P < 0.05). Meanwhile, the concentrations of blood urea nitrogen and blood ammonia were decreased with the addition of NCG. Results for antioxidant capacity and immune function showed beneficial effects of NCG, such as the increases in total antioxidant capacity, superoxide dismutase, glutathione peroxidase, IgG, IgM and IgA. Clear separations of plasma metabolic profiles between control and NCG groups were observed in the score plots. Sixteen different metabolites involved in metabolisms of amino acids, ketone bodies, butanoate and energy, as well as gut microbiome-derived metabolism were regulated by NCG supplementation. In conclusion, supplementation with NCG has the potential to enhance production performance, antioxidant capacity and immune function, and improved the metabolic profile of dairy cows under heat stress.
Highlights
Heat stress (HS) becomes a serious threat to dairy cow industry in certain circumstances, N-carbamylglutamate (NCG) is a novel feed additive that may be used to alleviate HS
This study found that NCG treatment improved antioxidant capacity, immune function, production performance, and metabolic profile of dairy cows under HS and provided new evidence for the better utilization of NCG
No significant difference was observed among dry matter intake (DMI), lactose percentage (LP), somatic cell count (SCC), and milk fat percentage (MFP) among NCG-treated groups and control
Summary
Heat stress (HS) becomes a serious threat to dairy cow industry in certain circumstances, N-carbamylglutamate (NCG) is a novel feed additive that may be used to alleviate HS. Arginine participates in protein synthesis and metabolism to improve intestinal absorption function, hormones secretion and nitric oxide (NO) production, which benefits the growth, development and production performance of dairy cows [1, 2]. Arginine is uneconomically used in cows for its high cost Due to these disadvantages, promoting the endogenous arginine synthesis will be an economic and alternative strategy to increase the supply of arginine for the animals. N-carbamylglutamate (NCG) is an analogue of NAG, which can enter the mitochondria to activate carbamylphosphate synthase-1 (CPS-1) and promote the synthesis of arginine. Previous studies have found that dietary supplementation of NCG could promote the metabolism of urea cycle and the uptake and utilization of nitrogen in sheep [6]. Several results suggested that NCG have positive effects on growth promotion, tissue development and reproductive performance in piglets, sheep, goats and broilers [7]
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