Abstract
The dual stress of reduced feed intake and increased milk yield in dairy cows early postpartum results in a negative energy balance. Rumen-protected glucose (RPG) has been reported to replenish energy, increase milk yield, and improve gut health. However, early postpartum cows often develop an insulin resistance, implying that RPG may not be well utilized and increased milk production may increase the liver’s fat oxidization burden. This study aimed to investigate the effects of RPG on the hepatic oxidative/antioxidative status and protein profile. Starting 7 d before expected calving, six pairs of cows were supplemented with rumen-protected glucose (RPG, n = 6) or with an equal amount of rumen-protecting coating fat (CON, n = 6). Liver samples were obtained from 10 cows 14 d after calving (d 14). Concentration of malondialdehyde and activity of glutathione peroxidase were increased and the activities of catalase and superoxide dismutase tended to increase in the livers of the RPG cows compared to the CON cows. The revised quantitative insulin sensitivity check index (RQUICKI) was decreased by RPG, but triacylglycerol concentration in liver was increased by RPG supplementation. The overall profiles of hepatic proteins were similar between CON and RPG. A partial least square regression was conducted to identify the proteins associated with liver lipidosis, oxidative stress, and antioxidative capacity. The top twenty proteins, according to their variable importance value, were selected for metabolic pathway enrichment analysis. Eighteen enriched KEGG pathways were identified, including metabolism, the citrate cycle, propanoate metabolism, the peroxisome, and type II diabetes mellitus. Our study showed that RPG supplementation reduced insulin sensitivity but increased the liver triglyceride concentration and the oxidative stress in early postpartum cows. Liver proteins related to lipidosis, oxidative stress, and antioxidative capacity, were positively associated with the glutamine metabolism, citric acid cycle, peroxisome, and type II diabetes pathways, which may indicate an increased risk of liver metabolic disorders caused by RPG supplementation in early postpartum cows.
Highlights
IntroductionPostpartum dairy cows experience a negative energy balance under the dual stress of insufficient energy intake due to anorexia and the increased energy demand for Antioxidants 2022, 11, 469
TAC was not influenced by rumen-protected glucose (RPG) supplementation (p = 0.35), but triacylglycerol content in the liver was increased by RPG supplementation (p = 0.02)
The revised quantitative insulin sensitivity check index (RQUICKI) insulin resistance index was decreased by RPG supplementation (p = 0.018, Figure 1)
Summary
Postpartum dairy cows experience a negative energy balance under the dual stress of insufficient energy intake due to anorexia and the increased energy demand for Antioxidants 2022, 11, 469. The negative energy balance in the early postpartum dairy cow is associated with metabolic disorders such as ketosis and hepatic lipidosis [3–5]. Fat-coated, rumen-protected glucose (RPG) was supplemented to dairy cows during the transition period, resulting in an improved milk production [1] and gut health [10]. Fat mobilization from adipose tissue can exceed the oxidative capacity of the liver, resulting in metabolic disorders such as fatty liver disease, an increase in reactive oxygen species (ROS), a reduction of paraoxonase activity, and the onset of oxidative stress [12]. Rumen-protected glucose supplementation has been hypothesized to ameliorate the energy deficit but was instead shown to increase the negative energy balance of periparturient dairy cows [1]. We speculate that supplemented glucose in the form of RPG may stimulate the mammary gland to produce more milk, leading to a greater energy demand
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