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Mitochondrial function in the liver and skeletal muscle of mid-lactation dairy cattle.

V. R. Favorit



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Mitochondrial function in the liver and skeletal muscle of mid-lactation dairy cattle.
V. R. Favorit*1, A. N. Kavazis2, W. R. Hood2, P. Villamediana1, A. L. Skibiel1. 1University of Idaho Moscow, ID, 2Auburn University Auburn, AL.

Most energy produced in the cell is through oxidative phosphorylation (OXPHOS) and mitochondrial activity changes according to cellular energy demand. At peak lactation, mammary OXPHOS machinery and ATP production are upregulated in association with increased mammary energy requirement and milk output. It is unclear if concurrent shifts occur in tissues with supporting roles in milk synthesis, such as skeletal muscle and liver. We assessed relationships between milk production and measures of mitochondrial function in these tissues at mid-lactation. Liver and skeletal muscle biopsies were taken from multiparous Holstein cows (n = 11) in mid-lactation (75 � 4 d). Milk yield was recorded daily to 80 d in milk (DIM) and milk samples collected for composition analysis (fat, protein, lactose) at 74 DIM. Mitochondria were isolated and oxygen consumption measured in a respiration chamber. Respiratory control ratio (RCR) was used as a measure of the functional and coupled state of mitochondria and calculated as the ratio of maximal ADP-stimulated respiration to basal respiration following ADP phosphorylation using either complex I (NADH-linked) or II (FADH2-linked) substrates. Mitochondrial emission of reactive oxygen species (ROS) was also measured. Correlation analysis was used to examine relationships between mitochondrial measures and average milk yield from 40 to 80 DIM (mid-lactation) only and from 5 to 80 DIM (i.e., early-to-mid). Liver complex II RCR at mid-lactation was positively correlated with early-to-mid milk yield, signifying increased fat substrate utilization to produce ATP and minimal proton leak (r = 0.74, P = 0.01). No association was observed between milk components and mitochondrial RCR or ROS. Mid-lactation milk yield was positively correlated with skeletal muscle mitochondrial ROS production (r = 0.66, P = 0.05) and tended to correlate with liver mitochondrial ROS production (r = 0.63, P = 0.1). Our results suggest that elevated energy demands associated with milk production are met with an increased efficiency of mitochondrial ATP production in liver but result in greater oxidant emission in skeletal muscle and liver.

Keywords: oxidative phosphorylation, lactation, metabolism.

Biography: I am first year Master's student studying lactation physiology. My research seeks to understand changes in mitochondrial function throughout the lactation cycle. We use liver and skeletal muscle samples from dairy cattle, due to the tissues' energetically demanding nature. Our goal is to improve our understanding of regulation and function to enhance milk synthesis.