Abstract
Early lactation is an energy-demanding period for dairy cows which may lead to negative energy balance, threatening animal health and consequently productivity. Herein we studied hepatic mitochondrial function in Holstein-Friesian multiparous dairy cows during lactation, under two different feeding strategies. During the first 180 days postpartum the cows were fed a total mixed ration (70% forage: 30% concentrate) ad libitum (non-grazing group, G0) or grazed Festuca arundinacea or Mendicago sativa plus supplementation (grazing group, G1). From 180 to 250 days postpartum, all cows grazed Festuca arundinacea and were supplemented with total mixed ration. Mitochondrial function was assessed measuring oxygen consumption rate in liver biopsies and revealed that maximum respiratory rate decreased significantly in grazing cows during early lactation, yet was unchanged in non-grazing cows during the lactation curve. While no differences could be found in mitochondrial content or oxidative stress markers, a significant increase in protein lysine acetylation was found in grazing cows during early lactation but not in cows from the non-grazing group. Mitochondrial acetylation positively correlated with liver triglycerides and β-hydroxybutyrate plasma levels, well-known markers of negative energy balance, while a negative correlation was found with the maximum respiratory rate and sirtuin 3 levels. To our knowledge this is the first report of mitochondrial function in liver biopsies of dairy cows during lactation. On the whole our results indicate that mitochondrial function is impaired during early lactation in grazing cows and that acetylation may account for changes in mitochondrial function in this period. Additionally, our results suggest that feeding total mixed ration during early lactation may be an efficient protective strategy.
Highlights
High yielding dairy cows are greatly challenged by the onset of lactation
Twenty-four multiparous Holstein-Friesian dairy cows calved in spring (664 ± 65 kg body weight (BW) and 3.0 ± 0.4 units of body condition score (BCS); 18/08/2015 ± 11 of calving date) grouped according to their due calving date, parity, BW and BCS were used in a randomized block design with two feeding strategies from calving to 180 ± 11 days postpartum (DPP): a non-grazing group fed 100% of a total-mixed ration (TMR) ad libitum and a grazing group (G1) which grazed on pasture and received supplementation
The interaction of DPP and treatment was significant for plasma β-hydroxybutyrate and for liver triglyceride (DPP X Treat: P< 0.05), as average concentrations were two-fold higher during early lactation for G1 versus G0 cows (Fig 1A and 1B), while remaining unchanged by diet in late lactation
Summary
High yielding dairy cows are greatly challenged by the onset of lactation. Lactogenesis results in a dramatic increase in total energy requirements, and insufficient dry matter intake may lead to negative energy balance [1]. In addition to the physiological changes attributed to early lactation, the environment, nutrition, is determinant in negative energy balance. Pasture dry matter intake is highly dependent on cow physiology and behavior as well as sward characteristics and, in addition, may result in increased energy expenditure due to activity (grazing and walking)[2,3,4]. Previous studies have shown that limited pasture allowance may lead to higher mobilization of energy reserves, poor reproductive performance and limit the productive responses of dairy cows [5,6,7,8]
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