The study objective was to evaluate the effect of grazing on early lactation changes in hepatic free glucose and glycogen concentrations and expression of genes related with gluconeogenesis in dairy cows. Primiparous Holstein cows (n=18, 3.2 +/- 0.2 BCS; fall calving) were used in a randomized block design and assigned, at calving, to two nutritional treatments during the first 61 days postpartum (DPP) of lactation: TMR ad libitum (TMR) or grazing of Medicago sativa plus 70% of TMR (PAS+TMR). Plasma and liver biopsies were collected at -7 and +42 DPP to measure plasma insulin and glucose, and hepatic free glucose and glycogen concentrations and mRNA abundance of genes related gluconeogenesis. Milk energy output was greater for TMR than PAS+TMR cows whereas plasma glucose and hepatic free glucose and glycogen concentrations did not differ between feeding strategies. Although insulin decreased from pre to postpartum, it was not affected by nutritional strategy. Hepatic pyruvate carboxylase (PC), citrate synthase (CS), and succinate dehydrogenase subunit D (SDHD) mRNA were greater while pyruvate dehydrogenase (PDH1A) mRNA tended to be less for TMR than PAS+TMR cows. Results would suggest TMR cows adapted their hepatic glucose and energy metabolism to the increased demands of their greater milk production.

In order to compare the energy partition between heat production (HP) and retained energy (RE) in early lactation of dairy cows fed with 100% total mixed ration ad libitum (TMR) or grazing cows supplemented with concentrate (P+C), 24 cows were used in a randomized block design. Cow HP (measured by the O-2 pulse technique), RE in milk (estimated by daily milk yield and weekly composition), RE in body tissue [estimated from changes in body weight (BW) and body condition score (BCS) recorded every 14 days] and metabolizable energy (ME) intake (estimated as HP + total RE) were used to calculate energy balance from 21 to 49 days in milk. Data were analyzed with a mixed model including feeding strategy as fixed effect and block as random effect. Production and RE milk were greater for P+C than TMR, whereas RE in body reserves was greater for TMR than P+C cows, determining that total RE did not differ between treatments. Neither ME intake nor measured HP was affected by feeding strategy but the residual HP, calculated as the difference between measured and predicted HP (based on NRC 2001 model), was 36% greater for P+C than TMR, not being different from zero P+C cows and representing this increase almost 10% of the estimated ME intake. Thus, results indicated that for grazing dairy cows in early lactation, maintenance requirements are increased when compared with the NRC model, which estimates them adequately for confined TMR cows.

Early lactation is an energy-deming 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 were supplemented with total mixed ration. Mitochondrial function was assessed measuring oxygen consumption rate in liver biopsies 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 β-hydroxybutyrate plasma levels, well-known markers of negative energy balance, while a negative correlation was found with the maximum respiratory rate 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 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.

The objective of this study was to estimate changes in body composition during the transition period of dairy cows with different feeding strategies during early lactation. Primiparous Holstein cows calved in autumn were used (n = 18; 528 ± 40 kg BW; 3.2 ± 0.2 BCS) in a randomized block design with two nutritional treatments. At calving and during the first 65 days postpartum (DPP), cows were assigned to either: (G0) total mixed ration (TMR) ad libitum (17kg DM/d offered; 70% forage, 30% concentrate) or (G1) grazing of alfalfa (Medicago sativa; 6-h am grazing in 3-d strips; pasture allowance=20 kg DM/d) + TMR (70% of ad libitum TMR; 12 kgDM/d offered). Cows were milked twice a day, milk yield was recorded daily, and all cows consumed 2.2 kgDM/day of a commercial concentrate at each milking. Cow BW and BCS were determined every two weeks from -21 to +60 DPP. At -7 and +42 ± 3 DPP, body composition was determined using the urea dilution technique. Data were analyzed as repeated measures with a mixed model including DPP and feeding strategy within DPP as fixed effects and block as random effect. Means were considered to differ when P < 0.05. Milk energy output during the first 42 DPP was greater (P = 0.05) for G0 than G1 cows (20.1 vs 18.3 ± 0.6 Mcal NEL/d) but loss of BCS from -7 to +42 DPP was greater (P = 0.04) for G1 than G0 cows. Cow body fat mass and retained gross energy (GE) decreased (P = 0.001) from pre to postpartum and these decreases were greater (P ≤ 0.20) for G1 than G0 cows (64.4503, and 59.4043 ± 2.5kg fat and 4007.65, and 4266.14 ± 129 MJ GE for -7 DPP and G0 and G1 at +42 DPP, respectively). In contrast, body protein and water mass were not affected by DPP or treatment. Relative to cow empty BW, body fat and GE content decreased (P ≤ 0.014) while body water and protein increased (P ≤ 0.04) from pre to postpartum. Although during the postpartum there were no differences in relative water and protein mass, relative body fat and GE content were less (P ≤ 0.001) for G1 than G0 cows (136.69 and 147.17± 5.2 kg fat and 9.2,and 9.7± 0.2 MJ GE for -7 DPP and G0 and G1 at +42 DPP, respectively). Negative energy balance during the transition period was more severe for G1 than G0 cows, probably associated to decreased DMI and increased maintenance requirements.

Primiparous Holstein cows (n = 18; 528 ± 40 kg BW, 3.2 ± 0.2 BCS) calved in fall were used in a randomized block design to study the effect of feeding strategy on production, metabolic, and endocrine responses in early lactation. At calving, cows were assigned within block to 1 of 2 feeding strategies during the first 65 d postpartum (DPP). Feeding strategies were either (G0) total mixed ration (TMR) ad libitum (17 kgDM/d offered; 70% forage, 30% concentrate) or (G1) grazing of alfalfa (Medicago sativa; 6-h am grazing in 3-d strips; pasture allowance = 20 kgDM/d) + TMR (70% of ad libitum TMR; 12 kgDM/d offered). Both groups consumed 2.2 kgDM/d of a commercial ration at each milking. Cows were milked twice a day, milk yield was recorded daily and samples were collected weekly for milk composition. Cow BW and BCS were recorded every 2 wk from −40 to +65 DPP. Blood samples were collected for metabolite and hormone analyses at −7 ± 2 and +42 ± 3 DPP. Data were analyzed as repeated measures with a mixed model that included: feeding strategy, DPP, and its interaction as fixed effects, block as random effect and calving date as a covariate. Milk yield (26.7 vs. 25.1 ± 0.58 kg/d), total solids (3.38 vs. 3.1 ± 0.09 kg/d) and NEL output (20.9 vs. 19.2 Mcal NEL/d) tended (P < 0.07) to be greater for G0 than G1 cows, being differences more marked from +30 to +60 DPP. Cow BW and BCS did not differ (P > 0.30) between feeding strategies. Concentrations of plasma NEFA decreased (P < 0.01) at +42 DPP when compared to −7 DPP and at +42 DPP tended (P = 0.10) to be greater for G0 than G1 cows (0.34 vs. 0.25 ± 0.03 mmol/L. Plasma BHB concentration at +42 DPP was greater (P = 0.02) for G0 than G1 cows (0.46 vs. 0.27 ± 0.05 mmol/L) as it decreased from −7 to +42 DPP only in the latter group. In contrast, plasma insulin was reduced (P = 0.05) in G0 than G1 cows at +42 DPP (11.7 vs. 7.2 ± 1.3 uU/mL) as it increased from −7 to +42 DPP only in the latter group. Concentrations of cortisol, leptin and adiponectin were not different (P > 0.20) at −7 than +42 DPP and neither differed between feeding strategies at +42 DPP. Metabolic and endocrine profile would indicate a greater lipolysis in early lactation in G0 than G1 cows which would be probably associated to their greater milk production.