Changes in Body Composition of Primiparous Holstein Cows with Different Feeding Strategies during Early Lactation

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 analysed 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.