Abstract #274

# 274
Carry-over effect of an individual feeding strategy on milk production of Holstein cows managed for extended lactation.
Charlotte Gaillard*1, Nicolas C. Friggens2, Martin R. Weisbjerg1, Jakob Sehested1, 1Aarhus University, Foulum, Tjele, Denmark, 2AgroParisTech, INRA UMR 0791 MoSAR, Paris, France.

Feeding can induce significant individual variation in cows’ milk production. Previous studies showed that an increase of energy density of the ration for a short period in early lactation induced greater total milk yield and persistency, defined by the shape of the lactation curve. The objective of our feeding strategy was to reduce the intensity of mobilization and thereby to sustain the mobilization for a longer period. We hypothesized that a supply of energy during the mobilization period of each individual cow will have a positive carry-over effect on milk production. A total of 53 Holstein cows performed extended lactations (461 ± 7 d). They were housed in free stalls with access to a milking robot. The group 1 (G1) were fed a control partially mixed ration, with a 60:40 forage:concentrate ratio (energy density 11.8 ± 0.1 MJ of ME/kg of DM), for the full lactation. The group 2 (G2) received a diet enriched in energy (ratio 50:50, energy density 12.1 ± 0.1 MJ of ME/kg of DM) followed by the control diet. The diet shift of G2 was defined individually when DIM ≥42, and live weight gain ≥0 kg/d on a 5 d average. The production data were smoothed using the fda package in R software. The daily smoothed data and the associated slopes were analyzed using a linear mixed effects model with parity and treatment as fixed effects. From calving to 42 DIM, an interaction indicated that the ECM of multiparous G2 was higher than for G1 (42.8 vs. 40.1 ± 1.5 kg ECM/d), while the primiparous presented opposite effects (29.0 vs. 32.5 ± 2.2 kg ECM/d) (P = 0.02). The 300 d following the shift in diet, G1 and G2 had similar ECM (35.0 ± 1.0 kg ECM /d, P = 0.76) but the curves had different slopes. From 0 to 100 d from shift, the ECM increased for the primiparous G2 while it decreased for the primiparous G1 (+0.008 vs. −0.01 ± 0.007 kg ECM/d, P = 0.04). From 201 to 300 d from shift, the ECM decreased faster for G2 than for G1 (−0.06 vs. −0.04 ± 0.008 kg ECM/d, P = 0.02). To conclude, the treatment had a 100-d positive carry-over effect only on primiparous persistency, as well as a 300 d negative carry-over effect on the ECM persistency for all the cows.

Key Words: extended lactation, persistency, individual feeding strategy