Consequences of an extended lactation for metabolism of dairy cows in different stages of lactation

An extended calving interval by extending the voluntary waiting period (VWP) reduces the calving frequency. Anextended VWP could be associated with altered metabolism, due to delayed gestation and more time in late lactationwith lower milk production. This study evaluated the metabolism of cows with different VWP during differentstages of lactation. Moreover, relations between cow characteristics before insemination and lactation performancewere analysed, to identify cows with lower risk for low milk production and increased body condition end lactation.Holstein-Friesian cows (n=153) were blocked and randomly assigned to a VWP of 50, 125, or 200 days (VWP50,VWP125, or VWP200), and followed from calving until 6 wk after next calving. Weekly, from 2 wk before until6 wk after both calvings, plasma samples were analysed for non-esterified fatty acids (NEFA), β-hydroxybutyrate,glucose, insulin, and IGF-1. During lactation, plasma samples were analysed for insulin and IGF-1 every 2 wk. Fatand-protein-corrected milk (FPCM) and body weight (BW) gain were calculated weekly. Cows were divided in twoparity classes (primiparous and multiparous). During gestation, multiparous cows in VWP200 had greater plasmainsulin and IGF-1 concentrations and lower FPCM compared with cows in VWP50 or VWP125, and greater BWgain compared with cows in VWP50 (3.6 vs 2.5 kg/wk). During gestation, primiparous cows in VWP125 had greaterplasma insulin concentration compared with cows in VWP50, but the VWP did not affect body condition or FPCM.During the first 6 wk of the next lactation, multiparous cows in VWP200 had greater plasma NEFA concentrationcompared with cows in VWP125 or VWP50 (0.41 vs 0.30 or 0.26 mmol/l). For primiparous cows, the VWP did notaffect metabolism, BW, or FPCM during the next lactation. Independent of VWP, higher milk production and lowerbody condition before insemination were associated with higher FPCM and lower body condition end of the lactation.Variation in these individual cow characteristics could call for an individual approach for an extended VWP.