Body condition score affects milk yield and energy balance of dairy cows after a short or no dry period

Abstract Text: Shortening or omitting the dry period of dairy cows is of interest because it limits the negative energy balance in early lactation, mainly due to a reduction in milk yield postpartum. Moreover, there are indications that individual cow characteristics, like parity or genotype, affect the response of dairy cows to a short or no dry period. The objective of this study was to evaluate the effects of prepartum BCS on the response of cows in milk yield, energy balance (EB) and plasma metabolites to a short or no dry period, compared with a conventional dry period. Holstein-Friesian dairy cows (n=167) were assigned randomly to three dry period lengths: 0 (no), 30 (short) or 60 days (conventional). Across  treatments, cows were classified on prepartum BCS as lean (BCS<3.0; n=64), normal (3.0≤BCS<3.5; n=60) or fat (BCS≥3.5; n=43). Feed intake and milk yield were recorded daily from week -8 till 14 relative to calving and averaged per week. Energy balance was calculated weekly. Blood was sampled weekly. Repeated measures ANOVA was performed to analyse the data. Data are expressed as LSMEANS ± SEM. Postcalving, milk production, EB, plasma free-fatty acids and β-hydroxybutyrate concentration were affected by BCSclass*dry period length interaction (P<0.05). More specifically, in fat cows milk yield and EB were similar between dry period lengths (milk: 39.9 ± 0.8 kg/d; EB: -113 ± 15 kJ/kg^0.75*d). In lean cows, however, shortening or omitting the dry period reduced milk yield (short: 38.5 ± 1.0 kg/d; no: 31.1 ± 1.1 kg/d) and improved the EB (short: -56 ± 19 kJ/kg^0.75*d; no: 89 ± 20 kJ/kg^0.75*d) compared with a conventional dry period. In normal cows, shortening or omitting the dry period reduced milk yield (short: 38.9 ± 1.2 kg/d; no: 30.1 ± 1.1 kg/d), compared with a conventional dry period. Between lean and normal cows, there were no differences in milk yield reduction or EB improvement due to dry period length. Results for plasma metabolites were in line with results for EB. In conclusion, prepartum BCS affects milk yield and EB of dairy cows after a short or no dry period. This might imply that the optimal dry period length for dairy cows depends on prepartum BCS. Currently, studies are ongoing to develop a decision support tool for dry period length based on individual cow characteristics, like parity and BCS, in order to optimize milk yield and cow health.

Keywords: energy balance, individual variation, metabolic status