Estimation of effectiveness of dairy production and mobilization of fat in dairy Holstein cows during the early lactation

Feed efficiency (FE) is widely used for estimation of the effectiveness of dairy production. However, our earlier findings suggest that FE may not be suitable for performance evaluation (Szura et al., 2020). Others proposed to use residual energy intake (REI = total NEL intake - expected energy intake) (Hurley et al., 2016). Based on data from an earlier study (Meyer et al., 2020), we examined the connection between FE, REI and fat mobilization during the fresh cow (FCP) and early lactation period (ELP) in Holstein dairy cows with initially lower (LBC) and higher (HBC) condition.

Fifty-three pluriparous cows at the Friedrich-Loeffler-Institute (FLI), Braunschweig, Germany were used to determine the estimated depot mass (eDM) of subcutaneous (SCAT) and abdominal (AAT) adipose depots by ultrasonography on day (d)-42, 3, 42 and 100 relative to parturition. Cows were allocated into the LBC (n = 27) or HBC (n = 26) group according to the eDM of SCAT on d-42. Average daily change (aDC) of adipose mass was calculated for the FCP (d3 to d42) and ELP (d42 to d100). Additionally, dry matter intake (DMI) and lactation performance were recorded, and FE and REI (Meyer et al., 2020) calculated for FCP and ELP.

The HBC cows had greater depot masses and mobilized more fat during FCP and ELP (p<0.01). The groups did not differ in DMI or energy corrected milk yield (ECM). HBC cows tended to have higher FE (p=0.075) and showed lower REI and more severe NEB (both p<0.01) compared to LBC cows. A positive correlation between aDC of SCAT and EB (r² = 0.23), as well as negative between aDC and FE (r² = 0.20) was found during the FCP. The aDC of both depots correlated negatively with FE (r² = 0.26 and 0.24, resp.; p < 0.01) and, positively with EB (r² = 0.13 and 0.29, resp., p ≤ 0.01) and REI (both r²=0.18, p < 0.01) during the ELP.

Our results indicate that neither FE nor REI are suitable for evaluation of performance efficiency in dairy cows during the fresh cow period. During early lactation the use of FE and REI may even lead to selection of cows for lipomobilization, thus possibly having negative impact on health.