Animal performance and production efficiencies of Holstein-Friesian, Jersey and Jersey × Holstein-Friesian cows throughout lactation

The objectives of this study were to examine changes in a number of measures of feed and production efficiency over the course of lactation; to investigate the consistency of breed differences over lactation, to determine the repeatability of each measure over lactation, and to evaluate the impact of the dry period (full lactation cycle) on efficiency measures over an entire lactation cycle. A total of 535 records, from 110 cows, were available for analysis; 37 Holstein-Friesian (HF), 36 Jersey (J) and 37 Jersey×Holstein-Friesian (F₁) cows under pasture based seasonal production systems. Animal measurements included milk production, body weight (BW), body condition score and individual dry matter intake (DMI). Estimates of DMI were available across six stages of lactation and during the subsequent dry period. Breed group had a significant effect on milk yield, fat and protein content, milk solids (MLKS) yield, BW and body condition score. Production efficiency variables included DMI/100kg BW, MLKS/100kg BW, net energy intake (NEI)/MLKS, residual feed intake (RFI) and the proportion of energy available for milk production having accounted for maintenance, NEL/(NEI-NEM). Efficiency, in general, tended to be highest in early lactation and declined as lactation progressed. The proportion of energy assigned to milk production NEL/(NEI-NEM) was highest in early lactation. Overall there were few incidences of breed by stage of lactation interactions observed. Repeatability estimates for DMI and efficiency variables were high, comparable in magnitude to that of milk yield. Rank correlations were also high through lactation indicating consistency in relative performance differences among cows across time. Dry matter intakes during the dry period were highest with the HF, intermediate with the F₁ and lowest with the J: 11.9, 10.3 and 9.0kg/d, respectively. Intake capacity (DMI/100kg BW) during the dry period was similar across the breed groups. Correlations for DMI, intake capacity and RFI during the lactating vs. non-lactating period were weak to moderate, indicating increased DMI and intake capacity during the lactating period are driven predominately by increased energy requirements for milk production. Consequently, associations between lactation efficiency and total lactation cycle efficiency were high.