Regular milking within natural suckling behavior interval minimizes differential somatic cell count in dairy cows milked by automatic milking systems

Objectives
Somatic cell count (SCC) is a reliable and approved parameter for the estimation of udder health. The main
cell types regarding somatic cells in the udder are lymphocytes, macrophages, and polymorph nuclear
leucocytes (PMN). The differential somatic cell count (DSCC) represents the proportion of lymphocytes and
PMN to total SCC, the remaining percentages to SCC are macrophages. So far, the effects of milk yield,
season, parity, milking frequency, days in milk, and major pathogens on the DSCC are already described. A
further known effect on udder health and SCC is the milking interval (MI). On farms with automatic milking
systems (AMS) the MI can vary for each cow compared to conventional milking systems. Regarding DSCC
and SCC, cows milked by AMS systems showed higher values compared to cows milked by conventional
milking systems. Therefore, the aim of this study was to evaluate the effect of MI on DSCC.
Materials and methods
Data from 27 dairy herds from Germany including 6,500 dairy cows and 43,229 recordings were evaluated.
The data resulting from milk yield performance testing were collected between January to December 2020. All
herds used automatic milking systems combined with free cow traffic. Milk yield performance testing data was
recorded 11-times per year on each farm and included the DSCC measured using the FOSS method
described by Damm et al. (2017). Date and time from each milking at the farms were available and used to
calculate each individual MI between milkings. MI ranged from 1 h minimum to 24 h maximum. Data of milking
interval >24 h were excluded. Means were compared using Wilcoxon test. P-values were Bonferroni adjusted;
the threshold for significance was set after adjusting to α < 0.05. A linear mixed model was used to estimate
the effect on DSCC including MI, milk yield, lactation, days in milk, and season as fixed effects and herd,
individual cow, and residuals as random effects.
Results
Mean MI was 10.6 h (±0.04 h SE). MI of ≤4 h resulted in the highest DSCC (52.3 ±1.0%). The DSCC
decreased significantly for cows showing a MI >4 and ≤6 h (39.0 ±0.6%) and had its minimum between MI >6
and ≤8 h (37.9 ±0.4%). MI between >8 - ≤10 h resulted in a DSCC of 40.5% (±0.4%). The DSCC increased for
MI >10 - ≤12 h and for >12 h MI (42.8 ±0.4%; 46.6 ±0.3%, respectively; all P-values < 0.001). Therefore, the
most frequently milked cows showed higher DSCC compared to cows between 4 and 8 hours MI. Considering
natural behavior, the suckling interval of calves from their mothers ranges between 4 to 6 times per day, which
results in a MI of 6 to 4 hours, representing the MI of the second lowest DSCC found in this dataset.
The standard deviation of the MI (MISD) expresses the irregularity of milkings. Data evaluation showed the

lower the MISD, the lower the DSCC. For MISD ≤2 h the DSCC was lowest (38.8 ±0.7%), compared to MISD >2
- ≤4 h (41.0 ±0.5%), MISD >4 - ≤6 h (43.2 ±0.7%), and MISD >6 h (48.1 ±1.1%). Irregular milking is also known
to impair udder health and increase the SCC of cows.
Conclusions
Milking interval between 4 to 8 hours minimizes DSCC, which aims the natural MI of suckling calves. A more
regular milking interval in AMS farms could reduce DSCC and therefore improve udder health. AMS farms
should strive their management and settings of the AMS to encourage cows to visit the AMS more regularly.
Acknowledgement
We kindly acknowledge the QNETICS GmbH, Erfurt, Germany, for providing the dataset of DSCC values and
milk yield recording data for this study.