The body condition of Simmental dairy cows an update to the reference curve for backfat thickness, with special consideration to the growth phase of younger cows

Introduction The measurement of backfat thickness (BFT) is a valuable tool for managing the herd health of dairy cows. The BFT correlates strongly with overall body fat reserves and can be used to estimate the cows' energy balance. We have optimized the reference curve published by POTHMANN et al. (2014) by the addition of 7,940 backfat values to give a reference curve with 12,966 data points and thus greater validity. We also generated a second curve for younger cows in their first and second lactation, which have a different energy balance from older animals. Materials and Methods Data were collected from 19 farms in Bavaria, Germany and in Lower Austria with herds ranging from 18 to 132 dairy cows. The average energy-corrected milk yield ranged from 5,715 kg to 10,051 kg per year. The data were intended to represent a cross-section of the population, so the health status of the animals was not considered during the selection process. Backfat was measured between the caudal one-quarter and one-fifth of a line between the Tuber coxae and the Tuber ischiadicum. Mean BFT was calculated and categorized into 20-day intervals of the reproduction cycle. We established reference curves with cubic regressions, including the dry off and lactation periods of all cows and of young cows in the first and second lactation separately. Results At the beginning of the dry off period, the mean BFT was 14.6 mm (+/- 5.4). The maximum value was reached 11 days before parturition and cows calved with an average of 16.8 mm (+/- 5.7) BFT. The nadir of 11.6 mm (+/- 5.2) BFT was reached 121 days after parturition, 11 days later than the value given in POTHMANN et al. (2014). Younger cows had 18.1 mm (+/- 5.4) BFT at the beginning of the dry period and calved with an average of 15.2 mm (+/- 4.9) BFT. Conclusion The updated reference curve will enable veterinarians and farmers to evaluate the energy balance of Simmental cows properly and to adjust the management and feeding measures accordingly. We recommend monitoring body condition on the herd level, comparing the average values of all cows in the same phase of lactation with the reference curve. The BFT reference of younger cows shows the importance of paying special attention to the body condition in the dry off and transition period.