Modeling milk urea of Walloon dairy cows in management perspectives

Abstract

The aim of this study was to develop an adapted random regression test-day model for milk urea (MU) and to study the possibility of using predictions and solutions given by the model for management purposes. Data included 607,416 MU test-day records of firstlactation cows from 632 dairy herds in the Walloon Region of Belgium. Several advanced features were used. First, to detect the herd influence, the classical herd × test-day effect was split into 3 new effects: a fixed herd × year effect, a fixed herd × month-period effect, and a random herd test-day effect. A fixed time period regression was added in the model to take into account the yearly oscillations of MU on a population scale. Moreover, first autoregressive processes were introduced and allowed us to consider the link between successive test-day records. The variance component estimation indicated that large variance was associated with the random herd × test-day effect (48% of the total variance), suggesting the strong influence of herd management on the MU level. The heritability estimate was 0.13. By comparing observed and predicted MU levels at both the individual and herd levels, target ranges for MU concentrations were defined to take into account features of each cow and each herd. At the cow level, an MU record was considered as deviant if it was <200 or >400 mg/L (target range used in the field) and if the prediction error was >50 mg/L (indicating a significant deviation from the expected level). Approximately 7.5% of the MU records collected between June 2007 and May 2008 were beyond these thresholds. This combination allowed for the detection of potentially suspicious cows. At the herd level, the expected MU level was considered as the sum of the solutions for specific herd effects. A herd was considered as deviant from its target range when the prediction error was greater than the standard deviation of MU averaged by herd test day. Results showed that 6.7% of the herd test-day MU levels between June 2007 and May 2008 were considered deviant. These deviations seemed to occur more often during the grazing period. Although theoretical considerations developed in this study should be validated in the field, this research showed the potential use of a test-day model for analyzing functional traits to advise dairy farmers.

Effects of some non-genetic factors on concentration of urea in milk in Polish Holstein-Fresian cows

“…) between 12 and 21 mg · dl −1 (Johnson and Young, 2003;Wattiaux et al, 2005;Stoop et al, 2007;Bastin et al, 2009) but close to levels observed in Canadian (Miglior et al, 2006) and Israeli (Ramirez et al, 2007) populations. The coefficient of variation was very high and stable for all test days, ranging from 44% to 48%.…”

“…The lowest MU was observed in winter months (192.2 mg · l −1 in January) . There is no consistent pattern in MU changes between months in the studies of different authors, but they generally report that the greatest concentration can be observed during the summer months (Godden et al, 2001;Arunvipas et al, 2003;Hojman et al, 2004;Wattiaux et al, 2005;Bastin et al, 2009). Only in the Canadian population were low MU concentrations observed not only during the winter but also, for example, in June (Arunvipas et al, 2003;Miglior et al, 2007).…”

“…Identification of energy balance problems solely on the basis of MU is inaccurate because of the large variability of this trait. The coefficient of variation of milk urea nitrogen (MUN) exceeds 30% (Stoop et al, 2007;Bastin et al, 2009). Furthermore, nutrition is the main, but not only, factor influencing the urea concentration in milk.…”

“…Milk urea concentration is also genetically determined. Average daily heritability ranges from 0.13 to 0.39 for the first lactation (Miglior et al, 2007;Bastin et al, 2009).…”

“…Production season is among the major factors that are a source of this variability. The results of some studies suggest that a higher MUN concentration is observed in the summer months (Godden et al, 2001; Arunvipas et al, 2003;Hojman et al, 2004;Wattiaux et al, 2005;Bastin et al, 2009). The same relation was reported by Rajala-Schultz and Savile (2003), but only for lowproduction herds.…”