Estimation of Genetic Parameters for Concentrations of Milk Urea Nitrogen

Abstract

The objective of this study was to use field data collected by dairy herd improvement programs to estimate genetic parameters for concentrations of milk urea nitrogen (MUN). Edited data were 36,074 test-day records of MUN and yields of milk, fat, and protein obtained from 6102 cows in Holstein herds in Ontario, Canada. Data were divided into three sets, for the first three lactations. Two analyses were performed on data from each lactation. The first procedure used ANOVA to estimate the significance of the effects of several environmental factors on MUN. Herd-test-day effects had the most significant impact on MUN. Effects of stage of lactation were also important, and MUN levels tended to increase from the time of peak yield until the end of lactation. The second analysis used a random regression model to estimate heritabilities and genetic correlations of MUN and the yield traits. Heritability estimates for MUN in lactations one, two, and three were 0.44, 0.59, and 0.48, respectively. Heritabilities for the yield traits were of a similar magnitude. Little relationship was observed between MUN and yield. Raw phenotypic correlations were all <0.10 (absolute value). Genetic correlations with production traits were close to zero in lactations one and three and only slightly positive in lactation two. The results indicate that selection on MUN is possible, but relationships between MUN and other economically important traits such as metabolic disease and fertility are needed.

Genetic relationship between milk urea nitrogen and reproductive performance in Holstein dairy cows

“…Butler et al (1996) reported a MUN of 22.8 mg/dl for nonpregnant cows, 21.3 mg/dl for cows later identified pregnant and overall mean values of 22.3 mg/dl. Other studies reported lower means of around 12 to 13 mg/dl (Wood et al, 2003;Mitchell et al, 2005), although the range was similar to our results (1 to 50 mg/dl). MU concentration is influenced Godden et al, 2001).…”

“…In all lactations, the concentrations of MUN were slightly elevated at the start of lactation, reaching minimal level in early lactation, and then rising steadily to maximum values at the end of the lactation. Wood et al (2003) reported similar trends in MUN with stage of lactation. Jonker et al (1998) found a decrease of MUN with advancing DIM from around the second month onward, leading to a curve for MUN similar to that for milk yield.…”

Modeling milk urea of Walloon dairy cows in management perspectives

“…The average MU at calving was close to 285 mg/L; it then decreased to 225 mg/L at approximately 30 to 40 DIM and finally rose slightly until 280 DIM to the same level as the one at calving. A similar trend was observed by Miglior et al (2007) and Wood et al (2003). As discussed by Wood et al (2003), this trend may be due to the physiological changes and the evolution of the metabolic demands of milk production across DIM.…”

“…A similar trend was observed by Miglior et al (2007) and Wood et al (2003). As discussed by Wood et al (2003), this trend may be due to the physiological changes and the evolution of the metabolic demands of milk production across DIM. However Godden et al (2001) and Wattiaux et al (2005) reported that the MU trend across a lactation was similar to the lactation curve.…”

“…Use of MU as a tool to evaluate dairy herd feeding is usually based on phenotypic values, generally the herd average MU from a bulk sample. However, as reported in several previous studies, MUN shows large variability within cows (Wood et al, 2003;Mitchell et al, 2005;Miglior et al, 2007). Moreover, several studies have shown the possibility of using solutions or predictions from a test-day model for production or SCC traits to advise dairy farmers (Van Bebber et al, 1999;Koivula et al, 2007).…”