Genetic parameters for milk urea concentration and milk traits in Polish Holstein-Friesian cows

Abstract

Milk urea concentration (MU) used by dairy producers for management purposes can be affected by selection for milk traits. To assess this problem, genetic parameters for MU in Polish Holstein-Friesian cattle were estimated for the first three lactations. The genetic correlation of MU with milk production traits, lactose percentage, fat to protein ratio (FPR) and somatic cell score (SCS) were computed with two 5-trait random regression test-day models, separately for each lactation. Data used for estimation (159,044 daily observations) came from 50 randomly sampled herds. (Co)variance components were estimated with the Bayesian Gibbs sampling method. The coefficient of variation for MU in all three parities was high (40–41 %). Average daily heritabilities of MU were 0.22 for the first parity and 0.21 for the second and third lactations. Average genetic correlations for different days in milk in the first three lactations between MU and other traits varied. They were small and negative for protein percentage (from −0.24 to −0.11) and for SCS (from −0.14 to −0.09). The weakest genetic correlation between MU and fat percentage, and between MU and lactose percentage were observed (from −0.10 to 0.10). Negative average genetic correlation with the fat to protein ratio was observed only in the first lactation (−0.14). Genetic correlations with yield traits were positive and ranged from low to moderate for protein (from 0.09 to 0.33), fat (from 0.16 to 0.35) and milk yield (from 0.20 to 0.42). These results suggest that the selection on yield traits and SCS tends to increase MU slightly.

Reliability of breeding values between random regression and 305-day lactation models

“…In previous studies with a Brazilian Holstein population from Minas Gerais state, Biassus et al (2011) found values ranging from 0.03 to 0.21 and 0.09 to 0.33 for fat and protein yields, respectively, estimated from random regression models. Rzewuska & Strabel (2013) and Abdullahpour et al (2013) reported very close average heritability values from 0.17 to 0.22, and 0.14 to 0.23, for fat and protein yields, respectively. Trajectories of permanent environmental variances of test-day fat and protein yields were quite constant between 30 and 240 days in milk, in all models, and coincided with the highest heritability of test-day yields in mid-lactation.…”

Association of SNP and STR polymorphisms of insulin-like growth factor 2 receptor (IGF2R) gene with milk traits in Holstein-Friesian cows

“…The genetic parameters obtained in statistical analysis did not differ from those obtained in big population of Polish H-F dairy cattle (Rzewuska & Strabel, 2013). This means that despite the small number of animals included in the analysis the results are not biased with big errors.…”

Genetic and environmental determinants of the urea level in cow's milk

“…According to Křížová et al (2013), the concentration of nitrogen fractions decreased during summer, while during winter it was higher (P <0.05). Rzewuska and Strabel (2013a) reported the association between the sampling month, air temperature, and MU. MU was high during the period from May to October, and the highest values were recorded in the summer months.…”

“…Genetic correlation indices (r g ) showed that the urea content in milk was negatively correlated with milk yield (r g = −0.097), positively correlated with fat content (r g = 0.140) and dry matter (r g = 0.125), and very weakly correlated with protein (r g = 0.038) and lactose content (r g = 0.071) ( Table 4). Rzewuska and Strabel (2013a) reported that the average daily heritabilities of MU were 0.22 for the first and 0.21 for the second and third lactations. Hossein-Zadeh and Ardalan (2011) reported that the average genetic correlation for MUN and lactose percentage was close to zero (−0.01), while the average genetic correlation was moderately positive for milk yield (0.24), net energy concentration of milk (0.31), fat (0.21), and protein percentage (0.30).…”