Abstract
The study was conducted to assess the effect of milk production, parity, stage of lactation, season and individual milk components themselves on milk urea nitrogen (MUN) concentration and other milk components of 3,219 Holstein dairy cows in Korean dairy farms. The MUN concentrations in Korean dairy cows were estimated to 16.68±5.87 mg/dl. Milk yield was negatively correlated with fat and protein contents and somatic cell counts (SCC) in milk (p<0.01). The increasing MUN concentration has positive correlation with yield and fat content. By increasing somatic cell, milk yield was reduced and MUN level was increased. Cows in spring and winter produced more milk over 1.43 and 0.93 kg/day, respectively, than cows in summer (p<0.01). Milk urea nitrogen concentrations of milk produced in summer and fall were significantly lower (p<0.01) than those in spring and winter. Both MUN concentration and somatic cell counts were highest in winter. Milk yield was lower (p<0.01) in the first calving than other calving time and was tended to increase until the fifth parity and then decrease. Milk urea nitrogen and SCC were not related to parity of cows in this study. Milk yield and SCC were positively related to lactation period while MUN concentrations and milk fat and protein contents were negatively influenced by stage of lactation. In the present study, the relationship between MUN and reproduction of dairy cows was also investigated. Cow produced milk in high MUN concentrations (greater than 18 mg/dl) had more open days than cows in MUN concentrations less than 18 mg/dl. However, no significant difference between MUN concentration levels and frequency of artificial insemination was found in this study. It is suggested that although MUN values for nutritional management and measures of production or reproduction are used, non-nutritional factors should be considered. (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 4 : 479-484)
Highlights
Dietary CP, RDP, RUP, dietary energy and protein/energy ratios are known to sensitively change serum urea and milk urea (MU) concentrations in the ruminant (Folman et al, 1981; Oltner and Wiktorsson, 1983; Macleod et al, 1984; Carroll et al, 1988; DePeters and Ferguson, 1992; Roseler et al, 1993)
It has been shown that a surplus of crude protein in the diet gives rise to a high concentration of urea in the blood and milk (Refsdal et al, 1985; Ferguson et al, 1988) and Carlsson and Pehrson
Milk samples were routinely analyzed for milk fat, milk protein, somatic cell counts (SCC) and milk urea nitrogen (MUN)
Summary
Dietary CP, RDP, RUP, dietary energy and protein/energy ratios are known to sensitively change serum urea and milk urea (MU) concentrations in the ruminant (Folman et al, 1981; Oltner and Wiktorsson, 1983; Macleod et al, 1984; Carroll et al, 1988; DePeters and Ferguson, 1992; Roseler et al, 1993). It can be predicted theoretically that concentration of urea in milk should increase if there is a surplus of rumen-degradable protein in the diet and/or if there is a deficiency of energy in the diet, and that the concentration should decrease if there is a deficiency of protein in the diet. It has been shown that a surplus of crude protein in the diet gives rise to a high concentration of urea in the blood and milk (Refsdal et al., 1985; Ferguson et al, 1988) and Carlsson and Pehrson (1993) observed very low MU concentrations in samples taken from cows on farms where the rations were low in protein
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