The Determination Of Milk Urea Nitrogen Content And Relationship Between Milk Urea Nitrogen Content And Fertility Traits Of Dairy Cows

Milk urea nitrogen(MUN) content is one important index of the Dairy Herd Improvement (DHI), could be used as an indicator of the reproductive performance of dairy cows. There are many differences between Chinese and foreign Holstein cows in breeding, management and diets.The simpling time and determination methods also effect the accuracy and precision of MUN content. Little information is available about the relationship between MUN centent and reproductive performance of Chinese dairy cows.This study was conducted to compare the determination methods of MUN content (Experiment 1), the impact of sampling time on MUN content and conventional ingredients in Milk (Experiment 2), the relationship between MUN content and fertility traits of dairy cows (Experiment 3).This study used infrared method, diacetyl monoxime method and urea nitrogen kit respectively fifty milk samples to compare the difference of MUNconcentration.. The results showed that there was no significant difference in MUN concentration by the Fossomatic 4000 Milk Analyzer, diacetyl monoxime method and urea nitrogen kit (P>0.05). Compared with the distilled water solution with urea nitrogen kit, diethyl ether solution with urea nitrogen kit gave lower MUN concentration (P< 0.01). The results indicated that the MUN concentration were similar between Fossomatic 4000 Milk Analyzer, diacetyl monoxime method and urea nitrogen kit. The determined error appeared when milk simple was dissolved by diethyl ether solution.In the second study, milk samples were routinely collected from milk meters at the time of the regular morning milking, middle milking and night milking, from 50 lactating Holstein cows, different time milk samples were mixed by 4:3:3 for composite samples representing the entire milking to compare difference of sampling methods on MUN and conventional ingredients in milk. The results showed that there was no significant difference in the content of total protein and lactose percent(P> 0.05), but extremely significant difference in butterfat percentage and the content of MUN, somatic cell count(SCC) (P<0.01), dry matter among milk simpled at different time. There were extremely significant linear correlation between between the composite milk and two of the comprehensive milk from morning simple,middle simple and night simple(R=0.693-0.947,R=0.502-0.961,R=0.848-0.996).A highest correlation coefficient was obtained between the composite milk and the comprehensive milk from morning simple and night simple.The results dicated that although single time of milk simple could not replace the composite milk, but the content of MUN and conventional ingredients in composite milk for DHI can be predicted according the morning simple and night simple.The trials in this part determined MUN concentration on the day of the first Artifical Insemination (AI) after postpartum and the conception rate after first insemination of two hundred and fifty five lactating Holstein cows fed normal diets formulated for high milk production.The results showed that the mean MUN concentrations on the day of AI averaged 21.22±5.45 mg/dL (n=155). For cows later determined to be pregnant (n=128) and nonpregnant (n=127), MUN concentrations were different (20.20±5.45and22.22±5.39 mg/dL, P<0.01), respectively. There was curve correlation between MUN and the conception rate after first insemination (y=-0.001x2+0.039x+0.18, R2=0.936,P<0.01), the conception rate peaked at 18 mg/dL MUN. The pregnancy rate of cows with MUN concentrations greater than 18 mg/dL was lower than in cows with less MUN.There was a extremely significant linear correlation between MUN concentration on the day of the first Artifical Insemination (AI) after postpartum and days to first service (y=3.169x+17.34, P<0.01). With MUN concentration on the day of the first Artifical Insemination (AI) after postpartum increased,days to first service also increased.In conclusion, the MUN concentration were similar between Fossomatic 4000 Milk Analyzer, diacetyl monoxime method and urea nitrogen kit, the comprehensive milk from morning simple and night simple can replace the composite milk. There was strong relation between MUN content and the conception rate after first insemination and days to first service. When the MUN content was more than 18 mg/dL, the conception rate after first insemination will be decrease. With MUN concentration on the day of the first Artifical Insemination (AI) after postpartum increased,days to first service also increased.