Abstract: 【Objective】 Due to the immature gastrointestinal function and low ability digest dietary, diarrhea or other nutritional diseases were easy to arise in suckling calves that bring about low survival rate. Compared with adult cattle, liquid milk replacer is the main feed for the early weaned calves. Thus, acidity of milk replacer emulsions has more important effect on calf health. But the change regulation, the normal value scope of blood gas parameters in calves are not in any systematic manner, so that it is unable to determine whether the appropriate dietary acidity is. To study the change regulations of blood gas parameter in calves, an experiment was carried out to investigate the variations of blood gas parameters in calves which fed liquid feed with different pH. 【Method】The pH values of a milk replacer (6.2, 5.5, 5.0 or 4.5) and the ratio of vegetable protein to total protein in the milk replacer (50% or 80%) were used to form an 2 × 4 factorial design in this experiment. Forty-eight neonatal healthy Chinese Holstein male calves were allotted into eight groups and each group was fed with one of the 8 milk replacer emulsions. The experiment lasted 63 d with 21 d for adaptation and 42 d for test. Growth performance was determined fortnightly, the intake of milk replacers and pellet diet were recorded every day. Blood samples were collected on 21 d and 49 d. The pH value, partial pressure of carbon dioxide (pCO2), partial pressure of oxygen (pO2), oxygen saturation (SO2), the concentration of [HCO3-](HCO3-), actual base excess (ABE), total carbon dioxide volume (TCO2), standard bicarbonate concentration (SBC), standard base excess (SBE) of the blood samples were determined. Data of growth performance or blood gas parameters were analyzed using the GLM or MIXED procedure of SAS software, the regression equations between blood gas parameters and milk replacer emulsion pH value were established by REG procedure, and the changes of blood gas parameters were analyzed using normal distribution test. 【Result】The results showed that the average daily gain were improved while the pH value of milk replacer decreased (P＜0.05). The pH value of milk replacer siginificantly affected blood pO2, SO2, HCO3-, ABE, TCO2, SBC and SBE (P＜0.01). pH value, pCO2, pO2, SO2, HCO3- and TCO2 showed a quadratic curve (P＜0.05) as milk replacer emulsion pH value decreased with R2 as 0.9201, 0.8481, 0.8600, 0.9445, 0.8631, 0.8141, respectively, meanwhile ABE, SBC, SBE were showed a linear turn (P＜0.05) with R2 as 0.9060, 0.8126, 0.8298. Blood pH and pCO2 were varied remarkably with the age of day increasing (P＜0.05). Blood gas parameters were in line with the normal distribution (P＞0.05) except for HCO3-, ABE, SBE. While the ratio of vegetable protein to total protein of milk replacer increased from 50% to 80%, the average daily gain and dry matter intake of calves decreased, but blood gas parameters were unaffected (P＞0.05). 【Conclusion】The blood HCO3-, ABE, TCO2, SBC,and SBE of calves aged 21 to 63 days significantly decreased with the pH value of milk replacer dropping. Blood gas parameters can be used as sensitive indices to evaluate the effect of dietary acidity on calves.

Key words: calves , blood gas analysis , milk replacer , pH value , acidity