Study On The Effect Of Dietary Chromium As Yeast Chromium In Dairy Cows' Diet

Two experiments were conducted for Studies on the effect of dietary chromium as yeast chromium in nonheat-stressed and heat-stressed dairy cows' diet. Experiment I60 milking Chinese Holstein dairy cows around 170 days were allotted to 5 groups of 12 cows, according to lactation number, calving da and daily milk yield. The dairy cows were collectively housed in a tied-stall and stanchion barn for 35 days. The index of temperature and humidity (THI) in the trial period averaged 58.40(55.20~67.40). The control and treatment I, II, III were supplemented 0, 0.35, 0.70 and 1.05 mg of Cr as chromium yeast /kg of concentrate respectively, the basic diet is the same. The result: (1) All the treatment didn't affect the daily milk yield, fat corrected milk( FCM) yield, milk fat, milk protein, and solid contents (P>0.05 ) compared to the control. The chromium concentration in milk of treatment IV didn't exceed 0.30mg/kg accord with the national standard of food. (2) Treatment IV reduced FT3 significantly (P<0.05). Treatment I, II, III had a trend to reduce FT3, but didn't differ significantly (P> 0.05).?Supplemental chromium didn't affect FT4, cortisol and insulin(P>0.05). Experiment II44 milking Chinese Holstein dairy cows around 120 days were allotted to four groups of 11 dairy cows, according to lactation number, calving date and daily milk' yield. The cows were collectively housed in a tied-stall and stanchion barn for 60 days. THI in the trial period averaged 81.50(72.21~89.50). The control and treatment I, II, III were supplemented 0, 0.40, 0.80 and 1.20 mg of Cr as chromium yeast /kg of concentrate respectively, the basic diet is the same. The result: (1) All supplementation levels of chromium yeast increased milk yield to some extent. Treatment II increased milk yield 6.26% (P<0.05), treatment I and III had a trend to increase milk yield, but didn't differ significantly (P>0.05) compared to the control. (2)Supplementing Cr at low levels had a trend to reduce milk fat, milk protein and solid contents compared to the control. However, with the increasing of supplementation levels, the milk contents recovered. (3)With the increasing of supplementation levels, it had a nonlinear trend to reduce the yield of FCM at the first and increase latter. Treatment II increased FCM yield 5.57%(P<0.05), treatment Iand III didn't differ significantly(P>0.05) compared to the control. (4)Supplementing chromium 0.80mg/kg concentrate decreased plasma FT3 and lad a trend to increase plasma insulin. (5)The supplementation increased plasma K+, Na+, Cl-, Ca2+,Mg2+ concentrations and OSM. Treatment I increased it significantly (P<0.05). (6)The supplementation increased plasma insulin, ALP, ALT, AST, GGT. However, with the increase of supplementation, the plasma enzyme had a trend to increase first and reduce latter. (7)Treatment I increased dry matter intake(DMI) significantly (P<0.05).