Effects Of Chromium Propionate On Production Performance,Blood Biochemical Parameters,Rumen Fermentation And Microbial Diversity Of Dairy Cows Under Heat Stress Environment

This study was conducted to evaluate the effects of chromium propionate on the production performance,the apparent total tract digestibility of dietary nutrients,blood biochemical parameters,rumen fermentation patterns and microbial diversity in dairy cows under heat stress environment.The effective dose of chromium propionate was explored,and milk concentration of chromium was detercted to provide a data basis for the use of chromium propionate in production.Sixtyfour Holstein cows in mid-lactation with similar milk production,days in milk,and parities were assigned to a completely randomized design to 1 of 4 groups.The treatments were:1)control group（CON;fed the basal diet with chromium content at 2.267 mg/kg DM）,and 2)to 4)low,medium and high chromium group（Cr-4,Cr-8 and Cr-12,respectively;chromium was supplemented as chromium propionate at 4,8 and 12 mg/d）.The experimental period was 49 days.Results:1)For different sampling time,the respiratory rate decreased quadratically with increasing chromium supplementation at 0900 h and 1500 h（P≤0.05）.For different sampling day,the respiratory rate decreased quadratically on d 10 and d 40（P≤0.05）with increasing chromium supplementation.Overall,the respiratory rate decreased quadratically（P<0.05）with increasing chromium supplementation,and lowest at Cr-4 group（P<0.05）.2)For different sampling time,the rectal temperature decreased quadratically with increasing chromium supplementation at 1400 h（P<0.05）and 2000 h（P=0.05）.For different sampling day,the rectal temperature decreased quadratically on d 20,d 40 and d 48（P<0.05）with increasing chromium supplementation.Overall,the rectal temperature decreased quadratically（P<0.05）with increasing chromium supplementation,and lowest at Cr-8 group（P<0.05）.3)For different sampling week,the daily mean milk yield tended to increase quadratically with increasing chromium supplementation on the second week,fourth week and fifth week（P<0.10）.Overall,with increasing chromium supplementation,the daily mean milk yield increased quadratically（P<0.05）,and the daily mean milk yield increased 1.50（P<0.05）,1.09（P>0.05）,and 0.24（P<0.05）kg,respectively.Overall,the DMI increased quadratically（P<0.05）with increasing chromium supplementation,and highest at Cr-4 group（P＜0.05）,and the DMI increased 1.87.1.78,and 0.71 kg,respectively.The feed efficiency tended to decrease quadratically（P=0.08）with increasing chromium supplementation.Overall,the average lactoprotein percentage and the average lactose percentage increased linearly（P≤0.05）with increasing chromium supplementation.However,adding chromium propionate in the diet of heat-stressed dairy cows had no effect on the average fat percentage,or total soild content（P>0.05）.Overall.with increasing chromium supplementation,compared with CON group,the milk urea nitrogen in Cr-4,and Cr-8 group decreased by 7.11%（P<0.05）and 5.57%（P>0.05）.respectively,while that in Cr-12 group increased by 1.54%（P>0.05）.Overall,with increasing chromium supplementation,compared with CON group,the SCC in Cr-4,and Cr-8 group decreased by 57.8%（P<0.05）and 20.3%（P>0.05）,respectively,while that in Cr-12 group increased by 23.9%（P>0.05）.4)Apparent total-tract digestibility of NDF,ADF,Ca,and P were not affected（P>0.05）with increasing chromium supplementation.Apparent total-tract digestibility of DM,OM,and CP tended to increase cubicly（P<0.10）with increasing chromium supplementation,and highest at Cr-4 group.Apparent total-tract digestibility of EE increased linearly（P<0.05）with increasing chromium supplementation,and highest at Cr-4 group（P<0.05）.5)For different sampling day,on d 30,T-AOC increased linearly（P=0.05）with increasing chromium supplementation.MAD tended to decrease linearly（P=0.08）with increasing chromium supplementation.HSP70 tended to increase linearly（P=0.07）with increasing chromium supplementation.GSH-Px tended to increase quadratically（P=0.06）with increasing chromium supplementation.SOD increased quadratically（P<0.05）with increasing chromium supplementation,and SOD increased by 10.92,14.82,and 7.95%,respectively.AST decreased quadratically（P<0.05）with increasing chromium supplementation,but highest at Cr-12 group.CR increased linearly（P<0.05）with increasing chromium supplementation,and highest at Cr-12 group（P<0.05）.AKP tended to decrease cubicly（P=0.07）with increasing chromium supplementation.T-CHO tended to increase quadratically（P=0.09）with increasing chromium supplementation.TG decreased linearly（P<0.05）with increasing chromium supplementation.GLU increased linearly（P<0.05）with increasing chromium supplementation,and GLU increased by 16.93,11.42,and 28.35%,respectively.BUN decreased linearly（P<0.05）with increasing chromium supplementation,and BUN decreased by 25.16,32.53,and 30.61%,respectively.T3 increased cubicly（P<0.05）with increasing chromium supplementation.PRL and GC increased quadratically（P<0.05）with increasing chromium supplementation.COR decreased linearly（P<0.05）with increasing chromium supplementation.For different sampling day,on d 49,T-AOC tended to decrease linearly（P=0.09）with increasing chromium supplementation.MAD increased quadratically（P<0.05）with increasing chromium supplementation.ALT and AKP tended to decrease cubicly（P=0.06）with increasing chromium supplementation.AST decreased linearly（P<0.05）with increasing chromium supplementation.T-CHO and TG increased quadratically（P<0.05）with increasing chromium supplementation,and highest at Cr-8 group.TP and GLB increased linearly（P<0.05）with increasing chromium supplementation.BUN decreased quadratically（P<0.05）with increasing chromium supplementation.6)Adding chromium propionate in the diet of heat-stressed dairy cows had no effect on the chromium content of milk or urine（P>0.05）.The chromium content of faeces increased linearly（P<0.05）with increasing chromium supplementation,and the chromium content of faeces increased by 11.9,25.8,and 40.7%,respectively.7)Adding chromium propionate in the diet of heat-stressed dairy cows had no effect on pH,NH3-N,Isobutyric or Isovalerate（P>0.05）.TVFA tended to increase quadratically（P=0.09）with increasing chromium supplementation.Acetate increased linearly（P<0.05）with increasing chromium supplementation.Butyrate and Isovalerate decreased cubicly（P=0.05）with increasing chromium supplementation.A/P increased linearly（P<0.05）with increasing chromium supplementation,and A/P increased by 8.3,18.0,and 15.0%.respectively.8)The Simpson index tended to decrease quadratically（P=0.06）with increasing chromium supplementation.The Shannon index tended to increase quadratically（P=0.08）with increasing chromium supplementation.Firmicutes,Bacteroidetes,and Proteobacteriawere on the taxonomic level are the dominant phylum,and the Firmicutes has the highest proportion.The relative abundances of Firmicutes.Bacteroidetes,and Planctomycetes increased quadratically（P<0.05）with increasing chromium supplementation.The relative abundance of Proteobacteria decreased quadratically with increasing chromium supplementation（P<0.05）.The relative abundance of the Tenericuteshas tended to increase quadratically with increasing chromium supplementation（P=0.06）.The relative abundance of the Spirochaetes increased linearly（P=0.05）with increasing chromium supplementation.The relative abundance of the Fibrobacteres and Candidatus_Melainabacteria increased linearly（P<0.05）with increasing chromium supplementation,and highest at Cr-12 group.At the level of genus taxonomy,the relative abundance of Succiniclasticum,Rikenellaceae_RC9_gut_group,and Ruminococcaceae_NK4A214_group increased quadratically（P≤0.05）with increasing chromium supplementation.The relative abundance of Ruminobacterwas decreased quadratically（P<0.05）with increasing chromium supplementation.The relative abundance of Lachnospira decreased linearly（P<0.05）with increasing chromium supplementation.The relative abundance of Ruminococcus₁ decreased cubicly（P<0.05）with increasing chromium supplementation.In summary,under the conditions of this experiment,feeding chromium 4-8 mg/head/day to dairy cows under heat stress environment in the form of chromium propionate can relieve heat stress of dairy cows,improve production performance and body antioxidant capacity,and improve Glucose and lipid metabolism and nitrogen metabolism,maintain the rumen micro-ecological stability and increase the Acetate to Propionate ratio,chromium supplementation does not affect the chromium content in milk.Higher feeding doses may affect the body’s antioxidant capacity and may cause liver damage.