Effect Of Dietary Supplementation With Chromium-picolinate On Production, Biochemical Parameters And Reproduction Of Dairy Cows Under Heat Stress

The trial was conducted to study the effect of Cr supplementation on production,blood parameters and reproductive performance of dairy cows under heat stress.24 lactating Holstein cows,weighing 593 kg,were divided into 4 groups(control group A,experiment group B,C and D),according to days in milk,parity and milk yield.Cows were from second and fourth lactation,and were from 15 to 24 days post-partum,with an average initial milk yield of 21.4 kg/d.Cows in the A,B,C and D groups correspondingly received the following Cr picolinate supplementation dosages:0,3.6,7.2 and 10.8 mg Cr/head per day(based on chromium).The results showed as follows:1.TH averaged 79.61 units(75.84-82.30).During the whole trial period (2008.7-2008.9),all dairy cows were under heat stress.2.The dry matter intakes of dairy cows were significantly increased by adding chromium picolinate(P＜0.05).The milk yields were increased by 8.35-9.34 percent by adding chromium picolinate(P＜0.05).When the chromium supplementation were 9.2,7.9 and 8.3 rag/head per day,the dry matter in take,milk,yield and FCM were maximal.The ratio of feed to milk yield had quadratic relationship with the level of chromium supplementation (R~2=0.7801,P＜0.001).Adding chromium picolinate had no significant effect on milk composition(milk fat,milk protein and lactose),when the milk yield was increased; meanwhile,the SCC was decreased by 3.4-7.9 percent by adding chromium picolinate compared with control group.3.The concentrations of plasma glucose and ratio of plasma glucose to insulin were significantly increased by adding 7.2 and 10.8mg/head per day chromium picolinate(P＜0.05).The concentrations of plasma urea nitrogen and NEFA were decreased by 2.7-4.7 percent and 5-11.7 percent,respectively,by adding chromium picolinate;the concentration of plasma total protein was increased by 0.6 percent and 0.8 percent by adding 7.2 and 10.8mg/ head per day chromium picolinate,respectively(P＞0.05).4.The concentration of IGF-1 was increased by adding 7.2 and 10.8rag/head per day chromium picolinate(P＜0.05),and the conversion rate of T4 to T3 also was increased by adding 7.2 and 10.Smg/head per day chromium picolinate(P＜0.05),5.The plasma enzyme activity of CK was decreased by adding 7.2 and 10.8mg/head per day chromium picolinate(P＜0.05);the plasma enzyme activities of LDH and AST were decreased by adding chromium(P＞0.05);The plasma enzyme activity of ALT was decreased by adding 7.2 mg/head per day chromium picolinate(P＜0.05).6.The intervals of parturition-to-estrus of dairy cows were shortened by 1.85,4 and 3.84 days by adding 3.6,7.2 and 10.8mg/head per day chromium picolinate,respectively.Adding 7.2 and 10.8mg/head per day chromium picolinate increased the conception rate of dairy cows from 33.3 percent to 50 percent.The concentrations of plasma estradiol(E2), progesterone(P4) and luteinizing hormone(LH) were significantly increased at 1st day after estrus of dairy or 10th day after estrus by adding 7.2 and 10.8mg/head per day chromium picolinate(P＜0.05).In conclusion,chromium supplementation significantly increased the DMI and milk yield,improved the energy metabolism and secretion of hormone,alleviated heat stress of dairy cows under heat stress.Chromium supplementation could also promote postpartum estrum,and increase the conception rate of first estrum.When the supplementation level of chromium was 9.2,7.9 and 8.3 mg/head per day,the dry matter intake,milk yield and FCM yield obtained the highest value;the supplementation level of chromium was 7.8 mg/head per day;the ratio of feed to milk yield was the lowest.