Study On The Effects Of Zinc Methionine On Lactational Performance And Reproductive Performance In Dairy Cows

The objections of this study are to determine the effects of the different levels of Zinc-Methionine(Zn-met) supplemented on on lactational performance and reproductive performance in dairy cows,and find out the suitable does.Sixty multiparity(parity 2or3),healthy dairy cows,which had the adjacent milk yield and body weight,and at 40-50 mean days in preterm.Cows were randomly assigned to four groups(A,B,CD),fifteen cows of each group.Groups were feeded with routine dietary(Zn37.15mg/kgDM),among which,group A was used to as the control group(routine dietary) andB,C,D groups were added 120mg/kg,240mg/kg,360mg/kg Zn-Met in routine dietary. Pretesting date was 10 days.The testing methods and targets were shown as below:Recorded milk weights from the 7th day postpartum to 15th day postpartum,and calculate the average day-milk yield;Milk samples were draw in 7th day and 14th day postpartum,and testing the milk fat,milk lactose,milk protein,milk Zn and the milk somatic cell counts(SCC);Blood samples were adopted at the 7th day postpartum,testing the levels of serum PRL; Blood samples adopted at the 1st day and the 12th day(oestrus and luteal phase) in oestrous cycle were used to test the levels of E₂ and P₄ in serum;In the experimental stage, registering the condition of parturition, the mean birth weight of calves,the first oestrus,the oestrus scycle postpartum and the conception rate of the first service after artificial insemination.The above targets were all took general average as indexes judging the reproductive performance of dairy cows.The results as follow:Effects on lactational performance:The milk yields of the B,C,D groups were 23.65kg/d,23.67kg/d,23.72kg/d,respectively,were 5.53%,5.85%,5.58% significantly higher than A group(22.41kg/d)(P<0.05), but no significant difference(P>0.05) among the B,C,D groups,furthermore, D group was 0.05 kg/d lower than the C group;With the augment of the levels of supplemented Zn-Met.the milk fat, milk lactose,milk protein of treatment groups increased in different extent than the control group,but no significant difference(P>0.05); With the augment of the levels of supplemented Zn-Met,the content of milk Zn increased significantly(P<0.05),but the increasing extent went down gradually.Group C,D were significantly different from group B(P<0.05),but there was no significant difference between group C and D;Th.e milk somatic cell counts(SCC) of group B.C and D decreased significantly than the control group.But with the augment of the levels of supplemented Zn-Met,the extent of decreasing diminished gradually.Effects on reproductive performance: The normal delivery of group B,C and D were 80%,93.33%,93.33%,respectively,were improved by a certain extent comparing with the control group; The mean birth weight of calves were not significantly different between the trial and control groups.But numerical datas shown that supplementing Zn-Met in dietary had the tendency to increase the birth weight of calves; Supplementing Zn-Met in dietary can make dairy cows express empathema earlier,and significantly(P<0.05).Among the trial groups,the advanced extent of the group C was comparatively large(5.8d);The oestrous cycles were all in normal range and not significantly different; The levels of serum PRL of group B,C and D were significantly(P<0.05) 1.46 ng/ml,3.08 ng/ml,3.45 ng/ml higher than the group A(control group). The levels of serum PRL increased with the augment of Zn-Met,but the extent of increasing diminished gradually,as well,the group B was significantly different from group B and D;Comparing with the control group,the trail group had the higher content of E₂ and P₄ both in oestrus and luteal phase. In oestrus,the content of E₂ improved obviously,and in luteal phase, the content of P₄ obviously,but all not significantly different(P>0.05);Comparing with the control group.the conception rate of the first service increased 6.66,20.00,20.00 percentage points.So,Zn-Met is good at increasing the conception rate of the first service.Results shown that, Supplementing Zn-Met in dietary had some certain promotion on the lactational performance and reproductive performance in dairy cows.Analysis indicated that,the 240mg/kg supplementing amount was the best in the normal dietary(Zn37.15mg/kgDM) and could be used as reference data of the Zn supplementing amount in dietary.