Studies On The Effects Of Different Diets On Endocrine, Metabolism Regulation And Lactation Performance In Periparturient Cows

The transition period of dairy cows （three weeks before calving to three weeks after calving） ischaracterised by endocrine and metabolic changes to accommodate parturition and lactation. Dairycows experience some degree of negative energy balance （NEB） during this period, which may affectthe susceptibility of cows to metabolic disorders and infectious diseases，as well as to milk production.The nutritional management strategy of transition period cows is essential to minimize NEB andmaximize cow’s genetic milk productive potential. Forage quality was reported to have a direct effecton milking potential and health status in cows. However, the data related to forage type andforage-to-concentrate ratio in transition period was limited. This study was designed to evaluate theeffects of two different diets on endocrine, metabolism regulation and lactation performance inperiparturient cows. The results would provide basic data for optimization of the dietary and improvingmilk quality of dairy cows. The results are as follows:1. Twelve multiparous, periparturient Chinese Holstein cows were enrolled in this study, whichwere randomly assigned to corn straw （CS） or mixed forage （MF） group. The CS diet:33.8%of cornstraw as the only roughage and66.2%of concentrate, The MF diet:58.6%of mixed forage （3.7%Chinese wildrye+28.4%alfalfa hay+26.5%corn silage） and41.4%of concentrate. The CS and MFdiets had forage to concentrate ratios of40:60and60:40, respectively. Dietary treatments were initiatedat approximately three weeks before the expected calving dates and continued until eight weeks aftercalving. Results shown that dietary treatments had no detectable effects on BW, BCS, DMI and somehormones （E₂, P₄, GH, PRL, INS and IGF-I） related to lactogenesis （P>0.05）. Cows in MF groupproduced more milk （P <0.05） from6-wk of lactation, and tended to produce more milk fat （P=0.07）and protein （P=0.10） compared with cows fed CS diet. Milk lactose yields （kg/d）, as well asproportions of milk fat, protein and lactose （%） did not differ between the two dietary treatments （P>0.05）. The milk SCC in CS group was significantly higher （P <0.05） than the MF group. Cows fed MFdiet experienced more severe negative energy balance （NEB）, and had higher concentrations ofβ-hydroxy butyric acid （BHBA） and non-esterified fatty acid （NEFA） than cows fed CS diet. In earlylactation, mammary cell proliferation rates were not affected by dietary （P>0.05）, but cows in CSgroup have higher mammary cell apoptosis rates than those in MF group （P <0.05）. In addition, theexpression of β-casein （CSN2）, κ-casein （CSN3）, Acetyl-CoA carboxylase （ACACA）, and fatty acidsynthase （FASN） were unaffected by diet （P>0.05）, but the expression of IGFIR were affected by diet（P <0.05）.2. Effects of different concentration (0,1,10and100ng mL^-1) of IGF-I on mRNA expression ofgenes related to milk protein and fat synthesis in bovine mammary epithelial cells cultured in vitro wereevaluated by Real-time PCR. The results shown that the mRNA abundance of IGFIR, IGFBP3, CSN1S1and CSN3did not differ significantly （P>0.05） within different concentrations of IGF-I. However, themRNA abundance of CSN2, ACACA, FASN and FABP3increased significantly （P <0.05）.3. This experiment was conducted to evaluate the effects of insulin on mRNA expression of genesrelated to milk protein and fat synthesis in bovine mammary cells cultured in vitro. Mammary epithelial cells were cultured for24h with the following hormone treatments: no hormones （NH, control）,hydrocortisone+prolactin （FP） or insulin+hydrocortisone+prolactin （IFP）. The mRNA expression ofgenes related to milk protein and fat synthesis were measured by Real-time PCR. The results shown thatinsulin, in the presence of hydrocortisone and prolactin, could stimulatethe expression of10genesdirectly involved in milk protein and fat synthesis. These genes included CSN2, CSN3, ACACA, FASN,SREBP1, STAT5B and ELF5in JAK2-STAT5signal pathway, as well as PI3K, AKT1and EIF4E inPI3K/Akt/mTOR signal pathway.