1818
Effects of replacing alfalfa hay and corn silage with corn straw in diets on main hormones in blood of dairy cows
To study the effects of replacing alfalfa hay and corn silage with corn straw in diets on main hormones related to metabolism in blood of Holstein cows, Twenty-four firstborn and healthy Holstein lactating dairy cows with similar DIM ( 55±27 d) and body weight (520±25 kg) were randomly divided into 2 groups. Diets contained similar concentrate mixtures with the same forage-to-concentrate ratio of 36:64 (dry matter basis). Different forage sources were then added: 17.30% alfalfa hay and 18.77% corn silage (MF); 36.07% corn straw (CS). The preliminary experiment lasted for 2 wks followed by a 60-day former experiment. The blood samples on d 61 were collected and evaluated the concentrations of insulin (INS), growth hormone ( GH), leptin (LEP),cortisol ( COR), insulin-like growth factor-1(IGF-1) and prolactin (PRL) in serum.
Compared with the MF group, the concentrations of IGF-1 (384.31 vs 311.73 %, P<0.01) and LEP (3.67 vs 3.12 %, P<0.05) in CS group were significanly increased, but the concentrations of PRL (175.51 vs 230.37 %, P<0.05) was decreased. No difference was observed in other hormones (P>0.05). Results showed that under the condition of the same concentrate, different forages can greatly affect concentrations of some hormones in the blood which closely relate to the changes of body's immune and production performance.
Keywords: corn straw, dairy cows, hormones