Effects Of Physically Effective Neutral Detergent Fiber On Milk Performance And Blood Biochemi- Cal Indexes Of Midlactation Dairy Cows Under Heat Stress

This experiment was conducted to determine the effects of physically effective neutral detergent fiber on intake, milking performance and blood parameters of dairy cows fed alfalfa hay-based diets with fixed forage proportion under hot weather conditions.25 lactating Holstein dairy cows, averaged milking 18.3+1.2kg/d, were divided into 5 groups(A,B,C,D and E) of 5 cows, according to day in milk, parity and milk yield. Cows were from second and third lactation, and were from 146+25DIM, fed as follows:US alfalfa hay 16.3%, corn silage 14.9%,Chinese wild rye 3.6%,beet pellet 10.0% and concentrate 55.2%(based on DM). The TMR were chemically identical but included different particle length alfalfa hay:1cm,50%1cm+50%4cm,4cm,25%lcm+25% 4cm+50%7cm,7cm. The experiment lasted 50d including 14d for adaptation and 36d for sample collection.The results showed as follows:1.THI lowest averaged 77.72 units,during the whole experimental period (2013.7-2013.9), and all dhe rectal temperature and respiratory frequency were above the normal physiological range of dairy cows,suggested that dairy cows were under heat stress.2. Increasing alfalfa hay particle length had a significant effect on dietary peNDFs.o level(P<0.05),for 12.22%,13.22%,13.91%,14.31%and 14.99% respectively, on peNDF1.18 level (P<0.05), for 23.77%,24.20%,24.28%,24.65%and 25.28% respectively.3. Increasing dietary peNDF1.18 level decreased dry matter intake,the order of DMI effect was 23.77% group>24.20% group>24.28% group>24.65% group>25.28% group, comparied with 23.33% group, the DMI of 25.28% group significantly decreased(.P<0.05).4. Increasing dietary peNDF1.18 level decreased milk yield, the 24.20% group was highest for milk yield, while the 25.28% group was the lowest; dietary peNDF level had a significant effect on milk fat, milk protein (P<0.05),24.28% group were the highest,and 25.28% group were the lowest for milk fat,and 24.28% group were the highest for milk protein, but no significant differences was observed on milk lactose and Feed/Milk (P>0.05).5. There was no obviously differences were observed on Cor or LPS(P>0.05).In conclusion, dietary peNDF level improved the heat-stressed dairy cows milk performance. When the dietary peNDF1.18 level were 24.20%,24.28%,24.28%and 24.20%, the milk yield, milk fat,milk protein and Feed/Milk were maximal.