Study On The Requirement Of Dietary Physically Effective Neutral Detergent Fiber For 8 To 10-month-old Holstein Heifers

The objective of this experiment was to evaluate effects of dietary peNDF levels on body growth and development, blood biochemical parameters, feed intake, feeding behavior, digestion, rumen fermentation and rumial cellulolytic bacteria in 8 to 10-Month-Old Heifers.And to determine the suitable peNDF content in diet of 8 to 10-month-old Holstein Heifers. Twenty-four Chinese Holstein heifers with similar month of age and body weight were randomly divided into 4 groups. During the 60-d periods, animals were offered one of four diets, which were chemically identical but included different peNDF8.0 levels:10.78%(group S), 13.50%(group MS),17.99%(group ML) and 19.80%(group L). Results shown as follows: Rumen pH was improved significantly with increasing peNDF content in diet (P<0.01).There were no effects on animal’s feed intake, the total volatile fatty acid content as well as acetate and butyrate percentage were no significant changes with altering peNDF level(P>0.05), whereas propionate decreased and the ratio of acetate to propionate were increased with increasing peNDF content (P<0.01). Ruminal ammonia nitrogen (NH3) concentration increased with increasing peNDF content(P<0.01). The relative population of rumen bacteria such as R. flavefaciens, R. Albus and B. fibrisovents was enhanced initially and then dropped. In contrast, the relative population of F. succinogene was decreased initially and then increased with increasing peNDF content (P<0.01). Body weight of heifers and their total eating time, total chewing time, eating and chewing time for per kilogram of dry matter, eating and chewing time for per kilogram of neutral detergent fiber were increased significantly by increasing peNDF content in diet (P<0.05),The average daily gain, total ruminating time and ruminating time for per kilogram of dry matter and neutral detergent fiber also improved slightly, but no significant differences were found(P>0.05). Body height, body side length, circumference index and body trunk index of animals were affected significantly by altering dietary peNDF level(P<0.05), however, there was no significant effect on blood biochemical parameters (P>0.05). Digestibility of DM, CP, NDF and ADF were increased initially and then decreased, in addition, that results in group MS(13.50%) was significantly higher than the other three groups (P<0.05). There were positive correlations between pH, ADG, total eating time, total chewing time, eating and chewing time for per kilogram of dry matter, eating and chewing time for per kilogram of neutral detergent fiber and the peNDF level. I was concluded that the suitable peNDF1.18 content in diet of 8 to 10-month-old Holstein Heifers was 24.44%～29.01%. And the suitable peNDF8.0 content was 19.96%～23.79%.