Influences of starter NDF level on growth performance and rumen development in lambs fed isocaloric and isonitrogenous diets.

Neutral detergent fiber (NDF), as the main component of structural carbohydrate in forage, is a vital factor impacting the performance of young ruminants. The objective of this study was to evaluate the effect of starter NDF level on the rumen fermentation and morphometrics of lambs fed isocaloric and isonitrogenous diets. One hundred Hu sheep lambs (18 days of age and 6.1 ± 0.1 kg body weight (BW)) were randomly assigned to 1 of the 4 starter diets differing in their NDF levels on a DM basis: 1) diet with 14% NDF (NDF14), 2) diet with 18% NDF (NDF18), 3) diet with 22% NDF (NDF22), and 4) diet with 26% NDF (NDF26). Lambs were fed milk replacer with designed starters from 21 to 60 days of age, and then transitioned to the same starter feed until 90 days of age. Six lambs from each treatment (close to the average BW of the correspongding treatment) were selected and slaughtered at 90 days of age for measuring rumen fermentation, anatomical and morphometric characteristics. Lambs receiving NDF22 and NDF26 starter diets had greater (P < 0.05) intake of starter and total DM, and average daily gain during the overall period, thereby heavier (P < 0.05) final weightsat 90 days of age compared with those fed NDF14 starter diet. At 90 days of age, lambs fed NDF22 and NDF26 starters had higher rumen pH, followed by lower propionate, higher acetate concentrations (P < 0.05), and a higher acetate to propionate ratio compared with those fed NDF14 and NDF18 starters (P < 0.05). No significant differences of the full and empty weight of reticulorumen were observed among treatments, however, the reticulorumen weight expressed as a percentage of the complex stomach weight was lower (P < 0.05) in lambs fed NDF22 and NDF26 starters compared with those fed NDF14 starter. Furthermore, NDF14 lambs had the thickest keratin layer and epithelium compared with those in the other treatments, but showed the thinnest muscle layer (P < 0.05). These results suggest that increasing starter NDF levels can ameliorate the rumen fermentation environment, and alleviate hyperkeratosis and plaque formation in the rumen epithelium. In summary, including 22% and 26% NDF in the pelleted starter can improve the performance of lambs.