Influence of dietary carbohydrate fractions on growth and development of prepubertal dairy heifers

Abstract Text: The objective of this study was to evaluate the effects of altering dietary non-fiber carbohydrates (NFC) on heifer growth, dry matter intake (DMI), feed efficiency, and blood and rumen metabolites.  Ninety Holstein heifers (145.3 ± 25.4 kg, 144 ± 26 d of age) were randomly allocated by body weight (BW) to 1 of 15 pens.  Pens were randomly assigned to dietary treatments of high NFC (HNFC; 40.7% of diet DM), low NFC (LNFC; 31.4% of diet DM) and low NFC plus fat (LNFC+; 31.9% of diet DM).  Diets were formulated to be isonitrogenous, with lower calculated ME for LNFC compared with HNFC and LNFC+.  Heifers were fed diets for 112 d, and forage:concentrate ratios were increased from 35:65 to 60:40 on d 57 of the study.  Body weights were taken every 2 wk, and hip and withers heights, body condition score (BCS), heart girth, hip width, and blood samples were collected monthly.  Rumen fluid was collected esophageally 6 h after feeding from 10 heifers/treatment (2 heifers/pen) to determine pH and volatile fatty acids (VFA) monthly.  Data were analyzed as repeated measures using PROC MIXED of SAS with pen as the experimental unit.  Feeding LNFC+ resulted in heifers that were 4.8 kg (P < 0.10) and 8.8 kg heavier (P < 0.01) at the end of the study compared with HNFC and LNFC, respectively.  Average daily gains (P < 0.01) and feed efficiency (P < 0.10) were greatest for LNFC+ from d 0 to 56; however, no treatment differences were observed from d 57 to 112.  Intake as a percent of BW was greatest for HNFC (3.3%) compared with LNFC (3.1%) and LNFC+ (3.1%) throughout the study (P < 0.01).  Heifers fed LNFC+ were taller at the hip and withers than heifers fed HNFC (P < 0.05) and LNFC (P < 0.01) on d 112.  Additionally, feeding LNFC+ resulted in greater BCS compared to LNFC (P < 0.01), but not HNFC (P > 0.10).  Rumen pH was lower for HNFC from d 0 to 56 (P < 0.05), but similar among treatments at d 84 and 112.  Proportions of acetate and butyrate were least and greatest, respectively (P< 0.01), for HNFC from d 57 to 112. Unexpectedly, increasing dietary NFC did not improve growth compared to lower NFC diets despite increased DMI, indicating that energy availability may have greater impacts on growth than dietary carbohydrates.

Keywords: heifer, carbohydrates, growth