Journal of Animal Science

Effects of forage:concentrate ratio and forage type on apparent digestibility, ruminal fermentation, and microbial growth in goats

G. Cantalapiedra-Hijar, D. R. Yáñez-Ruiz, A. I. Martín-García and E. Molina-Alcaide

Abstarc :

The effects of forage type and forage:concentrate ratio (F:C)on apparent nutrient digestibility, ruminal fermentation, andmicrobial growth were investigated in goats. A comparison betweenliquid (LAB) and solid (SAB)-associated bacteria to estimatemicrobial N flow (MNF) from urinary purine derivative excretionwas also examined. Treatments were a 2 x 2 factorial arrangementof forage type (grass hay vs. alfalfa hay) and high vs. lowF:C (70:30 and 30:70, respectively). Four ruminally cannulatedgoats were fed, at maintenance intake, 4 experimental dietsaccording to a 4 x 4 Latin square design. High-concentrate dietsresulted in greater (P < 0.001) nutrient digestibility exceptfor ADF. However, CP digestibility increased (P < 0.001)only for the high-concentrate diets including grass hay. Likewise,N retention, ruminal NH3-N concentration, and urinary excretionof purine derivatives increased (P < 0.05) with increasingconcentrate in animals fed diets based on grass hay (0.23 vs.0.13 g of retained N/g of digested N, 30.1 vs. 12.9 mg of NH3-N/100mL, and 11.5 vs. 8.40 mmol/d, respectively), but not (P >0.05) when diets included alfalfa hay. Total protozoa numbersand holotricha proportion were greater and less (P < 0.001),respectively, in high- than in low-concentrate diets. The F:Caffected (P < 0.001) ruminal pH but not total VFA concentration(P = 0.12). Ammonia-N concentration was similar (P = 0.13) overtime, whereas pH, VFA concentration, and protozoa numbers differed(P < 0.001) among diets. Estimated MNF was strongly influencedby using either the purine bases:N ratio obtained in our experimentalconditions or values reported in the literature for small ruminants.There was a F:C effect (P = 0.006) on MNF estimated from LABbut not from SAB. The effect of F:C shifting from 70:30 to 30:70in goat diets depends on the type of forage used. The MNF measuredin goats fed different diets was influenced by the bacterialpellet (LAB or SAB). In addition, the purine bases:N ratio valuesfound were different from those reported in the literature,which underlines the need for these variables to be analyzeddirectly in pellets isolated from specific animals and experimentalconditions.

Key Word :
bacterial pellet, goat, microbial growth, purine derivative, rumen fermentation

Volume 87, Number 2, February 2009