Relationships among forage chemistry, rumination and retention time with intake and digestibility of hay by goats

Abstract

Eight species of forage, a cool-season perennial (tall fescue (Festuca arundinacea)) and annual grass (winter wheat (Triticum aestivum)), four warm-season perennial grasses (caucasian (Bothriochloa caucasica), plains (B. ischaemum), old world bluestem, bermudagrass (Cynodon dactylon), and eastern gamagrass (Tripsacum dactyloides)), a warm season annual (crabgrass (Digitaria sanguinalis)) and a perennial legume (alfalfa (Medicago sativa)), were each cut at two or three maturities to provide a wide array of quality difference (n=20). Twenty wether goats (Capra hicus) were fed the hays in four different trials using an incomplete block design so that four different goats received each hay. Alfalfa produced the highest (25 g kg−1 body weight (BW)) and wheat the lowest (13.6 g kg−1 BW) organic matter (OM) intake. A number of the grasses provided less than 20 g kg−1 BW OM intake. Digestion of OM was also highest for alfalfa (>715 g kg−1) and lowest for bermudagrass (508 g kg−1). All measures and expressions of intake and digestibility were better related to ruminating and retention time than to forage chemistry, with the exception of crude protein digestibility. The best equations for predicting intake included a combination of mean retention time and forage acid detergent fiber (ADF) content (reciprocal and quadratic); that for digestibility included permanganate lignin (reciprocal), and the quadratic for ruminating and retention time. Equations for predicting the constraint on intake and digestible organic matter intake produced higher r2 than those for either intake or digestibility. Digestibility of ADF and neutral detergent fiber (NDF) were poorly predicted with either chemistry (r2≤0.20), or ruminating time (r2=0.43), but combinations of permanganate lignin content of NDF, retention and ruminating time produced reasonable equations.