Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2001
Publication Date: 3/25/2003
Citation: Coleman, S.W., Hart, S.P., Sahlu, T. 2003. Relationships among forage chemistry, chewing and retention time with intake and digestibility of hay by goats. Small Ruminant Research. Vol.50 pp129-140 Interpretive Summary: Hay or forage quality is important for marketing, for formulating supplements or for determining expected performance from animals fed the forage. Forage quality is difficult and expensive to assess. For instance, assessment for rate of gain or milk production requires about six animals (cows, goats, or sheep) and four to six weeks of daily feeding. It is very labor intensive. The chemical composition of forages has been used to predict forage quality with poor to moderate success. In general, the fibrous portion of the forage plant is responsible for the limitations to optimal production and various processes are involved for ruminant animals to eat, chew, digest and use nutrients found in forages. A series of experiments were conducted with a wide variety of forage types harvested as hay over several levels of maturity to create diversity in forage quality. Each hay was fed to four goats and the amount consumed, nutrients digested, and rate of gain measured. Chemical composition, the amount of time required to chew, and the time required to pass from the gastrointestinal tract was also determined for each hay. Regression equations were calculated using only hay chemistry, only chewing and passage time, or a combination to predict hay intake and digestibility. The combination of chemistry and processing time gave the best results. Eighty percent of the variation in dry matter intake and 90% of that in digestibility was accounted for by the explanatory variables. Average daily gain by the goats was moderately (42% of variation) related to digestible dry matter intake by the goats, from which digestible energy intake can be calculated.
Technical Abstract: Eight species of forage, a cool-season perennial (Festuca arundinacea) and annual grass (Triticum aestivum), four warm-season perennial grasses (Bothriochloa caucasica, B. ischaemum, Cynodon dactylon, and Tripsacum dactyloides), a warm season annual grass (Digitaria sanguinalis) and a perennial legume (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 so that four different goats received each hay. Alfalfa produced the highest DM, but lowest neutral detergent fiber (NDF) intake. All measures and expressions of intake and digestibility were better related to chewing and retention time than with forage chemistry, with the exception of CP digestibility. The best equations for predicting intake included a combination of mean retention time and forage acid detergent fiber (ADF) content (both linear and quadratic included); that for digestibility included NDF, ADF, permanganate lignin, chewing and retention time. Equations for predicting the constraint on intake and digestible dry matter intake produced higher R2 than those for either intake or digestibility. Digestibility of ADF and NDF were difficult to predict, although combinations of forage chemistry and chewing time produced reasonable equations.