Studies with the Australian Cashmere Goat. I. Growth and digestion in male and female goats given pelleted diets varying in protein content and energy level

Abstract

Some aspects of growth and digestion were studied in Australian cashmere goats in two experiments. In the first experiment, weaner goats (initial LW 13.4 kg) were given three ground and pelleted diets (11.3, 16.0, and 20.9% crude protein) at two levels of intake. Growth rates were highest in males fed the high protein (HP) diet ad libitum (149 g day-1) and lowest in females consuming the low protein (LP) diet at restricted intakes (30 g day-1). Increasing the protein content of the diet resulted in significantly greater liveweight gains, although the improved growth could be largely attributed to increased intake rather than to enhanced feed efficiency. Males grew faster, retained more nitrogen and used feed with greater efficiency than did females. A second experiment with fistulated goats (mean liveweight 16.4 kg) fed the LP and HP diets from experiment 1 showed that organic matter (OM) digestion was greater in goats fed the LP diet (67.9% v. 65.3%). In contrast, the proportion of OM digestion which occurred in the stomach was greater for goats fed the HP diet (76.7 v. 57.4%). For both diets all of the cellulose and hemicellulose digestion took place in the rumen; however, substantial amounts of starch escaped rumen digestion. Large losses of nitrogen across the rumen (4.9 g day-1) in goats given the Hp diet resulted in reduced flows (11.1 g day-1) of non-ammonia nitrogen (NAN) to the small intestine, compared with the LP diet (12.7 g day-1). Digestion of NAN in the intestines was greater in animals consuming the LP diet, possibly reflecting the greater intestinal contribution made by non-microbial NAN. For both diets the ratio of protein to energy available (11.0 and 10.2 g protein MJ-1 ME for LP and HP diets respectively) was estimated to be in excess of maximum tissue requirements for growth.