Comparing the effect of age and dietary energy content on feedlot performance of Boer goats

Abstract

The effects of three dietary energy treatments on the feedlot production characteristics of Boer goats were investigated, along with the time spent under feedlot conditions. A total of 66 goat kids with an average weight of 22.2±3.51kg were housed in individual pens at Elsenburg research farm. At the start of the trial, the goats were randomly allocated to one of three finisher diets that vary in energy content; low, medium and high energy (11.3, 12.0, and 12.7MJ ME/kg feed, respectively). The goats were divided further into groups of about 15 goats that were slaughtered at a registered abattoir after 40, 76, 112 and 146days in the feedlot. During the trial period, goats were supplied their respective trial diets ad libitum. Orts were weighed back once a week in order to determine feed intake. Growth was monitored by weighing the goats weekly. The live weights of the goats increased linearly (20.939+0.191x, where x represents days in feedlot) throughout the trial period. Overall, goats on the high energy diet had the lowest growth rate (202.0g/day versus 221.9 and 234.9g/day for goats on the low and medium diets, respectively; P<0.05). This may be as a result of the high starch content affecting the rumen environment and thus the utilization of nutrients for growth. Goats fed the low and medium energy diets presented the higher feed intakes (1236.4 and 1168.6 versus 1002.4g/day for low, medium and high energy diets, respectively; P<0.01). A tendency was observed for the feed conversion ratio (FCR) of goats on the high energy diet to be lower than that of the low and medium energy diets (P=0.06), while the FCR of the goats did not vary with time spent in the feedlot (P=0.40). Goats on the low energy diet had a lower dressing out percentage (45.8%, compared to 46.1 and 47.1%, for the low medium and high energy diets, respectively). This may be attributed to the higher proportion of fibre in the feed, which increases the gut fill and affects the digestibility of the feed. It was also observed that goats were able to adjust their level of feed intake in response to the amount of energy supplied in the diet. It is suggested that the diet with a medium energy content (12.0MJ ME/kg feed) closely resembles the requirements of Boer goats for growth and exhibits the best production characteristics.