Heat production and energy balance of sheep and goats fed sole diets of Acacia saligna and Medicago sativa

We hypothesized that the heat production and energy balance of small ruminants are affected by diet quality, in particular plants with high levels of detrimental secondary compounds, and that there are differences among livestock in the ability to utilize forage. The ability to utilize high tannin fodders would be very important in drylands for livestock production. Energy intake and change in energy balance in sheep (n = 10; 44.5 kg) and goats (n = 10; 36.5 kg) were determined when consuming an ad libitum sole diet of either Acacia saligna, a low quality, tannin-rich fodder or Medicago sativa (lucerne hay), a high quality fodder. Dry matter digestibility of A. saligna in goats was higher than in sheep, 44.6 and 25.9%, respectively, but was similar between ruminant species for M. sativa. Daily heat production of goats and sheep when consuming A. saligna was 360.4 and 321.0 kJ kg−0.75 day−1, respectively, and when consuming M. sativa was 432.3 and 445.8 kJ kg−0.75 day−1, respectively. There was no difference between livestock species, but heat production was higher on M. sativa than on A. saligna. Metabolizable energy intake of A. saligna was higher in goats than in sheep, 232.4 and 78.1 kJ kg−0.75 day−1, but there was no difference between goats and sheep when consuming M. sativa. Goats and sheep were in negative energy balance when consuming A. saligna but were in positive energy balance when consuming M. sativa. However, the energy loss in goats was less than in sheep when consuming A. saligna, 128.0 and 242.9 kJ kg−0.75 day−1, respectively, but there was no difference in energy gain between species when consuming M. sativa. Results indicated that (1) the lower heat production when consuming A. saligna than M. sativa is mainly a consequence of the lower dry matter intake and heat increment of feeding; (2) digestibility of high quality forage is similar between goats and sheep, but that goats are better able to digest poor quality forage; and (3) that goats can tolerate higher tannin levels than sheep. © 2007 Elsevier B.V. All rights reserved.