EFFECT OF WHOLE COTTONSEED ON ENERGY PARTITIONING AND NITROGEN-BALANCE IN SHEEP

Energy and nitrogen balance partitioning was studied in sheep given wh ole cottonseed (WCS), vetch hay and commercial concentrates. Sheep wer e offered diets containing 0 (CON) and 250 g/kg WCS at maintenance (LF ) and twice maintenance (HF) levels. Digested energy, metabolizable en ergy (ME) and heat production (HP) were measured in a balance trial co mbined with indirect calorimetry. Dietary ingredients were also incuba ted in sacco in sheep rumens. Feeding WCS resulted in decreased energy digestibility at HF (0.718 v. 0.751) but not at LF. Loss of energy as methane expressed as a proportion of gross energy intake for CON and WCS respectively was 0.078 and 0.057 at LF and 0.061 and 0.051 at HF. In both diets, HP was similar at LF. In contrast HP amounted to 0.657 of the ME for CON and only 0.61 for WCS at HF. Apparent nitrogen diges tibility was not affected by WCS consumption. Urinary nitrogen was sim ilar for both diets at LF, but at HF it was higher in the WCS diet. Th us at HF, retained nitrogen was 0.45 and 0.12 of apparently digested n itrogen for CON and WCS respectively. Ruminal degradation of organic m atter was proportionately 0.87 and 0.77 of apparent digested organic m atter in the total tract for the CON diet, at LF and HF respectively a nd 0.80 and 0.73 for the WCS diet, at LF and HF respectively. In the f our groups ruminal nitrogen degradation was equal to apparent whole-tr act nitrogen digestion. It was concluded that feeding WCS may decrease metabolic HP in ruminants. Utilization of WCS could be improved by ta king measures to decrease urinary nitrogen losses.