Nutrient selection by cattle, goats and sheep on natural Karoo pasture. 2. Nitrogen

The nitrogen (N) content of material selected by cattle, Boer goats, Dorper and Merino sheep on natural Karoo pasture was investigated. A pronounced seasonal variation in the N content of selected material was found. No correspondence was recorded between the N content of oesophageal extrusa and hand-sampled material. Cattle selected material with a lower (P < 0,01) N content (1,28 ± 0,28%) than Boer goats and sheep, with Boer goats (1,60 ± 0,35%) lower (P < 0,05) than sheep. The difference between Dorper (1,88 ± 0,35%) and Merino sheep (1,87 ± 0,37%) was not significant. Close correlations between the small stock species (r = 0,81-0,89) indicates a similarity in the seasonal N selection pattern of small stock on Karoo veld. Lower correlations between cattle and small stock (r = 0,43 - 0,61) shows that the N selection pattern of cattle deviates from that of small stock. A small but significant (P < 0,01) difference in extrusa N content between dry female (1,72 ± 0,44) and castrated male (1,65 ± 0,43) animals was recorded. Notwithstanding, high correlations (r = 0,87 - 0,95) suggest that N selection of dry females can be predicted from castrated males and vice versa. A highly significant difference (P < 0,01) in the N content of selected material was determined between years. An intraclass (animal species) correlation of r = 0,95 between years indicated a correspondence in the seasonal N selection pattern. A difference (P < 0,01) was recorded in N content of extrusa pooled for the first and last 2 days of the 4-day sampling period. This difference (4,2% units or 0,07% N) was, however, small. The N content of selected material is discussed together with its digestibility. It is concluded that small stock selected material with a

higher nutritive value than cattle on Karoo veld.