Thirty-six male Ethiopian Menz sheep (9 to 22 months old, average live weight 15·8 (s.d. 1·84) kg), given maize stover (1·5 times ad libitum) supplemented with either 75 g cottonseed cake (CSC), 114 g noug cake (NGC; Guizotia abyssinica) or 112 g sunflower cake (SFC) with or without maize grain, were used in an 88-day study comprising growth and balance trials. The trials were undertaken according to a randomized-block design with a 2 × 3 factorial arrangement.
There were no significant interactions (P > 0·05). Sheep consumed significantly more stover when supplemented with CSC compared with NGC and SFC (P < 0·05). Maize grain significantly increased organic matter intake (P < 0·001). Although CSC tended to support lower live-weight gains, the effect of protein was not significant. Maize grain increased live-weight gains (P < 0·01).
Urinary nitrogen (N) excretions were similar between CSC and SFC but about 0·22 higher with NGC (P > 0·05). The faecal N output was 0·33 (P < 0·01) and 0·18 (P < 0·05) higher with CSC than with NGC and SFC respectively. Maize grain had no effect on any of the N-balance measurements.
Cottonseed cake supported lower daily production of purine derivatives (PD) (P < 0·01), microbial purine (P < 0·01) and microbial protein (P < 0·01) than either NGC or SFC. Maize grain increased the daily excretion of total PD (P < 0·05), microbial purine (P < 0·05) and microbial protein (P < 0·05). Neither the protein source nor maize grain affected the efficiency of microbial protein synthesis. It was concluded that SFC was utilized more effectively both in terms of rumen microbial N synthesis, N retention and growth. The addition of a small amount of energy as crushed maize grain increased microbial N synthesis, N retention and live-weight gain.