This study compared the effect of supplementing maize stover (MS) with cowpea (Vigna unguiculata) haulms or commercial concentrate (CC) on feed intake, nutrient digestibility, live weight gain and carcass yield of male Ethiopian Highland sheep. Two cowpea genotypes, 12688 (forage) and IT96D-774 (dual-purpose), were used. A randomised block design was applied with groups of eight sheep, blocked by weight, allocated to one of six treatments; MS ad libitum either unsupplemented or supplemented daily with 150 or 300 g dry matter (DM) of either cowpea or CC. MS contained more neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin than either cowpeas or CC. Crude protein (CP) content of the forage-type cowpeas was higher than either dual-purpose or CC, while MS had the lowest CP content. Relative to the negative control group, cowpea at either level significantly (P < 0.01) increased both MS intake and total NDF and lignin. Supplementation significantly (P < 0.01) increased nitrogen (N) intakes relative to the negative control, with N intake for CC and dual-purpose cowpea (high level) being similar to the intakes for cowpeas at 150 g. N intake with the forage-type cowpea offered at higher levels was significantly (P < 0.01) greater than the other groups. No significant differences (P > 0.01) in MS intake were identified between cowpeas at either level or CC and, although intake level of CC increased, it did not differ significantly from the negative control group. Supplementation significantly (P < 0.01) improved average daily gain, with the negative control group losing weight over the experimental period, and increased final live weight, carcass cold weight and dressing percentage. Supplementation significantly improved the apparent digestibility of DM, organic matter and NDF, with no significant difference found between cowpeas at either level. N retention was negative for sheep offered only MS, but positive with all supplements, with cowpeas improving N retention to a greater extent than CC. Interestingly, N retention/N intake was higher with cowpeas offered at the lower level suggesting an improvement in utilisation efficiency. The results indicate that the supplementation of MS with cowpea enhanced ruminant production through improvements in digestibility and intake. Further, as production improvements associated with the two levels of supplementation did not differ significantly, it is suggested that where limited quantities of cowpea are available, it may be of greater nutritional benefit to offer smaller quantities over an increased number of animal days.

Six rumen cannulated sheep (26·1 (s.d. 2·24) kg live weight) given maize stover ad libitum were supplemented with either sunflower (Helianthus annus) cake (SFC), decorticated cottonseed (CSC) or noug (Guizotia abyssinica) cakes (NGC) with or without crushed maize grain. The 6×6 Latin-square experiment studied the degradation properties of the oilseed cakes and their effects and that of maize on the degradation of maize, maize stover and the composite diet.

Seedcakes differed in the degradability characteristics of dry matter and nitrogen: intercept (a) (P < 0·001); potentially degradable fraction (b) (P < 0·001); rate of degradation (c) (P < 0·001); and the effective degradability (P < 0·0001). The pooled sum of the degradabilities of the individual ingredients were significantly lower than that of mixed ingredients (composite diet) (P < 0·001).

The main effects of protein and maize were not significant on the degradation of maize stover. Maize had the tendency to depress the rates of degradation of stover by 0·52 with SFC.

Although the protein × maize interaction was not significant on maize stover degradability, it is important to note that maize had the effect of increasing stover degradation rate with CSC and NGC, but a depressing effect with SFC. Hence it was concluded that the carbohydrate effect on roughage degradation rate may vary as a function of the difference between the degradation rate of the energy and protein supplements.

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.