Responses to various protein and energy supplements by steers fed low-quality tropical hay. 1. Comparison of response surfaces for young steers

Response curves were established for different supplements, offered at intakes ranging from 0 to 20 g/kg liveweight (W).day to young Bos indicus crossbred steers fed low-quality Rhodes grass (Chloris gayana) hay ad libitum in two pen experiments. Supplements included protein meals of varying rumen-degradability (cottonseed meal (CSM) or fishmeal), as well as ‘energy sources’ comprising grains of high and low ruminal starch degradability (barley and sorghum) and a highly fermentable sugar source (molasses), with all diets adjusted for rumen-degradable nitrogen and mineral content. Unsupplemented steers gained 0.08 and 0.15 kg/day, in Experiments 1 and 2, respectively. Growth of steers increased linearly with intake of ‘energy source’ supplements in increasing order of molasses, sorghum and barley (all differences P < 0.05). Steer growth rate also increased linearly with fishmeal, albeit over a narrow intake range (0–4.1 g/kg W.day), whereas the response with CSM was asymptotic, showing a steep response at low intake before levelling at ~1.2 kg/day. All supplement types were associated with a linear reduction in hay intake by the steers (energy substitution) where the reduction was greater (P < 0.05) for barley and molasses (not different) than for sorghum (P < 0.05), and for fishmeal compared with CSM (P < 0.05). In concurrent metabolism studies with the same rations, organic matter digestibility of the total ration (561–578 g/kg DM, unsupplemented) was increased linearly by barley and molasses (both P < 0.05) but was unaffected by CSM and sorghum supplements. The efficiency of microbial protein synthesis in steers increased linearly, from 91 g microbial crude protein/kg digestible organic matter (unsupplemented), in both molasses and CSM-supplemented steers, with the trend for a higher response to molasses (P = 0.05), and appeared most closely related to digestible organic matter intake. The response curves from these studies provide the practical framework upon which to formulate rations for cattle grazing low-quality forages.

Effects of different forms of white lupin (Lupinus albus) grain supplementation on feed intake, digestibility, growth performance and carcass characteristics of Washera sheep fed Rhodes grass (Chloris gayana) hay-based diets

Protein is the major limiting nutrient in feeding ruminants especially in dryland areas. Thus, looking for locally available protein sources such as white lupin (Lupinus albus) grain is commendable. The objective of this experiment was to determine effects of supplementation of different forms of white lupin grain (WLG) on feed and nutrient intake, digestibility, growth and carcass characteristics. Twenty-five yearling male Washera sheep with initial body weight (BW) of 16.26 ± 1.41 kg (mean ± SD) were used. Animals were blocked into five based on their initial BW and were randomly assigned to one of the following five dietary treatments: Rhodes grass (Chloris gayana) hay (RGH) alone (T1) or supplemented with 300 g (on dry matter (DM) basis) raw WLG (T2) or raw soaked and dehulled WLG (T3) or roasted WLG (T4) or raw soaked WLG (T5). Supplementation with WLG significantly improved total DM and nutrient intake (P < 0.001), nutrient digestibility (P < 0.01), and average daily gain (ADG) and feed conversion efficiency (FCE) (P < 0.001). Carcass quality parameters were significantly (P < 0.001) higher for supplemented sheep. However, the difference in carcass quality parameters among supplemented groups was not significant (P > 0.05). It is concluded that roasting white lupin grain can lead to a better feed and nutrient intake and consequently better carcass quality. White lupin grain can be recommended not only for maintenance but also for optimum performance of ruminants.