Growth performance of ruminants fed different proportions of maize and sorghum grain

S Ncube, L R Ndlovu¹, B Tavirimirwa, G Tambo, R Mwembe and G B Nyamushamba²

Department of Research and Specialist Services, Matopos Research Institute P Bag k5137, Bulawayo, Zimbabwe
shadreck_ncube@yahoo.com
¹National University of Science and Technology, P.O. Box AC 939, Ascot Bulawayo, Zimbabwe
²Faculty of Agriculture, Women’s University in Africa, P O Box MP 1222, Harare, Zimbabwe

Abstract

Two experiments were conducted to determine the effect of combining maize and sorghum grain high in soluble proanthocyanidins (PAs) (3.466 A₅₅₀/g sample) on steer and wether feed intake, digestibility, growth and feed conversion ratio. The first experiment assessed the effects of combining maize and sorghum grain high in PAs (3.47 A₅₅₀/g sample) on intake and digestibility of the diets fed to wethers. Twenty five Dorper wethers (mean initial bodymass 37.3 ±5.3 kg) of 18 months of age were stratified by initial weight then randomly allotted to five diets in a complete randomised design within each body mass group with 5 replicates per group and were fed one of the following diets:100% maize (100M); 75% maize and 25% sorghum (75M:25S); 50% maize and 50% sorghum (50M:50S); 25% maize and 75% sorghum (25M:75S); 100% sorghum (100S). In the second experiment the effect of combining maize and sorghum grain on feedlot performance was evaluated. Thirty steers (12 months old) were allotted to 5 pens. The composition of the diets was as described in Trial 1.

 

 Feed intake of the wethers was not affected by the treatments.  Digestibility of dry matter (DM), organic matter (OM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) ranked 50M:50S>100M>75M:25S>25M:75S>100S.  The feed conversion of the steers was similar on all diets, but those fed the sorghum diet had greater average daily gains than those fed maize. Carcass traits were not affected by grain type. Results from this study indicate that sorghum grain is useful as a source of energy in pen fattening diets.

Keywords: digestibility, feedlot, intake, steers

Introduction

In Zimbabwe the standard high energy diet for pen fattening ruminant animals is based on maize, which is a major expense in livestock finishing rations. The increase in human population coupled with the decrease in maize output, has resulted in increased competition between humans and livestock for maize (Deepak et al 2013). Although sorghum grain is also a source of energy, it has not been routinely used because it has been considered less efficient than maize because of its highly variable chemical composition and feeding value (Manor 1987). The low feed efficiency of sorghum grain has been attributed to environmental factors (Brouk 2010), differences between varieties (Dykes and Rooney 2006) and presence of secondary compounds (mainly condensed tannins) (Rooney et al 2005).

 

The presence of secondary compounds (proanthocyanidin [PAs]) leads to reduced intake, dry matter and protein digestibility of sorghum grain. Sorghum varieties with pigmented testa layer such as brown sorghums (bird resistant) have high tannin compounds compared to non-pigmented varieties ( Dykes and Rooney 2006; Rooney et al 2005). Despite these limitations sorghum grain offers potential to serve as a substitute for maize in high energy diets for ruminants (Brouk 2010). The cereal is more suitable in drought prone areas of the country as it is more drought tolerant than maize. Improved animal performance has been observed when sorghum has been combined with maize in pen fattening diets (Larrain et al 2009; Ncube et al 2001; Smith et al 1992).

 

This research sought to examine the effect of combining maize and sorghum grain high in soluble PAs on steer and wether feed intake, digestibility, growth and feed conversion.

Materials and methods

Two experiments were conducted at Matopos Research Institute. The first assessed the effects of combining maize and sorghum grain high in soluble proanthocyanidins (PAs) (3.47 A₅₅₀/g sample) on intake and digestibility of the diets fed to lambs. The second evaluated the effect of combining maize and sorghum grain on steer growth performance with the following specific parameters of interest: feed intake, digestibility, growth and feed conversion.

 

Composition of the diets                                  

 

Nitrogen (N) content was similar for all treatments (Table 1). Acid-detergent fibre (ADF) was greatest with sorghum-based diets. Proanthocyanidins were generally low in all treatments compared to literature values (Boren and Waniska 1992). The calculated metabolizable energy (ME) was similar across treatments.

 

Trial 1

 

Animals, housing and treatments

 

Twenty four Dorper wethers (mean initial bodymass 37.3 ±5.3 kg) of  18 months of age were stratified by weight then randomly allocated to the five diets in a complete randomised design within each body mass group with 5 replicates per treatment, except for one treatment which had four replicates due to damage of the crate. The five treatments consisted of the following diets based on differing proportions of maize and sorghum grain containing soluble PAs  of 3.47A₅₅₀/g sample:

 

100M: 100 per cent maize based diet

75M:25S: 75 per cent maize and 25 per cent sorghum

50M:50S: 50 per cent maize and 50 per cent sorghum

25M:75S: 25 per cent maize and 75 per cent sorghum

100S: 100 per cent sorghum based diet

 

The composition of the diets is shown in Table 1.  The sorghum grain (cultivar Mutode) was grown at Matopos Research Institute, while maize (variety, SC501) was sourced from one farmer.

 

Feed was offered ad libitum twice a day, at 0800 and 1400 hours. Wethers were housed individually in metabolism crates so each animal was considered an experimental unit (replication). Intake, digestibility and N retention were measured over seven days following a 21-day adjustment period. Total collection of faeces was made to enable measurement of the digestibility of DM, OM, NDF and ADF. Daily collection of faeces was weighed, mixed thoroughly and a 10 per cent subsample taken and stored at -20⁰C pending analysis. Total urine collection was also done for nitrogen retention determination. Urine was collected daily, sub-sampled and stored at -20⁰ C pending analysis. Urine was preserved with 20 millilitres of 25 % sulphuric acid (3:1 H₂O: H₂SO₄, v/v).

 

Trial 2

 

Animals, housing and feeding

 

Thirty crossbred steers (mean initial bodymass 243±15.9 kg) of about 12 months of age were randomly allocated to five treatments in a complete randomized design (CRD) with six replicates per treatment. The compositions of the diets were as described in Trial 1.

 

The steers were housed individually and each was considered an experimental unit. The pens had concrete floors, asbestos roofing and the sides were made of wooden rails. There was a permanent feed trough at one end and a water trough at the other end of each pen. The steers were fed ad libitum for 60 days, but feed was offered twice a day, at 0800 and 1400 hours, to allow about 20 per cent refusals. Water was available at all times.

Measurements

 

Feed offered and refused was recorded daily.  Both fresh feed and refusals were analyzed to detect any tendency towards diet selection. Animals were weighed once per fortnight.  A starved (24 hours) bodyweight was obtained at the beginning and end of the 60-day feeding period.  At the end of the feeding trial the steers were slaughtered, and the standard grading and carcass assessment was made (Cattle Producers Association 1998).

 

Animal health

 

The lambs were drenched against internal parasites with Ridafluke® (3% suspension) a broad spectrum remedy for the treatment of wireworm, liver fluke and nasal worm at the rate of 2.5 ml per 10 kg body mass. Cattle were drenched 1ml per 5 kg body mass of 2.265 per cent Oxfendazole m/v Systamex® fluid against internal parasites with at the start of the experiment.

 

Metabolizable energy calculations

 

The metabolizable energy of feeds was calculated from their proximate analysis according to Equation 1 (Ministry of Agriculture Fisheries and Foods (1984), Equation 73):

 

ME (MJ/kg DM) = 12 + 0.008CP + 0.023EE – 0.018CF – 0.012ASH         (1)

 

Chemical analysis

 

Feed and refusals were analyzed for concentrations of N and ash (AOAC, 1990), NDF and ADF (Van Soest et al 1991).  Urine was analysed for total nitrogen.  Insoluble proanthocyanidins were estimated by the butanol-HCl method (Reed et al 1982). Soluble PAs were estimated by the butanol-HCl method (Hagerman 2011). Urine was analysed for total nitrogen content.

 

Statistical analysis

 

Analysis of variance was carried out using the General Linear Model procedure of SAS (SAS 2000).  For the two trials, the weekly intake data were analysed using General Linear Model for repeated measures. Where F values were significant (P ≤ 0.05), differences among treatment means were tested by Student's t-test at alpha error level at 0.05. The relationship between PAs, intake, digestibility and feed conversion ratio was obtained using Pearson correlation analysis. The model used was:

 

            Y_ijk= m + T_i + W_j + TW_ij + Î_ijk

Where:

 

            Y_ijk= is the measured response variable for the i^th treatment in the j^th week;

            m = is the overall population mean;

            T_i = is the effect of the i^th dietary treatment;

            W_j = is the effect of the k^th week on intake;

            TW_ij = is the treatment x week interaction;

            Î_ijk = is the random residual error associated with Y_ijk.

Results

Trial 1

 

Intake and digestibility of feedlot diets fed to lambs

 

Feed intake (g/kg^0.75) was not affected by the treatments (P > 0.05). Treatments ranked 50M: 50S>100M>75M: 25S>25M: 75S>100S (P ≤ 0.05) for dry matter digestibility and organic matter digestibility (Table 2).The N intake was similar across treatments. Faecal N output was lowest with 100M and highest with 100S, with the intermediate diets not differing from each other (Table 3). Urinary N output on the other hand decreased (P ≤ 0.05) with increase of sorghum grain in the diet. N retention was however not affected by treatments (P > 0.05).

 

Trial 2

 

Feedlot performance of steers

 

Intake and growth performance of the steers is shown in Table 4. Treatments ranked 100S>25M: 75S>100M>50M: 50S>75M: 25S (P ≤ 0.001) for feed intake (Figure 1, Table 4). Although not significantly different average daily gain of the animals was highest (P > 0.05) with 50M: 50S and 100S diets. Body mass changes decreased with time and were greatest (P ≤ 0.05) for the 100% maize based diet (Figure 2). Treatments ranked 50M: 50S >100M>100S>25M: 75S>75M: 25S (P ≤ 0.05) for feed conversion ratio. There was an interaction (P ≤ 0.001) between treatment and weekly intakes.

 

Carcass traits are shown in Table 5. There were no initial carcass weights, because of the breakdown of the slaughter facilities. Carcass weights, dressing proportions, fat score and carcass length were similar for all treatments.