Voluntary intake and digestibility of barley straw as influenced by variety and supplementation with either barley grain or cottonseed cake

The overall objective of this work was to investigate variation in grain yield (GY), stover yield (SY), fodder quality of stover and their association in sorghum and pearl millet. These relationships were investigated in India in 12 genotypes of sorghum and six genotypes of pearl millet grown under high fertilizer (HF) and low fertilizer (LF) application. Fodder quality of stover was assessed by digestibility and intake measurements in bulls. In sorghum, highly significant genotype-dependent variation was found for GY, SY and fodder value of stover regardless of level of fertilizer application. GY and fodder quality of stover were not inversely related and the genotype with the highest GY, for example, had also the best fodder quality in the stover. High GY and high fodder quality in sorghum stover seem to be compatible traits. In pearl millet, genotypic variation in GY and SY and quality was expressed under HF but not under LF application. No consistent significant genotypic differences were found for fodder quality measurements in pearl millet except for cell wall digestibility. Digestible organic matter intake (DOMI) when bulls were fed to appetite was considered the crucial determinant of stover quality in sorghum and pearl millet. Live weight changes in bulls estimated by DOMI varied genotype-dependently from −140 to +100 g per day in 300 kg bulls. However, this paper argues that genotypes promoting high DOMI are only suitable for farmers with sufficient amounts of stover to allow the feeding of animals to appetite. Farmers with restricted amounts of stover are better served by genotypes that promote high digestibility under restricted feed intake.

The overall objective of this work was the identification of simple, yet accurate, assessments of fodder quality of sorghum and pearl millet stover in crop improvement programs. Stover from 12 genotypes of sorghum and six genotypes of pearl millet grown under high and low fertilizer application was investigated for nitrogen, cell wall constituents, sugar, plant height, stem diameter, leaf number per plant and extent and rate of in vitro gas production of whole stover and of stover cell walls. Organic matter digestibility, organic matter intake, digestible organic matter intake (DOMI) and cell wall digestibility were measured in bulls. Significant genotypic variation was found for chemical, morphological and in vitro fermentation characteristics of stover but their relationship with digestibility and intake measurements was generally poor. While no single chemical, morphological or in vitro measurement described stover quality adequately, some combinations of these measurements resulted in good overall relationships with stover quality measurements. Across sorghum and pearl millet, 71% (P<0.0001) of the variation in stover cell wall digestibility in bulls was accounted by the lag phase of in vitro gas production from cell wall preparations and by acid detergent lignin and acid detergent fiber content of stover. In pearl millet, 98% (P<0.0001) of the variation in DOMI in bulls was accounted for nitrogen, lag phase and maximum rate of gas production and neutral detergent fiber content. The paper further discusses relationships between indirect animal performance measurements such as digestibility and voluntary feed intake (VFI) and animal productivity, e.g. live weight gain. VFI is shown to be a more crucial quality assessment in crop residues than digestibility and the relationship between both measurements was shown to be poor. It is argued that crop improvement programs should validate laboratory techniques as well as indirect animal performance measurements with direct animal performance measurements such as milk or meat production before deciding on laboratory selection criteria.

Eight varieties of maize, namely Awassa 511 (A511), Birkata, composite of best families (CBF), Dendane, drought tolerant population (DTP1), Guto, Katumani and Keroshet planted in 1995 cropping season were compared for grain and crop residue yield and nutritive value of the stover. Significant differences (p < 0.05) were observed in grain and crop residue yields of the varieties. Grain yield was highest (6.99 t ha⁻¹) in DTP1 and lowest (2.21 t ha⁻¹) in Keroshet. Stover and total crop residue yields were significantly higher (p < 0.05) in A511 than in CBF and Dendane. The stem was the largest portion in the stover varying from 31% in Dendane to 50% in A511. The stover of Birkata showed a high crude protein (CP) and low ash and fibre contents compared to the other varieties. The CP content varied from 28 g kg DM⁻¹ (Guto) to 61 g kg DM⁻¹ (Birkata). Crop residue yield and quality parameters, except CP content of the stover, were not negatively correlated with grain yield. The potential utility index varied from 61% (Keroshet) to 74% (CBF). The varieties with higher potential utility indices, except Guto, also had relatively higher solubility, 48 h DM degradability and effective degradability compared to the other varieties. The overall results showed evidence of varietal differences in grain and stover yield and stover quality and indicated the possibility of selecting for maize varieties that combine high grain yield and desirable stover characteristics.

Straws of seven rice cultivars from a plant breeding experiment were analyzed for their chemical composition and nylon bag organic matter (NBOMD) and cell wall degradability (NDFD) with and without 3 or 4% level of urea treatment. A significant (P < 0.01) variation of 70 and 100 g/kg in NBOMD and NDFD respectively was found among the different cultivar's untreated straws. Urea treatment improved NBOMD and NDFD by 80 and 100 g/kg, respectively, without differences between 3 or 4% levels of urea. The improvement in dry matter degradability (DMD) due to urea treatment was found higher in rice straw having lower DMD in untreated straw and was found to be negatively correlated ($\text{r = −0.87∗}$) with the digestibility of untreated straw. In another in vivo digestion trial on crossbred heifers, the organic matter digestibility (OMD), NDFD and digestible organic matter intake (DOMI) were found significantly (P < 0.01) higher in straw of Kasturi cultivar over that of Sita. In nylon bag studies, the soluble fraction a and degradation rate constant c were found higher for Kasturi straw over that of Sita. The DMI was dependent on fraction a ($\text{r = 0.98∗}$) and c ($\text{r = 0.97∗}$ at P < 0.05). In another study, nine straw samples of different cultivars were incubated for 48 h in the rumen of two fistulated animals fed on 4 different diets consisting of; I: Wheat Bhusa (WB) + Sorghum (S) + 1 kg Concentrate (C); II: S + 1.5 kg C; III: S + 200 g Sodium Bicarbonate (Bic) and IV: S + 450 g bic. The DMD, NDFD and ADFD of straws were significantly (P < 0.01) higher on diet II and IV than that on diets I and III. However, hemicellulose degradability was reduced on diets III and IV. Different straws of rice cultivars also differed significantly (P < 0.01) among themselves in their nutrient degradability. Bicarbonate-supplemented diets III and IV had significantly (P < 0.01) higher rumen pH over diets I and II. The zero h DM disappearance (solubility) of straws determined at 0, 1, 2 and 3 h post feeding differed significantly (P < 0.01). The initial pH of the straw was found to have positive effect on the degradability of NDF ($\text{r = 0.74∗}$ at P < 0.05), DM ($\text{r = 0.71∗}$ at P < 0.05), nylon bag solubility ($\text{r = 0.88∗∗}$ at P < 0.01) and acid insoluble ash (AIA) in NDF of digested ($\text{r = 0.81∗∗}$ at P < 0.01) and undigested straw ($\text{r = 0.71∗}$ at P < 0.05). However, rumen pH was negatively correlated ($\text{r = −0.75∗∗}$ at P < 0.05) with rumen nylon bag DM solubility and hemicellulose degradability ($\text{r = −0.81∗∗}$ at P < 0.01). Loss of DM due to 1 h hot water refluxing at pH 7.6 was found negatively correlated ($\text{r = −0.81∗∗}$ at P < 0.01) with NDF content of the straw.