Changing the Proportions of Grass and Grain in Feed Substrate Impacts the Efficacy of <i>Asparagopsis taxiformis</i>to Inhibit Methane Production <i>in Vitro</i>

Benefits of the red seaweed Asparagopsis taxiformis as an ingredient to manage methane (CH4) emissions from the red meat and dairy industries continue to evolve. Asparagopsis has been demonstrated to eliminate enteric CH4 emissions in vitro and reduce it greater than 80% in animals. Variability in animal studies is suspected to be associated with variable inclusion and proportions of grass and grain in the diet. This in vitro study aimed to elucidate effects of gradient grass to grain proportions in the fermentation using five steps from 100% Rhodes grass (RG) to 100% barley grain (BG). Gradient inclusion of Asparagopsis was in six steps of Control with no inclusion (C), Low (L), Low-Medium (LM), Medium (M), Medium-High (MH), and High (H) levels tested in three fermentation durations (24 h, 48 h, 72 h). There was significant effect of RG/BG and inclusion of Asparagopsis such that CH4 production decreased with increasing Asparagopsis independent of RG/BG;however, there was enhanced reduction at greater proportions of BG. Thus, the level of Asparagopsis required to completely inhibit CH4 production in vitro was decreased with decreasing RG/BG. Increasing the duration of fermentation had greatest effect on CH4 at C, L, and LM levels of Asparagopsis independent of RG/BG, although magnitude of CH4 production was greater for higher proportions of BG for the C and L levels. Digestibility of in vitro substrate increased with fermentation duration and increasing BG;however, there was no change associated with inclusion levels of Asparagopsis. Increases in total volatile fatty acids (tVFA) were observed with increased fermentation duration and concomitant with increasing substrate digestion. Increasing proportions of BG induced increase in tVFA. In contrast, and independent of changes in substrate, increasing inclusion of Asparagopsis had little effect on tVFA. The acetic and propionic acid ratio (AA:PA) decreased with decreasing RG/BG and increasing Asparagopsis. This pattern was most pronounced with 100% BG and MH-H Asparagopsis levels. Compared to control, there was decrease in the AA:PA ratio with addition of even L levels of Asparagopsis and with L compared to LM inclusion levels. Increasing levels of BG and Asparagopsis resulted in significant decreases in AA:PA ratios and CH4 production. This study has confirmed that gradient levels (ratio) of grass and grain in a feed mix impact the antimethanogenic efficacy of Asparagopsis during in vitro fermentation with rumen fluid.

Effects of Inclusion Levels of Sweet Potato Vine Silage on Feed Intake, Milk Production and Profitability of Lactating Crossbred Dairy Cows

Feed scarcity is a major challenge in smallholder production systems especially during the dry season. Sweet potato vines (SPV) contribute over 40% of the crop residues fed to dairy cattle but they are highly perishable resulting into losses of about 24% per season. Ensiling SPV mitigates seasonal feed shortages and assists in coping with seasonal feed price fluctuations. This study was conducted to evaluate the effect of sweet potato vines silage (SPVS) supplementation on the performance of lactating Ankole × Friesian crossbred dairy cattle. Four primiparous cows in early lactation were randomly allotted a basal diet of Rhodes grass (Chloris gayana) hay supplemented with dairy pellets and four graded levels of SPVS (0, 100, 200 and 300 g/kg of the daily ration) in a 4 × 4 Latin square design. The animals were given a one-week adaptation period followed by a two weeks data collection period for each diet. Dry matter intake (DMI), live weight changes, milk yield and composition were determined. Dry matter intake improved with addition of SPVS (P ≤ 0.05), with intake being highest (11.9 kg) in cows that were fed the highest SPVS level and lowest in cows that were not given SPVS (6.8 kg). Although animals on diets with 0, 100, 200 g of SPVS/kg of daily ration lost weight, there were no significant differences (P ≥ 0.05) in body weight changes across all treatments. Milk yield increased with SPVS supplementation by 1.5 - 1.7 kg per cow per day but there were no significant differences between the different SPVS supplementation levels. Milk fat and solids-non-fat differed (P ≤ 0.05) across the four diets but there was no consistent trend observed. Considering profit margins, supplementing dairy cows with SPVS at a level of 100 g/kg of daily ration was the most profitable at Uganda shillings 1290 (0.344 USD) per cow per day. In conclusion, SPVS supplementation improved DMI and milk yield but supplementation beyond 100 g/kg of the daily feed intake was not cost-effective.

Rumen liquor from slaughtered cattle as inoculum for feed evaluation

Use of nonlinear mathematical models has been majorly based on in vitro gas production(GP) data generated when substrates are incubated with rumen liquor from fistulated steers. However,existing evidence suggests that rumen liquor from slaughtered cattle of unknown dietary history also generates quantifiable in vitro GP data. Fitting and description of GP data obtained from 4 diets incubated with rumen liquor from slaughtered cattle was evaluated using single-pool exponential model with discrete lag time(EXPL), logistic(LOG), Groot's(GRTS) and Gompertz(GOMP) models. Diets were formulated by varying proportions of Rhodes grass(Chloris gayana) hay and a concentrate mixed on dry matter basis to be: 1,000 g/kg Rhodes grass hay(RGH) and 0 of the concentrate(D1), 900 g/kg RGH and 100 g/kg concentrate(D2), 800 g/kg RGH and 200 g/kg concentrate(D3), 700 g/kg RGH and 300 g/kg concentrate(D4). Dietary kinetics for the models were determined by measuring GP at 2,4.8,10.18,24.36,48.72,96 and 120 h. Model comparison was based on derived GP kinetics, graphical analysis of observed versus predicted GP profiles plus residual distribution and goodness-of-fit from analysis of root mean square error(RMSE), adjusted coefficient of determination(Adj-R^2) and Akaike's information criterion(AIC). Asymptotic GP, half-life and fractional rate of GP differed(P < 0.001) among the 4 models. The RMSE, Adj-R^2 and AIC ranged from 1.555 to 4.429,0.906 to0.984 and 2.452 to 15.874, respectively, forall diets compared across the 4 models. Based on the goodness-of-fit statistical criterion, GP profiles of D1 were more appropriately fitted and described by GRTS and GOMP than the EXPLand LOG models. The GRTS model had the lowest AIC value for D2(2.452). Although GRTS model had the most homogenous residual dispersion for the 4 diets, all the 4 models exhibited a sigmoidal behavior.Therefore, rumen liquor from slaughtered cattle of unknown dietary history can be used to derive nutritionally important feed parameters, but choice of the most appropriate model should be made based on fitting criteria and dietary substrates incubated.