The effect of maize vitreousness and a starch binder on in vitro fermentation parameters and starch digestibility in dairy cows

[摘要] ENGLISH ABSTRACT: Maize kernels consist of hard vitreous endosperm and soft floury endosperm, and the ratio of the vitreous to floury endosperm determines the vitreousness of the kernel. As ruminal fermentation and animal performance are higher for low vitreous maize, lower vitreous maize is favoured for inclusion in animal feeds. Very high ruminal starch degradability may, however, lead to metabolic disorder risks such as acidosis. The objective of this study was to evaluate various techniques for routine analysis to determine a rapid, simple, inexpensive method to predict maize vitreousness accurately. Secondly, the usability of Near-infrared spectroscopy (NIR) technology in the anmal feed industry to predict the fractional rate and extent of ruminal starch degradability in maize differing in vitreousness was investigated by means of in vitro starch disappearance. Thirdly, the effect of the treatment of maize with a commercial starch binder on rumen kinetics of lactating dairy cows was investigated by means of in vitro gas production and in vitro starch disappearance studies. For this part of the study, it was attempted to bind some of the maize starch (1 mm grind) in vitro with the treatment of a commercial starch binder. The fourth objective was to investigate the effect of particle size (1mm vs 4 mm grind) and a starch binder on in vitro disappearance of starch in low vitreous maize. The final objective was to determine the effect of starch binder treatment of low vitreous maize on the apparent total tract digestibility and production responses in lactating dairy cows.Ninety maize samples of different vitreousness were collected and subjected to NIR at a single absorbance of 2230 nm and PSI trough a single 106 μm screen. Samples were subsequently ranked according to vitreousness. The ten hardest and ten softest samples were selected to evaluate NIR, particle size index (PSI), and Rapid visco analyzer (RVA) rheological analyses as potential methods for the determination of maize vitreousness against X-ray micro-computed tomography (XCT). Significant relationships were found between NIR and PSI regarding hardness predictions, while the study with the smaller sample set (n = 10) showed significant relationships between PSI, NIR, RVA peak time (corresponding time required for a sample subjected to rheological analysis to reach peak viscosity) and RVA peak viscosity (the process of gelatinization and occurs at the equilibrium point between swelling and polymer leaching) in relation to XCT regarding maize vitreousness determination. All other rheological information data were not accurate to predict maize hardness. As NIR technology is already available and meets the requirements of speed, simplicity and inexpensiveness, it was concluded that NIR at a single absorbance of 2230 nm is the most accurate and practical method to determine maize vitreousness in the animal feed industry.Thereafter, six maize samples of decreasing vitreousness were selected from ninety samples with known vitreousness and subjected to in vitro starch disappearance at 0, 3, 6, 12, 24 and 48 h of incubation. The subsequently determined fractional rate of disappearance and predicted ruminal starch disappearance decreased significantly as maize vitreousness increased. Hardness indexes calculated from NIR analyses at a single absorbance of 2230 nm showed inverse linear and quadratic relationships for both fractional rate and extent of starch disappearance. It was concluded that NIR technology could be used to predict fractional rate and extent of starch disappearance from the rumen based on maize vitreousness.In a further study one low and one high vitreous maize sample were selected from the ninety samples with known vitreousness. Both samples were treated with equal amounts of a commercial starch binder (Bioprotect) and distilled water to determine the effect of the treatment on in vitro gas production and in vitro starch disappearance. The rate of in vitro gas produced from low vitreous maize was higher than that of high vitreous maize, irrespective of treatment. All other in vitro gas production parameters did not differ between treatments. In vitro starch disappearance values at 6, 12 and 24 h time intervals were, irrespective of binder treatment, higher with low vitreous maize compared to high vitreous maize. Starch binder treatment, however, did not affect in vitro starch disappearance.In a further in vitro study, maize samples of known low vitreousness were milled through 1 mm and 4 mm sieves, respectively. The milled samples were then thereafter treated with equal amounts of a starch binder (Bioprotect) and distilled water to determine the effect of particle size and treatment on in vitro starch disappearance after 0, 3, 6, 12, 24 and 48 h of incubation. Particle size reduction increased (P < 0.05) both fractional rate and extent of starch disappearance, while binder treatment showed a tendency (P < 0.10) towards decreased fractional rate and extent of starch disappearance. Despite no differences in ruminal kinetics with the binder treatment of 1 mm milled maize, treatment of 0.4 mm milled maize, however, indicated lower (P < 0.05) fractional rate and extent of starch disappearance. It was concluded that a reduction in particle size of maize with hammer mill processing changes rumen starch fermentation characteristics and that the treatment of 4 mm milled maize with a commercial starch binder may alter rumen fermentation kinetics.In the final trial, six primiparous Holstein dairy cows were used to investigate the effect of a starch binder (Bioprotect) treatment of low vitreous maize on total tract nutrient digestibility and production parameters of lactating dairy cows. Starch binder (10/L/tonne grain) or water treated maize were used in two TMR's. No differences in dry matter intake, milk yield, 4% fat corrected milk yield, energy corrected milk yield, milk fat concentration, milk fat yield, milk protein concentration, milk protein yield, milk urea nitrogen concentration or somatic cell count were found between binder treated or water treated maize. Apparent estimated ruminal pH and the ratio of milk protein (%) to milk fat (%) also did not differ between treatments. Although total tract dry matter and nitrogen digestibilities did not differ between treatments, total tract starch digestibility decreased (P < 0.05) when maize was treated with a starch binder compared to the water treatment. It was concluded that the commercial starch binder might not be an effective tool to manipulate total tract maize starch digestion in dairy cows, as is apparently the case with wheat and barley. However, when the prevention of acidosis in dairy cows that receive high amounts of low vitreous maize is the objective, then a starch binder may prove to be effective.

[发布机构] Stellenbosch University