Dietary vitamin E and lipid and color stability of beef and pork: modeling of relationships.

Dietary vitamin E supplementation provides a feasible option to extend the shelf life of meat. However, the costs of extra supplementation necessitate an accurate level of feeding to achieve the maximum return in product quality improvement. The current study aimed to quantify the effects of total dietary vitamin E intake on muscle α-tocopherol concentration in cattle and pigs, and to relate muscle α-tocopherol concentration to lipid oxidation and color of meat. Through computerized and manual searches, 13 studies with cattle and 10 with pigs were identified that have presented data on dietary vitamin E intake and muscle α-tocopherol concentration. Treatment means from 12 studies with beef and 14 with pork were used to evaluate the effects of muscle α-tocopherol concentration on lipid oxidation, as represented by thiobarbituric acid reactive substances in meat stored or retail displayed at chilled temperatures. With CIELAB a* (redness) values as an indicator of color development, the association between muscle α-tocopherol concentration and color could be evaluated with treatment means from 8 studies with beef and 5 with pork. Different treatments applied within studies resulted in 20 to 66 values available for the respective regression analyses. Relationships could be described effectively by different forms of the Mitscherlich model, which presented an initial value for y when x = 0, an asymptotic plateau, and the rate of change of y with increasing values of x. With the inclusion of experiment as a random effect, the relationship between total dietary vitamin E intake (x, IU/d for cattle and mg/d for pigs) and muscle α-tocopherol concentration (y, µg/g of meat) reached asymptotic plateau values at 5.71 and 4.83 µg/g of meat for cattle and pigs, respectively. The fractional accumulation rate (per total dietary vitamin E intake) of muscle α-tocopherol concentration was considerably greater in pigs (0.0130) than in cattle (0.00174). The form of the relationship between muscle α-tocopherol concentration and thiobarbituric acid reactive substances in pork was influenced by a single value, whereas muscle α-tocopherol concentrations could not be related to a* values in beef. This study presented viable models that could be applied in practice to calculate the amounts of supplemental dietary vitamin E needed to obtain the maximum profit from beef and pork.

Effect of dietary rumen-protected choline on milk production of dairy cows: a meta-analysis.

Research studies presented inconsistent results on the effects and action of choline in dairy cow diets. A meta-analysis was conducted to quantify the effects of dietary rumen-protected choline on production characteristics of dairy cows. Dry matter intake (kg/d), milk yield (kg/d), milk fat (% and kg/d), and milk protein (% and kg/d) were evaluated as dependent variables in models. The number of treatment means varied from 20 obtained in 7 studies for milk fat and protein contents to 34 from 11 studies (12 experiments) for milk yield. Accounting for experiment as a random effect, DMI, milk yield, milk protein content, and milk protein yield could adequately be related to levels of dietary rumen-protected choline chloride by a logistic model. Marginal responses in milk yield decreased from 131.5 to 0.037 g of milk/g of dietary rumen-protected choline chloride when supplementation increased from 6 to 50 g/d. From estimated values for the metabolizable Met supplied by diets, it appears that dietary rumen-protected choline chloride functions as a methyl donor to spare Met for milk protein synthesis. However, more accurate input data on Met status of diets are needed to confirm this. Within the range of 6 to 50 g/d of rumen-protected choline chloride, milk fat content decreased linearly at a rate of 0.00339% for a 1g/d increase in dietary rumen-protected choline chloride. This illustrates that dietary rumen-protected choline chloride has no effect on milk fat content. Numerous physiological and dietary factors probably related to responses obtained with dietary rumen-protected choline supplementation, and the precise mechanism of choline action in the lactating dairy cow warrants further investigation.