Fatty liver (i.e., hepatic lipidosis) is a major metabolic disorder of many dairy cows in early lactation and is associated with decreased health status and reproductive performance. In severe cases, milk production and feed intake are decreased. Therefore, a practical preventative or an efficacious treatment of fatty liver could save millions of dollars yearly in treatment, replacement, and production losses for dairy farmers. Fatty liver develops when the hepatic uptake of lipids exceeds the oxidation and secretion of lipids by the liver, which usually is preceded by high concentrations of plasma NEFA mobilized from adipose tissue. Excess lipids are stored as triacylglycerol in the liver and are associated with decreased metabolic functions of the liver. Liver can be categorized into normal liver or mild, moderate, or severe fatty liver; the latter can be subdivided further into nonencephalopathic severe fatty liver and hepatic encephalopathy. Insufficient or unbalanced dietary intake, obesity, and elevated estrogen concentrations are involved in the etiology of fatty liver, which is associated with greater incidence of dystocia, diseases, infections, and inflammations. Because even mild fatty liver is associated with decreased health status and reproductive performance of dairy cows, prevention of fatty liver by supplying cows with sufficient nutrients and a clean and health-promoting environment in the peripartal period would reduce production losses of cows more than would any treatment of fatty liver. This, however, might not be enough for cows that are obese or do not eat well, had calving difficulties or twins, have metabolic or infectious diseases, or are in severe negative energy balance because of high milk production immediately after calving. Potential and commonly used preventatives, as well as treatments, are discussed in the review. Currently, detection of fatty liver is possible only by minor surgery. Ultrasonic techniques offer a potential tool to noninvasively detect fatty liver. Future gene-array and proteomic studies may provide means to detect early molecular events in the etiology of fatty liver plus their connection with immune function and reproductive performance so that more effective treatments and preventatives of fatty liver can be developed. Such advances hopefully will make fatty liver a problem of the past.

Much research on carbohydrate and lipid metabolism in farm animals conducted over the second half of the 20th century has focused primarily on increasing the production efficiency and improving the quality and acceptability of animal-derived foods. Research was also performed with the express interest in greater understanding of biochemistry and metabolism of livestock species with ultimate application in the food industry. Knowledge about basic nutritional concepts and differences in metabolism among farm animals, however, has been accumulated and has been used successfully to better understand different health problems in humans such as obesity, atherosclerosis, diabetes, and others that are associated with disturbances in metabolism and nutrition. Here we focus on researchers who made major contributions to our understanding of the synthesis and degradation including digestion of carbohydrates and lipids during the past half-century and to our understanding of the growth and development of meat-producing animals (e.g., pigs and cattle) and milk-producing dairy cattle. These findings will serve as the basis for current and future animal biologists to develop newer concepts and methods for use in improving the efficiency of conversion of animal feed to food and the healthfulness of that food for human consumers.

Milk fatty acid composition and textural properties of butter are known to be affected by the cows' diets. We examined the phenotypic variation in milk fatty acid composition among cows fed the same diet to see if the variation was sufficient to produce butter with different textural properties. Ten cows were selected that tested higher (n = 5) or lower (n = 5) in their proportion of milk unsaturated fatty acids. Milk samples were collected a week after testing, and butter was prepared from the individual samples. Milk and butter samples were again analyzed for fatty acid composition. Butter at 5 degrees C was evaluated by a sensory panel for spreadability and by a texture analyzer at both 5 and 23 degrees C for hardness and adhesiveness. Milk and butter samples from cows with a more unsaturated milk fatty acid composition had a lower atherogenic index, and the butter samples were more spreadable, softer, and less adhesive. Thus, phenotypic variation in milk fatty acid composition among cows fed the same diet is sufficient to produce butter with different textural properties.

Three experiments were conducted to determine whether feeding 25-hydroxyvitamin D₃ (25-OH D₃) or 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂ D₃) improves the tenderness of longissimus dorsi (LD), semimembranosus (SM), and infraspinatus (IF) muscles similar to supplemental vitamin D₃ without leaving residual vitamin D₃ and its metabolites in muscle. In the first two experiments, 24 crossbred steers were used to determine the effects of different oral amounts of 1,25-(OH)₂ D₃ (Exp. 1; n = 12) and 25-OH D₃ (Exp. 2; n = 12) on plasma Ca²⁺ concentrations. In the third experiment, crossbred steers were allotted randomly to one of four treatments: 1) control placebo (n = 7); 2) 5 × 10⁶ IU of vitamin D₃/d (n = 9) for 9 d and harvested 2 d after last treatment; 3) single, 125-mg dose of 25-OH D₃ (n = 8) 4 d before harvest; or 4) single, 500-μg dose of 1,25-(OH)₂ D₃ (n = 9) 3 d before harvest. The LD and SM steaks from each animal were aged for 8, 14, or 21 d, whereas steaks from the IF were aged for 14 or 21 d. All steaks were analyzed for tenderness by Warner-Bratzler shear force and for troponin-T degradation by Western blot analysis. Supplementing steers with vitamin D₃ increased (P < 0.01) the concentration of vitamin D₃ and 25-OH D₃ in all muscles sampled. Feeding steers 25-OH D₃ increased (P < 0.05) the concentration of 25-OH D₃ in meat, but to an amount less than half that of cattle treated with vitamin D₃. Supplemental 1,25-(OH)₂ D₃ did not affect (P < 0.10) shear force values; however, there was a trend (P < 0.10) for supplemental vitamin D₃ and 25-OH D₃ to produce LD steaks with lower shear values after 8 and 14 d of aging, and lower (P < 0.10) shear force values for the SM aged for 21 d. Analysis of Western blots indicated that LD steaks from cattle supplemented with vitamin D₃ and 25-OH D₃ had greater (P < 0.05) troponin-T degradation. Antemortem supplementation of 25-OH D₃ seems to increase postmortem proteolysis and tenderness in the LD and SM without depositing large concentrations of residual vitamin D₃ and its metabolite 25-OH D₃.

One hundred thirty-eight Angus cross yearling steers (initial BW 390 ± 0.5 kg) were allotted by BW to a 3 × 2 factorial arrangement of 6 treatments (4 pens per treatment) to determine the effect of wet distillers grains (WDG) concentration (0, 20, 40% of dietary DM) in low-forage (12% hay) and high-forage (50% hay) diets on growth performance and marbling. Steers were implanted on d 0 with Component TE-S (VetLife, Overland Park, KS) and were slaughtered in 3 groups when final BW averaged 578 kg. Steers fed a low-forage diet gained BW faster (P < 0.001) than did steers fed a high-forage diet; the amount of WDG fed did not affect (P = 0.25) daily BW gain. Hot carcass weight and dressing percentage were greater (P < 0.001) for steers fed low-forage diets than for steers fed high-forage diets. Dressing percentage increased (P = 0.08) as WDG concentration increased. Longissimus muscle area (P = 0.08) and yield grade (P < 0.01) were greater for steers fed low-forage diets compared with steers fed high-forage diets. Longissimus muscle area (P = 0.02) and yield grade (P = 0.03) increased as WDG concentration increased. An interaction occurred for marbling (P < 0.01), fat thickness (P = 0.08), and PUFA content (P < 0.01). In steers fed low-forage diets, marbling score (325, 306, 265) and fat thickness (1.22, 1.07, 1.07 cm) decreased with WDG inclusion rates of 0, 20, and 40%, respectively, but in steers fed high-forage diets, marbling score (249, 282, 262) and fat thickness (0.89, 0.97, 0.81 cm) increased from the 0 to 20% inclusion rate and then decreased from the 20 to 40% inclusion rate. The inclusion of 0, 20, or 40% WDG increased PUFA content of beef from steers fed low-forage diets (6.9, 9.3, 10.6 g/100 g) but decreased PUFA content of beef from the 0 to 20% inclusion rate and then increased PUFA content of beef from the 20 to 40% inclusion rate in steers fed high-forage diets (8.5, 5.9, 7.8 g/100 g). In conclusion, when fed to a common BW end point, concentration of WDG in feedlot diets alters lean and adipose tissue deposition in beef cattle. Copyright © 2010. American Society of Animal Science .