Rabbits were fed cholesterol-free, semipurified diets containing 42% (wt/wt) casein or 21% casein plus one of the following nitrogen sources: soy isolate, amino acid mixture simulating casein, amino acid mixture simulating soy isolate, formaldehyde-treated casein or formaldehyde-treated soy isolate. Two additional groups of rabbits were fed the 42% casein diet and the diet containing casein plus soy isolate to which 0.4% (wt/wt) pure formaldehyde was added, this amount being identical to the amount of formaldehyde present in the diets with formaldehyde-treated proteins. Growth was somewhat reduced on the three diets containing 42% casein. The diet containing 42% casein to which no formaldehyde had been added induced severe hypercholesterolemia, the level of serum cholesterol after 8 weeks being about 10 mmol/L. The hypercholesterolemia was markedly reduced by the replacement of half of the casein by soy isolate, formaldehyde-treated soy isolate or formaldehyde-treated casein. No significant reduction of the concentration of serum cholesterol was seen when half of the 42% casein was replaced by an amino acid mixture imitating either casein or soy isolate. Formaldehyde per se did not significantly influence the level of serum cholesterol. We conclude that the differential tertiary structure of intact casein and soy isolate is an important factor in determining the cholesterolemic responses in rabbits to these proteins.

For wether sheep given 300 g hay and 800 g concentrates the addition of fat (beef tallow:palm kernel oil 9:1) to concentrates at 7 or 12% tended to decrease crude fibre digestibility and increased crude fat digestibility. For 2 rumen-fistulated cows given concentrates containing 7% fat, or 12% fat free or adsorbed on carrier, and 2 cows with fistulae and reentrant duodenal cannulae given concentrates with 12% fat in rations with hay:concentrate 1:2, there were no significant differences between diets in the digestibility of any nutrient; fat digestibility was decreased at feed intakes above maintenance, particularly with the 12% fat concentrates. The use of a carrier in the 12% fat concentrates did not affect nutrient digestibilities for sheep or cows. Inclusion of fat in concentrates increased the metabolizability of sheep diets but there were no significant differences among cattle diets, although methane losses tended to decrease as fat content increased. Additional energy from fat tended to be retained rather than used for milk yield. ME utilization for milk, storage and maintenance was 61-62.5%, tending to be highest with the 12% adsorbed fat. [See DSA 45, 5398 for part I.] (Abstract retrieved from CAB Abstracts by CABI’s permission)

Fat-supplemented concentrates were given to dairy cows with rumen and duodenal cannulae, and the effect on rumen fermentation and site of digestion of dietary components was studied. Treatments were feeding concentrates supplemented with 7% fat (treatment C7), supplemented with 12% fat (treatment C12) and supplemented with 12% fat adsorbed on a carrier (treatment C12C). Small but significant changes in rumen fermentation characteristics such as pH, total VFA (volatile fatty acids) and NGR (non-glucogenic/glucogenic ratio) were observed with treatments C12 and C12C as compared with treatment C7. Numbers of protozoa were severely reduced with treatments C12 and C12C, but not with treatment C7. Site of digestion of organic matter and energy was affected by treatments C12 and C12C but this could be attributed to increased postruminal fat digestion. Total digestion and site of digestion of carbohydrate fractions (crude fibre, neutral detergent fibre, starch, sugars) were not affected by fat supplementation. Recovery of hydrogen in CH4 actually measured was close to 90% of that estimated from the rumen fermentation balance. Nitrogen flow to the small intestine was not affected by replacing part of the carbohydrates by fat, indicating an increased efficiency of microbial protein synthesis in the rumen when fat was increased. (Abstract retrieved from CAB Abstracts by CABI’s permission)

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1. In a 3 X 3 Latin square design 9 cows were given long hay and a concentrate without supplemental fat or with 12% fat (11% tallow and 1% palm kernel oil) mixed with other ingredients or adsorbed on a carrier of Palabora vermiculite. During the 3rd week of treatment milk production was 21.4, 23.5 and 22.6 kg daily, respectively. With both fat-supplemented concentrates, milk fat content increased initially but then decreased sharply and was 3.55, 3.18 and 3.91% in week 3. At the same time protein was 3.19, 3.07 and 3.09%. Feed intake of cows given the fat supplements decreased. (Abstract retrieved from CAB Abstracts by CABI’s permission)