Urea levels, protein and diethylstilbestrol for growing steers fed purified diets

High-level dietary crude protein decreased backfat thickness and increased carcass yield score in finishing Hanwoo beef cattle (Bos taurus coreanae)

Recently, a high level of dietary crude protein (CP) has become of interest as a possible practice to improve the carcass quality of beef cattle, and its level has been increasing in the field. However, there is little scientific evidence that supports this. This study was conducted to test whether a high dietary CP level would improve growth performance, body metabolism, and carcass traits in Hanwoo beef cattle. A total of 32 Hanwoo finishing beef cattle (18 multiparous cows, six heifers, and eight steers) participated in a 12-weeks feeding trial. Two kinds of total mixed rations were prepared to contain two different CP; 156 g/kg for the control (CON) and 173 g/kg of CP for the treatment (HCP), while maintaining a similar level of metabolizable energy. The experiment was ended when more than half of the steers reached the target body weight (730 kg). Blood was collected at the end of the experiment. After harvesting, the carcass trait was evaluated at the slaughterhouse according to Korean standards. The carcass yield score and grade were also calculated based on revised criteria. Overall, dry matter intake, average daily gain, blood metabolites concentration, and the carcass traits, except for backfat thickness and the yield score, did not differ between the treatments. The HCP had lower backfat thickness than those of CON. There was no difference in the carcass yield grade, but the yield score was higher in the HCP treatment. According to the newly revised carcass grading criteria, both yield score and grade were higher in HCP than in CON. Increasing CP supply decreased the carcass’s backfat thickness without altering growth performance and body metabolism, resulting in improved yield score and grade. Therefore, feeding a high CP diet may be beneficial in the farm income, although it may also increase feed cost and nitrogen excretion to the environment.

Effects of dietary protein level in the early fattening period on free amino acids and dipeptides in the blood and Longissimus thoracis muscle in Japanese Black steers

The effects of crude protein (CP) concentration in feed using soybean meal as its source in the early fattening period on the levels of free amino acids (FAAs) and dipeptides in the blood, and the levels in the M. longissimus thoracis after slaughter were studied in Japanese Black steers. Sixteen steers were divided into four groups and given feed with a CP content of 12, 14, 16, or 18% of dry matter (DM) from 10 to 20 months old, and they were fed with the same level of CP (13.5-13.9% of DM) until slaughter at 30 months of age. There was no significant difference in the weight gain, carcass weight or marbling score between the groups. Concerning the serum FAA and dipeptide contents at 20 months of age, the alanine, tyrosine and tryptophan levels decreased, while the carnosine (Car) level increased, with increases in the CP level in the feed. Although there were no significant differences in the FAA contents of the Longissimus thoracis muscle between the groups, the Car content decreased with increases in the feed protein level.

Effect of carbon-4 and carbon-5 volatile fatty acids on growth of mixed rumen bacteria in vitro

Mixed ruminal bacteria (400 mg cells/liter) were incubated in artificial media containing ammonia, sodium carbonate, macrominerals, vitamins, sulfide, microminerals, acetate, propionate, and butyrate. When mixed carbohydrates (equal parts glucose, maltose, sucrose, cellobiose, and soluble starch) were added at 155 mg/liter per h for 10 h, average bacterial growth rate was slow, and dry weight yield was greater than 23%. Additions of isobutyrate, valerate, isovalerate, and 2 methylbutyrate had little influence on synthesis of bacterial dry weight, deoxyribonucleic acid, ribonucleic acid, or carbohydrate. When a timothy hay inoculum was used, isovalerate and 2 methyl-butyrate increased protein synthesis by 11.2 and 16.4%, but isobutyrate and valerate alone were without effect. All four acids combined increased bacterial protein by 18.7%. Responses with an inoculum of 60% concentrate and mixed hay were smaller and not statistically different from control incubations. Low concentrations of Trypticase (less than 250 mg/liter) improved efficiency of microbial protein synthesis from organic matter, but more was associated with decreased efficiency and utilization of extracellular ammonia.

Production responses of dairy cows fed diets supplemented with ammonium salts of iso C-4 and C-5 acids

A three-university study examined effects of ammonium salts of volatile fatty acids on dairy cows for a full lactation cycle. Objectives were a) to determine the most efficacious amount and ratio of two components, ammonium salts of C-5 acids and ammonium isobutyrate, and b) to compare responses of this optimum blend with the control in a response surface design. This design tested six blends of the two components defined by the center point and the five points of an equilateral pentagon from which response surfaces would be computed and a control. Each treatment consisted of 23 cows for a total of 161 multiparous Holstein cows. All cows were fed corn silage for ad libitum consumption, 1.8 kg of urea-mineral-vitamin-premix plus supplement based on corn grain and corn gluten meal according to milk production. Response surfaces, based on milk yield, defined an optimum blend composed of 61 g ammonium salts of C-5 acids plus 28 g ammonium isobutyrate per cow per day equivalent to 120 g aqueous blend (74% solids). The optimum blend was similar to the center point blend. Cows receiving the center point blend peaked higher and produced more milk, 4% fat-corrected milk, milk protein, and total solids than control cows. For the first trimester of lactation, milk yields for control and center point blend were 28.6 and 31.8 kg. The 305-day milk, 4% fat-corrected milk yields, and dry matter intakes (kg) were: control 20.5, 19.7, 17.3; center point blend 23.2, 21.6, 17.5. Increased milk production was associated with improved feed utilization. No effect on health or reproduction was observed.

Evaluation of protein nutrition by metabolizable protein and urea fermentation potential

Metabolizable protein and selected metabolizable amino acid requirements for lactating cows were described, and tentative values were established for differnt yields of milk.A new expression"urea fermentation potential of feeds," describes urea use in lactation rations for partial satisfaction of protein and amino acid requirements. Tentative urea fermentation values were established for the more common cattle feedstuffs. Four lactation rations were formulated with different fermentation values to illustrate the variable feeding value of urea in satisfying amino acid requirements at different yields of lactation. Urea had the highest feeding value in lower-protein rations when fed to cows with medium to low yields of milk.Conversely, urea, by the metabolizable protein system, had little or no feeding value in lactation rations having more than about12% protein on a dry matter basis or in rations supporting lactations in excess of 25 to 30 kg of milk per cow per day.