EFFECTS OF A DIETARY MIXTURE OF MEAT AND BONE MEAL, FEATHER MEAL, BLOOD MEAL, AND FISH-MEAL ON NITROGEN-UTILIZATION IN FINISHING HOLSTEIN STEERS

Our objective was to determine to what extent rate and efficiency of p rotein gain in finishing cattle can be enhanced by feeding an amino ac id-balanced mixture of undegraded intake proteins. The Cornell Net Car bohydrate and Protein System (CNCPS) model was used to formulate a cor n-based diet that would meet the rumen requirements for 410-kg large-f ramed steers with an estrogen implant and fed an ionophore. The CNCPS model was also used to formulate a highly undegradable intake protein (UIP) mixture from meat and bone meal, blood meal, fish meal, and hydr olyzed feather meal to provide the amino acids needed to supplement th ose derived from microbial protein to better meet amino acid requireme nts for growth. Four Holstein steers weighing 407 kg were offered a 90 :10 concentrate-forage diet at hourly intervals at 95% of ad libitum i ntake. The steers were injected with 500 mu g of estradiol-17 beta at 12-h intervals to mimic the effects of an estrogenic implant. Treatmen ts planned consisted of inclusion of the UIP mixture at 0, 2.5, 5, and 7.5% of the diet DM. Dry matter intake was fixed at 6.4 kg/d , and DM digestibility was not significantly affected by varying the amount of UIP addition. Apparent digestibility of N increased (P = .011) from 6 3.8 to 65.8, 70.7, and 71.5%, the amount of N absorbed increased (P = .001) fi om 73 to 84, 100, and 106 g/d, and N balance increased(P = .0 03) from 20 to 30, 33, and 39 gld when UIP was fed at 0, 2.6, 5.2, and 7.8% of diet DM, respectively. The efficiency of N use increased 39.7 %, and biological value increased 31.6% when the UIP mixture was added to the diet. Circulating concentrations of plasma urea N (PUN) were i ncreased(P = .017) from 4.5 for the control diet to 5.7, 6.2, and 6.1 mg/dL when the UIP mixture was added at 2.6, 5.2, and 7.8%, respective ly. Corresponding IGF-I concentrations were also increased from 491 to 558 and 624 ng/mL with 2.6 and 5.2% levels of UIP addition. Plasma gl ucose, NEFA, and insulin concentrations were not affected by feeding t he UIP mix. The rate and efficiency of N use for growth improved with addition of an amino acid-balanced UIP mixture to the diet.