Phase Feeding Strategies To Meet Metabolizable Amino Acid Requirements of Calf-Fed Holstein Steers

One hundred eight Holstein steer calves (114 ± 8 kg) were used to evaluate effects of phase feeding metabolizable amino acids (MAA) on growth performance and carcass characteristics. Three feeding strategies wae evaluated: 1) control, single-phase feeding (steers were fed a single urea-based growing-finishing diet that meets the average MAA requirements for the overall feeding period); 2) 2-phase feeding (steers were fed a diet formulated to meet the average MAA requirements for the first 112 d on feed, and thereafter finished on the control urea-based diet); and 3) 3-phase feeding (2 diets were formulated to meet average MAA requirements during the first and second 56-d feedlot feeding periods, and thereafter cattle were finished on the control urea-based diet). Two-phase feeding and 3-phase feeding management strategies produced similar (P > 0.20) growth performance. Multiple-phase feeding increased ADG (18%, P 0.20) on growth performance; however, multiple-phase feeding increased overall (351-d) ADG (6.3%, P 0.20) of 3-phase vs. 2-phase feeding strategies on carcass characteristics. Multiple-phase feeding increased hot carcass weight.

Key words: amino acid, cattle, feedlot, Holstein, phase feeding



In southwestern feedlots, Holstein calves are typically fed a single steam-flaked, corn-based diet throughout the entire growing-finishing period. This diet usually contains between 12 and 13 % CP, with urea as the sole source of supplemental N (Zinn et al., 2005). Although this diet meets the theoretical (NRC, 2000; Level 1) metabolizable amino acid (MAA) requirements across the overall (roughly 350-d) feedlot feeding period, it does not meet MAA requirements of calves during the initial growing phase (112 to 140 d; Zinn and Shen, 1998). Based on amino acid supply to the intestine as a percentage of requirements, Zinn et al. (2000) observed that MAA intake limited growth performance of Holstein steers during the first 112 d in the feedlot. There are no published reports in the scientific literature evaluating phase-feeding protein to calf-fed Holstein steers. The objective of this trial was to evaluate the practicality of 2- and 3-phase feeding strategies to meet MAA requirements on growth performance and carcass characteristics of calf-fed Holstein steers.

MATERIALS AND METHODS

One hundred eight Holstein steer calves (114 ± 8 kg) were used to evaluate effects of phase feeding MAA on growth performance. Calves originated from Tulare, California, and were shipped to the University of California Desert Research Center, El Centro. Upon arrival, calves were vaccinated for bovine rhinotracheitis-parainfluenza^sub 3^ (TSV-2, SmithKline Beecham, West Chester, PA), clostridials (Fortress 8, SmithKline Beecham, West Chester, PA), and Pasteurella haemolytica (One Shot, SmithKline Beecham), were treated for parasites (Dectomax Injectable, Pfizer Animal Health, New York, NY), and injected with 500,000 IU vitamin A (Vita-jec A&D "500", RXV Products, Porterville, CA). Steers were blocked by weight and allotted randomly within weight blocks to 18 pens (6 steers/ pen). Three MAA feeding strategies were evaluated: 1) control, singlephase feeding - steers were fed a single urea-based growing finishing diet formulated to meet the average MAA requirements for the overall feeding period - a standard Holstein feeding practice for Southwestern feedlots; 2) 2-phase feeding - steers were fed a diet formulated to meet the average of MAA requirements for the first 112 d on feed, and thereafter finished on the control urea-based diet, and 3) 3-phase feeding - 2 diets were formulated to meet average MAA requirements during the first and second 56-d feedlot feeding periods, respectively, and thereafter cattle were finished on the control urea-based diet. Composition of experimental diets is shown in Table 1. Control and phase-feeding diets were formulated to meet MAA requirements based on expected (NRC, 2000; Level 1) average animal BW and a 1.5 kg ADG. Steers were allowed ad libitum access to dietary treatments with fresh feed added twice daily. Steers were implanted with Synovex-C (Fort Dodge Animal Health, Overland Park, KS) upon arrival, Synovex-S (Fort Dodge Animal Health) on d 84, and Synovex-Plus (Fort Dodge Animal Health) on d 168 and 252. Cattle were shipped for slaughter when pen blocks reached an estimated final shrunk BW of 572 kg. Hot carcass weights (HCW) were obtained from all steers at time of slaughter. After carcasses were chilled for 48 h the following measurements were obtained: 1) LM area, taken by direct grid reading of the muscle at the 12th rib; 2) subcutaneous fat over the ribeye muscle at the 12th rib taken at a location three-fourths the lateral length from the chine bone end; 3) KPH, as a percentage of HCW; and 4) marbling score (USDA, 1997). Energy gain (EG, Mcal/d) was calculated by the equation: EG = ADG^sup 1.097^ × 0.0557 × W^sup 0.75^ (NRC, 1984). Maintenance energy (EM) was calculated by the equation: EM = 0.084 × W^sup 0.75^. From the derived estimates of energy required for maintenance and gain, the NE^sub m^ and NE^sub g^ values of the diet were obtained by means of the quadratic formula: x = (-b ± [radical]b^sup 2^ - 4ac)/2c, where a = -0.41 × EM, b = 0.877 × EM + 0.41 × DMI + EG, and c = -0.877 × DMI, and NE^sub g^ = 0.877 × NE^sub m^ - 0.41 (Zinn and Shen, 1998). For calculating steer performance, BW were reduced 4% to account for digestive tract fill. Final BW was adjusted for carcass weight by dividing carcass weights by the average dressing percent. Growth performance and carcass composition data were analyzed as a randomized complete block design (Hicks, 1973) using pens as the experimental unit. Treatment effects were tested using orthogonal contrast: single-phase vs. 2 - and 3-phase strategies; and 2-phase vs. 3-phase strategies. All animal care and handling techniques were approved by the University of California Animal Care and Use Committee.

Refer: http://findarticles.com/p/articles/mi_qa4035/is_200708/ai_n19511548
by Zinn, R A, Calderón, J F, Corona, L, Plascencia, A, Et al