One challenge the beef industry faces today is the supply of cattle. The feeder calf supply available in the Southeastern USA generally originates from small herds. Groups of feeder cattle are acquired through various auction markets or buying stations and are commingled with cattle of like frame size, weight, type, and gender. After an order is grouped, the cattle may be transported over many miles, which takes several hours, to reach a preconditioning/backgrounding or finishing facility in the Plains region. These cattle typically arrive at their new destination with unknown health histories and are considered at high risk of developing bovine respiratory disease (BRD). The development of BRD involves complex interactions between respiratory pathogens and stressors.
Approaches to managing this disease generally involve preventing or minimizing exposure of the animals to the various potential pathogens, decreasing the challenge load of the potential pathogens, and increasing the level of immunity to the respiratory pathogens. Good management practices that minimize stress on cattle should also be recommended. In general, if the level of immunity in a group of cattle can be increased, especially prior to an anticipated exposure, the severity of disease and number of clinically affected animals are decreased. Hence, veterinarians focus on developing preventive health protocols to increase resistance to the common respiratory pathogens through administration of respiratory vaccines. Several of these preventive health protocols utilize modified-live viral (MLV) vaccines. One of the concerns expressed by veterinarians and producers is that stressed cattle may not respond to vaccination with optimal immunity. Thus a common practical approach is the recommendation to administer a second dose of MLV vaccine, commonly referred to as ‘REVAC’ (revaccination), to allow more animals to develop immunity and thus protection when they are exposed to respiratory pathogens under normal field situations.
Our group has been engaged in ongoing research to evaluate how common practices intended to improve immunity in high-risk calves impact health and productivity. The objective of one such study was to compare the effects of administration of a MLV vaccine containing bovine herpesvirus-1 (BHV1), parainfluenza type 3 virus (PI3 V), bovine viral diarrhea virus types 1a and 2a (BVDV1a–BVDV2a) and bovine respiratory syncytial virus (BRSV) once or twice on the health and performance of high-risk cattle (Step et al., Reference Step, Krehbiel, Burciaga-Robles, Holland, Fulton, Confer, Bechtol, Brister, Hutcheson and Newcomb2009). Six hundred twelve crossbred beef cattle (average body weight = 483 lb (217 kg)) originating from auction markets in Arkansas and Oklahoma were assembled and shipped to the Oklahoma State University (OSU) Willard Sparks Beef Research Center (WSBRC). The cattle were randomly assigned to either SVAC (vaccinated once) or REVAC (vaccinated twice, 11 days apart). The cattle were observed daily by trained clinical evaluators. The preconditioning backgrounding period was for 60 days, at which time the steers were shipped to a research feedlot for finishing. The primary arrival health care protocol at the feedlot involved vaccination with the same five-way MLV vaccine or no vaccination. Therefore, one-half of the SVAC and one-half of the REVAC calves were vaccinated at feedlot arrival, and one-half of each group received no vaccine on arrival.
There were no significant differences in performance parameters measured in the SVAC and REVAC steers during the preconditioning backgrounding period. Morbidity due to BRD was significantly lower in the SVAC cattle (SVAC = 36.3%, REVAC = 44.5%; P = 0.04), as was total morbidity (SVAC = 37%, REVAC = 44.7%; P = 0.05). The days to first treatment were not different (SVAC = 7.62 days, REVAC = 7.21 days). No cattle exhibited any clinical signs consistent with BRD during the finishing phase of production. Additionally, there were no significant differences for performance parameters measured. Interestingly, the REVAC steers had a lower feed:gain (F:G) ratio than the SVAC steers during the finishing phase. The REVAC – finishing vaccination and SVAC – no finishing vaccination had higher marbling scores than the other two treatments (Step et al., Reference Step, Krehbiel, Burciaga-Robles, Holland, Fulton, Confer, Bechtol, Brister, Hutcheson and Newcomb2009).
In conclusion, given that no cattle showed signs of BRD in the finishing phase, it is likely that the preventive health protocol administered in the preconditioning backgrounding phase of production provided health benefits during the finishing phase of production. The REVAC cattle experienced higher morbidity than the SVAC cattle during the preconditioning backgrounding phase; however, the days to first treatment were the same for both treatments and occurred prior to the second vaccination for the REVAC group. Because morbidity occurred prior to the second vaccination of the REVAC cattle, the differences could not be attributed to the second vaccination and instead were most likely an artifact of the randomization process.
Observations indicate that commingling cattle from multiple sources with unknown health histories contributes to the BRD complex. The objectives of another research project were to determine the health and performance of ranch-origin calves administered various preventive health protocols and to evaluate the effect of commingling ranch-origin calves with calves of unknown health histories (Step et al., Reference Step, Krehbiel, DePra, Cranston, Fulton, Kirkpatrick, Gill, Payton, Montelongo and Confer2008). Five hundred nine crossbred beef steers were enrolled in the study. Two hundred sixty (MARKET) originated from multiple auction markets located in the southeast and assembled in Mississippi prior to shipment to OSU WSBRC. Two hundred forty-nine steers were from one ranch (RANCH). At weaning, the RANCH steers were randomly assigned to WEAN (shipped directly to OSU WSBRC), WEANVAC45 (administered preventive health protocol and weaned at the ranch of origin for 45 days) or WEAN45 (weaned at the ranch of origin for 45 days with no administration of a preventive health protocol [vaccinations]). The preventive health protocols included administration of five-way MLV vaccine containing BHV-1, PI3 V, BVDV1, BVDV2, and BRSV, and also a seven-way clostridial bacterin/toxoid and a Mannheimia haemolytica toxoid. Steers received a five-way MLV + five-way Leptospira vaccine at 14 days after initial processing. MARKET steers served as the controls. Half of each of the ranch-origin treatment groups was commingled with MARKET steers (COMM). The WEANVAC45 steers did not receive any vaccinations upon arrival or at 14 days at the OSU WSBRC; however, an endectocide was administered at arrival processing and these steers were processed through the same processing facility (pens, alleys, and chute) as the other treatment groups.
Fourteen steers were removed during the study due to severe respiratory distress. Regarding calf origin and commingling, morbidity rate attributed to BRD was significantly different for RANCH steers (11.1%), than MARKET steers (41.9%), and COMM steers (22.6%; P < 0.05). Mortality rate attributed to BRD was significantly lower in RANCH origin steers (0%) as compared with MARKET steers (3.1%) and COMM steers (2.1%; P < 0.05). The morbidity rate attributed to BRD was significantly less for the WEANVAC45 (9.5%) and WEAN45 (5.9%) steers as compared with the WEAN steers (35.1%; P < 0.05); morbidity between WEANVAC45 and WEAN45 steers was not significantly different. Hot carcass weights and USDA Quality grades were not affected by calf origin and commingling, but USDA Yield Grade was significantly greater for RANCH steers (2.61) as compared with MARKET (1.97) and COMM steers (2.28; P < 0.001). Even though attempts were made to eliminate factors that may have affected the outcomes, the WEANVAC45 steers had significantly heavier arrival body weights than the other steers; no factor was identified that would have contributed to this difference. The average health care costs per steer were significantly higher for WEAN steers (US $13.55) than for WEANVAC45 (US $8.34) and WEAN45 (US $8.53; P < 0.05) (Step et al., Reference Step, Krehbiel, DePra, Cranston, Fulton, Kirkpatrick, Gill, Payton, Montelongo and Confer2008).
In conclusion, the management of WEANVAC45 and WEAN45 steers yielded similar benefits and an economic benefit with lower average health care costs, as compared with the management of WEAN steers. Preconditioned steers (WEAN45 and WEANVAC45) experienced fewer negative effects when they were commingled with MARKET steers than calves that were weaned and immediately shipped from their ranch of origin (WEAN).
