Search
Author
Title
Vol.
Issue
Year
1st Page

# Journal of Animal Science - Article

1. Vol. 87 No. 1, p. 314-327

Published: December 5, 2014

2 Corresponding author(s):
View
Share

doi:10.2527/jas.2008-1201

# Feedlot health and performance effects associated with the timing of respiratory disease treatment1

1. A. H. Babcock*†,
2. B. J. White*2,
3. S. S. Dritz,
4. D. U. Thomson* and
5. D. G. Renter
1. Department of Clinical Sciences, and
Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan 66506

## Abstract

Generalized linear mixed models were developed using retrospective feedlot data collected on individually treated cattle (n = 31,131) to determine whether cattle performance and health outcomes in feedlot cattle were associated with timing of treatment for bovine respiratory disease (BRD) during the feeding phase. Cattle that died at any point during the feeding phase were removed from the analysis. Information on individual animal performance (ADG, HCW, quality grade, yield grade) and health outcomes (treatments) were incorporated into an economic model that generated a standardized net return estimate for each animal. Prices were standardized to minimize variation between economic outcomes due to market conditions allowing direct comparisons of health and performance effects between animals. While controlling for sex, risk code, and arrival BW class, potential associations between net returns and the timing of BRD identification were investigated using 2 categorical variables created to measure time: 1) weeks on feed at initial BRD treatment, and 2) weeks from BRD treatment to slaughter. The first model using net return as the outcome identified an interaction between weeks on feed at initial BRD treatment and animal arrival BW. Cattle with arrival BW between 227 and 272 kg (5WT) and 273 and 318 kg (6WT) displayed decreased net returns (P < 0.05) if treated during wk 1 as compared with subsequent weeks in the first month of the feeding phase. The cattle with BW between 319 and 363 kg (7WT) and 364 and 408 kg (8WT) exhibited decreased net returns (P < 0.05) if treated during the later weeks of the feeding phase compared with earlier in the feeding phase. The number of times cattle were treated contributed to variation in net returns for the 5WT and 6WT cattle. For the 7WT and 8WT cattle, HCW was the main factor contributing to decreased net returns when cattle were treated late in the feeding phase. The second model identified an interaction between weeks from BRD treatment to slaughter and arrival BW. The 181 to 226 kg of BW, 5WT, 6WT, 7WT, and 8WT cattle all exhibited decreased net returns (P < 0.05) when cattle were on feed fewer weeks from BRD treatment to slaughter. Cattle with more weeks on feed between BRD treatment and slaughter had greater HCW, decreased ADG, and more total treatments compared with cattle treated closer to slaughter. This research indicates that timing of initial BRD treatment is associated with performance and health outcomes.

### Assessment of Effects of WKTS

An interaction between WKTS and arrival BW class was identified, likely related to the biological differences among cattle in different arrival BW. The lighter BW classes had fewer cattle treated close to slaughter (e.g., 4WT wk 1 to 7), as compared with heavier cattle that had very few cattle treated far from slaughter (e.g., 7WT during wk 44 to 37). Sparseness of data for these weeks likely caused the relationship between estimated net returns and WKTS category to differ by BW class. This effect was evident when we truncated the data set to only wk 10 to 35 (93% of the data) and the interaction of WKTS and BW class was no longer present (data not shown). For all 5 BW classes that exhibited a significant WKTS effect, there was a similar pattern of decreased estimated net returns when cattle were slaughtered closer to their first BRD treatment date and greater net returns when slaughtered further from initial treatment.

Four performance factors were likely influencing differences in estimated net returns between WKTS for all BW classes: times treated, HCW, days on feed from arrival to slaughter, and ADG. Hot carcass weight was less when cattle were treated closer to slaughter. The reduction in total BW gain (as judged by HCW) may be related to the decreased time between treatment and slaughter that cattle have to regain BW lost after the disease event. Roeber et al. (2001) found that calves visiting the hospital 2 or more times had decreased HCW compared with healthy cattle and no statistical difference compared with cattle treated only once. Our data showed that differences in HCW among sick cattle were associated with how long the cattle were on feed from treatment to slaughter.

Days on feed tended to be less as cattle were treated closer to slaughter. Inferences from this should be carefully interpreted because treatment date could influence the slaughter date, thereby modifying the days on feed. Cattle in this feedlot were slaughtered in subsets within pens based on estimated level of maturity, and across all BW classes cattle treated late in the feeding phase were slaughtered sooner.

Average daily gain displayed an ascending pattern between WKTS categories as cattle were treated closer to slaughter. This result is somewhat surprising because cattle treated closer to slaughter displayed decreased HCW. However, combining this with the fact that these cattle were on feed fewer days, the overall affect was an increase in ADG over the entire feeding period. Because there were no differences in CYG among WKTS categories, it can be presumed that cattle were slaughtered at a similar degree of physiologic maturity. Thus, cattle treated farther from slaughter required more days on feed to finish; even though they finished with a heavier HCW, they were less efficient (in terms of ADG). Several authors (Wittum et al., 1996; Gardner et al., 1999; Thompson et al., 2006) have illustrated that a BRD event causes a depression in BW gain. Cattle treated early in the feeding phase (further from slaughter) have more days for a decreased rate of BW gain, causing them to require greater days on feed, yet decreased ADG compared with cattle treated in close proximity to slaughter. The number of times animals were treated displayed a descending pattern over WKTS categories. This finding could be attributed again to the days at risk for further treatment.

### Conclusions

Evaluating differences in estimated net returns relative to treatment from arrival time (WKFA) and slaughter (WKTS) illustrated a significant interaction with arrival BW class. When analyzing differences in performance and health outcomes, the only variables that significantly differed between any of the weeks on feed categories were number of times treated (WKFA and WKTS), days on feed (WKTS only), ADG (WKTS only), and HCW (WKFA and WKTS). Both sets of analyses indicated that the timing of initial BRD treatment is associated with health and performance outcomes.

In conclusion, we found that disease timing, when measured relative to arrival and slaughter, affects performance and health outcomes. Although our data were derived from a single feedlot, we have demonstrated that the number of times cattle are treated and HCW appear associated with weeks from arrival to first treatment. Cattle treated further from slaughter had greater estimated net returns related to an increased HCW that appeared to offset increased costs due to more treatments, longer days on feed, and decreased ADG. Further insight into the relationship between BRD timing and performance and health variables could lead to management options that more effectively mitigate the economic impact of this extremely important disease syndrome in feedlot production systems.

Key Words