The association between calfhood bovine respiratory disease complex and subsequent departure from the herd, milk production, and reproduction: an observational, retrospective study
By Aaron P. Schaffer, Robert L. Larson, Natalia Cernicchiaro, Gregg A. Hanzlicek, Steven J. Bartle, Daniel U. Thomson
Bovine respiratory disease complex (BRDC) is a multifaceted disease caused by a combination of viral and bacterial pathogens that affect immunosuppressed calves. Bovine respiratory disease complex is associated with considerable economic costs. However, it is difficult to determine a true cost of calfhood BRDC as little is known about the long term implications on subsequent cow productivity. Because of the excellent health and production records kept by individual dairies, there is opportunity to evaluate associations between demographic and management factors, and different production and reproduction parameters. Therefore, a retrospective, observational study was conducted to describe the frequency of calfhood BRDC occurrence in Holstein replacement dairy heifers and to determine the association between producer diagnosed BRDC prior to 120 d of age with the subsequent risk of departure from the herd (DFH), milk production, and calving interval on a large commercial dairy cattle operation in central Utah.
Details of the variable definitions and complete description of the many comparisons that were evaluated can be found in the complete article (Journal of the American Veterinary Medical Association, In Press). This summary will focus on the effects of calf hood BRDC and departure from the herd (DFH) and first lactation production.
The data for this study consisted of records from a single, commercial 5,000 cow dairy from January 1, 2007 to November 11, 2012. All calves were born on the farm and raised according to current industry standards. Calves were housed in individual hutches from shortly after birth until they were weaned and then moved into group housing at approximately 60 d of age. At 120 d of age, calves were moved into open-lot grower pens.
Of the 14,024 total animals included in this study population, 6.2 percent (868) contracted bovine respiratory syncytial virus prior to 120 d of age (BRDC120). Of those animals, 177 died, resulting in an overall mortality risk of 1.3 percent and a case fatality risk of 20.4 percent. The highest incidence rate of BRDC was during the first wk of age at 0.24 cases per 100 animal-days and the lowest incidence rate of BRDC was during the ninth and 18th wk of age at zero cases per 100 animal-days.
Eighteen percent (2,590/14,024) of all heifers departed from the herd prior to first calving. Only 17 percent (2,288/13,156) of heifers not diagnosed with BRDC120 departed prior to first calving compared with 35 percent (302/868) heifers that had been diagnosed with BRDC120. Of the 868 animals diagnosed with BRDC120, 52% (454/868) became ill pre-weaning and 48 percent (414/868) became ill post-weaning. Of the calves that became ill pre-weaning, 44 percent (201/454) departed from the herd prior to first calving compared to 24 percent (101/414) of the calves that became ill post-weaning.
A total of 7,287 cows had complete data and were included in the analysis of DFH between first and second calving, and of those cows, 6 percent (430/7,287) had been diagnosed with BRDC120. Of those with BRDC120, 29 percent (124/430) departed from the herd between first and second calving compared to 21 percent (1,418/6,857) of the cows that were not diagnosed with BRDC120.
Milk production was adjusted by DHI for location, age, and season of calving to a mature cow basis and projected to a 305 day lactation production to generate a 305 mature equivalent value (305 ME). In total, 4,005 cows had complete data sets for lactation-one production and were included in the analysis of lactation-one milk production, and of those cows, 7 percent (261/4,005) had been diagnosed with BRDC120. The statistical analysis indicated that the occurrence of BRDC was associated with a 233 ¬± 113 kg (513 ± 249 lb) decrease in 305 ME lactation-one production (P = 0.04). However, there was not an association between the occurrence of BRDC120 and 305 ME production in lactation-two (P = 0.67). Birth year and calving interval were both significantly associated with lactation-one and lactation-two production.
Our study found that calfhood BRDC is associated with an increase in the risk of DFH prior to first calving and between first and second calving. In addition, BRDC occurrence pre-weaning was associated with an increased risk of DFH prior to first calving compared to BRDC post-weaning, but the age at BRDC occurrence was not associated with DFH between first and second calving. Calfhood BRDC was associated with a decreased lactation-one milk production but a decrease in production was not noted in subsequent lactations. Calfhood BRDC occurrence in replacement dairy heifers has significant long-term effects on subsequent cow departure from the dairy herd and milk yield during the first lactation, which could impact on dairy profitability.