Blood parameters of young calves at abattoirs are related to distance transported and farm of origin

Abstract

Nonreplacement dairy calves, or bobby calves, are fasted and transported to abattoirs from as young as 5 d of age in Australia. The aims of this cross-sectional observational study were (1) to assess the welfare status, as measured by blood parameters, of bobby calves in the commercial supply chain after transport and lairage, and (2) to assess whether distance and duration of transport are risk factors for poor bobby calf welfare, as measured by blood parameters. We hypothesized that bobby calves transported greater distances would be more likely to show evidence of compromised welfare, as measured by blood indicators of hydration, energy status, and muscle fatigue or damage. We also hypothesized that there would be a large amount of variability in indicators of energy status between calves from different farms. We analyzed blood samples collected at slaughter over a spring and an autumn calving period from 4,484 Australian bobby calves aged approximately 5 to 14 d old from 3 different states, after transport, fasting, and lairage. Packed cell volume (PCV), plasma glucose, and serum urea, total protein, β-hydroxybutyrate (BHB), and creatine kinase (CK) were measured. Radio frequency identification ear tag data were used to estimate the distance that the calves were transported and to identify the farm of origin. Data were analyzed using linear mixed models, except for BHB, which was analyzed using a Goodman-Kruskal gamma test due to left censoring of the data. Twelve percent of calves showed evidence of anemia (PCV less than 0.23 L/L), and 11% had urea concentrations consistent with dehydration (urea more than 7.7 mmol/L). Thirty-six percent of calves had CK activity above normal resting values, and 1% of calves had CK >2,000 U/L, indicating muscle fatigue or damage. Distance transported had significant effects on all blood variables except urea and BHB. With increasing distance transported, calves were more likely to show evidence of a negative energy balance (low plasma glucose) or dehydration (high PCV or total protein). The estimated effect of distance overall was small, but for calves transported more than 500 km, plasma glucose concentration declined more per kilometer. The calves' farm of origin accounted for a reasonable amount of the random variation between calves for plasma glucose (20%). Our results suggest that longer transport distances may increase the risk of poor calf welfare (dehydration, negative energy balance) after transport, and on-farm calf management (e.g., nutrition, timing of feeding before transport) may affect transported calves' energy status; improving this area could result in better energy availability during fasting.