Effects of liver fibrosis on performance of beef cattle varies among breeds and producers

AVTRW meeting poster presentation, Moredun Research Institute, Sept 16th-17th 2019

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Introduction

This project emerged from a collaboration between Scotbeef Ltd and researchers at Moredun and SRUC. Consumers always want more information about where their food came from, and concerns of meat consumers typically focus on the health and welfare of the animals and any drugs the animal has been exposed to.

Scotbeef is one of Scotland’s largest red meat producers and currently collects extensive data on the animals slaughtered at their abattoirs. The data include, but are not limited to, data on the origins of the animal, the holding the animal was kept at, carcass parameters and performance, and carcass pathologies. There is currently no data on the drug or vaccine treatment: all of this is recorded by farmers but not passed onto Scotbeef and hence the consumer.

The ultimate aim of the project is to develop a mobile phone app that will enable farmers to record treatments and upload these records to Scotbeef’s data systems. This will enable each end product to be traced back to the farm and any drug and vaccine treatments given to the animal revealed.

The app is currently at the beta stage. In the meantime, our focus at Moredun has been the existing abattoir data and what it can tell us about treatments and disease. Our focus has been on pathologies of the liver, specifically fibrosis, which can be a result of active or past liver fluke (Fasciola hepatica) infection. Fluke are responsible for considerable health and economic costs in the sheep and cattle industries, but control is difficult. Neither sheep nor cattle appear to have effective acquired immunity; vaccine development is yet to succeed; drug resistance is growing; effective management requires also dealing with the intermediate mud snail host.

Since cattle do not appear to show effective resistance to fluke, they may be evoking some sort of tolerance mechanism- the ability to maintain health, productivity or fitness in the face of increasing stress, infection, or pathology. Promoting tolerance of fluke in cattle, through breeding or management, may be one strategy for disease control which has yet to be sufficiently explored.

Here, we aimed to (1) investigate associations between carcass pathology and performance parameters and (2) estimate among-breed and –producer variation in tolerance to liver pathology using data collected from one of Scotland’s largest abattoirs.

 

Methods

Data from 92,119 cattle slaughtered at Scotbeef Ltd in 2018 were analysed with linear mixed-effects models. The key response variables were age at slaughter (how long it takes an animal to be ready for slaughter) and daily dead weight gain. Key explanatory variables were presence/absence of liver fibrosis, abscesses and pneumonia, as well as fibrosis score (0-3). All models accounted for effects of breed and producer ID.

Since this is not a published study, and since if you’ve got this far, you’ve probably read the poster and chatted to me about the methods, I’m not putting any more details here. For more information on the analyses, contact me at adam.hayward@moredun.ac.uk.

 

Results

 

(17) age and pathology

Figure 1: Predictions from linear mixed effects models of carcass pathology and age at slaughter; points show model estimates and 95%CI. Plots in red show statistically significant associations.

 

(17) dwt and pathology

Figure 2: Predictions from linear mixed effects models of carcass pathology and daily dead weight gain; points show model estimates and 95%CI. Significant associations are shown in red.

 

(17) breed tolerance age

Figure 3: Results of a random regression model of the association between age at slaughter and fibrosis score showing variation between breeds; here the variation is non-significant (LRT = 2.95, DF = 2, P = 0.229) . The left-hand panel shows estimates from the model where the association is allowed to vary between breeds; each line represents a breed. The central panel shows a histogram of intercepts in the different breeds; i.e. it’s a histogram of age at slaughter where fibrosis score = 0 on the left-hand plot. The vertical red line shows the average age at slaughter. The right-hand panel shows the non-significant variation in slopes, represented as the difference in age at slaughter between an animal of a given breed with fibrosis score 3 and an animal of that breed with a fibrosis score of 0. For example, the vertical red line shows that animals from the average breed with a fibrosis score of 3 take 21 days longer to reach slaughter than animals from the average breed with a fibrosis score of 0.

 

(17) prod tolerance age

Figure 4: Results of a random regression model of the association between age at slaughter and fibrosis score showing variation between producers. Interpretation is as for Figure 3; in this case, there is significant variation (LRT = 65.76, DF = 2, P < 0.001) between producer slopes. 

 

(17) breed tolerance dwt

Figure 5: Results of a random regression model of the association between daily dead weight gain and fibrosis score showing variation between breeds. Interpretation is as for Figure 3; here, there is significant variation (LRT = 7.04, DF = 2, P = 0.030) between breed slopes.

 

(17) prod tolerance dwt

Figure 6: Results of a random regression model of the association between daily dead weight gain and fibrosis score showing variation between producers. Interpretation is as for Figure 3; there is significant variation (LRT = 66.42, DF = 2, P < 0.001) between producer slopes in this case.

 

Summary

What the results show

 Liver pathology, specifically fibrosis, is associated with increases in slaughter age and reductions in daily dead weight gain in beef cattle, accounting for variation between breeds and producers, and for the effect of treatment for fluke.

Further, increasing fibrosis score is association with production parameters to a different extent in different breeds and producers. In other words, animals of some breeds and from some producers seem to tolerance high levels of fibrosis: performance is not adversely affected in animals with high fibrosis scores compared to those with low or absent fibrosis. Meanwhile, animals from some breeds and producers do not seem very tolerant: animals with high fibrosis scores perform very poorly compared to those with low scores.

How we might interpret this

 Assuming that liver damage tells us something about fluke infection, the results suggest that fluke have a significant impact upon production parameters. These effects, however, are not universal, because breeds and producers differ in the extent to which liver fibrosis was associated with performance. If we can assume breed differences are largely genetic, and producer differences are largely environmental, the results suggest that tolerance of fibrosis, and potentially fluke infection, can be influenced by both genes and environment. This conclusion offers a glimpse at new methods for attenuating the impact of fluke on beef cattle performance and increasing the efficiency of food production.

 Some limitations

Liver fibrosis may be the result of factors other than fluke infection, although fluke infection is likely to be a major contributor. Further, the data do not tell us anything about whether infections are active or historical; such analysis required collection of fresh livers and enumeration of fluke. Finally on this note, higher fibrosis scores do not necessarily indicate a higher fluke burden; although some studies have shown a correlation, it may not be strong enough to draw firm conclusions.

 

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