Fodder beet’s effect on the liver

2 September 2019

What happens to a cow’s liver during the transition to a fodder beet diet? DairyNZ has been investigating.

 

Talia Grala, DairyNZ scientist.

Key points

  • Recent DairyNZ research has investigated the effect of fodder beet on cows’ liver metabolism.
  • Liver markers of stress do not increase during cows’ transition to fodder beet.
  • Liver function markers in the blood are minimally affected on a full allocation of fodder beet.
  • Cell protective mechanisms increase in the liver, but only in the short term.
  • Overall, fodder beet has only minor effects on liver health. DairyNZ recommends transitioning cows onto a fodder beet diet gradually to minimise ruminal acidosis and liver dysfunction.

Fodder beet benefits and risks

Fodder beet’s uptake has been exponential in New Zealand, as more dairy farmers adopt this high-quality, high-yield option for

Dawn Dalley

Dawn Dalley, DairyNZ senior scientist.

supplementary feed. The fodder beet bulb has a low nitrogen content and offers flexibility in that it can be either grazed in the paddock or lifted for storage.

However, the crop comes with risks. The beet’s bulb is 50 to 70 percent sugar, so is both palatable and rapidly fermented in the cow’s rumen. Rumen microbes must adapt to this high sugar content. If cows eat high quantities of fodder beet before their rumen microbes have adapted, they can develop ruminal acidosis and liver dysfunction.

Overseas studies have shown that acidosis can cause certain bacteria in the rumen to release toxins1, which trigger inflammation and stress throughout the body. Acidosis can change the metabolism of fat in the liver2. This overseas research involved cows with clinical ruminal acidosis, produced by purposely feeding a high-sugar diet. At DairyNZ, we wanted to know whether similar responses occur when cows transition onto fodder beet.

Testing liver stress markers

To better understand the effects of fodder beet on liver health, DairyNZ carried out a levy-funded trial* in May 2016. We compared non-lactating cows transitioning onto a diet of fodder beet (eight kilograms of dry matter per cow – 8kg DM/cow) and pasture silage (4kg DM/cow), with cows maintained on a diet of pasture (8kg DM/cow) and supplemental maize silage (4kg DM/cow). The cows were transitioned onto fodder beet over a 14-day period. We sampled blood and took liver biopsies twice: halfway through the transition (day seven), and after the cows had been on the full allocation of fodder beet for seven days (day 21).

We tested six biomarkers of liver function at both time points. Concentrations of these biomarkers typically increase in the blood when the liver is damaged, except for total protein (TP) concentrations, which decrease (Table 1).

Table 1.

Transitioning stage — results

During the transitioning stage, three markers – TP, haptoglobin (HP) and gamma-glutamyl transferase (GGT) – did not differ between cows fed fodder beet and those fed pasture. However, concentrations of the other three – aspartate aminotransferase (AST), bilirubin and glutamate dehydrogenase (GLDH) – were lower in the cows fed fodder beet than in pasture-fed cows. This indicates the cows were adapting well to the fodder beet diet, and no negative effects were detected in their blood during the transition.

Full beet allocation — results

In cows on the full fodder beet allocation, GGT remained unchanged, while AST, bilirubin and GLDH remained lower in cows fed fodder beet than in pasture-fed cows. However, TP was also lower in cows fed fodder beet than in pasture-fed cows, which indicates the liver’s ability to produce proteins is impaired. Additionally, HP increased in cows fed fodder beet, which indicates a response to inflammation (Figure 1). HP is also reported to have a role in lipid metabolism and development of fatty liver3.

Figure 1.

Recommendation for transitioning non-lactating cows to fodder beet

When cows start being fed a high-sugar diet, the most important changes to their rumen microbe population take approximately 14 days4. This is why DairyNZ currently recommends starting with one to two kilograms of dry matter (kg DM) fodder beet allocated behind a wire, then increasing by 1kg DM every second day for 14 days (providing all cows are eating the bulbs) until cows are eating about 9 to 10kg DM/day.

Measuring liver gene expression

Not all the genes of a cell (the DNA) are used at the same time. By measuring which genes are being used (or ‘expressed’) we can determine what processes are happening in a particular tissue (Figure 2).

Figure 2.

 

To determine if the altered production of liver stress markers affected the function of the liver, we measured the expression of key genes. We targeted genes that code for enzymes involved in glucose synthesis, lipid synthesis, fatty acid breakdown, cell stress and inflammation. Our first objective was to determine if fodder beet results in liver stress, and secondly, to determine if normal liver functions are affected by the transition.

The main difference between cows fed fodder beet and those on pasture was the expression of two genes involved in the stress response of the endoplasmic reticulum
(Figure 3). This stress response is initiated when the liver cells become stressed and produce misfolded proteins that do not function properly. These proteins can accumulate and cause cell death.

As part of the experiment, we also measured the expression of genes involved in the breakdown of fatty acids into ketones. Once cows were on the full allocation of fodder beet, these genes were more highly expressed in cows fed fodder beet than pasture. This indicates a change in the amounts of various volatile fatty acids absorbed from the rumen, due to differences in rumen fermentation between fodder beet-fed and pasture-fed cows5.

Expression of the other genes measured (those involved in glucose synthesis and fatty acid synthesis) didn’t differ between the pasture and fodder beet cows. This indicates that fodder beet has no adverse effects on glucose synthesis or excessive fat synthesis in the cow’s liver.

Careful transition, minor effects

Figure 3.

DairyNZ’s research shows that, when cows are properly transitioned onto fodder beet, there is only a minor effect on the liver. So, although transitioning cows onto fodder beet has to be managed carefully, the risk to cows is low if farmers follow the current recommendations.

To learn more about fodder beet, follow these links:

* This research was an aligned project with the DairyNZ-led Forages for Reduced Nitrate Leaching programme (FRNL). Learn more at dairynz.co.nz/frnl

 

References

  1. Plaizier, J. C., D. O. Krause, G. N. Gozho, and B. W. McBride. 2008. Subacute ruminal acidosis in dairy cows: The physiological causes, incidence and consequences. Veterinary Journal 176(1):21-31.
  2. Xu, T., H. Tao, G. Chang, K. Zhang, L. Xu, and X. Shen. 2015. Lipopolysaccharide derived from the rumen down-regulates stearoyl-CoA desaturase 1 expression and alters fatty acid composition in the liver of dairy cows fed a high-concentrate diet. BMC Veterinary Research 11(52). https://doi.org/10.1186/s12917-015-0360-6.
  3. Graugnard, D. E., K. M. Moyes, E. Trevisi, M. J. Khan, D. Keisler, J. K. Drackley, G. Bertoni, and J. J. Loor. 2013. Liver lipid content and inflammometabolic indices in peripartal dairy cows are altered in response to prepartal energy intake and postpartal intramammary inflammatory challenge. Journal of Dairy Science 96(2):918-935.
  4. Gibbs, S. J., and B. Saldias. 2014. Fodder beet in New Zealand dairy industry. Paper 4.3 in Proceedings of the South Island Dairy Event, Invercargill, New Zealand.
  5. Pacheco, D., S. Muetzel, S. Lewis, D. Dalley, M. Bryant, and G. C. Waghorn. 2019. Rumen digesta and products of fermentation in cows fed varying proportions of fodder beet (Beta vulgaris L.) with fresh pasture or silage or straw. Animal Production Science (Accepted).
  6. Ringseis, R., D. K. Gessner, and K. Eder. 2014. Molecular insights into the mechanisms of liver-associated diseases in early-lactating dairy cows: hypothetical role of endoplasmic reticulum stress. Journal of Animal Physiology and Animal Nutrition. https://doi.org/10.1111/jpn.12263.

This article was originally published in Technical Series September 2019

 

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