Ruminal acidosis and other metabolic disorders in cows grazing fodder beet crops: what do we know so far?

It is important to gradually transition cows onto fodder beet to allow the adaptation of rumen microbes to the high soluble sugar content of the crop to prevent ruminal acidosis and other non-acidosis related disease (e.g., liver dysfunction, chronic inflammation, deferred ketosis). While there is limited information available on the effects of fodder beet on the incidence of ruminal acidosis and other diseases there is increasing farmer interest regarding the health implications of feeding the crop. It is well known that in lactating animals, sub-acute ruminal acidosis (SARA) has production implications and can affect a significant of the herd. While the use of fodder beet during late lactation is increasing, the main period of time that cows are fed fodder beet is during the dry period prior to calving and there is minimal published information about this period.

Feeding fodder beet to non-lactating cows

While the implications of SARA on non-lactating cow performance are not well researched, it has been suggested that the body condition score gain could be affected by SARA. Cows with SARA may have reduced intake and a reduction in nutrient digestion which would affect the available nutrients are body condition gain. It was mentioned in the article by Dalley (2016) that detecting SARA in non-lactating cows is challenging because the best diagnostics appear to be VFA, lactic acid and ammonia concentrations, and rumen pH, all of which are difficult to measure as mentioned in artefact 7. There has been little research on the cause and nature of acidosis induced by fodder beet feeding, however, at DairyNZ in 2015 there were significant differences in the diurnal pattern of rumen pH in cattle offered fodder beet either during lactation or the dry period. As shown in Figure 1, in eight non-lactating cows where rumen pH was being monitored, the pH of three remained in the safe zone, on fell into the risk zone and four dropped into the danger zone.

Figure 1: Diurnal variation in rumen pH in eight non-lactating dairy cows offered a diet of 80% fodder beet and 20% cereal straw (Dalley, 2016).

It was suggested that the cause of the decline in rumen pH when fodder beet is fed is due to the production of lactic acid in the rumen, production of large amounts of weak volatile fatty acids and a failure to produce enough buffering in the rumen through saliva.

Feeding fodder beet to lactating cows

Research conducted at DairyNZ in cows fed fodder beet during late-lactation, offering above 30% of the diet (5.4 kg DM/cow/day) as fodder beet resulted in an increased incidence of acidosis in lactating cows fully transitioned to fodder beet. In the same study, a significant reduction in two amino acids (AA;arginine and citrulline) was observed (Pacheco et al., 2016) when fodder beet was included at higher levels. Recent reviews have proposed that some of the ‘non-essential’ AA play a major role as regulators of metabolism and studies in pregnant sheep have shown that arginine supplementation is associated with increases in birth weight of ewe lambs and foetal fat reserves. Therefore, research assessing the effects of feeding fodder beet to pregnant cows on the development and survival of their calves is needed. The long-term implications of the reduced arginine and other minerals require further study to ensure it is not having negative effects on metabolic processes. It is recommended that for this reason, farmers should err on the side of caution when allocating fodder beet to lactating cows. The impact of fodder beet allocation on calcium, phosphorus, and protein and fibre intake, relative to requirements could also have negative implications that we don’t know about. As shown in Table 2 when feeding fodder beet at greater than 40% of the diet this results in CP content, magnesium and phosphorus levels in the diet being lower than required for the lactating cow.

Table 1: Dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), calcium (Ca), magnesium (Mg) and phosphorus (P) intake of lactating dairy cattle offered increasing proportions of fodder beet in late lactation (Dalley, 2016).

Fodder beet	DMI	Pasture DMI	Fodder beet DMI	CP	NDF		Ca		Mg	P
% of diet	Kg/cow			% DM
0	18	18	0	19.1		45	0.79	0.25		0.34
20	18	14.4	3.6	17.0		39	0.76	0.29		0.30
30	18	12.6	5.4	15.9		36	0.75	0.31		0.28
40	18	10.8	7.2	14.9		33	0.73	0.33		0.26
Lactating cow requirements				16-18		>30	0.6-0.8	0.28		0.3-0.35

Fodder beet has become a really important crop in Southern farming systems and the lack of information available regarding risks associated with feeding fodder beet is a concern for dairy farmers relying on the crop. Therefore, dairy farmers are relying on research organisations such as DairyNZ to fill in research holes about the crop.

REFERENCES

Dalley, D. (2016). The foibles of fodder beet and other forage crops – animal and environmental considerations for successfully feeding forage crops. Proceedings of the SIDE Conference.

Pacheco, D., Waghorn, G. and Dalley, D. (2016). BRIEF COMMUNICATION: Plasma amino acid profiles of lactating dairy cows fed fodder beet and ryegrass diets. Proceedings of the New Zealand Society of Animal Production 76, 62-64.

A review: Physiological parameters to diagnose sub-acute ruminal acidosis in dairy cows

Ruminal acidosis is a bovine disease that occurs when there is a build-up of lactic acid in the rumen resulting in a decrease in rumen pH (Underwood, 1992). A build-up of lactic acid occurs when dietary carbohydrates are rapidly fermented in the rumen. This is typically a result of a diet with readily soluble carbohydrate content such as concentrates typically fed in housed cows overseas (Palizier et al., 2008) however; anecdotal evidence indicates that the recent uptake of grazing fodder beet in New Zealand has resulted in cows experiencing ruminal acidosis. Ruminal acidosis can be prevented by gradually transitioning cows onto the feed which allows the rumen microflora to adjust (Kleen et al., 2003) as well as feeding an adequate level of fibre in the diet to encourage rumination (Nocek, 1997). While appropriate management of cows grazing feed high in readily soluble carbohydrates is the best defence against rumen acidosis (Kleen et al., 2003), sub-acute acidosis is difficult to detect and clinical acidosis can be life-threatening. Due to the diet causing a decrease in ruminal pH it has been suggested that it may be possible to diagnose SARA by randomly sub-sampling the herd and measuring ruminal pH (Morgante et al., 2009). Sub-acute ruminal acidosis is indicated by a ruminal pH of 5.0-5.5 (Nocek, 1997; Kleen et al., 2003). The symptoms include decreased dry matter intake, reduced milk fat, diarrhoea, and loss of body condition (Nocek, 1997; Kleen et al., 2003; Palizier et al., 2008). Many cases of SARA may not be detected, as the current field diagnosis of SARA is not clearly defined and depend on ruminal pH measurements which are invasive, costly and are primarily suited for research purposes (Palizier et al., 2008). Therefore, measuring ruminal pH is not a practical tool for farmers to diagnose SARA related illness (Danscher et al., 2015). Various physiological parameters have been investigated to diagnose SARA however; the results have been conflicting (Enemark et al., 2004; Palizier et al., 2008; Morgante et al., 2009; Li et al., 2012; Danscher et al., 2015). The purpose of this review is to identify the physiological parameters that have been investigated to date and which of these are likely to be most accurate and practical for use on farm.

Faecal pH

Danscher et al. (2015) investigated the effects of SARA on the physiological parameters, blood, faeces and urine. In the study by Danscher et al. (2015) faecal pH was lower in cows with SARA. This is in agreement with the study by Morgante et al., (2009) however, conflicts with the results by Li et al. (2012) and Enemark et al. (2004) who showed no effect of SARA on faecal pH. Danscher et al. (2015) suggested that high soluble carbohydrate content in the diet could result in carbohydrates bypassing rumen fermentation, with subsequent increased fermentation and volatile fatty acid production in the hindgut explaining the reduction in faecal pH (Morgante et al., 2009; Danscher et al., 2015). Therefore, the discrepancy between studies in the relationship between SARA and faecal pH could be explained by differences in diet composition and therefore, faecal pH may not be an accurate predictor of SARA (Li et al., 2012).

Urine pH

In agreement with Gianesella et al. (2010), Danscher et al. (2015) also found that cows with SARA had lower urine pH than control cows. However, this is in disagreement with the study by Morgante et al. (2009) and Rouche et al. (2005) who reported no change in urine pH associated with SARA. Biologically, the effect of SARA on urine pH shown by Gianesella et al. (2010) and Danscher et al. 2015 can be explained as a response to decreased dietary cation-anion difference in cows with SARA which results in high blood acidity stimulating acid secretion by the kidneys and a subsequent decrease in urine pH (Danscher et al., 2015). As supported by Enemark et al. (2004), Morgante et al. (2009) described this as a difference in dietary composition and therefore, concluded that urinary pH was not suitable for predicting low ruminal pH due to the lack of a consistent relationship between the two.

Although there was an association between SARA and decreased faecal and urinary pH in the study by Danscher et al. (2015), the decreases were small and it is doubtful whether these decreases were large enough to be of diagnostic value. The conflicting results from previous studies also emphasises the issues associated with using these physiological parameters as indicators of SARA under field conditions (Enermark et al., 2004; Rouche et al., 2005; Morgante et al., 2009; Gianesella et al., 2010; Li et al., 2012; Danscher et al., 2015). More research is needed to determine if physiological parameters could be suitable indicators of SARA. However, it could be argued that the feeding situation influences the physiological parameters and therefore, the usefulness of physiological parameters to detect SARA would need to be tested under conditions similar to those experienced when grazing fodder beet, if these indicators were to have a practical application.

REFERENCES

Danscher, A. M., Shucon, L. Andersen, P. H., Khafipour, E. Kristense, N. B. and Plaizier, J. C. (2015). Indicators of induced subacute ruminal acidosis (SARA) in Danish Holstein cows. Acta Veterinari Scandinavica 57, 39-53.

Enemark, J., Jorgensen, R. and Kristensen, N. (2004). An evaluation of parameters for the detection of subclinical rumen acidosis in dairy herds. Veterinary Research Communications 28, 687-709.

Gianesella, M., Morgante, M. Cannizzo, C. Stefani, A. Dalvit, P. and Messina, V. (2010). Subacute ruminal acidosis and evaluation of blood gas analysis in dairy cow. Veterinary Medicine International, 1-4.

Kleen, J. L., Hooije, G. A., and Rehage, J. (2003). Subacute ruminal acidosis (SARA): a review. Journal of Veterinary Medicine, A, Physiology, pathology, clinical medicine, 50, 406-414.

Li, S., Gozho, G. N., Gakhar, N., Khafipour, E., Krause, D. O. and Plaizier, J. C. (2012). Evaluation of diagnostic measure for subacute ruminal acidosis in dairy cows. Canadian Journal of Animal Science 92, 353-364.

Morgante, M., Gianesella, M., Casella, S., Ravarotto, L., Stelletta, C. and Giudice, E. (2009). Blood gas analyses, ruminal and blood pH, urine and faecal pH in dairy cows during subacute ruminal acidosis. Comparative Clinical Pathology 18, 229-232.

Nocek, J. E. (1997). Bovine acidosis: implications of laminitis. Journal of Dairy Science 80, 1005-1028.

Plaizier, J., Keunen, D. O., Gozho, G. N. and McBride, B. W. (2008). Subacute ruminal acidosis in dairy cows: the physiological causes, incidence and consequences. Veterinary Journal 176, 21-31.

Underwood, W. J. (1992) Rumen lactic acidosis. Part I. Epidemiology and pathophysiology. Compendium on continuing education for the practising veterinarians 14, 1127-1133.

Interview with Kevin Lawrence

Following on from the last blog summary where I identified that some farmers have had great success with feeding fodder beet and others had faced large fatalities I wanted to talk to some industry experts about whether they considered the deaths to have been completely avoidable or that misleading information is available regarding the management of the crop.

On the 17^th July 2016 I met with Kevin Lawrence. Kevin Lawrence is a Senior Lecturer in Pastoral Livestock Health at Massey University. I spoke with Kevin Lawrence about his experience with feeding Fodder Beet following issues in the 2014 season. Dairy cows from Massey University’s No. 1 Dairy farm were winter grazed on fodder beet at Keebles. During the wintering period there were several fatalities on the crop. Kevin Lawrence identified poor management to have been the cause of death on the crop and said “the deaths were completely avoidable”. Firstly, Kevin identified that there was an issue with crop allocation. Because there was not enough room on the crop for all cows to graze simultaneously this resulted in some cows eating more than their allocated amount while others missed out. He identified this as a management issue that caused cows to gorge themselves on the crop and rumen acidosis resulting followed by death of the cow. He suggested that cows should never be fed hungry and supplementary feed should be fed before the fodder beet allocation. He also suggested the use of a headland to reduce competition and allow all cows to graze at once, reducing the potential for cows to over-eat. An additional recommendation which was carried out at Keebles was to allocate the crop perpendicular to the direction of the rows that the crop is sown as shown in Figure 1.

Figure 1: Recommended fodder beet break fencing alignment. Perpendicular to the rows of sown fodder beet as indicated by the two red lines.

Secondly, the biggest loss of animals was as a result of flooding where the cows were taken off the crop for a period of several days and then placed straight back onto the crop. He suggested that under these circumstances the cows should be “re-introduced” back on the crop, rather than allocating the same amount as when they were removed from the crop. Additionally, for these circumstances as well as transitioning cows onto the crop Kevin suggested developing a method for farms to detect when cows have transitioned using something that can be easily tested such as faeces, urine or milk.