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.