The safety and efficacy of nitrate N supplementation to Bos indicus cattle

Benu, Imanuel (2017) The safety and efficacy of nitrate N supplementation to Bos indicus cattle. PhD thesis, James Cook University.

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The aims of this study were to determine if nitrate (NO₃) can safely replace urea as a source of nitrogen (N) and deliver an effective dose to reduce the enteric methane emissions of cattle consuming low quality forages typically in northern Australia without any negative impact on growth rates and grazing activity.

A series of four experimental studies were conducted to test the safety of nitrate supplementation in Bos indicus steers.

The first experimental study was designed to compare two methods used for the analysis of methaemoglobin (MetHb). These methods were compared to each other for use with three different species of ruminant. The accuracy, precision and correlation of a co-oximetry method for measuring MetHb concentrations in whole blood was compared to the gold standard, Evelyn and Malloy (1938) method. This study indicated that the values obtained using co-oximetry for MetHb were in good agreement with the MetHb values obtained from the Evelyn and Malloy (1938) method. Therefore, the co-oximetry method was a safer and more robust method, and could be utilised for MetHb measurement in further studies.

The second experiment examined daily nitrate dose and feeding frequency on MetHb, carboxyhaemoglobin, oxyhaemoglobin, total haemoglobin, and haematocrit concentrations in the blood of twelve Bos indicus steers. This was also correlated with the dry matter intake (DMI) of the cattle to assess feeding preference for supplemented cattle. Indwelling venous jugular catheters were fitted to the animals and blood samples were collected at two hour intervals, over a period of seven days. Increasing dose rate of nitrate increased MetHb concentration in the blood of steers. For once a day nitrate feeding, the dose rates of 40 and 50 g nitrate/day had greater impact on MetHb values compared to 0 or 30 g nitrate/day.

Increasing dose rates of nitrate also affected the daily peak MetHb values in the blood of cattle. However, no significant effects of increasing dose rate of nitrate were observed in haemoglobin, deoxyhaemoglobin, carboxyhaemoglobin, haematocrit concentrations or DMI. Twice a day feeding of nitrate decreased the formation of MetHb in the blood of Bos indicus steers. Therefore, caution should be exercised when feeding nitrate, as an NPN source to cattle grazing on low quality pastures in northern Australia.

The animals were penned individually under low physiological stress in the second experiment and this, therefore, led to the question of would happen if exercise was imposed on the animals when feeding nitrate. Twelve Bos indicus steers were used in the third study to investigate the effects of nitrate dose rates on arterial blood gas, MetHb, carboxyhaemoglobin, oxyhaemoglobin, total haemoglobin, haematocrit, heart rate, and respiration rate after exercise. Increasing dose rate of nitrate decreased pO₂ in the blood of cattle. Steers treated with 50 g nitrate/day had a decrease in oxyhaemoglobin and a concomitant increase in MetHb and carboxyhaemoglobin compared with steers treated with 0 or 30 nitrate/day. Steers dosed with 50 g nitrate/day exhibited greater increases in heart rate immediately after the exercise regimen compared to those animals dosed with 0 or 30 g nitrate/day. However, no difference was detected in respiration rate, or rectal temperature between treatments, after the exercise regimen. Therefore, feeding nitrate to Bos indicus cattle resulted in a decrease in the oxygen carrying capacity of their blood.

In the last fourth experiment, ten Bos indicus steers were used to determine the effect of nitrate, or no nitrate, supplementation on MetHb, carboxyhaemoglobin, total haemoglobin, oxyhaemoglobin concentrations, DMI and body weight (BW) in cattle over a 70 day period. Blood samples were collected from the jugular vein of the animals before and at two hours intervals after treatments dosages were applied at three times (1100, 1300 and 1500h), on days 10, 30, 50 and 70. Nitrate treatment caused a greater increase of mean MetHb, peak MetHb and carboxyhaemoglobin concentrations in the blood compared to the other group which received no nitrate. Nitrate supplementation at a rate of 7.1 g/kg DMI produced a consistent MetHb profile that appeared to return to normal concentrations within 24 h. These results suggest that there was no apparent adaptation to nitrate feeding by rumen microbes. However, there was no significant effect of nitrate on the total haemoglobin, oxyhaemoglobin concentrations, DMI and BW of cattle. Consequently, there was no production advantage to feeding nitrate compared with feeding an equivalent amount of urea to steers.

Overall findings, suggest that nitrate supplementation at the rate of 50 g/day to Bos indicus cattle, consuming low quality forage in northern Australia, increased MetHb concentration in the blood and could have detrimental effects on their health. These studies found that another dosage regime could be implemented of twice daily dosing that would reduce toxicity of nitrate supplementation.

Item ID: 53105
Item Type: Thesis (PhD)
Keywords: Bos indicus, Brahman, carbon, cattle, Flinders grass, Iseilema spp., methaemoglobin, methane, nitrite, nutrition, supplements
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 4: Benu, I., Callaghan, M.J., Tomkins, N., Hepworth, G., Fitzpatrick, L.A., and Parker, A.J. (2016) The effect of feeding frequency and dose rate of nitrate supplements on blood haemoglobin fractions in Bos indicus cattle fed Flinders grass (Iseilema spp.) hay. Animal Production Science, 53 (10). pp. 1605-1611.

Date Deposited: 11 Apr 2018 22:13
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070204 Animal Nutrition @ 100%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8303 Livestock Raising > 830301 Beef Cattle @ 100%
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