summer phosphate supplementation of grazing beef cattle in zimbabwe

Phosphate supplementation for beef cattle on range

By Eddington GororoChinhoyi University of Technology, Zimbabwe

E-mail: [email protected]

Extensive areas of phosphorus-deficient soils occur throughout the world, especially in

tropical and subtropical areas (Zimbabwe included), and a deficiency of phosphorus

can be regarded as the most widespread and economically important of all the

mineral disabilities affecting grazing livestock (McDonalds et al, 2010). Phosphorus is

the most significant nutrient in short supply on green summer grazing. Summer

phosphate supplementation of beef cattle offers a simple and relatively cheap means

of increasing returns by a very considerable margin. Research in the sour-veld and

mixed-veld (Agro-ecological Zones I-III) areas of the country has indicated that

phosphorous supplementation in summer can result in increases in weight gains, in

fertility and in calf viability (Gammon, 1993). However, cattle have shown little or no

response to phosphorous supplementation in the sweetveld (mostly natural farming

regions 4 and 5) of the low veld areas of Zimbabwe.

The heavily leached soils of the high and middle veld areas and the resultant forages

are low in phosphorous and have for a long time been held responsible for low

production and reproduction problems in grazing cattle. For instance, in 1929,

Bisschop and DuToit showed that phosphorous (steamed bone meal) supplementation

increased weight gains of oxen by 30%, while supplemented cows weighed 20% more

and produced 30% more calves (van Niekerk, 1978). Following extensive research on

the subject at both Makoholi and Grasslands Research Stations, Ward (1968) and Grant

(1976) reported that phosphorous supplementation of breeding stock increases

summer gains by 18-45kg, calving rate by 4-5% and weaning weight by up to 10%. This

converts to more than a 20% increase in total weaner production per cow per year.

Table 1 below summarises the findings made by Grasslands Research Station when

they supplememnted steers on veld in summer. The experimental group was given a

50/50 mixture of monocalcium phosphate (MCP) and common salt.

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Table 1 Summary of performance of steers given a phosphate supplement in summer at Grasslands

Parameter Control (No P) Supplemented (P)Induction mass (6/11/1975) 186.5 184.0Finishing mass (23/6/1976) 256.0 298.5Total summer gain (kg) 69.5 114.5Response to supplementation (extra LW, kg) - 45.0Live mass into pens 256.0 298.5Live mass at slaughter 409 441.5LW Gain in pens 153.5 143.0Days in pens 111 83Feed Consumed (kg) Std pen diet 1070.8 878.8Average Feed intake (kg/day) 9.647 10.587LWG in pens (kg/day) 1.383 1.723FCE (kg feed/kg LWG) 6.976 6.145Carcass mass at slaughter (kg) 220.2 231.5

The supplemented group of steers gained 45kg more weight than the unsupplemented

group and took less time to finish in pens. This would certainly reduce the farmer

feed bill and increase turn over.

Table 2 summarises the results of research on phosphorous supplementation carried

out at Matopos, Makoholi and Grasslands research stations. The trials at Makoholi and

Grasslands were conducted on granite sands while the Matopos trial was done on red

clays. The increased weight gains due to phosphorous supplementation ranged from

14 to 18kg at the lower rainfall sites (Matopos and Makoholi) to 34-45kg at the higher

rainfall site (Grasslands). In the trials the supplement was given free choice (ad lib) in

mixtures containing monocalcium phosphate (MCP) and salt, or other carriers.

Phosphorous intake per head ranged from 2.5g to 4.7g per day at the drier sites, and

from 7.0g to 13.7g per day at the wetter site.

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Table 2 Summary of research on phosphate supplementation carried out in Zimbabwe

Site Stock category

Period (days)

P. Intake (g/d)

Extra LW (kg)

Extra LW value $1.40/kg

P. Cost ($8.00/kg)

Net Value (P)($/head)

Makoholi Lactating Cows

210 6 26.2 36.68 10.08 +26.60

Makoholi Yearling steers

180 2.5 18 25.20 3.60 +21.60

Grasslands Yearling steers

179 11 44.8 62.72 15.75 +46.97


210 7 34 47.60 11.76 +35.84


210 10 38 53.20 16.80 +36.40


229 7.8 34 47.60 14.29 +33.31


229 13.7 45 63.00 25.10 +37.90

Matopos Yearling steers

167 3.4 16.1 22.54 4.54 +18.00


167 4.7 14 19.60 6.28 +13.32


155 3.4 12.1 16.94 4.22 +12.72

*Economic evaluation is based on a standard 15kg, 7% phosphate block, selling at $7.80 each

In the Makoholi cow experiment, conducted over a six-year period, 26.2kg is the

average increase in weaner weight produced per cow per year. This amounted to an

increase of more than 20% per cow per year, made up by 7% increase in calving

percentage, 16% increase in weaning weight and a small reduction in calf mortality.

Products that can be used for phosphorous supplementation include monosodium

phosphate, bone meal, monocalcium phosphate, and dicalcium phosphate, usually in

combination with common salt for intake control. With ruminants, there appears to

be no difference among the above substances as sources of phosphorous and the

choice of supplement should be determined by the cost per kilo of phosphorous.

However, use of steamed bone meal is restricted due to the BSE scare; although its

use is still lawful when the beef product is not intended for export. In the medium

rainfall areas (+/- 600mm) the optimum levels appear to be 2.5-4.0g/day for young

stock and 6.0-9.0g/day for lactating cows. In the higher rainfall areas the optimum

levels are probably in excess of 8g/day for young stock and 10g/day for older

lactating cows.

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The economics

In spite of such overwhelming research evidence in favour of supplementation, a

surprising number of farmers do not make use of phosphate to increase summer gains,

conception rates and cow productivity. This may be due to a lack of awareness. But in

most other cases it is due to the feeling that the difference between animals doing

well in summer and those doing extremely well is not important. However, gaining

extra weight in summer is as important as reducing weight loss in the drier season

months. Many other farmers do not supplement phosphorous because they think that

it is not profitable. It should therefore be beneficial to analyse the economics of

phosphorous supplementation at present costs. The current cost and returns for

supplementation in each of the experiments has been included in Table 2 above. A

standard summer (7% phosphate) block on the market in Zimbabwe costs about $7.80

(which translates to approximately $8.00/kg P) and the increased live weight gain is

valued at $1.40/kg live mass.

It is then clear that a farmer could greatly increase profit per head by amounts

ranging from $12.00 to over $37.00 through phosphorous supplementation. The lowest

return per dollar invested would be 1:2.5 according to the analysis. At current beef

and phosphate prices, supplementation during the growing season in the sour and

mixed veld areas is highly profitable. The farmer will benefit superior animal

performance on penning and a shorter fattening and production period.

Conclusions

Supplemental phosphate is most critical during the wet season when animals

are gaining weight rapidly and energy and protein supplies are adequate.

Research has indicated little or no response to phosphate supplementation in

the dry season when grazing cattle are in a negative protein and energy

balance and are losing weight.

There is little or no response to phosphate supplementation of cattle grazing in

the sweetveld of the lowveld areas of Zimbabwe.

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Consistently high conception rates in excess of 80%, high summer gains and

minimal winter weight losses can be achieved by supplementing adequate

protein in the dry season and adequate phosphorous in the growing season.

Phosphorous sources available to the farmer include monocalcium phosphate,

dicalcium phosphate, monosodium phosphate, steamed bone meal and

commercial phosphate products such as licks, blocks and meals.

Economic return on phosphate mineral supplementation is high.

Reference

Gammon D. M. 1993. Advice on summer phosphate supplementation. The Farmer,

January 14 1993: 9.

Gammon D. M. 1997. Phosphorous supplementation of beef cattle on veld. The Farmer

November 6/13, 1997.

Grant JL 1974/1975. Division of Livestock and Pastures. DR&SS Annual Reports

1974/1975. Department of Research & Specialist Services, Harare.

McDowell L. R., Ellis G. L., and Conrad J. H. 1984. Mineral supplementation for

grazing cattle in tropical regions. World Animal Review 52:2-12

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summer phosphate supplementation of grazing beef cattle in zimbabwe

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