Required minerals for the improvement of poor quality roughages

Moustafa A. Naga
Faculty of Agriculture, University of Alexandria
Alexandria, Egypt

Summary
Introduction
Differences in mineral content between low and high fibre feeds
Recognition of mineral deficiencies

Summary

There are two main adjustments usually practiced during the manufacturing of feeds for ruminants. The first one is the addition of 2% calcium carbonate to bring the Ca/P ratio within its proper range (2:1). The second is the addition of 1% sodium chloride to compensate for the Na deficiency in most ingredients.

Analysis of roughages and mineral balance trials conducted using these ingredients showed some interesting phenomena: (a) roughages (contrary to cereal grains and protein meals) are richer in Ca and relatively poor in P (on average the ratio is 7.5:1). Thus roughage-based diets must be supplemented with P rather than Ca; (b) roughages need less supplementation with sodium chloride as the Na/K ratio in roughages is 1:3 compared with 1:10 in cereal grains/protein meals; (c) there are considerable differences in mineral patterns and in availability of roughages brought from different localities.

Introduction

Improvement of the nutritive value of crop residues and byproducts could be approached through:

* Getting rid of the barrier coating the plant cells which prevents the utilization of its digestible nutrients (e.g., by alkali or acid treatments);

* Supplementing the residue/byproduct with the deficient nutrient(s). This may be done by introducing a legume or supplements rich in protein, non-protein nitrogen, vitamin A and/or minerals.

This paper discusses the mineral mixtures which are appropriate for the supplementation of fibrous residues and byproducts when these are processed in a feed mill. Application of these mineral mixtures are designed to be within the molasses portion along with urea and vitamin A.

Differences in mineral content between low and high fibre feeds

Rice straw, maize stalks and horsebean straw contain more Ca and less P than cereal grains and protein meals. A similar trend was observed, but to a lesser extent, in Na and K (Table 1).

Table 1. Comparison between some mineral contents (%) of concentrates and roughages.

Concentrates			Roughages
Ca	P	Ratio	Ca	P	Ratio
0.16	0.63	1:4	2.24	0.30	7.5:1
Na	K	Ratio	Na	K	Ratio
0.14	1.44	1:10	0.39	1.17	1:2.9
Ingredients			Ingredients
Cottonseed cake			Corn stalks
Linseed cake			Rice straw
Peanut cake			Horsebean straw
Corn
Wheat bran
Maize bran

This draws attention to the fact that the traditional inclusion of 2% Ca-carbonate should not be applied to roughage-based diets which need, rather, the addition of a phosphorus source. Also, the normal allowance of 1% sodium chloride may be reduced by 50% for roughage diets.

Recognition of mineral deficiencies

The mineral content of the same ingredient was found to vary considerably over the country (Table 2).

Balance trials showed that roughages may contain high percentages of a certain mineral yet the animal is in negative balance when fed such a diet. It is speculated that this reflects the unavailability of the mineral irrespective of its high concentration in the feed.

The availability of minerals in roughages was tested in vitro. The ground sample was incubated for 12 hours in water (simulating the neutral pH in the rumen) and then, after centrifugation, the mineral fraction was estimated in the supernatent. The sediment was then incubated at pH 2 (simulating the conditions in the abomasum). The acid soluble mineral fraction was also estimated in the supernatent. Finally, the sediment was incubated for 12 hours at alkaline pH (8.2) simulating conditions in the small intestine. The sum of water, acid and alkaline soluble mineral fractions, expressed as a percentage of the initial mineral content, was considered to be an indicator of availability (Table 2).

A comparison between the available amounts of mineral consumed voluntarily in the roughage feed, and the standard requirements of the animal, indicates the gap which needs to be filled by the supplement (Table 3).

Table 2. Average percentages of differences in the content and availability of roughage ingredients from six governorates.

Mineral	Ingredient	Average difference (%) between governorates
		Content	Availability
Ca	Rice straw	334	63
	Corn stalks	182	78
	Horsebean straw	286	55
P	Rice straw	1850	38
	Corn stalks	138	21
	Horsebean straw	185	8
Fe	Rice straw	398	42
	Corn stalks	744	60
	Horsebean straw	1517	28
Na	Rice straw	218	87
	Corn stalks	819	67
	Horsebean straw	519	33
K	Rice straw-	281	31
	Corn stalks	152	45
	Horsebean straw	721	9

Table 3. Suggested formula of mineral mixture to supplement poor quality byproducts.

Mineral	Kg to be added per tonne (DM basis)
P	3.0
Na	0.5
Fe	0.5
Mg	0.6
Zn	0.1
Mn	0.1
Cu	0.1
Co	0.01

The homogeneous distribution of the supplement in the roughage requires some form of mechanical mixing. The chopped roughage can be sprayed with heated molasses (to 35-40°C) in which urea, vitamin A and minerals are dissolved, or mixed with a stirrer, and pumped from the molasses tank to the mixer (Figure 1).

The final product should be offered to lactating animals as a meal: the pelleted form is more suited for fattening animals.

There are indications that a specific mineral mixture should be formulated for each location and for different physiological functions (e.g., pregnant, lactating, dry, fattening, growing and young animals).

Figure 1. Components of the roughage manufacturing plant.