THE KEY ROLES OF UREA AND PROTEIN SUPPLEMENTATION IN INCREASING PRODUCTIVITY OF RUMINANTS FED CROP RESIDUES OR PASTURE
by
R.A. Leng

Emaciated cattle and buffaloes in the herds of small farmers in developing countries have been usually diagnosed as being energy deficient. Whilst it is self evident that these animals, fed largely on crop residues, are deficient in nutrients and total energy intake, the low energy intake appears to be due primarily to a fermentable N and/or protein deficiency in the diet. The apparent energy deficiency is a result of an inefficient (fermentable - N deficient) rumen which decreases the rate of fermentative digestion and also decreases the ratio of protein to energy in the products of rumen fermentation (which are microbial cells (65% protein) and the VFA's). The effect of the low rumen fermentative activities is a reduced feed intake. Correcting a N deficiency for the rumen microbes increases feed intake, digestibility and the ratio of protein to energy in absorbed products, but because the nutrients arising from digestion in the rumen are imbalanced to meet the requirements for productivity this remains fairly low. However, when supplements of bypass nutrients are given, productivity then increases substantially and correcting both a fermentable-N and amino acid deficiency is synergistic in increasing ruminant production.

The need for supplements of protein, long chain fatty acids and glucose to cattle given diets based on crop residues has been discussed in a companion paper.

The majority of livestock in the developing countries depends on low protein forages (straw or dry grass) for a considerable period of each year. In addition, competition with humans for the available milk means that young animals are often denied their full requirement for milk (the best balanced supplementary feed). Cattle and buffalo in the tethered husbandry systems in Asia and cattle in grazing systems in such countries as Africa require to grow, conceive, support the foetus and yield milk whilst fed on these crop residues.

It is my conviction that N deficiency of ruminants is the primary constraint to increasing ruminant production from these feeds and that it affects all aspects including fertility, growth and other production functions and even mature body size. The alleviation of N deficiency in the rumen and protein deficiency in the animal must lead to enormous increases in animal production without recourse to concentrate feeding. The evidence for this is discussed below. It indicates that the so-called “poor quality” forages are adequate to support moderate levels of all productive functions of ruminants provided they are supplemented with ‘catalytic’ amounts of protein meals and particularly urea. The evidence for this is discussed below for productive functions and different physiological states.

Puberty - Puberty tends to be a function of bodyweight rather than age. Because Hereford heifers supplemented with a bypass protein meal grew faster and reached a critical bodyweight earlier than unsupplemented cattle, these heifers were able to breed one year earlier (Table 1).

Conception - In studies with mature Hereford cows with calves at foot, supplementation with a bypass protein meal during periods when only dry native pasture was available for grazing had a large effect on conception rate (Table 2).

Male fertility - In the wet/dry tropics of Australia bulls are often placed in a herd four to six weeks after the onset of the wet season even though the bulls may have lost 20% of their bodyweight. Increased fertility of bulls on dry winter pasture (i.e. low N-low digestibility forage) can be achieved by feeding a protein supplement daily (Table 3). Most importantly the circumference of the scrotum decreased considerably when no supplement was fed and thus these animals tend to be less fertile and have a lower libido since scrotal circumference is an index of these reproductive characteristics (see Blockey, 1980).

Rate of bodyweight gain - Examples of the benefits of N supplementation of young cattle or pregnant cows on dry spear grass pastures are given in Table 4 where the synergistic effects of both urea and a bypass protein are well demonstrated.

Viability of new-born animals - Supplementation of sheep grazing dry native pasture with urea through the drinking water, and supplementation of cattle given dry native grasses with urea sprayed on the feed, improved the body weight of lambs and calves respectively at birth and also their subsequent survival rate (Table 5).

Milk yield - Small inputs of urea (as a molasses/urea block) increased milk yield considerably in buffaloes fed largely straw-based diets under village conditions in India (Figure 1). Feeding small amounts of fish meal to cattle in Bangladesh on treated (urea) straw increased milk yield markedly (Figure 2).

Ultimate body size - Feeding a protein meal during the dry seasons to cattle on native pasture resulted in large weight gain advantages and the mature body size was increased (see Table 6).

Body size is related to draught-power. Many oxen in developing countries appear to be stunted which is possibly brought about by a protein deficiency at critical stages in their life.

The replacement of two undersize oxen by a single well grown oxen and the introduction of improved agricultural implements would increase the availability of feed resources for other ruminant livestock.

From the above discussion low protein undernutrition at critical periods may be the single most important cause of low productivity of cattle in traditional-subsistence farming/grazing systems in Africa as compared with cattle raised on ranches in the same country (Table 7). In subsistence as compared to ranching systems the great difference is that animals are of a much lower bodyweight particularly at weaning. This could be related to the high competition for available milk by humans (see Figure 3).

Conclusion

Protein and fermentable-N supplements to cattle fed crop residues or on pasture appear to be critical for all aspects of animal production from fertility and conception, to survival, growth, pregnancy and lactation. This simple strategy of supplementation, if widely applied, could have enormous effects on the availability of animal products in developing countries. Massive improvements are possible without recourse to the use of grain-based concentrates.

Although the role of the protein meal is not always that of providing amino acids to the animal and it may be possible to substitute protein at times with other nutrients (bypass starch or long chain fatty acids), the practical implications are that in all developing countries, efforts should be made to provide protected protein meals targeted at the animal production industries. The molasses/urea block appears to be fast becoming an established tool for providing urea to tethered ruminants (see Leng, 1984).

REFERENCES

Blockey, M.A. de B. 1980 Testicle size in bulls. Animal Production in Australia. 13:52–53.

Hennessy, D.W. 1985 The role of protein in improving production of cattle grazing native pastures in sub-tropical New South Wales. Ph. D. Thesis, University of New England, Armidale.

Hennessy, D.W. 1986 Lactational anoestrus in first-calf heifers grazing native pastures in the subtropics. Proc. Aust. Soc. Anim. Prod. (submitted).

ILCA. 1985 Unpublished observations.

Leng, R.A. 1984 The potential of solidified molasses-based blocks for the correction of multinutritional deficiencies in buffaloes and other ruminants fed low-quality agroindustrial byproducts. In: The use of nuclear techniques to improve domestic buffalo production in Asia. IAEA, Vienna, pp 135–150.

Lindsay, J.A. and Loxton, I.D. 1981 Supplementation of tropical forage diets with protected proteins. In: Recent advances in animal nutrition in Australia (Ed. D.J. Farrell) University of New England Publishing Unit, Armidale.

Lindsay, J.A., Mason, G.W.J. and Toleman, M.A. 1982 Supplementation of pregnant cows with protected proteins when fed tropical forage diets. Proc. Aust. Soc. Anim. Prod. 14:67–78.

Saadullah, M. 1984 Studies on utilization of rice straw by cattle. Ph. D. Thesis, Royal Veterinary University, Copenhagen.

Stephenson, R.C.A., Edwards, J.C. and Hopkins, P.S. 1981 The use of urea to improve milk yield and lamb survival of Merinos in a dry tropical environment. Aust. J. Agric. Res. 32:497–509.

* - mated

All cows and calves grazed carpet grass pastures. Groups 1 and 2 were supplemented with 2.8 kg of a protein pellet twice per week during dry periods. Bulls were grazed with the heifers and with the control and supplemented 1 group in the first year and with all groups in the second year.

* After Lindsay et al. (1982). The hay was mature Heteropogon hay(spear grass)

** After Stephenson et al. (1981). The feed was mature Flinders grasshay.

Figure 1. The effects of introducing a molasses/urea block (20% urea) to a milking buffalo in a village in Mehsana, Gujarat, India. It took approximately 8 days before the buffalo consumed significant amounts of the block (500 g/d). Milk sold on its fat content (from records of milk sales) increased after a time lag of 7–10 days. The basal diet was millet straw with a handful of green forage (Kunju, Dave and Leng, 1985, unpublished observations).

Figure 2 Milk yield of native and crossbred cattle fed ammoniated (urea-ensiling) rice straw supplemented with fish meal (range was 0–400 g/d) (from Saadullah, 1984).

Figure 3. The influence of rainfall (active grass growth) on the milk offtake and meize purchases in Olkarkar ranch in Kenya. In periods of high milk production, maize purchases by the family are reduced, indicating substitution of cereal by milk in the family's diet. This shows the competition between human needs and those of the calves for available milk supplies (IICA, 1985).