CHAPTER 5 - FEEDING AND INDIVIDUAL SUPPLEMENTATION

Liu Jianxin
Zhejiang University
Meng Qingxiang
China Agricultural University

The nutritional constraints of most crop residues are low N content, high proportion of cell wall constituents, poor digestibility and low intake. Various methods have been used to attempt to improve low quality crop residues, including chemical, physical and biological treatments, supplementation of limiting nutrients and a combination of these (Preston and Leng, 1984; Liu, 1995). Cereal straws and stovers are the main crop residues, and ammoniation is the most viable method to upgrade them (Guo and Yang, 1994). This chapter discusses the feeding practices and supplementation strategies for ruminant diets based on ammoniated crop residues.

Quantity of straw offered to ruminants

Cereal straws and stovers may be used as the only feed or as part of the ration, depending on animal type and physiological stage. For the purpose of this technology, ruminants may be classified into two categories: meat animals and dairy cows.

Meat type (beef cattle, heifers, sheep and goats)

Many studies have been carried out to study the effect of ammoniated straw as the only roughage or as a large proportion of the diet of meat animals. In a trial with yearling steers, Xu (1989) compared the effects on animal performance of different levels of untreated and ammoniated wheat straw as the sole roughage. The results are summarized in Table 5-1. When untreated straw was offered at a high level (60 percent), daily gain was lowest due to poor total intake. Concentrate consumption per kg of gain was high, even at the maximum straw level, but it was much lower at the highest level of inclusion of ammoniated straw, indicating a saving effect.

Table 5-1. Intake of wheat straw, daily gains and feed conversion of steers

SOURCE: Xu, 1989.

Liu et al. (1991a) investigated the effect of substituting ammonium-bicarbonate-treated rice straw for hay in growing heifers supplemented with 10 kg maize silage or fresh Chinese milk vetch, plus 2 kg of concentrate. Heifers consumed more DM from ammoniated straw (5.1 kg/day) than from hay (4.0 kg). They had significantly higher daily gains (780 vs 578 g/day; P < 0.01). Similar results were obtained with ammoniated wheat straw in young bulls (Huang et al., 1987) and growing lambs (Dong et al., 1989), and with ammoniated rice straw in buffaloes and Holstein heifers (Zou et al., 1988), steers (Ma et al., 1989), and heifers (Zhao and Huo, 1990).

It can be concluded that ammoniated straws and stovers can be given to beef cattle, heifers, sheep and goats as sole roughage or as a major part of the diet.

Dairy cows

There are few reports on ammoniated straw for dairy cows, since it is widely believed that feeding it to high yielding cows may have adverse effects on milk production. However, the limited reports indicate that dairy cows perform well when they consume ammoniated straw.

Li and Wu (1991) compared straw intake and milk production in dairy cows given either untreated or anhydrous-ammonia-treated rice straw. Daily intake was 4.58 and 6.24 kg, and daily milk production 13.6 or 16.0 kg for untreated or ammoniated straw, respectively. In a trial with the ammonium-bicarbonate-treated rice straw, Liu et al. (1991b) found that 17-19 kg of milk could be obtained from Holstein cows when the ammoniated straw represented half of the intake (85 percent of roughage). These results were consistent with those of Ørskov (1987), where daily milk yield was 23.5-27.4 kg when ammoniated straw, as the sole roughage, was 35-60 percent of the diet.

It can be concluded that ammoniated straw is a good source of roughage for dairy cows, completely or partially substituting hay. However, it is certainly advisable to use other roughage sources in order to ensure a complete diet.

Supplementation with concentrate and protein

The first constraint for low quality crop residue use is usually N. It is desirable that supplementation ensures an almost continuous supply of ammonia-N. Urea is commonly used as a source of fermentable N, and can be sprayed on cereal straw or be mixed with energy supplements. At present, non-protein N supplements have not been widely fed by farmers in China, but urea is usually used as a source of ammonia to upgrade crop residues. With the development of animal production based on crop residues, ammoniation of cereal straw has been widely extended all over China (Guo, 1996).

Since fermentable N is not limiting in ammoniated straw diets, greater consideration should be given to rumen-protected amino acids. They may overcome specific deficiencies limiting production or may be catabolized to improve the supply of glucogenic substrates, which are also usually insufficient in straw-based diets (Preston, 1995). Protein supplements used in China are mainly oilseed cakes or meals, such as cottonseed cake (CSC) and rapeseed meal (RSM). Sometimes farmers provide their animals with by-products such as rice and wheat bran, or home-grown or self-mixed concentrate mixtures.

Effectiveness of protein supplementation

Typical data on animal performance is given in Table 5-2. In Henan Province, an experiment with 40 young Chinese Yellow bulls was conducted to investigate CSC supplementation levels with urea-treated wheat straw (Zhang et al., 1993). The cattle without CSC gained only 250 g/day, but with CSC gained significantly more (P <0.01). There were no significant differences between 2 and 3 kg, and between 3 and 4 kg of CSC, but there was between 1 and 2 kg. DM intake of wheat straw did not decrease when 1 kg CSC was supplemented, but it did at higher levels. The economic analysis indicated that a relatively high level of production and the highest profit were obtained with 2 kg of CSC.

Similar results were obtained in Hebei Province (Fan et al., 1993; Ma et al., 1990; Table 5-2). Supplementation with 0.25 kg CSC significantly improved feed utilization efficiency and feed efficiency (kg of feed DM/kg gain being reduced from 53 to 15). The group given 1.5-2.0 kg of CSC gained approximately 800 g/d, with only 8 kg feed consumed per kg gain. Further increases of CSC resulted in slightly faster gains at the expense of straw intake.

Table 5-2. Effects of supplementation with cottonseed cake (CSC) on performance of growing Yellow cattle fed untreated or urea-treated wheat straw

NOTE: (1) FCR = feed conversion ratio

Formaldehyde treatment was effective in improving protein use efficiency of RSM. In terms of nutrient digestibility and N use, formaldehyde-treated RSM compares favourably with treated soybean meal when given to sheep fed ammoniated rice straw (Liu et al., 1994). When an ammoniated rice straw-based diet was supplemented with 1.2 kg RSM, heifers had lower weight gains, whereas feeding a similar level of treated RSM resulted in considerably faster gains (15 percent on average) along with improved feed conversion ratio (FCR) and decreased feed cost (Liu et al., 1993) (Table 5-3). This was also the case when 1.8 kg of RSM was given. Adverse effects on animal health are unlikely when formaldehyde-treated RSM is supplemented in an ammoniated rice straw based diet (Wu and Liu, unpublished data).

Table 5-3. Supplementation effects of untreated or formaldehyde-treated rapeseed meal (RSM) on weight gain of heifers

SOURCE: Liu et al,. 1993

Response of supplementation with untreated and treated straw

There are consistent responses in performance to supplementation with protein or concentrate, but the effects are more pronounced when the straw has been chemically treated.

Meng and Xiong (1993) studied the effect of supplementing with different levels of concentrate on growth rate of Wuzhumuqin wether lambs fed untreated or ammonia-treated wheat straw. Concentrate mixtures were chosen to obtain minimum feed cost per unit gain. The results are summarized in Table 5-4. Intake of both untreated and ammoniated straw diminished with increasing levels of concentrate, while animals consumed more ammoniated straw than untreated. Ammonia treatment increased straw DM intake on average by 72, 51, 57 and 117 percent, resulting in higher total DM intake for ammoniated straw diet. Treatment of wheat straw with ammonia resulted in a significant improvement in weight change of sheep and in feed conversion. Supplementation with concentrate increased weight gain of wethers offered either untreated straw or the ammoniated, but the nature of the response differed according the type of straw. In order to obtain similar daily gains, larger amounts of concentrate were needed for untreated wheat straw than for ammoniated diets.

This indicates that benefits of ammoniation of straw are highest when the supplement level is low. The results show that minimum concentrate consumption per unit gain was obtained when the concentrate accounted for 45 percent of diet based on ammoniated wheat straw.

Table 5-4. Feed intake, digestibility and liveweight gain of sheep fed treated or untreated rice or wheat straw plus different levels of supplement

NOTES: (1) Meng et al. (1993) worked with Wuzhumuqin wethers (mean weight of 30.2 kg). (2) Liu et al. (1998) worked with Huzhou lambs (mean weight of 21 kg). (3) Ingredients: 82-86% maize meal; 11.5-11.8% CSC; 0-4.2% bone meal; 0.5-1.6% lime; 0.4-1.5% salt; and 0.2-0.8% mineral-vitamin premix. (4) Including 100 g of rice bran (DMI = 88 g/day).

Similar results were reported by Liu et al. (1998) (Table 5-4), with RSM as a supplement for Huzhou lambs offered untreated or ammoniated rice straw. The optimum level of RSM with ammoniated rice straw was 100 g/day, whereas 200 g/day had to be supplied to obtain the same liveweight gain with untreated straw. At existing prices (RSM at ¥ 1.50/kg, rice straw at ¥ 0.22/kg, and ammoniated straw at ¥ 0.27/kg), there is a benefit of ¥ 0.08/day from ammoniation, equivalent to ¥ 7.20/sheep for the normal 90-day fattening period.

Supplementation with green forages and readily digestible fibrous feeds

It is known that small quantities green forage can improve the usage of straw diets. Thus, introducing forage supplements may be an alternative strategy for increasing nutrient intake and improving ruminant performance. A wide range of forage supplements is available in China, depending on location. These include green forage, crop by-products and aquatic weeds.

Effects of supplementation with green forage

Chinese milk vetch (Astragalus sinicus L.) is cultivated in South China as green manure to improve soil fertility. Farmers traditionally offer surplus vetch to swine after ensiling. Liu et al. (1997) and Ye et al. (1996) evaluated the effect of supplementing with milk vetch silage on growth rate of heifers and rumen function in sheep given ammoniated rice straw diets (Table 5-5). Intake of ammoniated straw by heifers was slightly decreased as the level of vetch silage went up. When the vetch silage represented 20 or 30 percent of diet, growth rate was significantly higher than in the non-supplemented group (P <0.05). The highest gain was obtained at the 20 percent level, when concentrate consumption per kilogram weight gain was lowest (1.25 kg) (Liu et al., 1997).

The average ammonia-N level in the rumen increased with the increasing level of vetch silage (Ye et al., 1996). However, there were small differences in pH value and volatile fatty acid profiles among all groups. Protozoa population tended to decrease more quickly with the supplement. The microbial protein concentrations in the rumen fluid was related to the levels of vetch silage and reached a peak at 20 percent, possibly associated with saponins present in milk vetch.

Liu et al. (2001) substituted RSM with mulberry (Morus alba) leaves as a supplement for Huzhou growing lambs fed ammoniated rice straw. Total substitution with mulberry leaves gave similar growth rates, but at lower cost than RSM. The authors concluded that mulberry leaves could be used to supplement ammoniated straw diets in place of RSM.

Forage supplement level would depend on the type used, availability and the cost relative to straw. A maximum of 20-25 percent of a diet seems suitable.

The substitution rate would increase with the level of supplement. A limitation in China is that supplementary forages are usually in short supply in most areas.

Supplementation with readily digestible fibre

Prerequisites for all ruminal digestive processes are development of digestive consortia and their adhesion to ingested feed particles. Any feeding strategies that enhance adhesion of rumen microbes to feed particles and improve fibrolytic activity may be beneficial to feed utilization.

Table 5-5. Feed intake and liveweight gain of heifers, and rumen function of sheep, given rice straw and different levels of Chinese milk vetch silage

NOTES: (1) SEM = Standard Error of the Mean.
(2) Means with different superscripts differ significantly (P<0.05).
(3) Ratio of protozoa population before feeding to that at 6 hours post-feeding.

In a recent trial, Shi et al. (1997) studied the effect of added ammoniated rice straw on the growth rate of Holstein heifers receiving untreated rice straw. The results are summarized in Table 5-6. When half (w/w) of the untreated straw was replaced by ammoniated straw, heifers had significantly higher intake and gains, even slightly higher than those on ammoniated straw. A similar result was reported by Li et al. (1998), who compared the growth rate of cross-bred cattle offered ammoniated wheat straw or maize stover, either alone or in a 50:50 (w/w) combination (Table 5-6).

Table 5-6. Straw intake and growth of heifers fed rice straw plus various supplements or of cattle on ammoniated wheat straw, maize stover or a mixture

NOTES: (1) Shi et al. (1987) worked with heifers (344-353 kg). (2) Li et al. (1998) worked with cattle of 370 kg. (3) Liu et al. 2 (000) worked with heifers (139-141 kg). (4) Expressed as the depression in the intake of ammoniated rice straw produced by a unit increase in the BSS intake.

Bamboo cultivation is very popular in south China. Bamboo shoot shells (BSS) are the residue from industrial-scale processing of bamboo shoots, and represent a disposal problem because they have no use and can pollute the environment. Occasionally it has been observed that fresh BSS were palatable to cattle, their CP was 10-13 percent (on DM basis) and were easily degraded in the rumen, although neutral detergent fibre was high (65-70 percent on DM basis) (Wang, 1997). Considering BSS as a source of readily digestible fibre, Liu et al. (2000) observed the response in growth rate to supplementation in heifers given ammoniated rice straw. The results are summarized in Table 5-6.

Straw intake linearly decreased with the increasing level of BSS, but total dietary intake increased also (a substitution rate less than 1.0). Growth rate in heifers was improved significantly by the supplementation, and the optimum level was at 21 percent of total dietary intake.

It is inferred that supplementation with readily digestible fibre may improve utilization of basal diet and animal performance. However, further work is needed on this topic.

Use of multinutrient blocks

Since the early 1980s, both production and utilization of multinutrient blocks (MNBs) as supplements for ruminant animals have increased considerably in developing countries (Sansoucy, 1995). With the development of ruminant production, much progress has been made and new technologies have been developed in the manufacturing of MNBs in China since they were introduced in the late 1980s.

MNB manufacture

Ingredients

The MNBs developed in China contain molasses, urea, minerals and proteins, with the aim of supplementing cereal straw with fermentable N, soluble carbohydrates, minerals and other nutrients. The main ingredients have been: ground maize; rice bran and wheat bran; rapeseed meal; solidifiers and binders (cement, clay, etc.); bone meal; and vitamin premix (Chen et al., 1993a, b; Li et al., 1995; Zou et al., 1996; Gao et al., 1999). Molasses, a source of easily fermentable carbohydrates and a binder, makes blocks highly palatable. It has been demonstrated that mixing urea with molasses greatly decreases the release of ammonia-N in the rumen. Mineral premix usually contains Ca, P and Na as well as micro-elements such as Fe, Cu, Mn, Zn, I, Se and Co (Liu et al., 1995; Zhang et al., 1999).

In a series of demonstration trials in Gansu Province, where the basic diet was composed of wheat straw and other stubble, Chen et al. (1993a, b) selected three formulas, for cows, heifers and calves (Table 5-7). Many workers used molasses as an ingredient for blocks (Li et al., 1995; Yang et al., 1996; Guan et al., 1998). Liu et al. (1995) found a block formula without molasses, since molasses is expensive and in short supply in some regions.

Lime and cement have been commonly used as solidifiers and binders. Ordinary clay has been also proved to be efficient for making blocks (Chen et al., 1993a, b; Guan et al., 1998). Farmers in some regions used loess as a binder (H.W. Ye, personal communication).

Table 5-7. Formulas of multinutrient blocks for dairy cattle (on a percentage by weight basis)

Process for block manufacture and specifications

Depending on the technical process, MNB preparation takes two forms: by pressure (hot process), or by moulding (cold process). The moulding process needs neither sophisticated equipment nor much energy. Blocks produced by moulding had the following features (Ma et al., 1992): (1) When water was poured onto the surface of the blocks, blocks kept their shape after sun-drying; (2) Blocks maintained their shape intact when submerged in water for 1-2 hours, but completely dispersed after 4-5 hours; (3) Hardness increased when formaldehyde was included; (4) The shape of the blocks did not change under finger pressure.

Xia et al. (1994) developed a specialized machine to make blocks under pressure. This equipment saved space and labour, and the blocks could be easily produced. Drying was unnecessary since it used raw materials already dry. The blocks produced were compact, not deliquescent, and hard enough to control intake. They did not become mouldy nor did they lose shape when exposed to rain or sunshine.

Table 5-8 indicates the characteristics of two press machines for the formation of blocks, designed by Chen et al. (1993a, b). The blocks were made by mixing molasses and urea, and then heating. Salt was added, followed by the rest of the ingredients, having been previously mixed together. The complete mixture was then pressed and the resulting blocks were wrapped immediately. Blocks made using both press machines were hard enough, with a breaking strength of 44 kg/cm². The blocks were oblate, 25.6 cm in diameter and 8 cm in thickness, with a weight of 7.5 kg each.

Table 5-8. Characteristics of presses used for making the blocks

The blocks produced by Yang et al. (1996) were squares or compressed cylindroids with rounded holes (ca 1.5 cm diameter) in the centre. Each block weighed 2.5 kg. The breaking strength was 56.9 kg/cm². They did not moisten before 24 hour under low temperature (> 0°C) and high humidity (> 80 percent).

The urea-mineral blocks designed by Liu et al. (1995) had a breaking strength of 40 kg/cm². They were easily transported and fed to the animals. Even in situations of high humidity, there were no losses from mould or from hydration when they were offered to the animals over a long period.

In 1999, MOA set up a "block expert group." Based on results of previous studies and six months of research, an industrial production technology system was proposed. The MOA appraised it, and confirmed it "in the national leading position." The blocks have sold very well.

Results of blocks with animals

Beef cattle

In a growth trial with heifers, those having access to MNBs had daily gains of 835 g/day, 112 g/day higher (P<0.05) than the control group (Chen et al., 1993a, b). Animals supplemented with blocks reached 380 kg body weight (weight at first service) 65 days earlier. Other advantages observed during animal feeding trials on farms were better skin coat, better body condition, and lower death rate. The urea-MNBs without molasses were also palatable to both cattle and goats (Liu et al., 1995). Local Yellow cattle on grazings with access to blocks performed better than the control (370 vs 203 g/day). The animals with blocks had better body condition and looked healthier than the control group. An increased income of ¥ 0.57 could be obtained per beast per day.

Zhang et al. (1993) observed that daily gains were 15.6 percent higher, and consumption of roughage and concentrate per kilogram of gain were 16.9 and 13.3 percent lower, respectively, when beef cattle were supplemented with MNBs containing non-protein nitrogenous compounds (NPN). In another trial (Ma et al., 1995), beef cattle with access to blocks containing NPN had daily gains 353 g higher than those with no blocks (1 478 vs 1 125 g/day).

Dairy cows

Dairy cows supplemented with MNBs produced 1.06-1.47 kg (5.3-5.9 percent) more milk than those without blocks (Wang et al., 1995). Less metabolic disorders occurred in the supplemented animals. Increased net income attributed to the blocks was about ¥ 1 per cow per day. Chen et al. (1993a, b) found that cows having access to blocks had an average milk yield of 20.7 kg/day, which was 1.3 kg (6.7 percent) higher (P < 0.01) than the average of the control group. Additional advantages of blocks included increased conception rate (12.2 percent), decreased occurrence of diseases (22.5 percent), improved body condition (Chen et al., 1992) and increased income.

Urea-MNBs was given to Holstein cows in mid lactation by Xu et al. (1993). Cows produced 20.5 kg of milk, which was 4.1 kg (25 percent) higher than the average of the control group. It was estimated that cows consuming the MNBs increased income by ¥ 736 per head per year.

Sheep and goats

Xu et al. (1994) observed increased intake and improved daily gain (26.5 percent) in sheep having access to MNBs, compared to control animals. They also produced better quality wool with higher S and mineral content. Similar results were observed by Yang et al. (1996).

When hybrid goats had access to urea-MNBs for two months, average intake of the blocks was 39.5 g/day (Huang et al., 1999). Daily weight gain for goats was 85 with and 62 g/day without MNBs. Net income was increased by ¥ 10.78 with blocks. Liu et al. (1995) reported results with goats, which grazed on hill pasture during the day and were offered rice straw ad libitum in stalls at night. Goats with free access to urea-MNBs along with rice straw at night performed better than those in the control group. Gains were significantly higher in animals with blocks (95 vs 73 g/day). The effects of MNBs on performance of growing goats were investigated by Zhang et al. (1999). Goats with blocks had weight gains 38.3 percent higher than those without.

Buffaloes

Effects of feeding blocks to buffaloes have been observed by some workers (Lu et al., 1995a; Zou et al., 1996). When buffalo heifers on rice straw diets were supplemented with urea-MNBs, daily gains were 650 g, compared to 620 g for control animals. Feed cost and concentrate consumption per kilogram of gain were 9.82 and 33.3 percent lower for supplemented buffaloes than those without. Animals showed no signs of poisoning despite block intakes above 1.0 kg/d, indicating that the blocks were safe. Zou et al. (1996) selected a formula of MNBs for growing buffaloes that contained molasses, urea, grain by-products, minerals and vitamin premix. Intake of the blocks increased with time, and was 172.4, 330.2 and 374.1 g/day at 30, 60 and 80 days, respectively, from the start of the experiment. Compared to control animals, buffaloes with blocks showed higher weight gain (22.6 percent; 395.4 vs 484.6 g/day) and used 22.5 percent less feed and 22.8 percent less concentrate per kg of gain.

Concluding remarks

Ammoniated cereal straws and stovers can be offered to beef cattle, heifers, sheep and goats as sole roughage or as large proportion of the diet. Undoubtedly, supplementation has one of the greatest potentials for improving cereal straw use by ruminants. Animal productive performance can be greatly improved by supplementing with protein sources, concentrate or highly digestible forages, or a combination. In order to obtain satisfactory animal performance, a small amount of protein supplement (below 20 percent of diet DM) is sufficient with ammoniated crop residues, but more protein supplements are needed with untreated straw. The supplementation level with forage depends on the type of forage and basal diet used. A high substitution rate would be possible when higher levels of forage are supplemented. Manufacture and utilization of MNBs as supplements for ruminant animals have increased considerably in China. Much progress has been made and new technologies have been developed since this technique was introduced in the late 1980s. It has been demonstrated that MNBs can be used to improve the productive performance of animals with access to low quality roughage. It was discovered that use of feeding blocks cut methane emissions by half, reducing its contribution to environmental pollution.