Rapeseed meal and urea as a protein source for growing bulls on alkali-treated straw-based feeding

Between the ages of 3 1/2 and 10 months, 12 bulls took part in an experiment in which 1) Tower rapeseed meal or 2) urea plus rapeseed meal was used as a protein source in a diet based on dry alkali-treated straw. In group 1 the rapeseed meal composed 32 % of a concentrate mixture also containing barley, oats, molassed beet pulp and minerals. The average daily consumption of rapeseed meal was 1.2 kg/animal and it contributed 58 % of the digestible crude protein supply. In group 2 urea composed 2 % of the concentrate mixture and the average daily consumption was 84 g/animal. In this group urea contributed about 38 % and rapeseed meal 20 % of the digestible crude protein supply. The palatability of the concentrate mixture was good in both groups. The average daily intake of alkalitreated straw was 2.3 kg/animal or 0.77 kg dry matter/100 live weight kg. Treated straw was the only roughage received by the animals from the age of 6 months. Up to that age the animals also received hay, on average 840 g per animal and day. The average daily live weight gain in group 1 was 1072 g/animal and in group 2 it was 1111 g; the carcass weights in the respective groups were 169 kg and 176 kg, and the feed conversion rates were 4.08 f.u. and 4.16 f.u./kg live weight gain. The differences between the group were not significant (P > 0.05). Almost all the animals showed pathological changes in their inner organs, which may mean that alkali-treated straw sounds not to be suitable as the only roughage source for growing bulls.


Introduction
The use of straw as the only source of roughage for growing bulls has been restrict- ed by its low digestibility and high bulk.It has also been difficult to find an economical domestic source of valuable protein for straw-based feeding in countries like Fin- land, where cultivation is limited by the northern location.The development of methods for improving the energy value of straw and the production of new rapeseed varietes that are low in antinutritional substances and can be cultivated in Finnish conditions as well has now made it possible to start rearing bulls on straw-based feeding.In this experiment the feed consumption, growth rate and health of the animals were investigated in bulls receiving alkali straw and rapeseed meal and urea together with grain concentrates.

Experimental procedures
The experiment was performed with 12 growing male bulls, 10 Ayrshire and 2 Friesi- an, which were divided by age, live weight and breed into two comparable groups.The animals mean age at the beginning of the ex- periment was 110 days and their mean weight 140 kg.
The experiment lasted about 7 months, including an adaptation period of three weeks, in which the diet was gradually changed to that of the experimental regime.The experimental diets consisted of alkali- treated straw fed ad libitum, with hay during the first months of the experiment (Fig. 1), and a concentrate mixture consisting of bar- ley, oats, molassed beet pulp and a commer- cial mineral mixture.As an additional source of protein, one group received rapeseed meal (RSM group) and the other group urea + rapeseed meal (UREA group Table 1).
The bulls were fed individually twice a day at a level which satisfied the energy and protein demands of animals growing at a rate of 1000 g/day (DAENiCKEand Rohr 1974).They 1.12 DCP, g/f.u.170 171 f.u.= feed unit = 0.7 starch equivalent DCP = digestible crude protein were weighed on two days at the beginning of the experiment and once a week during the experiment.The quantities of grain and the protein sources were adjusted as the weights increased, using weight intervals of 20 kg.
The rapeseed meal used in the experiment was the Tower variety, in which the content of glucosinolates was only 0.2 % of dry mat- ter and that of tannins 1.3 °7o.
The straw was mainly wheat straw.It was dry alkali-treated with a mobile machine (JF SP2000), in which the straw is chopped, and alkali solution added and mixed with the straw.The amount of NaOH added was 4.3 % of the dry matter of the straw.The unreacted base was determined by titration to pH 8 with 0.1 HCI.The residual NaOH averaged 0.96 % of the dry matter.
The chemical analyses of the feeds were made by standard procedures.The feeding values of the concentrates and hay were calculated from the digestibility coefficients ob- tained from NJF Tables (Anon. 1969,Table 2), but the value for the treated straw was calculated from the results of a digestibility trial performed with adult rams.The digestibility coefficients of the different constit- uents of the treated straw were as follows: organic matter 70 %, crude protein 20 %, crude fat 50 °7o, crude fibre 85 % and N-free extract 60 %.The value number used cal-  the palatability of the concentrate mixture was good.The daily amount of rapeseed meal consumed by the animals was 1.2 kg and this supplied about 58 % of their digestible crude protein.

Results and discussion
Feed intake and growth rate In the UREA group, the mean consump- tion of rapeseed meal was 400 g per animal and day and that of urea 84 g/day, the maxi- mal amounts of urea being 40 g/100 live weight kg.In this group the bulls received about 38 % of their digestible crude protein from urea and 20 % from rapeseed meal.The palatability of the concentrate mixture was good in this group also.The alkali treatment improved the feeding value of the straw.The amount needed for a feed unit was about 2.2 kg, or less than for hay (Table 2).The amount of untreated straw generally needed for a feed unit is 5.5-6.0 kg (Anon. 1969).On average the bulls consumed 2.3 kg (variation I.B- kg) straw per day, or 0.77 kg DM/100 kg live weight.The contribution of straw to the total DM intake in the UREA and RSM groups was 34 and 33 °7o, respectively.The intake of treated straw varied widely between the animals.Similar intakes of alkali-treated straw have been obtained in other experiments with growing bulls (Arnason 1980).
In the RSM group the roughage/concen- trate ratio, calculated from the dry matter, Table 3. Live weight gain, feed consumption and slaughter results.
Groups RSM UREA After 6 months of age, the treated straw was the only roughage given to the bulls.The daily intake of straw was then 4.3 kg/ animal.Between the age of 3 and 6 months they also consumed hay, the average daily amount being 840 g/animal.was 39/61 and in the UREA group it was to 181 kg.The dressing %in both groups 40/60.This can regarded as reaching the optimal level (McCullough 1969).
The live weight gain was even and similar in the two groups; it was somewhat higher in the UREA group, but the difference was not significant (P > 0.05) (Fig. 1, Table 3).The feed conversion rate was also similar in the two groups, or on average 4.1 f.u./kg live weight gain.

Slaughter results and the health of the animals
By the age of 10 months all the animals had reached a carcass weight of at least 160 kg.In the RSM group it varied from 161 to 183 kg and in the UREA group from 163 averaged 49 %.
After slaughter, irritation of the mucous membrane of the small intestine was noted in all the animals; one animal had a liver abscess and there were three cases of inflammation of the kidneys.It has been reported from Norway that bulls fed on 4.7 kg DM ( = 69 %of total DM) of dry alkali-treated straw had heavier kidneys than bulls fed on untreated straw.In addition, after 12 weeks of feeding treated straw diarrhoea occurred and growth was retarded (Arnason 1980).

Fig
Fig. I. Live weight gain and feed consumption in different groups.

Table 1 .
Average percentages of different components in the concentrate mixture during the experi-

Table 2 .
The mean chemical composition and feeding value of the feeds.
contained 32 % rapeseed meal (Table1).Although this proportion of rapeseed meal was about twice as high as is generally 134In the RSM group, the concentrate mixture