A. J.
MACDONALD
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the poor quality of its proteins, for it is very possible that accessory food fac-
tors, such as vitamin B 2 , might have been at a sub-optimum level for growth.
Further, as experiments at Illinois [Lippincott, 1936] have demonstrated that
extracted soya bean meal gives better results than ground soya bean meal and,
as it is well established that chicks make poor utilization of rations containing
considerable amounts of fat, it is probable that the level of fat in the ground
soya beans may have had a depressing effect on the rate of growth. As the
unpublished data obtained from previous experiments carried out by the
author at the Rowett Research Institute, Aberdeen, had shown that extracted
soya bean meal supplemented by salt gave results somewhat similar to those
obtained with separated milk, it is possible that better results might be ob-
tained by using soya beans that have been subjected to a suitable process of
oil extraction. Hayward and his co-workers [1937] found that extracted
soya bean meal subjected to heat gives much better results than unheated soya
bean meal. As separated milk is often an expensive article of diet, it is pro-
posed to investigate these factors more fully in a further series of experi-
ments.
Though separated milk was the sole milk product used, experiments by
other workers [Card, 1926 ; Kempster and Parker, 1936 ; Swift, Black and
Voris, 1931] demonstrate that whole milk, separated milk, buttermilk, dried
skim milk and dried buttermilk have approximately the same nutritive value,
when fed at similar protein levels.
The results with soya bean meal supplements, though not so satisfactory
as those with milk, should not preclude the use of soya bean meal when milk
is difficult to obtain or very expensive, for additions of soya bean meal and
salt very materially improve the nutritive value of cereal rations. However,
from the results obtained in Experiments 3, 4 and 5 it appears advisable to
give milk during the early stages of growth.
The optimum protein levels in the ration of growing chicks have been
investigated by a number of workers. Heuser and Norris [1930] conclude
that chick rations should contain at least 20 per cent protein. Swift and his
co-workers [1931] state that the best growth results are obtained with rations
containing over 20 per cent protein. Hammond and his co-workers [1938]
conclude that optimum growth in young chickens is obtained by feeding ra-
tions containing 21 per cent protein. In all the 5 experiments under review,
where milk was used as the sole protein-rich food, the rate of growth of the
Leghorns and Rhode Island Reds compares favourably with standard figures,
even though the protein levels at all periods were very much lower than 20
per cent. The percentages of protein consumed by the different groups show
a considerable similarity, the consumption being high from 0-8 weeks, low
from 8-16 weeks and high from 16-24 weeks. In Groups 4 and 5, however,
the protein consumption remained fairly steady throughout. This was pro-
bably due to the fact that the milk turned sour in the feeding vessels and was
consequently more readily consumed than sweet milk. The average protein
percentage figures in the food consumed for all 5 milk groups were.—Period
1(0-4 weeks) 14.6, period 2 (4-8 weeks) 14.8, period 3 (8-12 weeks) 13.2,
period 4 (12-16 weeks) 13.3, period 5 (16-20 weeks) 14.1 and period 6
(20-24 weeks) 14.3. Though it is quite possible that slightly better growth