Milk yields determined by a lamb-suckling and an oxytocin technique were compared using a control group of four ewes. Both methods showed a similar linear decrease in yield with advancing lactation, but the oxytocin method gave 23% more milk presumably because residual milk was included.
When the diet of lactating ewes was changed so that the amounts of hay and commercial concentrates were reduced in favour of flaked maize, such severe acidosis developed when 39·5% of this food was introduced abruptly or 53% more gradually over one week, that the trials were discontinued.
Rolled barley, which probably ferments more slowly, was therefore used instead of flaked maize. Levels up to 62·9%, gradually introduced over a period of 3 weeks, also produced acidosis whose severity varied greatly in individual ewes.
Milk yield was also determined by the oxytocin technique for ewes receiving normal diets followed by those rich in rolled barley, and the milk was analysed for fat, protein and lactose. The composition of the milk was extremely variable during rolled barley feeding, but there was an indication of an increase in the percentage of crude protein and also fat, after a marked fall in the latter in the milk of two ewes with the change to the low-fibre diet.
Diet had little effect on yields of milk and its components but, on the rolled barley diets, the rate of decrease of these yields was arrested (or even reversed in the case of fat), with a high degree of significance (milk yield P < 0·05, fat yield P < 0·01, protein yield P < 0·01). These observations are discussed, in the light of knowledge on the effect of diet on molar proportions of volatile fatty acids in the rumen.