No abstract

A series of experiments is presented, describing the development of the rumen function in grazing lambs and the effects of' diet on the rumen development of artificially reared lambs. In grazing lambs the volume of the abomasum contents showed little change with age. The volume of the rumen contents increased with age, and the rate of' this increase was most marked from 3 weeks of age onwards. The volume of the rumen contents, relative to both the liveweight and the volume of the abomasum contents, was constant from 8 weeks of age onwards. The rumen volatile fatty acids (V.F.A.) concentrations in grazing lambs increased from birth and reached adult levels at 8 weeks of age. The total quantity of V.F.A. present in the rumen at a given time, relative to liveweight, increased up to 8 weeks of age but from this age onwards was approximately constant. The rumen ammonia nitrogen (N) concentrations in grazing lambs were high for the first few weeks after birth, but showed a continuous fall, reaching adult levels at 5 weeks of age. The quantity of ammonia N present in the rumen at a given time, relative to liveweight, increased up to 8 weeks of age and then remained approximately constant. The rumen volumes, V.F.A., and ammonia N concentrations were normal only in lambs that had been fed roughage. When lucerne chaff was fed to young lambs, the digestibilities of the dry matter, crude protein, and crude fibre were high, irrespective of whether the previous diet had been milk or chaff. The ad libitum dry matter intake from roughage, relative to the liveweight, increased up to 8 weeks of age and then remained approximately constant. When roughage was fed to lambs which had been reared on 'milk' (a preparation from dried cows' milk) only from birth to 9 weeks of age, the rumen V.F.A. concentrations rose immediately and levelled off at adult levels within 1 week.

1. A general survey of the histological changes of the fore-stomachs of the lambs from 46 days of foetal life to 77 days of post-natal life is presented.2. In all the rumen foetal specimens the mucosal surface was smooth. At birth small, conical papillae were visible and from this age onwards these papillae increased rapidly in size and tended to be long and tongue-shaped in appearance. Little change occurred in the appearance of the rumen papillae after 56 days of age.3. The outlines of the reticulum reticular ribs were visible in the 100-day-old foetal specimen. At birth the normal honeycomb-like structure of the reticulum was well developed, but the papillae on and between the reticular ribs were small and had rounded tips. From 20 days of age onwards the reticulum features increased in size and the papillae became pointed in shape.4. At 46 days of foetal life the omasum wall was folded to form developing laminae and by 70 days of foetal life laminae of four orders were present. The main age changes in the appearance of the mucosal surface from this age onward was an increase in the length of the laminae, the formation of small conical papillae on the laminae, and an increase in the inter-laminae spaces.5. All three fore-stomachs showed the same general histological changes with age. The epithelium changed from a stratified cuboidal type in the foetal specimens to a keratinized, stratified, squamous epithelium in the post-natal specimens. The basal layer of the epithelium became folded to form papillae, reticular ribs and laminae, and in the rumen and reticulum further folding of this layer took place to form papillary bodies.

1. Thirty-two single lambs were grazed together on pasture. At weekly intervals, from birth to 112 days of age, two lambs were slaughtered and various organs weighed immediately after death. Also the alimentary tracts of seven adult sheep were obtained immediately after death.2. The rumen had the fastest growth rate of the four stomachs, followed by the reticulum, omasum, and abomasum, in that order.3. Immediately after birth the four stomachs altered rapidly in their relative proportions, but by about 66 days of age they had reached approximately adult proportions.4. The weights of the liver, heart and kidneys, relative to live weight, decreased during the first few weeks of life, and thereafter remained constant.5. The weight of the spleen, relative to live weight, increased during the first week of life and thereafter remained constant.

The effect of the plane of nutrition in the first 13 weeks of post-natal life of cattle on their subsequent growth rate, body shape, and carcass composition up to 12 months of age was studied. No compensatory growth to 12 months of age was observed in calves reared to 13 weeks on low planes of nutrition. There were no significant differences between Friesian and Hereford x Friesian calves, or between males and females in empty body weight or weight gains. Treatment up to 13 weeks of age had no effect on heart girth, round, head length and width, and cannon bone length, but the remaining body measurements were reduced by low planes of nutrition during this period. Differences in carcass composition were largely a reflection of the differences in empty body weight. The carcasses of the males were heavier than those of the females and the females contained a higher proportion of fat. Carcass composition, as estimated by shin dissection, indicated that Friesian calves contained more muscle than the Hereford x Friesians, and the males more muscle than the females.