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IntroductionIt is now over 20 years since experiments were first carried out in the U.S.A. on the possibility of developing satisfactory milk replacers for calves by combining separated milk with cheap vegetable or animal fats, but it is only in the last few years that the use of high-fat milk replacers has been realised commercially on farms in the U.K. One of the main reasons for this apparent slowness in development was that much of the early work was carried out before the significance of fat stabilisation and the importance of vitamin E in the nutrition of the calf had been fully realised and disappointing results were often obtained, particularly with unsaturated vegetable oils such as unhydrogenated cottonseed and soyabean oils. A further reason for some disappointing results seems to have been a lack of appreciation of the need for adequate emulsification and/or homogenisation of the fat in the milk replacer. More recent experiments have established the types of fat which can be included in milk replacers and also provided information on methods of inclusion to give the most satisfactory results in terms of animal performance.In the digestion of milk replacers it should be appreciated that when whole milk or a liquid milk replacer is fed to young calves a sucking mechanism operates and the milk by-passes the rumen and reticulum, by closure of the oesophageal groove, and enters directly into the abomasum or true stomach. The milk or milk replacer thus avoids fermentation in the rumen and is enzymically digested in the abomasum and intestines. Although digestion by the milk-fed calf is therefore similar in some respects to that of simple-stomached animals it is essential to recognise that important qualitative and quantitative differences between the calf and other species of farm animal do occur. For example the liquid-fed calf shows poor ability to digest ~t a r c h l -~ and little improvement due to adaptation in more prolonged feeding experiments,6 compared with a rapid development of ability to utilise starch by the young pig7 and a high efficiency of utilisation by the young chick.8 The liquid-fed calf also shows poor ability to digest vegetable proteinsgJ0 compared with the ability of the young pig7 and chick.8 With regard to fat, reported digestibilities of 83-93 % for certain animal and vegetable fats other than butterfat in milk replacers fed to calves2J-20 show that the young calf is inherently capable of adequately digesting a number of different fats as alternatives to butterfat. Although in this ability to digest fats the young calf shows some similarity to pigs and poultry, the differences in digestion and absorption of food constituents which are known to occur between pre-ruminant calves and other animal species are sufficient to emphasise the need for caution in any attempt to apply results obtained with other species to the calf. Incorporation of fat into milk replacersFat can be incorporated into milk replacers either by melting the fat and mixing it with separated milk powder or by hom...

A pilot study has been carried out to investigate the clinical use of an infrared diode laser in the treatment of a number of retinal vascular conditions. A hand-held device was employed initially and subsequently a further prototype was developed for use in conjunction with a standard slit lamp microscope. Thirty-three eyes in thirty patients were treated for conditions such as proliferative diabetic retinopathy, exudative retinopathy and branch and central retinal vein thrombosis. Regression of neovascularisation was observed in 13 of 16 eyes (81%) with proliferative diabetic retinopathy and in six of eight eyes (75%) with branch retinal vein occlusion. Four eyes were successfully treated for established or incipient rubeosis iridis following central vein thrombosis. Focal photocoagulation applied to five eyes for diabetic exudative maculopathy resulted in partial resorption of the exudates. These results are presented together with information on the ease of use of the laser and its reliability. The implications of the development of this instrument in the context of its place in ophthalmic therapy are discussed.