Oesophageal extrusa samples were collected from sheep grazing monospecific swards of four temperate perennial grasses. The in vitro digestibility and the proportion of green plant material in the extrusa samples were related exponentially to the yield of herbage on offer. The digestibility of ingesta was highly correlated with the yield of green herbage. When the yield of green herbage exceeded c. 550 kg/ha the sheep selected a diet more digestible than the mean of the green plant material on offer, and when there were low amounts of green herbage available the ingesta was less digestible than the green plant material on offer because of the low proportion of green plant material eaten. A relationship between the proportion of green plant material in extrusa samples and the green herbage yield was determined for each species, and no significant difference in regressions between species was found. It is suggested that the pooled relationship obtained in this study may be used to predict the proportion of green plant material in the ingesta of sheep over a range of grass species and yields.

S U M M A R YMeasurements of skeletal size were made at 2-3-month intervals on 30 Border Leicester x Merino castrate male (wether) sheep between 2 and 27 months of age. Fifteen sheep were fed ad libitum on a high-quality diet and the other 15 half the average amount consumed by the first group, age for age. The ad libitum group grew faster and were larger in all body dimensions on each occasion, except for leg length at 27 months which showed no statistical difference between groups. When the groups were compared over the live-weight range common to both (16-44 kg) the unrationed animals were consistently wider at the shoulders but smaller in leg and chest dimensions.The relationship between each body component and age is described by a Mitscherlich equation and the relationship with live weight by a linear equation in which both variables are log transformed. Separate relationships were determined for each sheep and tested for differences within and between groups.

SUMMARYCorriedale and Dorset Horn castrate male (wether) lambs reared at pasture were weaned at 19 kg live weight (LW), brought indoors and fed a high protein diet such that half of each group grew at ca. 200 g/day and the other half at ca. 100 g/day. Animals were slaughtered at 25 and 30 kg LW and chemical composition (protein, fat, energy, water and ash) of the body determined. The relationship between each body component and shorn empty-body weight was examined by regression analysis.Within levels of feeding the results were similar in the two breeds. When comparisons were made between feeding levels, the slower-growing animals contained more fat, energy and ash than the faster-growing group, less water, but similar amounts of protein at any given empty-body weight.

Techniques are described for assessing the effectiveness with which lipids may be protected against ruminal degradation. A simple in vitro test was developed using pancreatic lipase, and this test may have application in quality control of the commercial production of protected lipid supplements, as it is applicable to supplements containing polyunsaturated or saturated lipids. All the in vitro tests overestimate the actual in vivo biological effectiveness, and this is probably due to mastication and greater microbial activity in vivo than in vitro. The poor biological response of some protected lipid supplements is most probably due to the incomplete entrapment of lipid droplets in the protein matrix.

The digestion of nitrogen other than ammonia (NAN) in the small intestine of sheep fed on forage diets has been estimated by developing a structural relationship y = a+bx, where y = NAN (g/d) leaving the ilium and x = NAN leaving the abomasum. In this relationship the intercept a represents endogenous NAN passing from the ileum and the slope b the indigestibility of abomasal NAN; hence ( 1-b ) gives true digestibility. The values obtained (mean &SE) were: a = 1.04�0.32 and b = 0.34 � 0.02 , which indicated that the true digestibility of NAN leaving the abomasum was 66%. The amino acid composition of endogenous NAN leaving the ileum was estimated in ileal fluid collected from sheep whose rumens had been emptied and which were maintained by infusion of volatile fatty acids, minerals, vitamins and small amounts of amino acids into the stomach. The values obtained did not differ substantially from mean values obtained for abomasal and ileal digesta from sheep fed on four forage diets. Total amino acids (g/16 g NAN) in abomasal and ileal digesta and endogenous ileal fluid were 74.4, 62.9 and 82.5 respectively. From information on the true digestibility of abomasal NAN and the amino acid composition of digesta, estimates were made of the true absorption coefficients of individual amino acids from the small intestine. Values were mostly greater than 70% of the amount leaving the abomasum but for cystine the value was only 52%.

Human forehead skin incubated in vitro is known to metabolize testosterone to 17-oxosteroids faster than the reverse reaction, while axillary skin rapidly metabolizes androstenedione to 17 beta-hydroxysteroids, such as testosterone and 5 alpha-dihydrotestosterone. While this has been confirmed using a larger number of patients, some indication has been found that 17 beta-hydroxysteroid oxidoreductase activity declines with age in the axilla. The relative rates of 17 beta-oxidation and reduction (direction of operation of skin 17 beta-hydroxysteroid oxidoreductase activity) were not altered by variety of incubation conditions. Large amounts of a membrane-bound 17 beta-hydroxysteroid oxidoreductase, showing preference for NAD as coenzyme and testosterone (rather than androstenedione) as steroid substrate, were found in forehead skin from one patient. On the other hand, the main axillary skin enzyme in skin from another patient was soluble and showed preference for NADP and androstenedione. It is postulated that 17 beta-oxidation and reduction in skin is controlled by the relative amount, the coenzyme preferences and the kinetic properties of these two enzymes.

ABSTRACT.-Heart rates, respiratory rates, body temperatures, ad libitum 'day'and 'night' food consumption and body weight changes have been examined in 15 mature Merino wethers shorn in moderate environmental conditions. All sheep showed a depression in food consumption for two days after shearing. Sheep that gained weight during the next three weeks then increased their food consumption at night by approximately 30% although the average daily consumption was only increased by 5%. Sheep that lost weight showed a depressed food consumption throughout the three week period after shearing. Marked increases in the temperature difference between ear skin and air as well as thermal tachypnoea during the warmest period of the day were recorded in all sheep 14-16 days after shearing. This indicated that the critical temperature for all sheep had decreased by about 10oc. These signs of acclimatisation appeared at similar times in all sheep, suggesting that increased resistance to body cooling developed at similar rates in weight gain and weight loss sheep and independent of the origin of body heat production. The results of the investigations are discussed in relation to the concept that the initial response to cold stress includes a depression in food intake and that the duration of this depression is a function of the cold stimulus and the strain it induces in the sheep.

Some aspects of digestion were studied in small groups of fistulated wether lambs from two breeds, Dorset Horn and Corriedale. The Iambs were given a ground and pelleted diet of equal parts hay and concentrates once daily at two levels of intake. At the same liveweight (25 kg), the higher intake was associated with reduced digestion of organic matter (OM) and fibre in the whole gastro-intestinal tract; rumen mean retention times were also reduced, as was the proportion of OM digestion which occurred in the rumen. An increase in the amount of protein entering the intestines appeared to be composed of both undegraded dietary protein and microbial protein. Despite a reduction in the digestibility of non-ammonia nitrogen in the intestines, more crude protein was digested there per unit of digestible OM intake (25.9 v..23.6%; P < 0.05). Differences between the breed groups were smaller than those associated with level of feeding. Nevertheless, particularly at lower relative intakes, rumen mean retention times were longer, rumen digesta content was greater, and rumen OM and fibre digestion tended to be greater in the Dorset Horn lambs; crude protein digestion in the intestines per unit of digestible OM intake also tended to be less at the low intakes. More than three-quarters of the cellulose digestion but less than half the hemicellulose digestion occurred in the rumen. The proportion of the urea synthesized that was degraded in the gastrointestinal tract (0.24-0.30) was consistently lower in these lambs than has been reported for adult sheep.