1. Increasing the pH of abomasal contents of the sheep in vitro reduced the concentrations of ultrafilterable calcium and magnesium due to the binding of these ions to suspended material in the digesta. In the presence of this material such binding prevented the precipitation of calcium phosphate and magnesium ammonium phosphate which would otherwise have occurred about pH 6·0. Calcium and magnesium soap formation was eliminated as a possible factor contributing to the reduced concentrations of ultrafilterable calcium and magnesium.

2. At saturation the binding capacity of the material was greater for calcium than magnesium. Although some of the binding sites were common to both ions calcium was more strongly bound. The bound and ultrafilterable forms of both elements were in equilibrium.

3. The significance of these findings is discussed.

1. A co-ordinated trial has been carried out at twenty-two centres to compare the value of wheat, crushed or ground, with that of fine wheat offal (weatings) when fed in equal amounts in the rations of growing pigs.

2. Pigs fed the wheat rations grew faster (8·7% improvement for crushed wheat, 6·3% for ground), had. more efficient food conversion (9·0 and 6·5%) and yielded heavier carcasses for a given final live weight (1·4 and 1·3%) than pigs fed weatings but were fatter at the shoulder (5·6 and 7·5%) and the loin (11·2 and 13·1%); all these effects were highly significant. Differences in length of carcass were not significant.

3. Improvements in growth rate and food conversion were significantly greater with crushed wheat than with ground wheat. None of the other differences between crushed wheat and ground wheat was significant.

4. An economic appraisal has been made which shows that, on the basis of certain assumptions, the feeding of wheat would have resulted in higher profit per year than the feeding of weatings under the price structure and system of grading prevailing during the period of the experiment.

5. Changes in the price structure (average price of bacon pigs, differentials between grades and cost of wheat and weatings), in the average quality of the carcasses (length of the carcass and fat at the shoulder and loin) and in the size of treatment effects on food conversion, all have a substantial effect on relative profits. The appraisal suggests, however, that feeding wheat would be more profitable than feeding weatings when the above changes were extremely severe.

The exhausting effect of dura for a single year in a rotation was shown. Rotations including dura consistently yielded less than those including lubia or fallow. With 2 successive years of dura the reduction in yields of cotton was extremely large.

Substantial increases in yields of cotton were obtained when the first fallow of the CFF rotation was replaced by lubia. The superiority of the rotation CLF appeared to be firmly established in the Gezira, where the soil was known to be deficient in nitrogen. By growing lubia, instead of leaving a fallow 2 years preceding cotton, an average annual increase of 0·65 k.p.f. of cotton was obtained. Itwas interesting to note that fertility of rotation CLF over CFF was still increasing.

When synthetic amino acids are added to an allvegetable diet the amount of nitrogen eliminated in the urine is reduced and the nitrogen retained as tissue protein is correspondingly increased.

The requirements of the weanling pig for essential amino acids have been critically examined, the work involving both growth trials and nitrogenbalance determinations in the metabolism crates.

The addition of synthetic lysine and methionine to a low-protein vegetable diet had a striking effect on the thriftiness of the pigs. It is possible to secure almost as good growth and economy of food conversion on a cereal diet supplemented with as little as 6 % ex. soya-bean meal, when the amino acids are added in appropriate amounts, as is obtained on a similar diet containing sufficient white-fish meal to support maximum growth

1. A cross-bred sheep was fed successively with supplements of dried skim-milk or lactose. The effect of the supplements on the lactase activity of the rumen liquid was followed.

2. Lactase activity was expressed as mg. lactose hydrolysed per ml. rumen liquid, or per mg. protein nitrogen. The enzymic activity fluctuated considerably after a change in the diet, and did not become constant even when the ration remained the same for 7 weeks.

The reproductive performance of 253 female Romney sheep of different ages has been studied from 1958 to 1960. Comparisons of the reproductive performance were made between ewes grazed on red clover pastures and ewes grazed on perennial rye-grass and white clover swards. The red clovers were oestrogenic during all periods of utilization.

The ingestion of oestrogenic red clovers caused the ewe lambs to accept the male before the start of the normal breeding season. No corpus luteum was found in the ovary of these lambs thus induced into oestrus. The subsequent reproductive performance of these ewe lambs at 2 years of age was not affected. The oestrus per se or the regularity of oestrus of the young (1½-year-old) or the aged (5½-year-old) ewes was not affected by the diet of oestrogenic red clover.

The ingestion of oestrogenic red clover did not affect the reproductive performance of the young ewes at 2 years of age, but did cause a protracted lambing season and a reduced level of lambing performance in the aged ewes at 6 years of age. No endometrial cyst was found in the aged ewes. It was suggested that the reduced level of reproductive performance of the aged ewes could have resulted from an unfavourable environment within the ewe, for the process of fertilization or implantation of the fertilized ova during the breeding season.

1. A total of twenty-one Merino lambs varying in age from 2 to 11 weeks were slaughtered.

2. The enzymic activity of their rumen contents was measured on a variety of carbohydrates and on protein.

3. Enzymic activity was expressed as mg. carbohydrate hydrolysed/mg. protein nitrogen/hour.

4. When compared with the rumen contents of adult sheep, lactase and proteolytic activity decreased with age; maltase, sucrase and fructanase activity increased; amylase activity decreased from 2 to 11 weeks though adult values were similar to those of the 2-week-old lamb.

5. The rumen contents of the lamb were as efficient as those of the adult sheep in their ability to hydrolyse a wide variety of carbohydrates and protein.

The use of a bone biopsy technique for skeletal studies with sheep is described. Histological examination of samples of pelvic bone removed at about mid-lactation from Scottish Blackface ewes grazing on two hill farms revealed little or no evidence of skeletal resorption. This was in agreement with the results of in vivo radiography carried out in this and another field experiment reported as part V of this series (Benzie, Cresswell, Duckworth, Hill and Boyne, 1961).

1. Studies on the mineralization of the skeletons Scottish Blackface wethers and breeding ewes have been carried out on three widely scattered and differing Scottish hill farms using field radiography and bone-ash analysis.

2. Regular small autumnal improvements in the density of the ewes' skeletons were detected by in vivo radiography using the right radii although, in general, the radii of the ewes were at all times considered to be in good condition (for Scottish Blackface sheep on the hill) and underwent no marked resorption (as judged from in vivo radiographs) during pregnancy and lactation. This was contrary to what was expected in view of the results of previously reported laboratory experiments (Benzie et al. 1955, 1956, 1959) and also in view of commonly held beliefs that hill pastures are, in general, deficient in calcium or phosphorus, or both of these dietary factors.

3. There were few significant flock differences (both ewes and wethers) for the values assigned to the radiographs or for the results of skeletal ash determinations even though the flocks were maintained in widely separated and differing locations and husbandry systems.

4. It is suggested that further field work along these lines may be of great value to the obtaining of a clearer understanding of the ewe: hill pasture relationship.

A factorial experiment designed to determine the time of ovulation relative to oestrus and to the cessation of progesterone treatment in cyclic maiden ewes, and subsequent fertilization of ova, is described. Seventy-two ewes were used. Factors were: (a) type of service (natural v. A.I with fresh undiluted semen v. A.I. with semen diluted 1:1 with heated cows' milk); (b) frequency of progesterone (daily v. every 2 days); (c) post progesterone withdrawal treatment (500 i.u. PMS v. no PMS); (d) week of treatment (3 successive weeks); and (e) days within weeks (2 successive days). Insemination was carried out on the third day after cessation of progesterone without reference to the results of teasing with vasectomized rams.

Progesterone (20 mg.) administered every 2 days was as effective as 10 mg. administered daily for suppression of ovulation. PMS resulted in a highly significant increase (P < 0·001) in the numbers of ewes which ovulated and which exhibited oestrus after progesterone, and in the number of fertile ewes (P < 0·05).

There was a considerable spread of time of onset of oestrus and of ovulation. This was unaffected by any treatment. Most ewes were served 24–96 hr. (peak 48–84 hr.) and ovulated 48–108 hr. (peak 72–108) after cessation of progesterone. The time relationships of oestrus, ovulation and ovum transport appeared normal.

1. The study of the photoperiodic responses of varieties and forms of the genus Avena has revealed considerable diversity within the group.

2. The investigation of a number of forms differing in geographical distribution confirms the close relationship between photoperiodism and region of origin. There appears to exist a definite relationship between the geographic origin of a given form and the limits of its tolerance to short day. The forms from the more southerly latitudes suffered less from short day than those of northern origin.

3. Panicle exsertion was entirely suppressed under photoperiods of 12 hr. and less in A. sativa varieties Victory, S. 84 and Black Supreme, which have been selected for high yielding ability in more northerly latitudes.

4. Plants which failed to produce exserted panicles in varietal tests were dissected, and it was found that floral differentiation had not been inhibited by the shortened photoperiods, but that the full elongation of the internodes, especially the upper internodes, had been suppressed.

5. Selection experiments with progenies of the cross Wintok × A.fatna form Cc 3872 grown under different photoperiods confirmed a highly selective response to daylength, thus indicating that this response is under genetic control.

1. Two panels of eight students, with no previous experience in scoring bacon sides for eye-muscle qualities or for fatness, co-operated in an experiment involving thirty-five photographs of back rashers of bacon presented to them in batches of twenty at a time. The members of the first panel made their assessments without any guide, whereas those of the second were provided with sets of photographic reference standards showing a graded sequence of rashers scoring from 0 to 10 for each of the two characteristics involved.

2. Those provided with the reference standards spread out their scores over the available range more than those who judged without them.

3. Judging discrimination between markedly different groups of rashers was improved when the reference standards were available. This was not true of discrimination between similar rashers since repeatability of scoring was to some extent decreased when the standards were used.

4. When the reference standards were not available, these inexperienced judges tended to adjust their level of scoring according to the quality of the batch of rashers being assessed. This adaptive effect was eliminated when reference standards were available although apparently random fluctuations of level of scoring from batch to batch still occurred.

5. Differences between judges due to their different uses of the available range of scores were less marked, although not entirely eliminated, when reference standards were used by the naive judges. Systematic differences between the scores awarded by various judges remained, as did a few differences of opinion on the relative quality of certain examples.

A factorial experiment is described in which seventy-two spayed crossbred ewes were used in four successive tests at intervals of 15 days in a study of factors affecting the detection of oestrus. Variates introduced in each test were: (a) number of rams to eighteen ewes (one or three); (b) size of mating paddock (17 acres or ⅕ acre); (c) dose of oestrogen (oestradiol benzoate, ODB: 10·0, 15·6, 24·4 μg.).

All ewes were primed with progesterone for 12 days prior to ODB injection and joining. The number of ewes detected in oestrus and the mean number of ewes served per ram were recorded.

In the four successive tests, thirty-two, fortyseven, forty-six and forty-one ewes were served (P < 0·05). Three rams working together detected ninety-eight ewes in oestrus while rams working individually detected sixty-eight (P < 0·001). Size of mating paddock had no significant effect (17 acres, 89; Jacre, 77).

The mean number of ewes marked per ram when used singly was indistinguishable from the mean number when rams were in groups of three (8·5 and 9·3). This resulted in multiple coverage of oestrous ewes when group joined (average 2·3 rams per ewe).

A factorial experiment is described in which thirty-six aged and thirty-six maiden spayed crossbred ewes were used in four successive tests at intervals of 15 days in a study of factors affecting the detection of oestrus. Variates introduced into each test were: (a) freedom of rams (free or tethered); (b) size of mating paddock (17 acres or ⅕ acre); (c) age of ewe (maiden or aged); and (d) dose of oestrogen (oestradiol benzoate, ODB: 10·0, 15·6, 24·4 μg.).

All ewes were primed with progesterone for 12 days prior to ODB injection and joining. The number of ewes detected in oestrus and the number and identity of rams which served each ewe were recorded.

In the four successive tests 29, 33, 36 and 30 ewes were served.

Significant main effects were: (a) freedom of rams—free 77, tethered, 51 (P < 0·001); (b) size of mating paddock—17 acres 49, ⅕ acre 79 (P < 0·001); (c) age of ewes—aged 57, maiden 71 (P < 0·05); and (d) dose of ODB—10·0 μg., 20; 15·6 μg., 41; 24·4 μg., 67 (P < 0·001).

Significant interactions were: (a) test number × age (P = 0·01), and (b) test number × dose of ODB (P < 0·05). The number of maiden ewes served increased and that of aged ewes decreased withsuccessive tests. There was a barely significant ohange in the slope of the ODB D/R line.

Ewes showed no obvious preference for tethered rams of any particular breed. There was a positive correlation between the performance of rams when free and tethered.

1. The utilization of the energy of the same ration by sheep and by cattle was measured using three steers and three sheep in twenty-one and twentyfour experiments, respectively. Five different amounts of the ration were given to each steer and six different amounts to each sheep.

2. No differences of any magnitude were found in the percentage losses of dietary energy in faeces, in urine or as methane if comparisons were made at comparable nutritional levels. Faecal energy losses increased and urine energy losses and methane production fell with increase in feeding level, the feeding level being defined as the ratio of food intake to that required to attain an energy retention of zero.

3. The net availability of metabolizable energy for maintenance was the same in both species at 80·4%. The net availability of energy for the production of fat was 53·5 ± 1·4 in sheep and 51·4 ± 2·6 in cattle.

4. The results are discussed in relation to the effect of the amount of food given on the utilization of its energy. It is pointed out that net energy per unit of food declines with increasing intake, due firstly to a decline in digestibility and secondly to the fact that oxidative processes operative at and below maintenance are more efficient processes than is the synthesis of fat.