The frequencies of calving difficulties were computed for 458 calvings of first and second parity Friesian, Ayrshire and Jersey dams with pure and crossbred progeny in all possible combinations. It was found that heavier breeds of dams have higher frequency of difficult calvings. For each breed of dam there is also a direct relationship between the mean birth weight of the calves and the frequency of calving difficulties associated with the breed or cross of calf.

An index of calving difficulties calculated in the form of a discriminant function which combined both the birth weight of the calf and the calving weight and parity of the dam was: Z = log BW−0· log DW−0·10 P,

where Z is the index of calving difficulties, BW and DW are respectively the birth and dam weight and P the parity variable withthe values of one for second parity and zero for the first.

The lactation curve in cattle has been explained by the expression yn = Anbe-cn where yn is the average daily yield in the nth week, and A, b, and c are constants. In general, in a sample of 859 Friesian lactations recorded during 1964–65 daily yield was depressed during the winter months (18·8% in January) and stimulated during the spring (14·7% in May) to an extent which was independent of the stage of lactation. Winter calvers on the other hand tended to produce more in total lactation than spring calvers (14·5% for animals calving in November as opposed to those calving in April).

Using a suitable technique it is possible to predict month by month output from a cow, or herd, accurately enough to furnish a basis for forward planning.

Data from a boar progeny testing scheme based on ad libitum feeding were analysed to test the hypothesis that the resultant correlations of food conversion ratio with related factors would differ from those found under conditions of restricted feeding.

The results support the hypothesis, showing that the primarily genetic correlations derived from boar effects for growth and conversion ratio, are lower than those reported elsewhere for restricted feeding. It was also shown that these primarily genetic correlations could vary between breeds, the leanness associated with rapid growth in Wessex not being found in Large White, and that the correlations due to residual effects containing a greater environmental component varied widely from test to test.

It is concluded that the parameters used in the design of a genetic improvement scheme should be derived specifically for each breed and feeding system. However, if the marked variability in phenotypic correlations noted here is generally applicable, this could present a difficult problem in the design of pig improvement programmes with multiple objectives.

Two experiments were carried out to compare the performance and carcass quality of pigs given diets based on barley, wheat or maize meal, and another two experiments comparing these cereals, flaked maize and sorghum. In general, differences in the utilization of feed for live-weight gain could be related to differences in the digestible energy content of the cereals used in the diet, although in some experiments pigs behaved atypically on individual diets. Flaked maize was consistently inferior to the other cereals in the efficiency of conversion of its digestible energy, possibly because of its poorer amino acid balance and its low levels of lysine and tryptophan in relation to energy. Differences between experiments in the performance of pigs fed on the various diets are also discussed. Differences between treatments in killing-out percentage and predicted lean percentage were small, and carcasses of pigs from all treatments were acceptable for bacon curing.

A dramatic fall in the colostral whey proteins of nine sows occurred within 24 hr following the birth of the first piglet. The mean levels fell from 19·6 g/100 ml to 4·1 g/100 ml, 50% of this fall occurring within 4 to 6 hr. It is suggested that as early-born piglets will be able to obtain colostrum of a much higher protein concentration this may give them some physiological and immunological advantages over later-born littermates.

Colostral whey protein levels do not change during the first 4 hr from the start of parturition when suckling is prevented. Both early and late-born piglets returned to the sow at the end of this period are able to suck colostrum of a high protein concentration. Removal of piglets from the sow and the presence of an attendant did not affect the farrowing process.

Data were obtained on 3028 lambs born during five successive years from 1961 to 1966 at Ras El-Hekma Desert Research Station in the Western Coastal Egyptian Desert. Breed groups involved in the study were Hungarian Merino, Syrian Awassi, native Barki sheep, and nine of their crosses. The characters studied were birth weight, weaning and yearling weights, pre- and post-weaning average daily gain and yearling greasy fleece weight. The effects of breed group, year of birth, sex, age of dam and type of birth on these characters were investigated.

The results obtained showed that Barki lambs excelled Merino lambs in all the traits related to body growth. Merino lambs, on the other hand, excelled Barkis in fleece weight. Barki lambs also excelled Awassi lambs in all traits except birth and weaning weights. In all characters except pre-weaning gain, the first cross of Merino and Barki (½M½B) was markedly superior to all the other crosses and pure breeds. The two third-crosses, ⅜ M ⅝ B and ⅝ M ⅜ B, were similar to each other in their productive traits and were slightly inferior to the first cross. The two back-crosses, ¼M¾B and ¾M¼B, were markedly different from each other, the former being better than the latter. The three-eighths Merino group is suggested for developing a new strain of sheep for the semi-arid regions. The effects of the environmental factors on the six characters studied were all highly significant except for the effect of sex on fleece weight and the effects of age of dam and type of birth on growth from weaning to yearling ages. The most important factor affecting the different traits was year of birth. Type of birth and age of dam were important sources of variation only for the characters studied till weaning age, but became of little importance thereafter. The effect of sex was pronounced only on yearling weight.

Records on 695 lambs were collected over a period of 5 years from 1961/62 to 1965/66, at Ras El-Hekma Desert Research Station, 230 km west of Alexandria. The characters studied were birth, weaning and yearling body weights, pre- and post-weaning daily gains and greasy fleece weight.

Birth, 120-day and 365-day body weights were 3·4, 18·2 and 33·4 kg respectively. Greasy fleece weight at 16 months of age was 3·29 kg. Heritability estimates of birth, weaning, yearling weights, pre- and post-weaning daily gains and greasy fleece weight were 0·22, 0·45, 0·41,0·45 and 0·29 respectively. Genetic and phenotypic correlations between birth, weaning and yearling weights were all positive and significant. Genetic correlations between fleece weight and body characteristics were negative and low.

The ability of two groups of six Merino wethers aged 6 and 66 months to digest a lucerne ration was examined in order to detect possible biases in the use of faecal nitrogen as a faecal index substance. Earlier work with this technique had indicated a difference in selectivity between young and older sheep. No difference in ability to digest the ration was observed and it was concluded that the earlier observation was not an artefact in the faecal nitrogen technique. Oesophageal fistulae were prepared in 120 sheep differing in breed, sex, age, strain and previous history. Determinations were made of the nitrogen content, and in one experiment of the in vitro digestibility of the diet selected by sheep grazing various pastures. Significant differences in the nitrogen content of the diet selected by sheep varying in breed, age and previous grazing history were recorded on some pastures on some occasions but not on others. No significant differences were observed between sheep varying in strain or sex. No reason could be suggested for the occasional differences between groups in the nitrogen content or digestibility of the diet selected, but it appeared unlikely that it would be a major source of variation in the productivity of the different groups at pasture.

Digestibility was estimated in vitro from a total of 167 oesophageal fistula samples collected over a period of 16 to 24 months from adult sheep grazing eight Phalaris tuberosa-Trifolium repens pastures stocked continuously at rates of from 2·5 to 37·1 sheep per ha. Corresponding estimates of the nitrogen content of the faeces and of the fistula samples, the live weight and faecal output of the sheep, and of the herbage availability of the pasture were obtained.

The observations were stratified on the bases of stocking rate, digestibility, month of the year, herbage availability or organicmatter intake. Relationships between digestibility estimated by the fistula technique and faecal nitrogen content (model B) and between digestibility and faecal nitrogen content, nitrogen content of the dietary dry and organic matter, and faecal output per unit live weight (model A) were calculated for each stratum.

There were significant differences between relationships derived for the various stocking rates, levels of digestibility, times of year, levels of intake and levels of herbage availability; predicted values of digestibility for given values of the independent variables differed by as much as 20 units of digestibility. Model A was substantially more precise than model B.

Differences between estimates of digestibility, derived by the fistula technique and by a general faecal nitrogen—digestibility relationship, established by Lambourne and Reardon (1963a) were calculated. The differences were related to digestibility and to herbage availability.

The implications of these results are discussed and it is concluded that faecal nitrogen content is not a satisfactory index of the digestibility of the diet selected by grazing sheep.

Two experiments were carried out to study the energy requirements of young fattening lambs for maintenance and production. Forty weaned lambs were used in each experiment, 20 being allocated to a high level of feeding (900 g air-dry feed per day) and 20 to a low level (540 g). The animals used in Experiment 1 were approximately 12 months of age and their mean live weight was 35·3±4·03 kg. Those in Experiment 2 were approximately seven months of age and their mean live weight was 36·7 ± 4·57 kg. Experiment 1 continued for 100 days and Experiment 2 for 47 days. Three digestibility trials, involving three animals from each feeding level, were carried out during the course of each experiment to obtain precise estimates of digestible organic matter intake (DOMI). The estimated mean DOMI required for maintenance for a 45-kg lamb was 400 g (0·88 lb) or 1500 kcal metabolizable energy per day. The estimated maintenance requirement was not affected by the age of the animal. The DOMI required for production ranged from 1·55 kg per kg live-weight gain for the younger animals to 1·71 kg for the older animals. Both these requirements were lower than those obtained by other workers and those suggested by the Agricultural Research Council (1965).

Thyroid activity was assessed in two groups of crossbred lambs and in Dorset Horn lambs fed ad libitum, by measuring the rate constant (K4) for the release of 131iodine from the gland. The results demonstrated a highly significant curvilinear correlation (P<0·001) between growth rate and the rate constant (K4) in experiments based on individual measurements in animals from three populations.

Separate work carried out on the measurements of both thyroid size and RNA/DNA ratio suggests a need for caution when these are interpreted as parameters of thyroid activity. In the growing animal these may be more reflective of the growth of the thyroid gland itself, differences which may be governed by factors not directly related to variations in hormone secretion rate.

The findings are discussed in terms of an explanation of the contradictory results obtained where attempts have been made to alter the thyroid status of growing animals by the use of thyroid hormone analogues and thyroid depressant drugs.

Eighty-two Scottish Blackface castrated male sheep were used to test whether, from weaning to near maturity, the gigot grew exactly proportionally to the half carcass and whether the tissue in the gigot grew at the same rate as the respective tissue of the half carcass.

While slight deviations from exact proportionality of growth occurred, none could be adjudged significant or important. If the gigot does not grow directly proportionally to the half carcass the data suggested that the gigot tended to grow slightly more slowly than the total half carcass over this period. If gigot muscle does not grow proportional to the total muscle the data suggested that gigot muscle might grow slightly more slowly. If growth of bone tissue is not directly proportional between the gigot and the half carcass the tendency was for the gigot bone to grow slightly faster than total bone while the fatty tissue of the gigot showed a slight tendency to grow more slowly than the half carcass fatty tissue.

In the first of two experiments, steers which received a single implant of 60 mg hexoestrol grew 24% faster than non-implanted controls and 7% faster than steers given 30 mg. The growth rate of the steers given a single implant of 60 mg did not differ significantly from that of animals implanted twice with 30 mg or 5 times with 15 mg. In the second experiment, steers given 60 mg grew 23% faster than controls and their feed conversion efficiency was 13% better; the hexoestrol treatment resulted in a saving of 131 kg feed per animal. The tenth-rib joints of steers given 60 mg had a higher crude-protein content and lower fat content than those from non-implanted animals.

The LDH values in blood plasma of Pietrains and Large Whites are significantly different during moderate stress (sampling of blood), being higher in the Pietrains. The difference is largest in the LDH-5, the muscle iso-enzyme. Not only are the values higher, but the isoenzyme is also demonstrable in more individual animals.

More stressful situations (forced muscular exercise) result in a rise in plasma LDH-5 in both breeds; the rise is larger in the Pietrains. Two possible causes for the higher LDH-5 values in Pietrain blood plasma are suggested.

Three trials have been made with growing pigs to measure the digestibility of four samples of wheat offal. Two samples were measured at the levels of 0, 20, 40 and 60% of the diet and two samples were measured at the levels of 0 and 60% of the diet. The offal replaced equal quantities of glucose in the diets and no attempt was made to equalize nutrient levels between diets.

Apparent digestibility coefficients of the diets declined with increasing dietary wheat offal content, but the digestibility of wheat offal did not change with level of inclusion. No differences in digestibility occurred between offals from hard and soft wheats, apart from a low N digestibility in one sample of soft wheat offal. The average digestible energy and TDN contents were 2810 kcal/kg and 63·1 for samples of offal containing 12·5% moisture.