A comparison was made between the Heal digestibility of the amino acids in pigs obtained by the use of a basal diet, the apparent Heal digestibility obtained with a semi-synthetic diet where peas were the sole protein source and the true Heal digestibility obtained with synthetic and nitrogen-free diets.

A latin square design with three periods of 3 weeks was used to measure the dry-matter intake, live-weight gain and water intake of 12 British Friesian calves offered an all-concentrate diet ad libitumin wet form. The diets contained 30% (B), 20% (C) or 15% (D) dry matter. A further six calves were given the same diet in dry form (A) throughout the experimental period. Digestibility and nitrogen balance were measured on four calves on each treatment at the end of the experimental period. In addition, two Ayrshire calves, each fitted with a permanent abomasal cannula, were used to study the site of digestion of the feed when given in dry or wet form.

The mean dry-matter intakes of the calves given the dry and wet feeds were 75·5 and 80·8 g/kg W0·75 per day respectively and mean daily live-weight gains were 849 g for the calves on both types of feed. The mean dry-matter intakes of the calves given the wet diets were 80·9 (B), 81·2 (C) and 75·5 (D) g/kg W0·75 per day, and the live-weight gains (g/day) were 857 (B), 879 (C) and 812 (D). None of these differences were significant. The intake of water by the calves was significantly increased by reducing the dry-matter content of the diet. The form or dry-matter content of the diet offered had no effect on the digestibility of dry matter (76·1%), organic matter (77·9%), energy (75·8%) or crude protein (75·8%) or on nitrogen retention (32·5% of N intake).

The rumen was the main site of digestion for all Tour diets and an average of only 7% of dietary starch passed undigested through the abomasum.

Results of an experiment involving a total of 24 individually-fed pigs, covering the growing period between about 40 and 210 lb. live-weight, indicated that the addition of 20 g./ton griseofulvin to the diet had a slight depressing effect on the rate of growth of the pigs. It had no significant effect on the efficiency of food utilisation, but caused a small reduction in daily food consumption.

Three trials, each involving 24 pigs, were conducted to assess the value of Hormonexa as a feed supplement for pigs slaughtered at 90 kg live weight. Rations were compounded from a variety of feeding stuffs to different protein levels and the pigs were fed on various nutritional planes. Hormonexa was added to these rations at the rate of 1·32 kg per 1000 kg meal.

In all three trials growth rate and food conversion efficiency were not affected significantly by the addition of the supplement. There was a tendency for the pigs receiving the supplement to be slightly leaner but in only 1 out of 39 measurements of fat thickness was the difference between control and supplemented pigs statistically significant (P< 0·05).

No benefit from this feed supplement has been demonstrated in terms of animal performance or carcass quality under a range of feeding systems.

Forty-two pigs representing equal numbers of entire males and females were used to study the effects on the performance and body composition of four restricted levels of feeding (14·5, 20·3, 24·9 and 29·4 MJ digestible energy per day), and of offering the same diet (14·5 MJ digestible energy per kg and 210 g crude protein per kg) ad libitum between 20 and 45 kg live weight.

Over the four restricted feeding treatments there were no significant differences between the sexes for the performance and body composition of four restricted levels of feeding (14·5, 20·3, 24·9 and 29·4 MJ digestible energy per day), and of offering the same diet (14·5 MJ digestible energy per kg and 210 g crude protein per kg) ad libitum between 20 and 45 kg live weight.

Although ad libitum energy intake was the same for both sexes (34·2 MJ digestible energy per day), raising digestible energy intake from that provided by the highest restricted feeding treatment (29·4 MJ/day) to ad libitum resulted in marked differences between the sexes for performance and body composition.

For males, raising digestible energy intake from 29·3 to 34·2 MJ/day improved the rate of live-weight gain and protein deposition by 0·15 and 0·10 respectively but had no further effect on food conversion ratio or body fat. The same increase in digestible energy intake for females improved growth rate by only 0·065, had no further effect on the rate of protein deposition but increased markedly food conversion ratio and body fat.

In pigs the quantification of breakdown and synthesis by powers of body protein led to the estimation of turn-over related protein retention efficiency by the equation kP = {1 + [1 − (P/α) (2/9)Q]−1/6}−1, with α the limit value of whole body protein (P) maturity, so that 0 ≤(P/α)≤1. The factor 2/9 is derived from diffusion attributes indicated by cell and nucleus geometries α and Q represents a scaled transformation of intake, 0 ≤ Q ≤ 1, such that a value of Q = 1 may represent ad libitum intake and Q = 0 the intake at the maintenance requirement. Published observations on finishing steers provide estimates of whole body protein synthesis and breakdown at pre-determined levels of intake in confirmation of the theoretical (2/9)Q power associated with (P/α) in kP. Further confirmation of the (2/9)Q power in cattle follows from satisfactory agreement between an estimate of conventional multiple regression retention efficiency and the turn-over related retention efficiency calculated at the given level of intake, for the mid point of the body mass interval covered by the regression estimate. In addition, a simulation experiment on cattle from the literature gives power estimates of protein breakdown and synthesis in general agreement with those accepted for pigs. Examples on both fine and coarse diets are employed to suggest a general rule for prediction on diets causing submaximal efficiency due to suboptimal intakes.

In sheep, evidence derived from estimates of conventional multiple regression efficiencies suggests that the rule (a-b) = (2/9) Q for the calculation of kP should be reserved for the description of compensatory growth. Protein retention efficiency for ordinary growth should be described by an adaptation of the rule derived for suboptimal intakes.

To mimic the abnormal patterns of follicular growth in the early post-partum period, heifers were injected with 15 mg oestradiol and 37•5 mg progesterone every 12 h for 7 days starting on day 15 of the oestrous cycle. Control and treated animals (no. = 8 per group) were monitored by daily ultrasonography and plasma hormone measurements. Five treated animals had quiescent ovaries for 11 days during which period oestradiol concentrations exceeded 30 pg/ml. After this, the first post-treatment follicular wave produced a normal ovulatory follicle. The other three heifers had quiescent ovaries for 17 days during exposure to high oestradiol values but this was followed by the formation of persistent follicles. The prolonged exposure to oestradiol probably disrupted normal LH surges in the latter animals. Growth rates and internal diameters for normal, ovulatory and prolonged persistent follicles were similar for the first 6 days after emergence, but the persistent follicles grew larger (P < 0·05) than normal follicles over the next 20 days. Luteinization of a subsequent persistent follicle was observed in one heifer. For 2 to 3 days prior to follicular growth, FSH concentrations were similar in controls, and heifers with ovulatory or persistent follicles (P > 0·05). When follicles first emerged and for the next 4 days, oestradiol concentrations were greater in follicles which later persisted (P < 0·05). For the second half of the life-span of persistent follicles, oestradiol concentrations were basal, thus the structure remained for many days after endocrine function had declined. These observations allow new interpretation of previously confusing findings in subfertile cattle presented to veterinarians.

Thirty-six male Ethiopian Menz sheep (9 to 22 months old, average live weight 15·8 (s.d. 1·84) kg), given maize stover (1·5 times ad libitum) supplemented with either 75 g cottonseed cake (CSC), 114 g noug cake (NGC; Guizotia abyssinica) or 112 g sunflower cake (SFC) with or without maize grain, were used in an 88-day study comprising growth and balance trials. The trials were undertaken according to a randomized-block design with a 2 × 3 factorial arrangement.

There were no significant interactions (P > 0·05). Sheep consumed significantly more stover when supplemented with CSC compared with NGC and SFC (P < 0·05). Maize grain significantly increased organic matter intake (P < 0·001). Although CSC tended to support lower live-weight gains, the effect of protein was not significant. Maize grain increased live-weight gains (P < 0·01).

Urinary nitrogen (N) excretions were similar between CSC and SFC but about 0·22 higher with NGC (P > 0·05). The faecal N output was 0·33 (P < 0·01) and 0·18 (P < 0·05) higher with CSC than with NGC and SFC respectively. Maize grain had no effect on any of the N-balance measurements.

Cottonseed cake supported lower daily production of purine derivatives (PD) (P < 0·01), microbial purine (P < 0·01) and microbial protein (P < 0·01) than either NGC or SFC. Maize grain increased the daily excretion of total PD (P < 0·05), microbial purine (P < 0·05) and microbial protein (P < 0·05). Neither the protein source nor maize grain affected the efficiency of microbial protein synthesis. It was concluded that SFC was utilized more effectively both in terms of rumen microbial N synthesis, N retention and growth. The addition of a small amount of energy as crushed maize grain increased microbial N synthesis, N retention and live-weight gain.

In this study, the effects of breed composition and predictor dimensionality on the accuracy of direct genomic values (DGV) in a multiple breed (MB) cattle population were investigated. A total of 3559 bulls of three breeds were genotyped at 54 001 single nucleotide polymorphisms: 2093 Holstein (H), 749 Brown Swiss (B) and 717 Simmental (S). DGV were calculated using a principal component (PC) approach for either single (SB) or MB scenarios. Moreover, DGV were computed using all SNP genotypes simultaneously with SNPBLUP model as comparison. A total of seven data sets were used: three with a SB each, three with different pairs of breeds (HB, HS and BS), and one with all the three breeds together (HBS), respectively. Editing was performed separately for each scenario. Reference populations differed in breed composition, whereas the validation bulls were the same for all scenarios. The number of SNPs retained after data editing ranged from 36 521 to 41 360. PCs were extracted from actual genotypes. The total number of retained PCs ranged from 4029 to 7284 in Brown Swiss and HBS respectively, reducing the number of predictors by about 85% (from 82% to 89%). In all, three traits were considered: milk, fat and protein yield. Correlations between deregressed proofs and DGV were used to assess prediction accuracy in validation animals. In the SB scenarios, average DGV accuracy did not substantially change when either SNPBLUP or PC were used. Improvement of DGV accuracy were observed for some traits in Brown Swiss, only when MB reference populations and PC approach were used instead of SB-SNPBLUP (+10% HBS, +16%HB for milk yield and +3% HBS and +7% HB for protein yield, respectively). With the exclusion of the abovementioned cases, similar accuracies were observed using MB reference population, under the PC or SNPBLUP models. Random variation owing to sampling effect or size and composition of the reference population may explain the difficulty in finding a defined pattern in the results.

Man-animal relationships are involved in the process of fox domestication. Handling being an important part of man-animal contacts, causes stress responses in farm-bred blue foxes. The purpose of this study was to determine how prenatal stress induced by handling pregnant vixens influences certain morphometric and hormonal parameters of adrenocortical and gonadal function in the prepubertal offspring. Blue fox females were subjected to daily handling sessions, each of 1 min, in the last trimester of pregnancy (term = 52 days). Plasma concentrations of ACTH, cortisol, progesterone, oestradiol and testosterone, as well as the in vitro adrenal and gonadal production of steroids were measured by radio-immunoassay in control (C, no. = 56) and prenatally stressed (PS, no. = 56) blue fox cubs of both sexes at the age of 6 to 7 months. Prenatal stress decreased plasma concentration of cortisol (C: 31·0 (s.e. 4·3) v. PS: 22·7(s.e. 1·6) ng/ml, P < 0·05) as well as progesterone (C: 1·00(s.e. 0·10) v. PS: 0·65(s.e. 0·05) ng/ml, P < 0·05) in female cubs. Prenatal stress did not cause any changes in adrenal or gonadal weights, plasma concentrations of testosterone or oestradiol, or in vitro adrenal or gonadal steroid production, in either sex. It is concluded that persistent handling of pregnant blue foxes did not affect the prepubertal development of the reproductive system but resulted in disregulation in the hypothalamic-pituitary-adrenal axis in the female offspring.

At birth, the Barki lambs used in this experiment were randomly allocated to three groups which numbered 133, 126 and 154 lambs of both sexes weaned at the ages of 10 weeks (Group I), 12 weeks (Group II) and 16 weeks (Group III) respectively.

The most pronounced differences between the three groups of lambs in their body weights took place at the age from 4 to 6 months. Group II lambs performed as well as or even slightly better than the other two groups, which leads to the conclusion that as far as the body weight of lambs is concerned there is no need to extend their suckling period more than 12 weeks.

The three groups of lambs varied little in their mortality rates from 2·5 to 12 months of age.

Groups of Dorper lambs were castrated at three ages: shortly after birth, and at two and four months of age. All were slaughtered at an age of six months and the carcasses subsequently weighed, graded, measured and scored. The results indicate no marked differences in either weight or quality of carcass between the treatments. It is concluded that the operation can safely be carried out, depending upon circumstances, at any stage between birth and four months.

Sorghum panicle residue (SPR), a by-product of Sorghum vulgare, obtained in the manufacture of brooms and wisks, has potential as a partial substitute for grain in growing-finishing diets for feedlot lambs. Accordingly, 48 Pelibuey×Katahdin lambs (initial weight=16.2±4.3 kg) were used in an 84-d growth-performance trial to evaluate its comparative feeding value. Lambs were blocked by weight and assigned within weight groupings to 12 pens (4 lambs per pen). The SPR was finely ground before it was incorporated into the diet. The basal diet contained 60% whole grain sorghum (WGS; DM basis). Dietary treatments consisted in the replacement of WGS with 0, 50, or 100% SPR. Replacement of WGS with SPR decreased (linear effect, P=0.04) average daily gain (ADG), and tended to increase (linear effect, P=0.06) dry matter intake (DMI). Replacement of WGS with SPR decreased (linear effect, P<0.01) gain efficiency (ADG : DMI), and observed dietary net energy (NE), as well as hot carcass weight, dressing percentage, kidney–pelvic–heart fat, and back fat thickness (linear effect, P⩽.05) Other carcass characteristics and wholesale cuts as a percentage of cold carcass weight were not affected by dietary treatments. It is concluded that SPR is a palatable feed ingredient for inclusion in finishing diets for feedlot lambs. The comparative NE values for SPR are 1.50 and 0.91 Mcal/kg for maintenance and gain, respectively, 75% the NE value of WGS. These NE values reflect the greater fiber content of SPR. To the extent that dietary energy density limits energy intake (and hence daily weight gain), appropriate constraints on level of SPR incorporation is warranted.

In a paper of this kind it would be very easy to be over ambitious and therefore be tempted to go too far in an effort to establish relationships between the physical and the other factors which have influenced the livestock policy of this region. Apart from the complexities of these relationships which make it difficult to determine their influence, there is generally a large gap in our knowledge of the physical data relating to livestock farming. For example it is only fairly recently that we have come to realise the subtle influence that certain “trace elements” have on the health of ruminant livestock, and also the marked differences that exist in the feeding value of grass of varied species according to the type of farming practised.

During the early stages of investigations concerned with the dietary requirement of dairy calves for certain amino-acids (Blaxter & Wood, 1952a), we had occasion to devise rations simulating milk to meet the calves’ basic requirements. These consisted of reconstituted dried skim-milk powder, glucose, trace elements, lard as a source of fat and a concentrated solution of vitamins A and D in arachis oil. The diet was comparatively cheap and the growth of the calves which were given it appeared quite satisfactory, at least for the first month. Then, quite suddenly, some animals developed alarming symptoms of muscular and cardiac derangement and some died. Examination of the calves at post mortem showed the presence of muscular degeneration which appeared comparable to a similar type of degeneration which had been observed in guinea-pigs and rabbits given rations low in vitamin E content (Goettsch & Pappenheimer, 1931). The ration which we had been giving to the calves contained only a few milligrams of vitamin E, since experiments in America had suggested that E deficiency in cattle took several years to produce (Gullickson & Calverley, 1946).

A review of recent trends in animal science is used to provide a flavour of how, from a purely technical viewpoint, evolving biotechnology may influence animal production systems in the foreseeable future. The areas considered are: the nutritive value of foods and forages, animal health and welfare, the temporary alteration of production traits to meet an immediate goal, and the permanent alteration of traits to meet an immediate goal, and the permanent alteration of traits by genetic selection or by the production of transgenic animals. In improving the nutritive value of foods, modern biotechnology has produced food grade enzymes and amino acid supplements. Genetically engineered cereals, grasses and legumes, rich in essential amino acids, are on the horizon. In disease prevention, genetically engineered vaccines may be preferable to conventional ones in that they have a defined composition, with a degree of control during manufacture which allows amino acid substitution within the peptide to confer specificity to a particular serotype.

Modern techniques with the potential to promote a transitory alteration in a production trait involve either immunization against an inhibitory biochemical pathway or active promotion of a stimulatory pathway by the administration of recombinant-derived hormones and proteins. Strategies for permanent alteration of traits by gene transfer, initially directed to enhancing growth, are now shifting in emphasis towards the transfer of genes for enhanced nutrient digestion, disease resistance, and improved product quality. The role of recombinant DNA technology in the development of diagnostic probes for use in genetic selection programmes and in the monitoring of disease is also expanding rapidly.

In all areas of animal science, molecular biology is promoting a better understanding of the underlying mechanisms that control production. By so doing it should ensure that science fulfils its primary rôle of providing animal production industries with a range of options from which to choose the most acceptable way forward.

1. The primary growth of perennial ryegrass was cut between 7 and 9 June and ensiled with formic acid at 2·5 1/t. The regrowth was cut on 24 July; part was dried at high temperature (dried grass), the remainder was left to dry in the field (hay). The dried grass (DG) and part of the hay were ground and pelleted, the hay being pelleted alone (PH) or with the addition of formaldehyde at 20 g/kg crude protein (PHF). The remainder of the hay was offered in the chopped form (CH). The four supplements (CH, PH, PHF, DG) were offered at two levels, 6·5 (L) and 130 (H) g dry matter per kg live weight to 54 British Friesian steers (initial live weight, 110 kg) receiving the silage ad libitum.

2. The silage had a high pH and a high proportion of the total nitrogen was in the form of ammonia, indicating poor fermentation. The solubility of nitrogen in the supplements was highest (262 g/kg total nitrogen) in CH, progressively less in PH and PHF and lowest (122 g/kg total nitrogen) in DG.

3. Total dry-matter intake was highest with DG at the higher level of inclusion. Dry-matter intake was significantly higher for PH and PHF than for CH (P < 0·001). However, intake of digestible energy did not differ between hays. Live-weight gain was increased from a low level of 0·24 kg/day (silage alone) by all supplements, but this effect was greater with DG than with the hays (P < 0·001). Level of supplementation increased live-weight gain from 0·54 to 0·74 kg/day.

4. Supplements of dried grass gave higher live-weight gains than did hay made from the same sward. However, the results indicate that supplementation of badly preserved silage with grass hay of good quality can produce acceptable levels of performance of up to 0·70 kg/day in 4-month-old steers. Processing of the hay had little effect on animal performance.

The effect of monensin supplementation on suckling male dairy calves was studied on a commercial farm. Twenty-eight calves were given monensin supplements from the age of 1 week and compared with a similar group not given monensin. During a 52-day suckling period, the supplemented calves gained 0·12 faster, with little difference in the conversion ratio of metabolizable energy into live weight. During the subsequent 42 days, there was no difference in daily gain, but the supplemented animals were 0·064 more efficient in the conversion of metabolizable energy into live weight.

One of the causes of culling dairy cows is low milk yield and to the extent that this has any genetic basis one might expect the daughters of old cows to outyield their contemporaries from younger and hence less selected mothers. This is quite apart from any confounding effects resulting from the non-genetic influences of dams' parity. The rate of genetic improvement derived from the culling process will be modified within a population by the extent to which farmers choose to retain the progeny of older rather than younger cows. Milk yields for recorded cows in Scotland, available to the Livestock Records Bureau, have been used to obtain some information on these points.