Two experiments were conducted to determine whether the depression in fibre digestion caused by inclusion of fat in diets could be alleviated by addition of urea and whether the physical incorporation of fat in itself caused a reduction in rate of fibre digestion.

Early-weaned lambs were given dried grass containing either 65 or 130 g/kg of tallow with or without 15 g/kg of urea. Fat inclusion caused a linear depression in intake and fibre digestibility. The depression in intake was partly alleviated by urea inclusion, but urea did not affect fibre digestibility.

The physical incorporation of fat into dried grass did not in itself appear to depress rate of digestion. It is suggested that if coating of feed particles is important then this would be due to non-esterified fatty acids in the rumen and not to triglycerides.

In two trials, male Suffolk sheep were weaned at birth and reared artificially. Animals were ranked on weight at about 90 days and groups comprising the fastest- and slowest-growing animals were selected. The selected rams were subsequently progeny-tested to the same age, with some progeny reared with their dams in normal field conditions and others reared artificially.

In Trial I, performance tests were obtained on 35 rams and progeny tests of seven of these (three low and four high), with records on 34 artificially reared and 144 naturally reared progeny on one farm. The regressions of progeny on sire 90-day weight were 0·29 ± 0·12 and 0·19±0·09, respectively.

In Trial II, performance tests were obtained on 86 rams, sampled from five source flocks. Rams were selected in pairs of high and low performance from each source, and both members of the pair sent to the same one of seven farms for progeny testing. Ten pairs had progeny tests, comprising 62 artificially reared and 567 naturally reared progeny. The regressions of progeny on sire weight were, respectively, 0·05 ± 0·06 and 0·13 ± 0·03 if source of sire was fitted in the model, and little different, 0·06 ±0·05 and 0·14 ± 0·03 if source of sire was ignored. Progeny from a 2nd year from some sires in Trial II gave rather smaller regression coefficients: 0·06 or 0·09, with source of sire fitted or ignored, respectively.

Taking the two main trials together the pooled estimates (ignoring source of sire) of doubled progeny-on-sire regression for 90-day weight were 0·20 ± 0·10 for artificial rearing (a heritability estimate) and 0·30 ± 0·06 for natural rearing. These results suggest that early weaning is an effective method of selecting sires for growth rate.

The effects of breed type and season on semen quality and libido were examined. Tests were carried out in autumn, winter, spring and summer using 47 rams of five breeding groups, namely the the Fleisch Merino, the Ossimi, the first cross and the two parental backcrosses. All the rams were born and reared locally.

Except for the percentage of abnormal sperm cells and time to first mount, semen quality and libido were not affected by breed type. There was little consistent evidence of heterosis in any of the traits examined. All traits except time to first mount were significantly affected by season. Semen was of better quality in autumn and spring than in winter and summer. With one exception all aspects of libido were depressed in winter.

Breed × season interactions were significant in six of the 10 traits studied but showed no consistent trends.

The reproductive performance of Merino rams was not adversely affected by the environment. This indicates the feasibility of introducing new breeds so far as semen quality and male libido are concerned.

The coefficients of inbreeding and the degree of relationship for British Friesian bulls used for artificial insemination by the Milk Marketing Board in sample years between 1955 and 1972 and for random samples of registered females from the same years have been calculated. The average coefficient of inbreeding was lower in bulls (0·5%) than in registered females (2·7%). The average degree of relationship was 0·7% for bulls and 2·6% for heifers.

A system of time-controlled feeding has been developed to give a considerable degree of control over the food intake of animals without eliminating individual variation.

The system is based on the Calan-Broadbent electronic feeding doors and animals are conditioned by certain electrical and sound stimuli to use the doors only during prescribed periods. Clock mechanisms control the time intervals when electric power to the doors is on or off.

Times and durations of feeding can be adjusted so that a predetermined level of intake is obtained, and a heavy demand on labour is avoided.

In the present trial, British Friesian and Jersey cattle on a time-controlled feeding regime were compared with animals given access to food ad libitum. A significant reduction in food intake due to time-controlled feeding was detected in both breeds over a 6-month period.There was no evidence to suggest that the particular time-controlledfeeding regime restricted one breed more than the other.

From July 1975 to January 1977, 225 cows in three autumn-calving dairy herds were condition-scored, weighed and milk-recorded at monthly intervals. The condition score at calving was related to the ability of the animal to achieve potential milk yield. This potential milk yield was denned by the lactation curve prediction. Animals below condition score 2 at calving did not achieve their predicted milk yield, and those above condition score 2½ yielded more than their predicted milk yield. Cows in poor condition at calving gave low, late peak milk yields with a high persistency, and those in good condition at calving gave high, early peak milk yields with a lower persistency. A positive relationship of 25 ± 1·6 kg live weight per unit of condition score was established within cows in months 1 to 7 of lactation. After month 7 of lactation foetal development caused changes in live weight without changes in score.

High (1·31 kg/1) or medium-density (1·17 kg/1) dried grass pellets of 9, 12 or 18 mm diameter were given to British Friesian male calves of 7 to 14 weeks of age as supplements to chopped hay (Experiment 1). Pellets were given ad libitum but with access limited to two periods of 1½ h per day, and hay was given ad libitum for the remaining 21 h. In Experiment 2, high (1·34 kg/1) or medium-density (1·14 kg/1) dried grass pellets of 18 mm diameter were given to British Friesian male calves of 26 to 30 weeks of age. Pellets were given as supplements to chopped hay as in Experiment 1.

There was no effect of pellet size or density on total intake of organic matter or live-weight gain by calves in either experiment. With the exception of animals given pellets of 12 mm diameter in Experiment 1, animals in both experiments consumed less pellets of high density than of medium density, but they were able to compensate for low pellet intake by eating more hay.

The coefficients of variation for intake were higher in Experiment 1 than in Experiment 2, and higher for the intake of pellets than for total intake. There was a progressive increase in the intake (g organic matter/kg M0·75 per day) by calves in Experiment 1, whereas in Experiment 2 intake increased for the first 10 days and then remained constant. On average the proportion of pellets and hay consumed did not change in Experiment 1, but in Experiment 2 the proportion of pellets in the feed consumed increased from 53·5 to 60·6%.

British Friesian and Jersey cows were mated either to high contemporary comparison (CC) bulls for their first pregnancy and to low bulls for their second pregnancy, or vice versa. Sixteen proven bulls were used, four ‘high’ and four ‘low’ in each breed. Least squares analysis of data on 175 lactations gave estimates of each bull's effect on his mates' milk yield in the ensuing lactation, but there were no significant differences between bulls for this ‘mate effect’. The high bulls tended to depress their mates' milk yield in the subsequent lactation and the low bulls tended to increase it. Weighted regressions of the ‘mate effect’ on breeding value had negative slopes for both breeds and for first and second lactations, separately or combined. The high CC bulls appeared to depress their mates' milk yield by at least 10% of the amount by which their daughters' yield was expected to increase.

To estimate the effect of supplementation on hay: grain substitution rates, 18 experimental rations were evaluated in digestibility trials, each using four steers (300 kg live weight) housed in metabolism stalls. Four hays (digestible dry matter = 40 to 62 %) were given to appetite, supplemented with maize grain plus urea at several different levels, up to 2·5% of animal live weight, and substitution rates were estimated as the slope of the linear regression of hay intake on grain intake. General substitution rates were independent of hay quality, and the pooled rate was 830 g (Sb = 0·036) per kg of grain dry matter. Nevertheless, the analysis of the observed partial substitution rates and those in the literature, suggests a possible interaction between the effects of hay digestibility and grain level on substitution rates.

1. Three trials were conducted to investigate in cattle of different ages the digestibility of whole barley and whole oat grains in diets with approximately a 1:1 ratio of hay to concentrates. The cattle used were four 17-month-old steers in Trial 1; four non-lactating cows in Trial 2; and six heifers at 7, 10, 13 and 16 months of age in Trial 3. 2. Steers and cows completely digested the starch in the rolled cereals and the steers digested more of the starch of whole barley than the cows. The digestibility of starch in whole oats was high (0·72) and similar in both types of cattle.

3. The heifers when 7 months of age had the highest coefficients of starch digestibility for both whole barley and whole oats (0·62 and 0·83 respectively). Digestibility of starch declined with age, but this effect was masked by variations within and between animals at different ages. It is concluded that barley should be rolled before feeding but with oats the benefits from rolling are likely to be small and possibly only worth while when given to adult cattle.

During lactation 30 sows were given a basal diet containing 0·39% lysine or the same diet supplemented with 0·1, 0·2, 0·3 or 0·4% Llysine. In addition a group of six sows was given a high protein/high lysine control diet containing 17% crude protein and 1·06% lysine. Piglet weight gain, sow milk yield, milk contents of total solids, protein, fat and energy and efficiencies of utilization of energy and protein for milk production increased progressively as dietary lysine levels were raised to 0·59 %. Sows receiving the lysine-supplemented diets had markedly higher efficiencies of conversion of dietary protein into milk protein and lower efficiencies of energy utilization than those given the high protein/high lysine control diet.

Nitrogen retention and biological value of the dietary protein increased quadratically with increasing dietary lysine concentrations, reaching maximum values at 0·59% lysine.

Apparent digestibilities of isoleucine, lysine, methionine, threonine and valine in the basal diet were closely correlated with digestibility of nitrogen. Plasma lysine concentrations remained depressed and relatively constant at low dietary levels of lysine, but increased sharply at 0·59 % dietary lysine coinciding with a marked drop in circulating concentrations of other essential amino acids.

In an experiment which showed that the results of a genotype comparison are influenced by the design of the test, 16 castrated male and 16 female pigs of each of Large White (LW) and Gloucester Old Spot (GOS) breeds were allocated equally among four treat- ments: WW—rationed by weight and slaughtered by weight; A A—rationed by age and slaughtered by age; AW—rationed by age and slaughtered by weight; and WF—rationed by weight and slaughtered after a common total feed intake. The experiment was designed so that performance of LW would be similar on all treatments, and the degree to which the GOS differed from the LW on each of these treatments was then evaluated. All pigs started on the experiment at 12 weeks of age, at which time mean weight of the LW was 14% greater than the mean for the GOS. The only between- breed difference that was statistically significant (P<0·05) on all treatments was weight of lean. Average daily gain and efficiency of feed conversion were significantly different between breeds only on the WW treatment. Weight of fat was significantly different on WW and AW but not on AA or WF.

Analysis of data from British Saddleback females mated to Landrace males on 18 multiplying units for a commercial breeding company shows that the important herd effects known to affect litter size in pigs are truly environmental in origin.

Sixteen healthy ewes of the Marwari breed were randomized and four ewes allocated to each of the following treatments: control, 0·5%, 1·0% and 1·5% sodium chloride in the drinking water. Blood volume, total body water, extracellular fluid volume, intracellular fluid volume and interstitial fluid volume were determined. The results showed that Marwari sheep have a remarkable tolerance to saline water. There were no significant changes in body water compartments accompanying the changes in salinity of the water. It was also concluded that sheep can subsist on drinking water containing concentrations of up to 1·5% sodium chloride for a period of 6 months or more without exhibiting signs of change in body water distribution.

Thirty-six Corriedale rams were weaned at 3 months of age and subjected to four treatments until 2½ years of age. The treatments consisted of two levels of nutrition, with rams on the high level of nutrition being maintained approximately 15% heavier than those on the low level, and two levels of sexual experience. Sexually experienced rams were kept throughout with ewes that were infertile but showed regular oestrus and inexperienced rams were reared in monosexual groups isolated from females except during periodic mating tests. These 2-h tests were carried out at intervals of 3 to 4 months commencing when the rams were 6 months old. Up to 17 months of age there were no significant differences between treatment groups in the development of ability to serve ewes, except that low nutrition reduced the number of rams which had served ewes at 10 months of age. Between 17 and 28 months of age, rams kept with ewes tended to achieve more serves per test during the breeding season than rams kept without ewes.