A simple expression relating the standardized selection differential (i) to the intensity of selection (p) is given by

i≏0·8+0·41 ln (R−1)

where R equals 1/p. This linear expression may allow simpler solutions to some optimization problems in selection than does the conventional formula for selection differential on truncation of the normal curve.

Using the expression, formulae for the maximum immediate response and optimum selection intensity in mass selection have been developed, taking account of the loss in performance through inbreeding. These formulae were used to study the effect on response of the total number of animals tested. The maximum response over a specified period of time, allowing for the loss in genetic variance from inbreeding, has also been considered. The optimum intensity of selection may then be well below that necessary for the maximum immediate response.

1. Forty-five Large White gilts were given 2·20 kg daily of a diet containing 14·0% crude protein during three successive pregnancies. During a 6-week lactation they received 5·30 kg daily of one of three diets containing 19·0% (HP), 16·5% (MP) or 14·0% (LP) crude protein.

2. Daily milk yield was estimated on the 10th, 20th, 30th and 40th day of lactation. Milk samples were obtained from the same sows for the determination of protein, fat, lactose and total solids on the 11th, 21st, 31st and 41st day.

3. One sow and litter from each treatment in each lactation was placed in metabolism cages during lactation and estimates of nitrogen and dry matter excretion obtained.

4. As the concentration of protein in the diet decreased the average 42-day gain in litter weight from birth increased significantly in the first lactation. This trend continued in the second lactation although it was not significant but did not appear in the third.

5. There was no marked difference in daily milk yield between treatment groups.

6. There was a significantly greater loss of live weight by the sows on the lower levels of protein in the first lactation. These differences were not significant in the second and third lactations.

The errors of the slaughter and tritiated water techniques of estimating energy retention were compared in a group of grazing sheep deprived of feed and water for 48 hr. It was calculated that the mean energy retention of the experimental animals would have had a standard error of 3·64 Mcal if estimated by the slaughter technique, and 1·56 Mcal if estimated by the tritiated water technique. It was concluded that in other experimental groups the precision of the relationship between energy content and live weight is likely to be the most important determinant of the relative precision of the two methods. In neither method would worthwhile gains in precision result from knowledge of the weight of the contents of the alimentary tract.

The effects of culling, natural wastage and different correction and exclusion procedures on estimates of lactation parameters have been examined in test station records of 1042 Danish Red cows. A total culling rate of 20% was applied to the initial material, of which 11% represented obligatory culling for disease, injury and infertility and 9% ‘paper’ culling for performance at four different stages of lactation.

Exclusion and correction of short records generally resulted in overestimates of the sample mean and underestimates of the selection differential produced by culling. In all instances, the variance of the sample prior to culling, and the loss of variance attributable to culling, was underestimated in samples containing short or corrected records.

It was concluded that field data cannot provide material suitable for objective studies of selection and that a reappraisal of the effects of age, lactation, season, etc., in the controlled conditions of test stations may well be justified. An absence of culling in test stations contributes to the large estimates of variance and heritability characteristic of station material.

Coat and skin samples were taken monthly from three Wiltshire ewes for two years, and then fortnightly between the spring equinox and the autumn equinox of 1968.

The fleece comprised kemp and wool, having a weight of 1·1 kg and a length of 50 mm. In summer all the primary fibres had a latticed medulla, and although the secondaries were smaller than the primaries, they were relatively coarse and often medullated, over one-third having a latticed medulla at the peak period. The overall mean S/P ratio was 3·5.

Follicle development was studied in four lambs from birth to 84 days. Only 27% of the secondaries lacked fibres at birth, and all had fibres at 14 days. There was a trend of increasing medullation in the primary fibres. Shedding primary follicles were seen from birth onwards, and shedding secondaries from 28 days, although obvious casting of the birth coat did not begin until 84 days (at the beginning of June).

There was a basic seasonal cycle of follicle activity starting in March and lasting until September; inactivity began in September, reached 100%, and continued at this level until March. Subsidiary cycles suspected from the monthly samples were confirmed by the fortnightly samples. Thus peaks of inactivity in June and August separated three cycles of growth of two months duration. Only 80% of the primaries and 50% of the secondaries became inactive in June, with 50% of the primaries and 30% of the secondaries, in August.

Twenty-four Southdown and 24 Welsh Mountain year-old female sheep, half on high-plane and half on low-plane nutrition, were shorn and given two acute cold exposures in climate chambers. For 2 weeks before and 2 weeks between exposures the sheep were kept in a subcritical (+ 8°C) or a thermoneutral (+30°C) environment. Before the temperature treatment each sheep received an injection of Brucella abortus vaccine. Blood samples were taken during exposure to + 8°C and + 30°C and during the acute cold exposures for estimation of free fatty acid (FFA), protein-bound iodine (PBI), glucose, acetone, serum protein and antibody levels. FFA and glucose levels alone were measured in 32 similarly treated Scottish Blackface sheep.

1. Low plane sheep had higher PBI levels at all temperatures, and higher glucose levels during acute cold exposure than high plane sheep. Otherwise most major effects were attributable to ambient temperature.

2. At +8°C the PBI, FFA, glucose, serum protein and acetone levels were higher than at + 30°C.

3. Blackface sheep had lower FFA and glucose levels than Southdown and Welsh sheep at both temperatures.

4. During acute cold exposure, PBI, acetone and FFA levels increased further. PBI levels were highest in sheep previously at + 30°C, and acetone highest in sheep previously at + 8°C. Very high FFA levels were recorded, especially in sheep not previously cold-acclimatized.

5. Glucose levels increased initially, but fell towards the end of acute exposure, suggesting that relatively less carbohydrate and more fat was utilized for energy metabolism during this period.

6. Serum protein levels fell during acute exposure, possibly because protein catabolism increased. The proportions of albumin and γ-globulin increased and decreased respectively.

7. No effects of temperature on antibody levels were detected.

An experiment was undertaken to examine the possibility that progressive adjustments in tissue insulation on the trunk might occur following repeated wind cooling. Two sheep were exposed at right angles to an air flow of 12 mph for 6 hr daily on each of 7 consecutive days.

When first exposed to the wind the heat loss from the fleece-covered surfaces increased due to a reduction in insulation and apparently increased vaso-dilatation. After the first day there was a progressive increase in surface vaso-constriction before exposure and a gradual decrease in the extent of the vaso-dilatation during exposure. The results indicate the possibility of centrally-induced peripheral adjustments in blood flow occurring on the trunk of the sheep in response to repeated wind cooling.

Histological examination of the rumen wall in intensively managed beef cattle confirmed the superficial nature of many of the lesions present and failed to reveal evidence of secondary bacterial infection. Of the lesions described, only intra-mucosal abscesses and their subsequent erosions proved to be significantly related to the occurrence of hyperkeratosis of the rumen mucosa. The remaining lesions, vacuolation of the stratum granulosum, acute microscopic ulceration, congestion of the submucosa and the presence of leucocyte aggregations in the submucosa, were all independent of this hyperkeratosis.

Twenty-four sows from three nutritional regimes imposed until weaning of their third litters were used to investigate the influence of weight and body condition on ovulation rate.

For low-, medium- and high-plane sows respectively, mean corpora lutea numbers at 3 to 6 days post coitus were 13·8±0·78, 16·4±0·87 and 15·2±1·01 (not significantly different); conception rates at first service were 50, 87·5 and 100% percentages prenatal mortality were 36·1±7·95, 67·2±7·26 and 41·7±7·26, and mean numbers of pigs born alive were 9·0±1·19, 5·2±1·09 and 8·8±1·09.

Pooled data indicated no significant effect of body weight but a significant effect of weight loss during the preceding lactation on ovulation rate (P<0–01).

An experiment to test the effect on the voluntary food intake of lambs of giving diets containing 0, 20, 40 and 60% of either coarse or finely ground oat husks, in either a loose or pelleted form, is described and the results discussed. The results showed that voluntary intake was uniformly depressed with increased dilution of the diet with oat husks when the oat husks were coarse and the diet given loose. However, when the oat husks were finely ground and when the diet was pelleted the response to dilution was much modified and in the case of older, heavier lambs intake initially increased with dilution. It is concluded that ruminants may sometimes be able to respond to increased diet dilution so as to maintain their maximum digestible-energy intake but that the attempt is often thwarted to varying degrees according to the physical form of the food. An hypothesis is suggested for the pattern of response in food intake to be expected according to the type of food given.

A feeding trial was conducted on 24 individually-fed pigs given either a diet containing plant protein with insufficient Iysine and methionine or the same diet with optimal Iysine and methionine levels. Supplementation of the diet with synthetic amino acids significantly improved daily live-weight gain, feed conversion, nitrogen balance, loin eye muscle area and total yield of lean muscle.

Pigs receiving insufficient Iysine and methionine were characterized by lower haemoglobin and creatinine values accompanied by a decreased level of glutamic oxaloacetic transaminase.

There were highly significant differences in the blood and liver Iysine levels of the two treatments, and significant differences in the fresh muscle and in the pressed muscle juice Iysine levels.

The ratios between liver and blood Iysine levels and between dietary or muscle Iysine levels and % of nitrogen retention were calculated and found to be the same on both treatments.

The accumulation of Iysine in liver and muscle was linearly related to the blood Iysine level and to N retention and Iysine intake.

Milk and butterfat production data from eight herds of dairy cows in Australia for the years 1963 and 1964 were analyzed for relationship with serum transferrin type. In the 932 lactations considered D2/D2 cows produced 521 ± 152 lb of milk more than A/A cows and lactated 15·3 ± 7·8 days longer after correction for season. There was no difference in fat percentage of the milk. The production of A/D2 cows was also significantly higher than A/A cows, but less than D2/D2 cows. Allowing for differences in lactation length still left a significant difference between D2/D2 and A/A cows in milk yield.

The best estimate of the effect of replacing a TfA by a TfD2 gene, allowing for season, was 170 lb more milk (P<0·01) and 6·5 days longer lactation (P<0·05), while TfD1 did not differ from TfA in either yield or lactation length.

Twenty-four Friesian calves were fed from twelve weeks of age on six diets containing 15 or 30% ground barley straw, the straw being ground through screens of and in.

From twelve weeks to seven months of age (120–250 kg) the calves had mean growth rates of 1·15 kg/day with a feed conversion ratio of 4·15: 1. From seven to eleven months of age (250–380 kg) the corresponding figures were 1·16 kg/day and 5·53: 1, and in the final fattening period of 11–14 months (380–500 kg), 0·92 kg/day and 8·19: 1.

These differences between stages of fattening were highly significant. There were no differences in performance due to the particle size of the straw or to the proportion of straw in the diet.

The growth of pigs kept continuously or intermittently in metabolism cages was compared with that of animals penned in groups. The ten continuously caged grew more slowly and contained more fat at slaughter than their penned littermates.

In trials 1 and 2, supplements of urea and cottonseed meal increased the protein content of the basal diets from 12·2 to 14·0–14·6%, but had no significant effects on growth rate or carcass characteristics. In trial 3 the effect of cottonseed meal on growth rate was almost significant but urea had less effect. In trial 4, the basal diet contained 11·0% protein; soya bean meal increased this to 13·1% and had an almost significant effect on growth rate. Lysine and lysine + urea had no effect.

Three treatments involving isocaloric diets with the same levels of lysine and methionine but different crude protein levels were imposed on pigs from 50 to 200 lb live weight. Significant treatment differences were obtained only during the period from 50 to 120 lb live weight when pigs on the 17% protein diet (barley+soya bean meal+white fish meal) had the fastest growth rates and best food conversion efficiencies and pigs on the 11% protein diet (barley only) were the poorest. Pigs fed barley alone also had the fattest carcasses.

Variation in scrotal wool cover influenced the percentage of abnormal cells in the semen of rams exposed in the hot room. The percentage of abnormal cells was highest in the rams with maximum wool cover on their scrota, intermediate in those with scrota completely devoid of wool cover and minimum in those with intermediate (2 to 3 cm) scrotal wool cover.

Two changeover treatments were studied over a 5-week period in eight early-weaned concentrate-fed Holstein calves of initial weight 160 kg. Fresh forage was given ad libitum for one week (A) or two weeks (B); calves on the latter treatment also had 500 g daily of maize meal. All calves received 300 g/100 kg live weight of a protein supplement and had free access to sodium and phosphorus-rich minerals. A rumen inoculation was given after seven days of forage feeding, at which point a liquid molasses/urea mixture was introduced, first in small amounts and then after a further seven days ad libitum. The forage was then restricted to 3 kg/100 kg live weight. Both treatments were effective in raising rumen pH and buffering capacity to the point of allowing the establishment and maintenance of protozoa, chiefly Entodinium and Isotricha spp. Protein N as a percentage of the total N of rumen contents was about 90 with the all-concentrate diet, fell to 35 with the roughage diets and then rose again to 80–90 by the end of the experiment.

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.

Volume 11, part 3, pp. 362-363