Results of four experiments involving a total of 124 pigs covering the growth period between about 40 and 210 lb. live-weight indicated that:

1. The growth rate and efficiency of food utilisation of pigs receiving liquid skim milk up to a maximum of 5¼ pints per head per day, was better than that of pigs receiving a balanced all-meal diet. This was equally so whether the liquid skim milk was fed throughout the growing period or was abruptly removed from the diet at either about 75 lb. or 120 lb. live-weight, provided the all-meal diet fed subsequently contained adequate protein.

2. The addition of 0·1% copper sulphate to the meal fed with liquid skim milk significantly improved the growth rate and efficiency of food conversion.

3. The addition of 0·2% dl-lysine and 0·1% dl-methionine to the meal fed with liquid skim milk had no effect on the performance of the pigs.

4. Withdrawal of a protein supplement from the rations of pigs after they reached about 120 lb. live-weight adversely affected their performance.

An experiment was started in 1950 designed to find out what proportion of the difference in milk yield between herds is genetic in origin. Sixty-five pairs of twins were split at birth equally between farms having high-yielding herds and farms having low-yielding herds. A previous paper on this experiment reported on the growth of the twins, the present paper on milk yield and on management practices in the herds.

Twenty-four pairs of twins survived to complete one lactation and these provide an estimate of 24%±18% for the genetic part of the difference between the herds.

Aspects of rearing of the twins and of management of the herds were examined. Twins in the high-yielding herds were served and calved earlier than those in the low-yielding group but they had a longer interval between service and calving. Differences between average heifer yields and average cow yields were from one-and-a-half to two times greater in the high- than in the low-yielding herd group. There were no obvious quantitative differences in feeding practice between the two groups although differences in body size suggest that twins in the high group were done better. For the age at first service there was a positive rank correlation of 0·30 between body size differences and subsequent differences in first lactation milk yield. There was no single factor of management or environment which appeared to be the cause of the yield difference between the herds.

1. Eight Ayrshire milk cows were grazed for four 3-week periods from July to October 1957 in a balanced sequence on two strip-grazed and two free-grazed paddocks, each of two acres. Feed intake and digestibility were estimated by the chromic-oxide faecal-nitrogen method.

2. There was no significant difference in average feed digestibility between the treatments. Free grazing cows ate 30·4 lb. dry matter per day and strip grazing cows 28·9 lb. The difference was just significant (p<0·05). There was no significant difference in milk yield, live-weight or live-weight gain per cow.

3. Total feed output per acre was 11% greater on strip grazing when measured by utilised starch equivalent but only 1 % greater when measured by estimated feed consumption. The data suggest that strip-grazed cattle needed less energy for grazing.

4. The results are discussed with reference to their accuracy, their implications on grazing management and their correspondence with estimates of food requirements based on indoor feeding standards.

1. Records used to compile the Contemporary Comparisons of 57 Friesian, 8 English Ayrshire and 11 Scottish Ayrshire A.I. bulls, each with at least 100 ‘effective daughters’ were analysed.

2. For each bull, the herd-years were divided into three equal groups on the basis of the average heifer yield of both daughters and contemporaries (high-, medium-, and low-producing herd-years) and three independent Contemporary Comparisons were calculated for each bull, one at each of the three yield levels.

3. In the data from England and Wales, the mean Contemporary Comparison declined with increasing mean level of production. This decline was such as to imply that some 20% of the differences in production between herds were genetic in origin. A possible explanation lies in the gradual change from Dairy Shorthorn to Friesian and Ayrshire which has taken place in England and Wales, but not in Scotland, during the last 15 years.

4. The variance within progeny groups within herd-years increased from the low level to the high but the coefficient of variation decreased slightly. The variance between sires also increased with the mean level of production but almost exactly in parallel with that within sires so that the heritability and consequently the accuracy of the progeny test for milk yield was effectively the same at all production levels.

5. The correlation between the true breeding values of the bulls at the different levels was very close to one.

6. From these results it is concluded that there is no need to provide special strains within breeds to suit particular management levels or to concentrate progeny testing in the higher-producing herds and that daughter records from all herds, irrespective of level of production, can be used with equal confidence.

Comparisons have been made of a calf early-weaning concentrate mixture in which 50% of the total nitrogen was derived from groundnut meal and a similar mixture having 33% of the nitrogen from groundnut and 19% from white-fish meal.

In a feeding trial with 9 pairs of Aberdeen-Angus crossbred calves which were weaned at 3 weeks and then fed ad libitum, those given the ‘groundnut plus fish meal’ ration ate 4% less concentrate and gained 6 lb. more in weight over an 81-day period than their pair mates fed the ‘groundnut’ ration. Neither effect was significant.

There were no differences between the two rations in their digestibility or their ability to promote nitrogen retention when food intake was equalised.

1. The fat-corrected milk yields and butterfat and solids-not-fat percentages of the milk of heifers reared on the four planes of nutrition described in part 1 of this series are compared, i.e. high high (HH), high low (HL), low low (LL), low high (LH).

2. The most significant feature of the F.C.M. yields was the poor performance of the HL group in each lactation. When variability due to differences in lactation length had been eliminated the yields of the HL group in the first and second lactations were found to be significantly lower than those of the other treatment groups.

3. In the first lactation the mean B.F. percentages of HH, LH, HL and IX animals were respectively 3·92, 3·85, 3·81 and 3·74. These differences were significant at the 5% level. When the weekly yields and percentages of the HH and LL groups were compared it was found that the difference was almost entirely confined to the first 6 weeks of lactation. In the second and third lactations the mean B.F. percentages of all groups were similar.

4. Only in the second lactation were the S.N.F. percentages significantly different between groups. No explanation can be offered.

5. A comparison of the live-weight changes of HH and LL animals following successive calvings showed that recovery by the LL animals was most rapid immediately following first parturition and also during the first and second dry periods.

6. The plane of nutrition during rearing had no apparent effect on the pattern of change in milk yield and composition between first and third lactations, except that HH animals showed a more uniform rate of fall in S.N.F.% between one lactation and the next compared with the other three groups. Heifer lactations were longer and the milk had higher contents of B.F. and S.N.F. than later lactations.

7. The estimated feed costs of the rearing from birth to first calving of the HH, LH, HL and LL animals were markedly different.

8. The results are discussed in relation to practice.

Harnesses for the total collection of faeces from both ewe and wether sheep are described and field experience with them is reported.

1. Attributes desired in the gammons of bacon pigs are discussed, together with the methods whereby they are measured.

2. An experiment is described in which 16 judges made visual assessments of the qualities of the gammons of 10 carcasses of bacon weight from photographs, both of the fresh carcasses and of the cured bacon sides.

3. The judges did not show a high level of agreement in their rankings of the gammons. Although the overall rankings by the panel of the gammons on the fresh carcasses and on the bacon sides were similar, neither ranking was related to the composition or yield of the gammons.

4. The judges showed better agreement in their rankings of photographs of the cut surfaces of these 10 gammons and the cross-sections of the cooked gammons produced from them; in this case their preferences were related to the lean content of the gammons.

5. A second trial in which 25 judges scored 12 actual bacon sides for the quality of their gammons showed an even lower level of agreement between the judges' rankings, and again there was little agreement between the overall rankings of the panel and the results of dissections.

1. A field investigation to estimate the mean weight and chest girth of unserved Friesian, Ayrshire and Dairy Shorthorn heifers of between 3 and 24 months of age was carried out.

2. Data from 1,620 Friesians, 725 Ayrshires and 455 Dairy Shorthorns in the North of England were obtained, with a mobile weighbridge and a. spring-loaded steel tape in the winter 1958–59.

3. It was found that on average the Friesians were heavier and had a greater chest girth than the Ayrshires and Dairy Shorthorns, which did not differ significantly.

4. These heifers were apparently reared on planes of nutrition which, judged by conventional feeding standards, may be described as ‘low’.

5. After eliminating the linear effect of age by covariance analysis, highly significant differences between herds and between sires in weight and chest girth were found.

6. The investigation demonstrated the feasibility and value of collecting field data on body size.

In three trials involving 288 hoggets the influence on growth rate of implanting 15 mg. hexoestrol or 12 mg. stilboestrol was compared. In one trial the influence of adding excipient to either stilboestrol or hexoestrol to increase the surface area of the implant was also assessed. Live-weight gain was calculated for each time interval after implantation and it was concluded that after approximately 140 days the influence of implantation had largely disappeared. For optimum benefit to live-weight gain implantations should be made approximately 100 days prior to slaughter.

In all trials, implantation with synthetic oestrogens resulted in extra daily live-weight gain, the increase for all animals amounting to 31% extra daily gain for hexoestrol and 26% for stilboestrol. The addition of excipient to the implant diminished the initial growth response and reduced the extra gain achieved.

Implantation with the synthetic oestrogens significantly increased the final live-weight on the farm, live-weight before slaughter and carcass weights when groups of animals from each treatment were slaughtered together.

Stilboestrol and hexoestrol implantation resulted in an extra 4·7 and 6·1 lb. full live-weight; 3·7 and 5·3 lb. empty live-weight and 1·3 and 2·8 lb. extra carcass weight respectively, compared to controls killed at the same time.

Where hoggets had received a high-plane diet, treatment did not affect killing-out percentage, but where the level of nutrition was lower a decrease of up to 1% was observed. In all trials treatment with the synthetic oestrogens resulted in an increase in pelt weight and in one trial this increase was up to 2 lb.

Implantation with hexoestrol and stilboestrol increased the size of the gut full and empty in two of the trials. The differences were reduced when the gut weights were corrected to 100 lb. empty live-weight. The weight of the thyroid gland or the total weight of the trachea, heart and lungs were not affected by treatment.

The approximate rate of uptake of hormone from a 12 mg. implant of stilboestrol was assessed by the decrease in the weight of dried tablet removed at slaughter from 30 to 200 days after implantation. The linear regression y (uptake in mg.)=3·029+0·039x (days from implantation) fitted the data best, giving an approximate average uptake over this period of 39 micrograms of stilboestrol per day.

Data from Danish Progeny Testing Stations were used to investigate the relationship between the colour of meat and feed efficiency in pigs. For groups slaughtered during the summer there was a highly significant correlation. As the amount of feed consumed per unit live-weight gain declined so the meat became paler. For groups slaughtered in winter and for data pooled over the whole year, there was no significant correlation. Possible explanations of these findings are discussed.