John Hammond

ANIMAL BREEDING IN RELATION TO NUTRITION AND ENVIRONMENTAL CONDITIONS

1. The action of the gene on the characters of an animal is limited to those manifestations which are physiologically possible if the gene is to survive. Environmental conditions affecting the physiology of the animal will therefore have a selective action on those genes which give rise to characters in harmony with the environment concerned. The main problem in animal breeding is to be able to direct the course of evolution and to select genes giving rise to increased development of certain characters.

Further observations on the factors controlling fertility and foetal atrophy

I n a previous paper (1) some of the factors which control fertility in domestic animals were discussed. These for purposes of clearness in investigation were divided into two groups: (1) The factors which control the number of eggs shed; and (2) The factors which control the number of eggs which develop to reach birth size. By this means the way in which the various factors which affect fertility could be determined, for example, it was shown that the effect of age on fertility, the literature of which has been reviewed by Harris (2), is due to the number of eggs shed at each oestrus period. Young sows examined had on the average 14 corpora lutea in the ovaries while old sows had 20 corpora lutea.

A crossbreeding experiment with cattle, with special reference to the maternal effect in South Devon—Dexter crosses

An investigation was carried out to determine the extent of the maternal influence on size of calves at birth and during subsequent stages of growth, by making reciprocal matings between large South Devon and small Dexter cattle. As a preliminary to the experimental results, data concerning the respective parent breeds were analysed. From the first part of the study the following information was obtained: 1. The mean weight at birth of purebred South Devon calves was 100·3 ± 1·47 lb. with a tendency, though not statistically significant, for male calves to be heavier. Calves born during the months April to July appeared to be heavier than those born at other times, but the age of the dam had no definite effect on the birth weight of offspring. It was found, however, that the sire may influence birth weight to a significant degree. 2. The mean period of pregnancy for South Devon females, carrying purebred foetuses, was 287·0 ± 0·42 days, the tendency being for males to be carried longer, but the difference of 0·97 days was not statistically significant. A statistically significant difference indicated that winter calvers carry their foetuses longer as a rule, but though heifers have shorter gestation periods than cows, the difference of 1·6 days was not significant.

Control of ovulation in the cow

1. Cows and heifers were injected shortly before slaughter with an extract of horse pituitary or with pregnant mare serum gonadotrophin. 2. These substances were administered at different times of the cycle or in pregnancy; various doses were given simultaneously with removal of the corpus luteum. 3. A series of animals were given 1500 or 5000 i.u. at intervals from 5 days before to 3 days after expression of the corpus luteum; up to thirty ovulations were so obtained. 4. A small number of cows have been treated and left to calve; there have been several twin and triplet births.

The mucous secretion of the cervix of the cow

The secretions of the cervix are of interest because of the changes that occur in them during the oestrous cycle and during pregnancy. It is probable that these changes have an efEect in assisting or hindering the ascent of the spermatozoa to the Fallopian tubes after their deposition in the vagina.

On the relative growth and development of various breeds and crosses of sheep

Records of the live and carcase weights of sheep exhibited at the Smithfield Show from 1893 to 1913 have been treated statistically. The results show the average weights, rates of growth, and proportions of the carcase in the different breeds of sheep at 9 months and at 21 months of age (see Tables II and V). On the average of all breeds the rate of growth declines from 4·7 lbs. per week from birth to 9 months of age to 1·7 lbs. per week from 9 to 21 months of age. The carcase percentage increases with age on the average from 61 per cent, at 9 months to 65 per cent, at 21 months and with it the percentage of fat from 5·7 per cent, at 9 months to 64 per cent, at 21 months. On the other hand the proportions of pluck, skin and alimentary canal (“Unaccounted for”) decrease with age. Ratios of early maturity are given for the various breeds and the factors which affect it are discussed. The average weights, rates of growth and proportions of the carcase are given for the different crosses of sheep (see Tables IX and XIII). From a comparison of crossbreds with pure breeds it would appear that crossing leads to increase in live weight and probably more early maturity. There is an indication that the proportions of carcase, fat and pluck are less but the proportions of skin and alimentary canal are greater in crossbreds than in the pure breeds of sheep. There is greater variation in live weight in the Cheviot and Blackface breeds than in the Leicester, Southdown, Hampshire and Suffolk breeds; in the latter breeds variability decreases but in the former breeds it increases with age. Variability in live weight at 9 months old has steadily increased from 1893 to 1913 but at 21 months old there has been little change. Some parts are more variable in their proportion to live weight than are others. Fat and alimentary canal are most variable, skin and pluck slightly less variable, while the proportion of carcase is less variable even than live weight. The variability of the proportions of carcase, pluck and alimentary canal increase while the variability of the proportions of fat and skin decrease with age. Within a breed and among animals of the same age the heaviest sheep generally have the highest carcase and fat percentage and the lowest percentage of pluck, skin and alimentary canal. A high proportion of carcase is correlated with a high proportion of fat and a low proportion of skin and alimentary canal at 9 months old. At 21 months old the same holds true with the exception that the sheep with the highest carcase percentage have not the most fat. The proportion of pluck does not appear to be correlated with any other part of the body except inversely with the live weight. During the period 1893–1913, although individual breeds show differences, the majority have increased in live weight at 9 months old but at 21 months old have remained practically constant in weight. The sheep exhibited in 1840 were very much fatter than those shown in the Carcase Classes of to-day and are probably comparable with those of the present-day Live Classes. Since 1840 Leicesters have shown a great increase and Southdowns a small increase in weight. The carcase percentage of sheep both at 9 and 21 months of age has steadily decreased during the period 1893–1913; this has been attended by an increase in the proportion of pluck, skin and alimentary canal. There is an indication that the influences which affect sheep in their first year of life (store period) affect their ultimate size. The seasonal variation in the weight attained by sheep is dependent on the rainfall; a high rainfall through increased root and fodder crops causing increased live weight.

Measuring growth in farm animals

There are various ways of measuring growth, as actual weight, percentage increment, or weight per day gained. Which method is used will depend on the purpose for which it is required. For agricultural purposes the third method is generally adopted, as it forms a basis for daily food requirements and, conversely, also enables the rate of growth to be controlled exactly by regulation of the food intake. The live-weight growth curve of the animal as a whole is made up of the sum of the different parts and tissues of the body, each of these growing at different rates.

Hormones in Meat Production

A recent development of much interest to the livestock farmer is the use of synthetic oestrogens in the production of beef and mutton. Numerous trials have proved that such hormones, implanted under the skin or fed in concentrates, not only increase the rate of liveweight gain in cattle and sheep but improve carcass quality and the efficiency of food conversion. The practice is already common in the U.S.A. and is spreading in the U.K.

A membrane component of the cellular slime mouldDictyostelium discoideum rapidly labelled with [32P]orthophosphate

Abstract After labelling Dictyostelium discoideum (Strain Ax-2) for 30 min with [ 32 P]-orthophosphate a material was observed in cytoplasmic extracts, which cosedimented with polyribosomes in sucrose density gradients. The radioactivity in this material was insensitive to ribonuclease and deoxyribonuclease but was partially solubilized by alkali. All the radioactivity was rendered soluble in trichloroacetic acid by treatment with sodium deoxycholate. Most of the 32 P counts were extractable in chloroform-methanol (2:1, v/v) and upon analysis by thin-layer chromatography the isotope was found in various phospholipids, chiefly phosphatidylethanolamine with some in lecithin and phosphatidylserine. Upon examination in an electron microscope the material was found to be composed of membrane, glycogen and an unidentified amorphous material.

The Biology of Beef Production

Farming for BeefBy Dr. Allan Fraser. (Agricultural and Horticultural Series.) Pp. 144 + 24 plates. (London: Crosby Lockwood and Son, Ltd., 1950.) 10s. 6d. net.