1. Eight calves of each of two breed types, Friesian (Fr) and Brahman × Friesian (FB), were fed ad libitum on one of two diets; the digestibility of the dry matter of the diets was 72% and 63%. Eight calves were kept at 34°C and eight at 17°C. In a second experiment six of the calves previously exposed to 34°C were subjected to daily exposures to a radiant heat load at 32°C air temperature, while fed on the diet of lower digestibility.

2. Rectal temperatures and respiratory rates were higher, and food intakes and growth rates were lower, at 34°C than at 17°C. However there was only a small difference in growth rate between the two temperatures after the effect of temperature on food intake had been removed by regression.

3. At 34°C FB calves had lower rectal temperatures and respiratory rates than Fr calves, and when fed on the diet of higher digestibility FB calves ate more and grew faster than Fr calves at both temperatures; however there were only small corresponding differences between the breed types for calves fed on the diet of lower digestibility at both temperatures.

4. At 34°C FB calves had lighter (weight) hair coats than Fr calves and FB calves had lighter coats at 34°C than at 17°C; the latter difference was not apparent for Fr calves. Nevertheless, neither rectal temperature nor respiratory rate was significantly affected for either breed by removal of the hair coat at 34°C.

5. In the second experiment the rectal temperatures of FB calves increased by smaller amounts during exposure to radiant heat than was the case for Fr calves; FB calves had faster sweating rates than Fr calves during these exposures.

Eight pregnant beef cows and four rumen-fistulated cows were given 1·67 kg barley dry matter per day and 5·1 kg chopped oat straw dry matter treated by one of four different methods. The straw treatments (given in a 4 × 4 Latin square design) were (A) nil, (B) sodium hydroxide (25 g/kg straw, dry matter basis), (C) a fully soluble liquid supplement containing urea, calcium, phosphorus, sodium, trace elements and vitamins (40 g/kg straw, dry matter basis), and (D) sodium hydroxide plus liquid supplement. In the absence of liquid supplement 0·3 kg per day of the straw dry matter was not consumed, and with the sodium hydroxide plus liquid supplement treatment the cows would have consumed more straw than was offered. Sodium hydroxide increased the digestibility of the straw organic matter from 0·46 to 0·50 (P <0·05), and this was further increased to 0·53 (P <0·01) for the combined sodium hydroxide plus liquid supplement treatment. The calculated metabolizable energy intakes from straw were increased from 31 (nil) t o 36 by either the sodium hydroxide or liquid supplement treatments (P <0·05) and to 41 by the combined treatments (P <0·001). Sodium hydroxide tended to increase the concentrations of n- and iso-butyric acids in the rumen liquor.

A randomized block experiment, using 30 British Friesian cows, was used to assess the effects of offering supplements containing 172 and 234 g crude protein per kg dry matter in addition to grass silage which had a very high digestible organic matter in the dry matter of 769 g/kg. The animals, which had a mean calving date of 1 February, were blocked according to calving date and lactation number and allocated at random within each block to the two treatments. The treatments were applied from day 8 of lactation until the animals went to pasture on 13 April and both supplements were offered at the same rate of 7·6 kg per day. The total yields of milk produced during the experimental period were 1626 and 1650 ±38·4 kg and the mean daily yields during the final week were 24·8 and 25·6 ± 0·58kg for the medium and high protein supplements respectively. The mean live weights for the two groups were 524 and 544 ± 5·5 kg, and body condition score 2·9 and 3·3 ± 0·34 for the medium and high protein supplements respectively at the end of the treatment period. No significant treatment effects on milk composition were recorded at any stage during the experiment. Analysis of blood samples taken during the final week of the experiment showed plasma urea levels, at 220 and 290± 18 mg/1 for the medium and high protein supplements respectively, to be significantly different.

A change-over design experiment, comprising four periods each of 4 weeks' duration, was used to evaluate three silage types each fed with two levels of protein in the supplement in a 3×2 factorial arrangement. The three silages were high digestibility unwilted (A), high digestibility wilted (B) and low digestibility unwilted (C). The supplements had crude protein contents of 152 and 240 g/kg dry matter, and were offered at a standard rate of 10 kg undried weight daily. The mean silage intakes were 9·3, 9·5 and 8·6 ±0·19 kg dry matter/day for A, B and C respectively, but protein content of the supplement had no significant effect on the intake of silage. Milk yield was significantly affected by both silage type and protein content of the supplement, with the mean yields being 23·6, 23·9 and 22·0 ± 0·49 kg/day for A, B and C respectively, and 22·4 and 24·0 ±0·40 kg/day for the medium and high protein supplements respectively. Although there was no significant interaction between silage type and protein content of the supplement, the greatest response to increased protein was obtained with B. Neither silage type nor protein content ofthe supplement affected animal live weight or milk composition (other than fat content, which was significantly affected by silage type). Blood plasma urea levels were 281 and 405 ± 28·0 mg/1 for the medium and high protein supplements respectively.

Total ration digestibility and nitrogen balances were carried out on three animals per treatment. The digestibility of dry matter, organic matter and nitrogen was significantly affected by both silage type and level of protein in the supplement. The output of nitrogen in the urine was also significantly affected by both these factors.

A randomized block experiment using 108 British Friesian cows was conducted over a 2-year period to assess the effects of level and pattern of concentrate allocation during early lactation on the performance of cows which calve during January and February. The three concentrate levels were 280 (L1), 405 (L2) and 530 (L3) kg during a 74-day post-calving period, and the two systems of allocation were either a uniform daily allowance (uniform system) or a high input for the first 4 weeks after calving followed by a low input (high/low system). The animals had ad libitum access to medium-quality grass silage during the indoor period and in both years were turned out to pasture on 9 April. At pasture they were grazed rotationally in treatment groups at a stocking rate ranging from 6·4 cows ha-1 in the early-grazing season to 4·9 cows ha-1 in the late-grazing season.

Mean milk outputs for the indoor feeding period were: high/low system 1577 (L1), 1705 (L2) and 1764 (L3), uniform system 1583 (L1), 1676 (L2) and 1783 (L3) ±33·8 kg; and for the total lactation were high/low system 4625 (L1), 4906 (L2) and 5148 (L3), uniform system 4830 (L1), 4933 (L2) an d 5301 (L3) ±118·9 kg.There was no significant interaction between level and system of concentrate allocation. Feed intake, milk composition, animal live weight and body-condition data are also presented.

A combined nutritional balance and comparative slaughter experiment using 20 animals compared entire male and castrate male cattle when pair-fed at high and medium levels of feeding and slaughtered at a constant 400 kg live weight. The carcasses were dissected into lean meat, separable fat, and bone, and the edible portion of the carcass was further analysed for crude protein, fat and water.

There were no significant differences between entire and castrate animals in their ability to digest energy, nitrogen or modified acid detergent fibre. The mean metabolizable energy values (MJ/kg dry matter) of the diets were 10·6 for castrates and 10·9 for entire animals. Live-weight and carcass gains (kg/day) for each treatment were respectively: entire high feeding level, 1·10, 0·69; entire medium feeding level, 0·91, 0·57; castrate high feeding level, 0·92, 0·57; castrate medium feeding level, 0·79, 0·48. Castrate carcasses contained significantly (P < 005) less lean meat and more separable fat. The edible portion of these carcasses also contained significantly (P < 0·05) more total fat but less protein and water than entire carcasses. Daily carcass protein gain was significantly higher for entire animals (P < 0·001) but daily energy gain was not significantly different. The most efficient conversion of dietary metabolizable energy and crude protein to either live weight or carcass meat production was obtained by the use of entire animals and the high level of feeding.

In three trials conducted in 3 successive years, Africander, Brahman, Tswana, Tuli and crossbred cattle were injected intramuscularly with 500 jug of cloprostenol on two occasions 11 days apart to synchronize oestrus. The cattle were inseminated 72 and 96 h after the second injection. Controls of the same breeds were exposed to natural service for a period of 22 days. In all trials the conception rate to natural service was significantly higher (P < 0·01).

Conception rates to both breeding methods were highest in Tuli and crossbred cattle and lowest in the Africander and Brahman. Non-lactating cows showed higher fertility than suckling cows and maiden heifers.

Vasectomized bulls used in one trial were shown to be useful in the selection of breeding cows suitable for oestrus synchronization. Further studies are justified to maximize the benefits of a potentially valuable method of breeding beef cattle in ranching conditions.

Continuous reciprocal backcrossing results in individuals which are 67% heterozygous, and which, assuming a linear relationship between heterozygosity and heterosis, would be expected to exhibit 67% of the heterosis found in Fi hybrids. An experiment was undertaken to investigate this relationship in the reproductive traits of mice. By crossing and repeated backcrossing in both directions using two unrelated strains of outbred mice, females were produced which were 25, 50, 75 and 100% heterozygous. The crossbred females and the two purebred strains (922 females in all) were mated to a sire line of a genetically distinct strain to standardize foetal heterosis. The reproductive performance of females with different percentage heterozygosity gave estimates of maternal heterosis. A significant positive linear relationship was found between heterozy-gosity and heterosis in litter size, total weight of litter and individual weight of progeny both at birth and at weaning. The relevance of these results for livestock breeding is discussed.

The problem of applying a linear constraint on expected selection responses in a two-character independent culling levels scheme is investigated. A general equation is derived, the solutions of which specify the culling levels satisfying the constraint applied. Examples are given to demonstrate how different constraints can be applied by transforming one or more of the characters under selection.

Four experiments were conducted to study the performance of pigs weaned at 10 days on to diets containing different amounts of flaked maize.

Digestibilities of dry matter and energy of flaked maize were found to be 0·87 for pigs between 11 and 16 days of age.

Starter diets containing 0, 250 or 375 g flaked maize/kg, given from 10 to 35 days, resulted in growth rates of 254, 254 and 213 g/day respectively and the reduction with the high level of maize was significant (P< 0·001). Feed conversion ratio was unaffected by treatment and averaged 1·08.

When the starter diets were replaced at about 24 or 27 days by a cereal-based diet containing 200 g dried skim milk/kg there were no significant differences in performance between 10 days and 10 kg live weight due to starter diet, and growth rates were similar t o those obtained when the starter diets were given to 35 days. However, there was a consistent trend of lower food intakes, poorer feed conversion ratio and, consequently, poorer growth during the immediate post-weaning period on the starter diet containing 375 g flaked maize/kg.

The efficacy of feed additives in enhancing the performance of growing pigs, together with the effect of different protein levels (18 v. 16% from 13 to 18 kg body weight and 16 v. 14% from 18 to 39 kg body-weight), were evaluated in three experiments with 412 pigs. In Experiment 1, from 13 to 39 kg body weight, pigs receiving 55 p.p.m. carbadox (C) produced a greater (P<0·05) average daily live-weight gain than did the non-medicated (NM) pigs and those receiving 275 p.p.m. chlortetracycline-sulphamethazine-penicillin (ASP) with a similar but non-significant (P>0·05) trend n i daily feed intake and gain/feed ratio. The ASP pigs also produced a greater (P<0·05) weight gain than the NM pigs. The higher dietary protein level sequence produced a greater (JP<0·05) weight gain and gain/feed ratio.

In Experiment 2, from 16 to 39 kg body weight, NM control pigs achieved high weight gains, and all the feed additive treatments studied [C+106 p.p.m. of the worming agent pyrantel tartrate (C+P); ASP+8 mg of the worming agent levamisole-HCl per kg body weight fed once on day 7 of the experiment (ASP+L); and 113 p.p.m. tylosin+13 p.p.m. of the worming agent hygromycin B] were similar to the NM controls in daily feed intake, weight gain and gain/feed ratio. However, in Experiment 3, the C+P and ASP+L treatments resulted in a greater (P<0·05) weight gain with a trend toward greater daily feed intake than did the NM control treatment from 17 to 35 kg. The weight gain of the ASP+L pigs was also greater (P<0·05) than that of 165 p.p.m. oxytetracycline and NM pigs from 35 to 57 kg. From 57 to 96 kg all the pigs received the same NM control diet and their weight gains were similar. The gain/feed ratio was similar among the treatments within each of the weight periods in Experiment 3. Pigs slaughtered at the beginning and at various stages during Experiments 2 and 3 were free of internal parasites and migration damage.

1. Many apparently normal nursings occur in the absence of milk ejection, but little is known about their frequency or causes. The present paper reports an observational study in which the incidence of these incomplete nursings was studied in detail.

2. Nine lactating sows were studied throughout a 5-week lactation in each of two environments. One was a normal commercial farrowing house, and the other a cubicle in which the sow and litter were effectively alone. Extended (3 h) observations were made on each litter at various ages.

3. Twenty-seven per cent of all nursings were found to be incomplete with little difference between the grouped and alone sows. Incomplete nursings often occurred within 40 min of a complete nursing and increased the interval between successive complete nursings. They also occurred most frequently during the 2nd and 3rd weeks post partum.

4. Irrespective of the housing condition the sows initiated the same proportion of all nursings and a similar percentage of these were incomplete.

5. Incomplete nursings appear not to be an artefact caused by crowding many lactating sows together, but they may reflect some form of discomfort of the sow. The problem of real and apparent nursing intervals is discussed.

Observations were made on the distribution of ovulations between the two ovaries, the distribution of foetuses between the two uterine horns, the total numbers of cotyledonary burrs, and the weights and numbers of foetal cotyledons for each foetus in 80 Finnish Landrace × Dorset Horn ewes killed between 50 and 145 days of gestation. While ovulations were randomly distributed between right and left ovaries, viable foetuses were more evenly distributed between right and left uterine horns. Migration of embryos between the horns contributed to this relative balance but early foetal mortality, which increased with ovulation rate, tended to upset it. The mean number of foetal cotyledons per foetus depended on litter size and distribution, and at any fixed litter size was substantially reduced in those ewes with six or more ovulations. Foetal weights were also relatively low in these ewes. The total weight of cotyledons per foetus decreased by about 12% for each increase of one in number of foetuses, as compared with a 20% decrease in number of cotyledons but only a 7 to 11 % decrease in the weight of the individual foetuses. Comparisons between foetuses within the same litter led to similar trends in the ratios of cotyledon numbers, cotyledon weights and foetal weights. It is suggested that the presence of some very small lambs in large litters should not be attributed to maternal under-nutrition in late pregnancy.

Sheep from the Soay, Southdown, Finnish Landrace and Oxford Down breeds were serially slaughtered at 40, 52, 64 and 76% of their estimated mature body weight. Breed and sex comparisons of muscle distribution wee made at these degrees of maturity. Comparisons were based on 12 individual muscles obtained from the prime retailjoints. Together, these 12 muscles represented about 41 % of total weight ofmuscle in the carcass. Highly significant breed and sex differences in the weight of individual muscles were obtained, but these differences were greatly reduced when values were expressed as a percentage of total muscle weight.

On a percentage basis, there were significant changes with stage of maturity in only three of the muscles studied, although most individual muscles showed an initial percentage decrease with increasing maturity (from 40 to 52%) but almost no change thereafter. Significant breed differences in muscle distribution were found. The individual muscles examined, when combined, comprised 40·8, 43·4, 40·5 and 39·8 % of total muscle weight respectively in the Soay, Southdown, Finnish Landrace and Oxford Down. No breed was significantly above average for every individual muscle, but the Southdown had the highest percentage in 6 out of 12 and might therefore be said to have had the most preferred muscle distribution. For most muscles examined, the percentage was slightly higher for females than for males, with totals for all 12 muscles of 41·9 and 40·4% respectively.

In order to investigate the effects of type of breed on carcass composition, an examination was made of 361 lambs from four breeds: Clun Forest and Colbred (termed ewe breeds); and Suffolk and Hampshire (termed ram breeds). The animals were in four carcass weight groups averaging 15, 17, 19 and 21 kg.

Percentage subcutaneous fat was influenced more by carcass weight than by breed, whereas both carcass weight and breed had similar effects on percentage lean. At the mean carcass weight of 18 kg, Colbreds, the leanest breed, had a similar value for percentage lean (about 57 % of carcass tissue weight) to the carcasses over all breeds weighing 15 kg; and Cluns, the fattest breed, had a similar value (about 54%) to those weighing 21 kg. Since the ram breeds were intermediate in composition between the two ewe breeds there was no effect of type of breed on carcass composition. The breed differences were related to eventual mature size and to the stage of maturity at each carcass weight, as judged by body length and bone weight measurements. However, Colbreds were bigger and leaner than published estimates of their mature weight suggested. Humerus weight was a good predictor of lean or total fat weight, explaining 83 % ofvariation when used as a predictor along with carcass weight.

Type of breed had a marked effect on internal fat deposition, the ewe breeds having heavier weights of both kidney knob and channel fat (KKCF) and caul fat (omental fat) than the ram breeds; and on the length oflimb bones, the ewe breeds having longer but thinner bones than the ram breeds. The order of the relative growth of the tissues and fat depots was: subcutaneous fat > caul fat > KKCF > intermuscular fat > lean > bone. Therefore, the internal fat depots were later maturing than intermuscular fat.

The percentage of prime cuts in the carcass was not affected by carcass weight. Colbreds had significantly lower values than the other breeds. Suffolks had the lowest lean to bone ratio.

Seasonal fluctuations in oestrous activity and live weight were studied in ewes of the Marwari breed indigenous to the Rajasthan Desert in north-western India. Of the ewes examined 80 to 100% were in oestrus every month of the year, indicating thereby the non-seasonality of female reproductive activity in this breed. On average, each ewe exhibited heat 18 times a year. The incidence of silent heats was low (4·2 %). The average length of an oestrous cycle was 17 days, while the actual period of oestrus varied from 24 to 48 h with an average of 36 h. No seasonal effect on these activities could be observed. The maximum and minimum body weights of the animals were recorded during the autumn (October) and summer (June) months respectively. The body weights differed significantly (P<0·05) between months. Sexual activity in these animals is, therefore, apparently not affected by changes in body weight. The continuous nature of oestrous activity in Marwari sheep may be economically exploited by regulating the lambing season according o t the prevailing ecological conditions and market demands, without the use of hormones.

Micronization followed by grinding of brown-seeded sorghum increased starch availability in vitro but had no effect on proximate composition of the grain. In diets containing 70% of sorghum in ground or micronized and ground form, apparent digestibility of dry matter and nitrogen and nitrogen retention by growing pigs were improved (2·5, 5·0 and 12·2% respectively). Addition to the diet of 0*2 g polyethylene glycol per g crude protein in the sorghum fraction produced similar effects. In the ground cereal diet inclusion of polyethylene glycol increased apparent digestibility of gross energy (3·8%) and improved metabolizable energy content by 5·5%, but i n the micronized and ground cereal diet the additive had no effect.

ANIMAL PRODUCTION, Volume 28, Part 2, pp. 157-170

GROWTH, FOOD INTAKE AND COLD EXPOSURE IN MICE

1. Cold Exposure of Adolescent Mice

N. Bateman and J. Slee