Genetic responses from selection strategies based on selection among all potential parents of the following year's crop were compared with those based on selection only within progeny crops. In the former group of strategies the duration of stay of an individual in the breeding herd is determined by the estimated breeding value of that individual, whereas in the classic model selected individuals of the same sex all remain in the breeding population for the same period. The former group of strategies, termed ‘parent selection’ strategies, were consistently superior in genetic response to the progeny selection strategies with a very large relative advantage under some conditions. The superiority of strategies that make more efficient use of genetic differences between own or parental age was greater among parent selection strategies than among progeny selection strategies. Similarly, increases in female to male mating ratios, fertility and survival rate generally resulted in larger increases i n genetic response in the more efficient strategies. The effect of changes in number of male and female age groups differs markedly between strategies.

The influences of age at first pregnancy and number of suckling young on maternal performance of mice were studied. Mean mating ages for early-pregnant and normal-pregnant females were 27 and 52 days respectively. Litter size from parturition (day 0) to day 12 of lactation was standardized to either 8 or 12 pups. The more rapid (P<0·01) growth rate and feed conversion efficiency of early-pregnant dams from mating to parturition continued from 0 to 12 days of lactation but occurred primarily in the first 3 days of lactation, so that there were no differences in body weight or feed intake from days 3 to 12 of lactation. There were no age at pregnancy effects on total mammary gland DNA, RNA or RNA/DNA ratio at day 12 of lactation or on individual progeny weights or feed conversion efficiency of litter growth from 3 to 12 days of lactation. Dams suckling eight young had a lower (P<0·01) feed intake, gain and feed conversion efficiency from 0 to 3 days of lactation. From 0 to 12 days of lactation, these dams were smaller, consumed less feed and their individual progeny weights were larger (P<0·01). Dams suckling eight pups had smaller (P<O01) mammary glands, less (P < 0·05) mammary gland DNA and a higher (P<0·05) RNA/DNA ratio. Interactions between pregnancy age and number suckling were not significant. Feed intake of the dam from 0 to 12 days of lactation was influenced more by litter weight gain (34%) than either dam weight gain (5%) or metabolic body size (6%). Maternal performance of mice, based on pup growth and mammary gland growth and function, was not affected by early pregnancy.

Forty-eight Large White ♂× (Landrace × Large White) ♀ male castrate pigs were individually fed, on a live-weight-based scale between approximately 23 kg and 88 kg live weight, similar daily in-takes of digestible energy, crude protein and total lysine from four diets (12 pigs per diet) of widely differing compositions and nutrient densities. The digestible energy contents (MJ/kg) (1), crude protein (%) (2) and total lysine (%) (3) contents of the diets were: diet A (1) 11·40, (2) 14·40, (3) 0·82; diet B (1) 12·90, (2) 16·50, (3) 0·94; diet C (1) 14·96, (2) 19·20, (3) 1·09 and diet D (1) 18·28, (2) 23·30, (3) 1·32. To give the required daily nutrient intakes, relative to diet A (100) the intakes of diets B, C and D were 87·5, 75·0 and 62·5 respectively. Growth rates, carcass weights (from dissimilar but non-significantly different slaughter weights), killing-out percentages and the digestible energy required to produce a unit of carcass improved progressively from diet A to diet D. In these variables the significant differences tended to lie between diets A and B on the one hand compared with diets C and D on the other. The weights of lean tissue dissected from the carcass were similar for all pigs. The weights of dissected fatty tissue and backfat thicknesses increased from diet B to C to D but only the differences between diets B and D were statistically significant.

A quantitative model of energy intake and utilization by ewes in various physiological states grazing a pasture of perennial ryegrass is presented. The model consists of two major components: a forage intake component incorporating forage availability and maximum potential intake as affected by age of the grass and physiological state of the ewe; a second component representing energy utilization by the ewe for maintenance, growth, pregnancy, lactation and wool growth.

The behaviour of the model was examined and found to be consistent with published information. Partial validation of the model was accomplished by comparing the model output with actual experimental data not used to construct the model.

Heat transfer coefficients are used to calculate convective and radiant heat losses from pigs of 4, 20 and 60 kg body weight at 20 and 30 °C environmental temperatures for different wind speeds. Comparisons with heat losses estimated from whole-animal calorimetry suggest that calculations with heat transfer coefficients can lead to useful approximate estimates of heat loss from the pig.

Experiments were conducted to observe the taste responses of male and female calves to various levels of sodium salts, chloride solutions, and trace minerals. Animals were penned individually and given a completely pelleted ration ad libitum. Trace mineralized salt was freely available.

Using water as a basis for determination, a non-discrimination zone was established. This zone represented an intake ranging from 63 to 37%. Preference threshold was set at 80% of intake, while the rejection threshold was set at 20% of intake. Responses were determined by expressing the intake of the test solution as a percentage of the total intake during the test period. Responses at a given chemical concentration were measured during two 8-hr periods.

Taste response observations were made on the following: 0·02, 0·08, 0·32 or 1·25% sodium chloride (NaCl), sodium sulphate (Na2SO4), sodium bicarbonate (NaHCO3), sodium carbonate, monobasic sodium phosphate (NaH2PO4), dibasic sodium phosphate (Na2HPO4), ammonium chloride, potassium chloride, calcium chloride, magnesium chloride, and manganese chloride. In addition, observations were made when 0·02, 0·08, 0·32 or 1·25% NaHCO3, Na2SO4, or Na2HPO4 were offered in opposition to equal concentrations of NaCl. The responses to 5, 10, 20, 40 and 60 p.p.m. concentrations of cupric chloride, zinc chloride, molybdenum trioxide and cobaltous chloride were observed also.

Two milk replacers identical in composition except for the protein source, which was either fish-protein hydrolysate (FPH) or dried skim milk, were offered either twice or four times daily to castrated British Friesian male calves in four ratios: 100 FPH 0 Milk; 67 FPH 33 Milk; 33 FPH 67 Milk and 0 FPH 100 Milk. Concentrates and hay were offered ad libitum, and the calves were weaned at 42 days of age. Feed intake and calf live weight were recorded to 100 days of age.

There were no differences in growth rate up to weaning due to frequency of feeding. Up to 67% FPH there were no differences in growth rate but calves on the 100% FPH diet showed a 40% depression in growth compared with the other three levels. Up to 100 days there was no apparent effect of treatment on live-weight gain, but only differences of 12 to 13% would be significant.

The results indicate that at least two-thirds of the milk protein could be replaced by FPH. The need for further work using dried material and FPH from other species is discussed.

1. In a comparative slaughter experiment, 12 female pigs (six at 80 kg and six at 100 kg) were allocated at first oestrus to each of five treatments: Treatment 1 initial slaughter, or Treatments 2, 3 and 4 mated and given 19·5, 25·8 or 32·1 MJ ME/day for the last 100 days of pregnancy, or Treatment 5 not mated (virgin) and given 25·8 MJ ME/day over a similar period. Pigs on Treatments 2, 3, 4 and 5 were given the same amount of protein and were killed about 123 days after first oestrus. Piglets were removed at birth.

2. Total protein deposition (carcass+viscera+piglets) was increased from a total (±SE) of 5·50 to 8·47 (±0·43) kg as ME intake was increased from 19·5 to 32·1 MJ ME/day. About 75% of the increase in protein deposition was in the carcass component. The average response to ME was 2·2 ± 0·58 g total protein deposition per MJ increment in ME.

3. The once-mated pigs deposited similar amounts of total protein to the virgin pigs but significantly less (P<0·05) carcass protein, when this was corrected to the same amount of carcass fat deposition.

4. Increasing energy intake from 19·5 to 32·1 MJ ME/day increased total fat deposition from 2·8 to 16·0 kg. The average response to ME was 13·5 ± 1·53 g fat deposited per MJ increment in ME.

5. There were no significant differences between the once-mated and virgin pigs in their calculated maintenance requirement, nor in the efficiency with which ME surplus to requirement for maintenance was utilized for energy retention. The average maintenance requirement for all pigs was 530 (95% limits 303·882) kJ/kg0·85. day. The average efficiency of utilization of ME for energy retention was 58·5 ± 6·2%.

6. There was no evidence of any pregnancy anabolism other than that involving the conceptus, the needs of the dam specific to pregnancy and preparation for lactation.

In one experiment, 227 female sheep in two age groups were reared on low (107 sheep) and high (120 sheep) levels of nutrition from birth to 12 mo of age after their dams had been given low and high levels of nutrition during the last 6 weeks of pregnancy. From 12 mo, 47 of the low-level sheep and 51 of the high were grazed on poor hill pasture to provide a low-level adult nutritional environment while 46 of the low level and 52 of the high were grazed on good quality pasture to provide a high-level adult nutritional environment. These treatments were continued for 5 production years for one age group and 4 production years for the other.

Live-weight differences associated with rearing treatment persisted throughout the experiment in both adult environments. Lifetime lamb production was significantly affected by both rearing and adult treatments.

The effects of these treatments on reproductive potential were examined in a second experiment by determination of ovulation rate when the sheep were brought into uniform good body condition at mating after the end of the first experiment. Potential ovulation rate was significantly affected by rearing treatment but not by adult treatment, although live weight and body size were affected by both.

It is concluded that while reproductive potential is related to body size it may also be influenced by the pattern of early growth during unidentified developmental stages.

For a crossbreeding experiment six lines of pigs were developed from six breeds: Belgian Landrace (B), Pietrain (P), Dutch Landrace (N), Dutch Yorkshire (G), Duroc (D) and Hampshire (H). Out of 10 different litters per line, one female and one castrate male were housed and fed individually from 20 to 96 kg. All pigs were offered feed twice daily for 20 min exactly.

Maximum differences in feed intake between the lines increased from 150 g at 25 kg to more than 500 g at 95 kg live weight. Daily intake of Pietrain pigs was lower than that of all other lines. Differences between the N, H and G lines were small. The difference between the feed intake of males and females increased from zero at 27 kg to 230 g at 75 kg. Differences in daily gain were greatest between the P and G lines, and doubled during the growing period from 80 g to 170 g.

Differences in daily gain between the N, H and B lines were small. Pietrain pigs and, to a lesser extent, Belgian Landrace pigs produced more meaty carcasses but both had poorer meat quality than other other lines. It is concluded that differences in feed intake might be the main causal factor for the existence of differences between biological types of pigs.

Two fibrous roughages, wheat straw and cotton hulls, were treated with 0, 40 and 80 g sodium hydroxide (NaOH)/kg roughage, applied in amounts of water calculated to bring the roughages to moisture contents of 30 and 60%. The effects of these factors on the nutritive values of the two roughages were examined using a 2 × 3 × 2 factorial design.

Digestibility trials, in vitro and in vivo, and a 9-mo feeding trial were carried out with the roughages soon after treatment. Concentrates were limited to 6 kg/head per day throughout the animal experiments and roughages were offered ad libitum.

Neutral detergent fibre decreased by 7·8 and 13·5% with the 40 and 80 g application rates of NaOH respectively.

The treatment of both roughages with NaOH increased considerably their in vitro dry matter digestibility and total solubles after enzyme treatment, the increases being related to the rate of application of NaOH. Digestibility in vivo was improved only by the 40 g NaOH treatment.

Treatment with NaOH reduced the voluntary intake of both roughages. Only the 80 g/kg treatment had a positive effect on rate of live- and carcass-weight gain. On the other hand, NaOH improved very significantly the efficiency of conversion of metabolizable energy into live and carcass weight and increased significantly the degree of fatness of the animals. These results indicate a marked improvement in the nutritional value of both roughages due to NaOH treatment. The reason for the small response in rate of gain may be explained by a shortage of protein owing to a possible reduction in its digestibility. Cotton hulls excelled wheat straw in almost every respect. Animals on NaOH-treated cotton hulls bloated chronically unless some long straw was given. Moisture level had practically no effect on performance.

The effects of the treatments on rumen or blood constituents were small.

Commercial lamb carcasses were surveyed in 1971/72 as part of the development programme for a national classification scheme for Great Britain. Carcasses of 421 castrated male lambs were evaluated and their left sides dissected. The sample comprised seven groups representing the main breed types in the national population. Within these groups, lambs were selected from three regions on each of three occasions corresponding with the beginning, middle and end of the normal slaughtering season for each group.

The overall means (±SD) for side weight and percentage subcutaneous fat in the side were 8·3 ± 1·8 kg and 12·6 ± 3·2 respectively. When adjusted to the overall mean subcutaneous fat percentage (constant % SF), the breed-type side weight means ranged from 6·4 kg (Welsh Mountain) to 10·8 kg (British Longwool). At constant% SF, lambs slaughtered earlier in the season were lighter than those of the same breed type slaughtered later.

Significant differences (P<0·05) were recorded between breed-type groups in fat distribution and lean/bone ratio. These were reflected as important differences in percentage lean at constant % SF, group means ranging from 54·5 (lambs by Suffolk rams out of Scottish Halfbred ewes) to 56·7 (lambs by British Longwool rams out of hill ewes).

When lambs of the same breed type from different regions were compared at constant % SF and constant side weight, there were few important differences in carcass characteristics.

The results are discussed in relation to the classification scheme which has since been introduced by the Meat and Livestock Commission.

Three groups of four mature boars were housed in individual pens for 3 mo under one of the following social conditions: near ovariectomized female pigs induced into sexual receptivity at 2-week intervals; isolated from female pigs but either with or without visual and physical contact with neighbouring boars. The total number of copulations achieved in six mating tests throughout the period was significantly greater (P<0·01) for the boars housed near sexually receptive females than for those housed in the other two social conditions. For the subsequent 3 mo all boars were housed near sexually receptive females and no significant differences were found between the three groups for total number of copulations.

Seventy-two lactating dairy cows were used in a 4x 3 factorial experiment to assess the effects of the protein content of concentrates on the response to concentrate feeding level. Concentrates containing 12,18 and 24% crude protein in the dry matter were given at each of four levels of feeding: 0·25, 0·36, 0·47 and 0·58 kg/kg milk for a 7-week experimental period. Milk yield, milk energy output, liveweight change and the percentage solids-not-fat and protein in the milk were significantly affected by both the level of concentrate feeding and the protein content of the concentrate. Response curves for the effect of level of concentrate feeding on milk output and liveweight change were computed for each of the three protein levels, and although there was no significant interaction between these two main factors the benefit from increased protein in the concentrate was shown to depend partly on the level of feeding at which the concentrate was used. At low feeding levels the response to an increase in protein content of the concentrate tended to be smaller than that obtained at high feeding levels. At no stage was there any marked response to protein content in the concentrate above 18%. The response curves have been used to demonstrate the interchangeability of level of concentrate feeding and protein content of the concentrate as means of supporting a given level of milk production.

Pre-weaning growth data from 3822 calves reared in 11 Victorian herds were analysed. The results suggested that the superiority of males (bulls) over castrated males (steers) in pre-weaning growth was due, at least partly, to the early castration of poorly growing male calves, i.e. to the effects of early selection. The extent of this selection bias was further examined using results from similar studies and from experiments in which bulls and steers were selected without bias. These studies strongly supported the view that the superiority of bulls over steers was primarily due to selection and not to sex effects. If sex did influence the bull-steer difference it was of no statistical or practical importance.

In the Victorian data, the ratio of bulls to steers was higher in subclasses in which average growth rates were higher. When selection effects are correlated in this way with other environmental effects such as age of dam effects further biases may arise in estimation of those effects and hence in individual or mass selection.

The results indicated, therefore, that unless bulls and steers are treated as one sex biases can arise in both individual selection and progeny selection.

Using pre-weaning records of 3822 calves from 11 Victorian herds, mean male and female growth rates and corresponding sex differences were calculated for each dam age and herd-year class. From these means simple regression equations relating sex differences and growth rates were calculated. There was a close similarity between equations based on dam age means and those based on herd-year means while correlations between sex differences and male growth rates were high.

These results showed that sex differences and female growth rates could be predicted reliably from the level of environment as measured by male growth rate. Sex differences predicted by these regression relationships differed markedly from those predicted by the simple multiplicative and simple additive models generally used in adjusting for sex differences in selection.

The results also suggested that other differences such as breed differences may be predictable in the same way and that such differences are determined primarily by the level of environment per se rather than differences in the nature of the components contributing to that level.

In a long-term experiment, the performance of British Friesian, Ayrshire and Jersey cattle and their first and second crosses was evaluated over 526 first and 477 second lactations. Live weight at 18 mo of age and the ratios of lactation yield to live weight were examined as well as milk yield and composition of milk.

Percentage heterosis in each combination of two pure breeds was estimated. For the three first crosses combined, heterosis for 305-day milk yield averaged 6·4% in first and 3·7% in second lactations. Heterosis in live weight at 18 mo averaged 2·9%; none was found in the Ayrshire × British Friesian crosses, but the others averaged 4·7%. Second crosses overall had an average live weight near to that of first crosses, but their milk yields were lower and, in the combined lactations, approximately equalled the purebreds' total.

Components of variance due to breed and environmental factors were calculated. Breed accounted for 50% of variance in live weight at 18 mo but less than 10% of variance in milk yield.

The influence of fertility on heterosis is discussed with reference to earlier findings, and economic implications are considered.

Seasonal variation in testis diameter and sperm output was studied in five Finnish Landrace (Finn) and five Tasmanian Merino (Merino) rams, together with five crossbreds between these breeds (Finn-Merino), five selected phenotypically from the Finn-Dorset breed type for high juvenile testis diameter (Finn-Dorset-High) and four for low juvenile diameter (Finn-Dorset-Low). There was marked seasonal variation in testis diameter for each of the breed types. The time of the seasonal increase in testis diameter varied among the breed types, the Merino rams starting earliest—49 days before the Finns. The characteristics of seasonal variation in testis diameter thus showed similarity with the characteristics of seasonal variation in the reproductive performance of females of the breed type. Breed differences in response to season were also demonstrated by a significant breed by season interaction for sperm production, but there were no indications of a useful association between variation in sperm production and variation in the reproductive performance of related females. Overall, differences in adult testis diameter were small relative to those among juveniles.

1. Wilted (32% dry matter) Italian ryegrass was conserved: (A) untreated; (B) with 16·3 g/kg dry matter (4·6 1/t of fresh material) of an 85% w/w formic acid additive; (C) 12·1 g/kg dry matter (2·3 1/t fresh material) each of 85% formic acid additive and formalin (40% w/v formaldehyde); (D) 5·8 g/kg dry matter (1·3 1/t fresh material) each of 85% formic acid additive, formalin and a 96% w/v solution of propionic acid. The silages were individually fed ad libitum to 40 15-mo-old British Friesian steers of about 350 kg initial live weight.

2. Treatment with additives inhibited fermentation, resulting in silages with higher levels of water soluble carbohydrates and lower levels of organic acids than untreated material. Lower levels of ammonia N and higher levels of true protein indicated that some protein protection resulted from the formaldehyde treatment.

3. Formic acid alone (B) had little effect on digestibility but significantly (P<0·05) enhanced dry-matter intake, live-weight gain and nitrogen retention relative to the control (A)

4. Whereas the application of formaldehyde (Treatments C and D reduced the digestability in vivo of nitrogen, significant increases in nitrogen retention were recorde relative to the control (A). Dry matter intake was not affected significantly by treatment with formaldehyde, but at the higher level of application (Treatment C) daily gain was significantly reduced compared with the control (A). These effects are discussed in relation to possible changes in VFA patterns within the rumen and to the levels of formaldehyde used.

Mixtures (1: 1) of whole-crop dried wheat or barley, with peas or beans as a nitrogen supplement, were fed ad libitum to four groups of 16 6-mo-old male castrate sheep for a period of 42 days in 1971. The mean dry-matter consumptions (kg/day) and live-weight gains (g/day) were: wheat+peas 1·69, 264; wheat+beans 2·05, 288; barley+peas 1·80, 282; and barley+beans 1·81, 229. This experiment was repeated in 1972. The differences between treatments were non-significant.

Dried pelleted whole-crop maize was fed ad libitum to British Friesian steers for 90 days, in conjunction with molasses and one of three protein sources, soya bean meal, urea or whole crop beans. The dry-matter intakes (kg/day) and live-weight gains (kg) were: maize+soya 9·68, 1·26; maize+urea 9·38, 10·4; and maize+beans 9·72, 1·15.

Dried maize in conjunction with urea, whole crop beans and dried grass to supply crude protein levels between 9 and 11% was fed to 48 Hereford × British Friesian steers. The dry-matter intakes (kg/day) and live-weight gains (kg/day) were: whole crop maize, 8·35, 0·87; whole crop maize+urea, 9·55, 1·0; whole crop maize+whole crop beans, 7·44, 0·70; whole crop maize+dried grass, 8·94, 1·15; whole crop maize+rolled barley, 9·30, 1·23; and dried grass + rolled barley, 9·24, 1·21. Although there was no significant difference in live-weight gain between the treatments, two levels of performance were apparent.