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.

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.

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.

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.

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.

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. The reproductive performance of 128 first-lambing ewes born during 1966–71, and of 118 ewes kept on a twice-yearly lambing system during 1968–1972/73, in a commercial flock of Finnish Land-race sheep in Finland, was analysed.

2. The first-lambing ewes were exposed to the ram throughout the year, except in June and July. Out of 95 ewes born between January and May, 92 (97%) lambed at the age of 376·4 ± 29·9 days, and out of 20 born between July and September, 15 (75%) lambed when 323·8 ± 50·4 days old.

3. The average litter sizes at first lambing were 1·6, 1·9 and 2·6 for ewes with average ages of 324, 388 and 534 days, respectively; the 5-mo litter weights averaged 41·7, 45·7 and 70·5 kg per ewe for the three groups.

4. In the twice-yearly lambing system 55% of ewes lambed once within a calendar year and 45% lambed twice. The number of consecutive lambings and the number of lambs born per ewe per year were 1·52 ± 0·29 and 4·03 ± 1·18, respectively. The consecutive lambings of the 118 ewes, over a period of 1½ to 5½ yr, did not indicate any decline in reproductive performance.

5. The estimated lambing-to-conception interval in consecutive lambings was 116·6 ± 64·3 days; February had the lowest conception rate (0·7%) and November the highest (20·8%); April (16·5%) and September (15·5%) were similar.

6. Litter size was not affected by year, age of ewes, or lambing period. The mean lamb mortality up to 14 days of age, based on 1168 lambs born dead or alive, was 12·8% and the annual ewe wastage averaged 21·9%

7. For ewes which lambed twice within a calendar year, the lambing to conception interval was 71·7 ± 24·7 days. Such ewes produced 5·0±1·4 lambs per calendar year and the combined 5-mo weight of both litters was 168·2 ± 43·2 kg per ewe.

Birth weights, weaning weights (75 days of age) and pre-weaning average daily gains of 291 lambs and post-weaning average daily gains, feed conversions and market weights of 136 ram lambs were studied. The lambs were of three fat-tailed Iranian breeds of sheep, Karakul, Mehraban and Naeini, and their crosses with Corriedale and Targhee rams.

The crossbreds were significantly superior to the purebreds in all the traits studied, by approximately 7% in the pre-weaning traits and up to 18·4% in the post-weaning daily gain. Among the purebreds, Mehraban lambs were superior to the other two breeds in the preweaning traits and final weight.

The progeny of the Targhee and Corriedale rams were similar in performance except for feed conversion, in which the lambs sired by Targhee rams were more efficient. Breed of dam had a significant effect on the pre-weaning traits and feed conversion. Mehraban ewes produced lambs with the highest pre-weaning average daily gain and weaning weight among the crossbreds, but they were the least efficient lambs after weaning.

Age of dam significantly influenced the pre-weaning but not the post-weaning traits. Lambs born to 4-yr-old ewes were the heaviest and those born to 2-yr-old ewes were the lightest at birth. The lambs reared by 2-yr-old ewes had significantly lower rates of growth and were the lightest at weaning. Sex had a highly significant effect on the pre-weaning traits in favour of the male lambs.

Food intake, eating rate, weight change and fasting metabolic rate were measured on 12 animals of each of the following breed-types: Hereford × Shorthorn (HS), Brahman × HS (BX) and Africander × HS (AX). Measurements were made on ad libitum and fixed levels of lucerne and ad libitum and fixed levels of low-quality tropical pasture hay (approx. 1·2% N) during feeding periods of about 100 days' duration.

The BX and AX were heavier and either gained more weight or lost less weight than the HS on all diets. At feeding levels close to maintenance, which included the ad libitum pasture hay diet, adjustment for differences in either live weight or intake did not alter the unadjusted ranking of the breeds. On ad libitum lucerne, however, adjustment for either weight or intake showed higher gain in the HS than in the BX. The voluntary food intake per kg live weight was consistently and significantly highest for the HS and lowest for the BX. Rates of eating were not significantly different for the different breed-types but they were higher for high-quality lucerne and for the lower level of feeding. Fasting metabolic rate per kg live weight was highest for the HS and lowest for the BX; the difference between the breeds varied with the previous dietary treatment. The ratio of voluntary food intake to fasting metabolism was practically constant between breeds and animals within breeds, though different between diets.

Correlations for animals within breeds and years between the various parameters within diets and between diets are presented.

The milk production of three groups of cows grazing on veld and receiving different amounts of concentrates during winter and the first 8 weeks of lactation was studied over four successive calving seasons. Calves were weaned at either 150 or 240 days.

Cows offered most concentrates and those whose calves had been weaned early in the previous year produced more milk per lactation (P < 0·01) than other cows but weaning age did not affect yield/cow per year. Data for each treatment in each year were considered as a separate class. Regression analyses showed that milk yield increased with cow weight at calving and with calf birth weight. Changes in cow weight during early lactation, after adjusting for initial weight, were directly related to milk yield.

In a concurrent experiment, three groups of heifers were confined in pens and given sufficient amounts of a complete diet to promote either gain, maintenance or loss of weight during lactation. Heifers that gained or maintained weight produced significantly (P<0·01) more milk of a higher solids-not-fat and protein content than those which lost weight. Food intake had a significant (P < 0·01) positive effect on milk yield but the effects of weight and weight change on milk yield were negative after adjusting for food consumption.

A randomized block experiment was conducted using 27 British Friesian cows to assess the effects of three levels of concentrate input (589 (H), 456 (M) and 316 (L)±19·2 kg/cow) on performance. The animals, mean calving date of 6 January, were blocked according to calving date and allocated at random to treatments. All concentrates were given during the post-partum indoor feeding period (mean of 86 days) in addition to access ad libitum to grass silage. All animals received equal concentrate inputs/kg milk produced for 29 days after calving, following which the concentrate inputs were reduced, the reduction depending upon treatment. The milk outputs during the treatment period were 2147, 2075 and 1850 ± 75·8 kg and live weights at the end of the period were 504·1, 500·0 and 468·8 ± 4·96 kg for the H, M and L levels of concentrate supplementation respectively. Six animals per treatment were rotationally grazed at pasture at a stocking rate of 6·0 cows/ha for 11 weeks following the indoor feeding period. Performance at pasture was not affected significantly by previous treatment, with the milk outputs for the pasture period being 1647, 1673 and 1738 ± 53·0 kg, for the H, M and L treatments respectively. The milk outputs during the total indoor feeding plus grazing period at 3887, 3852 and 3636 ± 103·5 kg for the H, M and L treatments respectively did not differ significantly. Milk composition data are also presented.

Equations relating biomass to cumulative food ingested ad libitum were defined in rats from weaning to 200 days of age. Two inbred lines of the IIM strain: α, of medium adult weight, and b, of low adult weight, were fed on two different diets, × and Z. The following groups were formed: αX, αZ, bX and bZ. Body weight and food intake were recorded over a 1-day period every second day. For each of the four groups, body weight, W, could be described as a function of cumulative food intake (F) by the equation:

Each exponential term was assumed to measure the behaviour of a portion of the biomass. The first exponential term implied an intense growth and a high initial efficiency, which became effectively zero by about 100 days of age. The second exponential term implied a weak growth and a low but significant efficiency of food utilization. Type of diet influenced level of intake and was important at early ages (<100 days). At 46 days of age, animals of both lines were heavier and more efficient when fed on diet Z. The genetic influence determining final adult weight becomes evident after 46 days of age.

Data from a large field trial comparing the performance of contemporary crossbred ewes from traditional and experimental prolific rams were used to study two factors, (1) the influence of lambing at 1 yr of age on subsequent ewe performance and (2) the effect of level of farm performance on the difference between the traditional and the prolific types. Neither effect was found to be important.

The effects of three diets on the performance and carcass quality of lambs of the Makui and Moghani breeds of sheep were studied. Thirty-two Makui and 33 Moghani lambs, 6 to 7 mo of age, were kept on feedlots and given three diets for 77 days. The diets each contained a barley, alfalfa meal and corn silage base plus different levels of urea, molasses and dried beet pulp.

The average daily live-weight gains (ADG) of lambs fed on diets I (no urea), II (0·8% urea) and III (1·4% urea) were 218, 208 and 204 g respectively, while feed conversion ratios (FCR) were 6·3, 6·6 and 6·8 respectively. The overall ADG for Makui and Moghani lambs were 213·6 and 206·6 g respectively and the FCR were 6·4 and 6·9 respectively. None of these differences was statistically significant. The mean dressing percentages of lambs fed on diets I, II and III were 52·5, 52·7 and 53·9 respectively, and those of Makui (53·1) and Moghani lambs (53·3) were similar. There were only minor differences between the carcass characteristics of the two breeds and these were not influenced by the different diets.

Grass silage with a dry-matter content of 20·7%, and containing 18·9% crude protein and 67·0% digestible organic matter in the dry matter was self-fed to 20 lactating dairy cows for 18 weeks. In addition, 9 kg of brewers' grains with a dry-matter content of 28·8% was offered to each cow daily. The two supplement treatments were a barley mix and a groundnut cube containing 11·9 and 33·5% crude protein in the dry matter respectively. The barley was given at the rate of 4 kg/10 kg milk, and the groundnut at 1·5 kg/10 kg milk. The mean daily yields of milk were 18·9 and 19·4 kg/cow on the barley and groundnut treatments respectively and did not differ significantly.