A rigid system of grazing management was examined for 2 years using rotations of fixed length. Rotations of 21 and 35 days were compared at low (3 calves+ 3 heifers/ha) and high (4 calves+ 4 heifers/ha) stocking rates. The calves and heifers grazed the paddocks on a leader/follower basis.

Average growth rates for the 21- and 35-day rotations were respectively 0·75 and 0·78 for calves and 0·78 and 0·83 kg/day for heifers, but these differences were not significant. The 35-day rotation produced 6% more live-weight gain and 4% more herbage dry matter/ha than the 21-day rotation. The high stocking rate produced 14% more live-weight gain but 3% less herbage dry matter/ha than the low stocking rate. The total percentage utilization of herbage dry matter for the whole season was similar for 35- and 21-day rotations, averaging 90%. There were no significant interactions between length of rotation and stocking rate.

Suffolk and Rambouillet female sheep (ewes) were kept in pens where daylight was gradually reduced and were treated, or not treated, with hormones to obtain four lambing cycles in 2·5 years. Oestrus in May, June and July was induced more easily (P<0·01) in Rambouillet than the Suffolk ewes. The advantage of higher conception rates in the Rambouillet ewes during anoestrus was offset by the higher prolificacy rates in the Suffolk in the other three lambing cycles. On average, each breed produced 128 lambs per 100 ewes exposed per lambing cycle. This corresponds to 5·1 lambs per ewe in four lambings, which is equivalent to 2·04 lambs per ewe per year. Under the conditions of the experiment, the addition of Syncro-Mate pessaries (20 mg fluorogestone acetate) and pregnant mare serum gonadotrophin (PMSG, 5 ml/ewe, 50 IU/ml) to the treatment of reduced daylight did not affect the ovulation or conception rates.

In a study involving over 300 pelves from lambs of known age at slaughter it was shown that time of ossification was poorly related to age of lamb. The youngest lamb with an ossified pelvis was a female aged 22·4 weeks and at the other end of the scale a third of a group of 45-week-old castrated male lamb pelves were not ossified. Female lamb pelves ossified earlier than castrated male lamb pelves. Carcasses with ossified pelves at a given age tended to be heavier than those with pelves not ossified and pelves of well-fed lambs probably ossified before those of poorly fed lambs. The results indicate that the suggested Codex method for a carcass classification or grading system for dividing lamb carcasses into those under and those over 6 mo of age at slaughter was not accurate. The reason for wanting such a classification is also questioned.

An investigation was undertaken to evaluate the crossbred boar per se, and also to assess the value of including the American Hampshire into a first-cross sire. Groups of three boars were placed on each of 20 farms. Each group contained a purebred white (Landrace or Large White), a crossbred white and a crossbred Hampshire boar. Co-operators were asked to obtain at least six litters by each boar, record their performance to weaning, and provide a sample of the progeny of each boar to be reared under standard conditions to slaughter at 90 kg live weight. Breeding of the boars did not affect either the level or variability of litter performance. Differences in performance and carcass traits between the progeny of purebred and whitecross boars were found only for ‘eye-muscle’ area and fat depth ‘C’. Pigs sired by Hampshire-cross boars had carcasses which were 2% shorter than those from white boars.

Weaning increased forage intake and depressed live weight; differences in intakes and growth rates of lambs born to South Australian and Fine wool Merinos were small. At 21 days, sucking lambs received less than 2% of their digestible organic matter from pasture and half the lambs weaned at this age died but the survivors consumed twice as much forage as unweaned sheep in the 14 days following weaning. At 49 days, unweaned lambs obtained approximately 41% of their digestible organic matter from pasture, and weaning resulted in less mortality and a proportionally smaller increase in forage consumption.

The discounted gene flow method was used to study the effect of varying financial discount rates and accounting period on the present value of the genetic merit conferred by each insemination.

Over the range from 8% to 16%, each 1% increase in the discount rate reduces the value of the dairy and beef consequences of an insemination by about 5% and 4% respectively, Virtually all of the economic benefit arising from an insemination is complete within 20 years, with about 90% of it being realized in the first 10 years and 98% in the first 15 years.

Data on incidence and severity of infection with bovine infectious keratoconjunctivitis and proportion of eye margin pigmentation were collected over 3 years in a mixed herd of Hereford × Shorthorn (HS), Africander x HS, Brahman x HS, grade Africanders and purebred Brahmans. Both sexes were scored at 3 and 8 mo but only females were scored at 15 mo. At all ages, the incidence of infection was greatest in the HS and lowest in the Brahmans in which no infections were recorded. The severity of infection and proportion of bilateral infections were also greatest in the HS animals.

Infected animals were lighter at all ages than comparable uninfected animals. HS females which showed signs of infection at each age were 22·8 kg lighter at 15 mo than those which had never shown signs of being infected. The magnitude of the weight difference was directly related to the severity of infection.

In the HS breed, both the incidence and severity of infection were related to the proportion of eye margin pigmentation. At 15 mo, 68% of HS females with full eye margin pigmentation were infected compared to 96% of comparable unpigmented animals. At 15 mo infected HS females with full eye margin pigmentation were heavier than unpigmented contemporaries. It was concluded that the lower weight of infected animals was primarily the result of the disease rather than vice versa.

Fifty-three Landrace × (Landrace × Large White) young female pigs (gilts) were fed ad libitum from selection at 20 kg live weight until mating at the second oestrous period. All gilts were subjected to a change of environment at 55 kg live weight, and the male was introduced daily from 64 kg live weight. Gilts were mated twice at second heat, and slaughtered on the 20th day of gestation. There was a range in age at puberty from 135 to 235 days (mean 178·9 ± 3·4 days), and in weight at puberty from 70 to 125 kg (mean 90·5 ±2·3 kg), indicating that there is a potential in some animals, at least, to attain sexual maturity at a very young age. Neither gilt age norweight at puberty significantly affected ovulation rate at second oestrus, conception rate or embryo survival during the first 20 days of gestation.

Gilts sired by one boar reached puberty significantly earlier (P < 0·05) than did the offspring of three other boars.

Digestible energy (DE) values were determined for 15 pig diets with pigs 8 to 18 weeks old by standard digestibility procedures. The 15 diets contained 4360 to 4920 kcal gross energy (GE)/kg dry matter (DM), 2750 to 4070 kcal DE/kg DM, 2·8 to 15·8% crude fibre (CF), 2·4 to 21·1% acid-detergent fibre (ADF), and 7·3 to 33·8% neutraldetergent fibre (NDF).

The prediction equations obtained were all highly significant. DE was most accurately predicted when the fibre value used was NDF, the regression equation being: DE = 4314·37·22 NDF (residual SD + 265). The inclusion of GE in the regression equation considerably improved its accuracy: DE = 1·510 GE-2579·39·37 NDF (residual SD ±127).

However, the greater digestibility by pigs of NDF in diets containing sweet lupin seed meal (SLSM) resulted in these diets being more efficiently digested than diets containing other common protein supplements. Omitting the four diets containing SLSM from the regression analysis resulted in an even more accurate prediction equation: DE = 1·177 GE-1085·40·22 NDF (residual SD±107). It is suggested that this equation may be used to predict DE of pig diets compounded from commonly used constituents.

A total of 178 castrated male cattle (steers), the progeny of Charolais, Hereford and Limousin bulls mated to Holstein-Friesian and Ayrshire cows, were raised from 8 months of age to 545 kg (slaughter weight) on fast- or slow-gaining regimes. The steers on the fast gaining regime were fed a grain mixture with little hay, while those on the slow-gaining regime grazed all summer and were wintered on hay supplemented with a little grain.

The steers on the fast-gaining regime were more efficient in feed conversion ratio, had 0·42 kg per day higher live-weight gain, reached slaughter weight 306 days earlier, and had 2% higher dressing-out percentage, 5·7 mm thicker fat and 5 mm2 larger area of m.longissimus thoracis than those on the slow-gaining regime.

Charolais-sired steers on both regimes had the fastest gain and were the first to reach slaughter weight. Limousin-sired steers raised on the fast-gaining regime had the highest dressing-out percentage, and the largest area of m. longissimus thoracis on both regimes. Hereford-sired steers had the thickest fat cover and the smallest area of m. longissimus thoracis. Little difference was found between the steers from Holstein and Ayrshire cows.

Fifty-four pigs weaned at 3 weeks of age were allocated at an average weight of 5·4 kg to two experiments to examine the effects of diets having digestible energy (DE) concentrations ranging from 2910 to 3940 kcal/kg.

In the first experiment pig growth performance and the dry-matter digestibility of the experimental diets were measured between 3 and 8 weeks of age. The composition of the carcass at 8 weeks of age was correlated with the composition of various carcass joints.

In the second experiment pig growth performance was measured over the live-weight range 5-4 to 20 kg.

The findings were:

1. Growth rate was linearly related to DE intake.

2. The optimum DE level for maximum growth was 3640 kcal/kg.

3. The efficiency of utilization of DE for growth did not vary in the first experiment but was poorest at a DE concentration of 3245 kcal/kg in the second.

4. The DE content of the diet had no significant effect on carcass characteristics at 8 weeks of age in the first experiment or at 20 kg live weight in the second.

5. The proportion of fat and lean in the 8-week carcass was significantly (P < 0·01) correlated with that of the shoulder joint.

The intake and digestibility of diets containing dried grass supplemented with either molasses or tapioca was studied with 12 Friesian steers in two experiments, using a Latin square design. Three periods were used, each containing 3 weeks preliminary followed by a 10-day collection period. In both experiments long, artificially dried grass was given to appetite (treatment A). The other treatments in Experiment 1 were 25% molasses plus 75% dried grass (B) and 50% molasses plus 50% dried grass (C). In Experiment 2 the treatments were 21% tapioca plus 79% dried grass (D) and 42% tapioca plus 58% dried grass (E). There was no significant difference in dry matter or organic matter intake between the diets, though the intakes in both experiments tended to be lower when the dried grass was supplemented with either molasses or tapioca than when it was given alone. Nor were there any significant differences in the digestibility of dry matter or organic matter between the diets in either experiment. In both experiments the digestibility of crude fibre was significantly lower (P<0·05) when either molasses or tapioca was given with the dried grass than when the grass was offered alone.

Twelve Ayrshire cows which had reached or just passed peak lactation were selected and divided into two balanced groups. One group was fed strictly according to yield. The other was fed overall according to yield, but was subjected to a 4-day cycle of energy intake. For 2 days energy intake was 12·2% above calculated requirements and for the next 2 days intake was 12·2% below calculated requirements. The treatment was imposed for 10 weeks and milk yield and composition, body weight and blood composition were measured in both groups of cows. A significant variation in daily milk yield and daily solids-not-fat yield was found to follow the feed cycle. Blood composition showed no significant variation.

Growth performance and carcass quality (linear measurements) were studied in pigs grown from 25 to 90 kg on barley stored and prepared in different ways. Half the barley was dried to about 14% moisture content for storage and half was not dried but treated with 0·8% propionic acid. Each was given after hammer-milling (3·2 mm screen) or rolling. A total of 144 pigs was used at four centres.

The performance and carcass quality of pigs given acid-treated barley were as good as those given dried barley. While feed utilization, expressed on the basis of air-dry feed, was poorer for pigs fed on acid-treated barley this difference disappeared when account was taken of the different moisture contents of the barley samples. Pigs fed on diets based on milled barley grew more quickly, had better feed utilization but greater fat measurements than pigs fed on rolled barley. There was a significant interaction between storage method and feed preparation (milling or rolling). Pigs given the acid-treated barley grew more quickly when it was in the milled form than when it was rolled, whereas for the dried barley there was a small, non-significant difference in favour of the rolled form.

The densities of about 1000 limb bones, excised from 110 carcasses of four breeds of cattle ranging in age from 6 to 36 months, were measured by the method of weighing in water. The density of individual bones varied considerably ranging from 1·24 to 1·71 gcm-3 Some of this variation was due to differences between the various bone types within a limb, the cannon bones being more dense than the tibia and radius/ulna which in turn were more dense than either the humerus or femur. Age and breed also influenced density; the older the animal the more dense were its bones and the bones of Jersey cattle were more dense than those of Herefords of the same age. These findings conflict with an assumption that has been made hither to in theoretical analyses of the densitometric method of estimating the composition of carcasses, where skeletal density has been generally taken as constant.

Digestibility of dry matter, energy and cell wall was measured in two series of digestibility trials in which sheep were fed on pelleted mixed rations containing either 32·0 or 22·6% cell wall at various levels of intake. There were significant depressions in digestibility of all nutritive components as the level of intake increased. The ration lower in cell wall showed smaller declines in dry matter and energy digestibility but a greater decline in cell wall digestibility. The results indicate that the cell wall fraction of concentrate-supplemented rations for sheep is a primary factor in the decline in digestibility observed with increase in level of intake.

An ‘indicator muscle’ (m. flexor digiti V brevis) was removed in its entirety from several Large White and Landrace pigs of varying fat depth (measured over the eye-muscle area). The total muscle fibre number was measured in transverse sections for each muscle. Significant inverse relationships were found between this fibre number and fat depth measurements. These and other results suggest that fibre number is related to lean meat content. Fibre number was also shown to be highly correlated with fibre density and as thinner fibres (i.e. higher fibre density) are associated with more tender meat, fibre number may be associated with quality as well as quantity of meat.

In 1972 a comparison was made between rotational creep grazing (R—8 paddocks) and set stocking (S—2 paddocks) for ewes and their twin lambs at 3 stocking rates viz. 20 (H), 17 (M) and 14 (L) ewes/ha.

The herbage intakes/kg live weight of the R ewes were similar to those of the S ewes in period 1 (c. 7th week of lactation) but higher i n period 2 (c. 10th week of lactation). The intakes of the lambs were not affected by the grazing management in periods 3 or 5, but in period 4 the R lambs had a higher intake than those on S. The overall lamb growth rates were also higher on R compared with S. The carcass outputs (net of supplementary feed) were higher for any R treatment compared with any S treatment being 453, 451 and 427 for R and 419, 379 and 380 for S at the H, M and L stocking rates respectively.