A procedure to estimate economic values for use in selection indices is developed. A profit function is specified and a production function that links output to the several inputs developed. The profit function is maximized by equating the partial derivatives of the function with respect to each input to zero and simultaneously solving the resulting system of first-order equations for optimal levels of the variables. These variables include economic values for animal traits and levels of exogenous, producer-supplied inputs. The economic values are then used in a selection index. The resulting index value is therefore determined by the average values of the traits, the available inputs and their prices, output price and the specified production function. The procedure has the flexibility, through varying these parameters, to provide index solutions that are tailored to suit individual production conditions. A numerical example is provided.

1. Two groups of ewes were given a dietary supplement containing 40 g of either ‘protected’ tallow (PT) with only 3% linoleic acid or ‘protected’ safflower oil (PP) with 57% linoleic acid for 28 days prepartum and 30 days post-partum.

2. Although the birth weights of the lambs were unaffected by dietary treatment, the lambs in the PT group gained weight approximately 20% faster than those in the PP group.

3. The gross compositions of the milks of both groups of ewes were similar but the milk fat obtained from the PP group contained about twice as much linoleic acid as was found in the PT group.

4. Dietary treatments did not affect the haematocrits, red blood cell (RBC) or white blood cell numbers of the lambs. However, the haematocrits were higher at birth than at 10 days later and the RBCs were found to be less fragile at birth than at 10 days later.

5. The ratio of trienoic/tetraenoic fatty acid in the plasma lipids of the lambs was positively correlated with live-weight gain. Male lambs grew faster than females and twins faster than triplets and the trienoic/tetraenoic ratio was higher in males than females and higher in twins than in triplets.

6. These results showed that although it was possible to increase the linoleic acid content of the milk of ewes and of the blood lipids of their lambs by feeding protected safflower oil, no increase in lamb growth was obtained.

Groups of spring-born Galway (G) and Fingalway (F) ewe lambs were fed a concentrate diet either ad libitum (H) or at a restricted level (L) during the period 25 July to 16 October 1974 in order to induce differences in body weight at the start of the breeding season. The mean live weights of the GL, GH, FL and FH groups on 16 October 1974 were 37·8 ± 1·3, 44·6 ± 1·3, 35·1 ± 1·1 and 41·9 ± 1·2 kg respectively. More than 95% of the lambs in all four groups attained puberty before 28 February 1975. Galway ewe lambs reached puberty later in the breeding season and were older and heavier at puberty than Fingalways. Animals fed ad libitum were heavier at puberty and attained puberty earlier in the season and at a younger age than those on the restricted feeding regime.

Both conception rate and litter size were lower in Galways than Fingalways. There was no evidence of any effect of the nutritional treatments on conception rate or litter size. The mean body weights at puberty for ewes which lambed and those which were barren were 41·9 ± 0·49 and 41·5 ± 0·78 kg respectively. The birth weight and growth rate of the progeny of the ewe lambs was similar for the two breeds and was not influenced by the previous nutritional treatment of the dams. The total lamb mortality between birth and weaning was 40·3%, and 72% of all deaths occurred within 48 h of birth. Losses among twins (48%) were particularly heavy.

The effect of energy intake during the final 12 weeks of pregnancy on the production of 59 Blue Grey (Shorthorn × Galloway) (BG) and 56 Hereford × Friesian (HF) cows inseminated with Hereford semen was studied over 2 years.

Energy intakes ranged from 34·3 to 78·2 and from 30·3 to 58·2 MJ ME/day for a 500 kg cow in the 2 years respectively. The cows were fed ad libitum for 22 weeks after calving.

Plasma 3-hydroxybutyrate concentrations in late pregnancy were closely and inversely related to energy intake.

In the first year there was a curvilinear relationship between calf birth weight and pre partum energy intake, maximum birth weights occurring at an intake of about 58 MJ ME/day. Over the lower range of intakes in the second year the relationship was linear and positive; the difference in calf birth weights between extreme levels of intake was 15%.

Pre partum energy intake had a small inverse effect on voluntary food intake some 16 to 20 weeks after calving, and a large inverse effect on cow live-weight change throughout lactation, but had no measurable effect on milk production or calf growth rate.

HF cows gave birth to heavier calves which grew more quickly in the 2nd year, had higher voluntary food intakes during lactation, and produced more milk than did the BG cows.

The rectal temperature and respiratory rates of German Brown, Friesian, German Brown/Friesian crosses, N'Dama and German Brown/N'Dama (BN) crosses were studied with a view to establishing baseline data for cattle in the humid tropical environment of Nigeria.

Mean morning (38·62°C) and late afternoon (39·19°C) rectal temperatures for the various breeds were found to differ significantly (P<0·01). However, general breed differences as well as differences between heifers, milking cows, bulls and calves were not significant. Respiratory rates (counts/min) were also significantly higher (P<0·01) in the afternoon than in the morning and appeared related to changes in atmospheric temperature and relative humidity. Breed differences in respiratory rates were also significant, being within the range 17 to 34 in N'Dama, 24 to 43 in BNs and 29 to 51 in the German Brown and Friesian.

Heat tolerance indices were very high (89 to 91) for all the breeds studied but showed that the Friesian and German Brown were less heat tolerant than the BNs, and the N'Dama and White Fulani. The results indicate the need to consider diurnal changes in rectal temperature and respiratory rates in the use of these parameters for clinical diagnostic purposes.

The amylase (Ami) phenotypes have been determined in sera collected from 244 heifers before 6 months and after 2 years of age. Fifty of these animals exhibited a change in phenotype from Ami C to an apparent Ami BC with age. Using a modified electrophoretic technique these apparent heterozygotes were reclassified as Ami C(E). Eight hundred and nineteen cows, which had previously been shown to have a highly significant excess of heterozygotes at the Ami locus, were also retyped by this modified technique. The apparent heterozygote excess was not found as it was now possible to differentiate between Ami C(E) and Ami BC.

The digestibility of oat straw treated with anhydrous ammonia was studied in four Shetland-type ponies in a 4×4 Latin square experiment. The experimental diets which contained soya bean oil meal, corn, sugarcane molasses, and 65% straw were: (1) straw treated with anhydrous ammonia, (2) untreated straw, (3) untreated straw plus urea, (4) untreated straw plus soya bean oil meal. Digestibility of the dry matter was 15% greater (P<0·01) and digestibility of cellulose 28% greater (P<0·01) in diets containing ammonia-treated straw than in those containing untreated straw. Ammonia treatment increased the nitrogen content of the straw by 50%, and nitrogen intake was 18% greater when the ponies were fed diet 1 than when fed diet 2. The nitrogen of the treated straw was utilized as efficiently as the nitrogen of the diet containing untreated straw supplemented with soya bean oil meal. However, the amount of nitrogen provided by the diet of ammonia-treated straw was not sufficient for nitrogen balance in the ponies. Ammonia treatment of oat straw did not affect the utilization of Ca, P, or Mg.

1. A deterministic model for thermoneutral heat production of growing pigs on barley-based diets has been developed and validated. The model variables are live weight (20 to 100 kg) and metabolizable energy intake (not less than maintenance). The root-mean-square error for 62 data is 049 MJ/day (3·2%).

2. A deterministic model for heat production of growing pigs below their critical temperature has been developed and validated. The model variables are: air temperature, air velocity, floor type, live weight (20 to 100 kg), and group size. The root-mean-square error for 78 data is 0·77 MJ/day (5·6%).

3. The two heat production models are combined to give a model for the lower critical temperature for growing pigs.

4. These models may be used to quantify and compare the effects on energy balance of different combinations of nutrition and environment. They should help to clarify the issues when practical decisions in pig production are made and should also help in the design of nutritional and physiological experiments.

Sixty pigs, equal numbers of boars and gilts of the two breeds Large White (LW) and Gloucester Old Spot (GOS), in litter groups of three, were divided equally between an initial slaughter group and two treatment groups; H, given a diet with 149 g/kg crude protein (CP) at a daily level of 0·1 W0·75; and L, given a diet with 193 g/kg CP at a daily level of 0·075 W0·75. The cumulative total amount of feed given to each pig was the same, 175 kg, but H received more energy per day. All pigs received the same CP per day but L received more CP in total. Pigs started on experiment at 12 weeks of age. The treatments differed mainly in their ability to promote fat deposition: H pigs grew faster than L, due mainly to a greater deposition of fat (as measured by the weight of subcutaneous fat produced) rather than lean (as measured by the weight of hind limb lean produced). H pigs had a poorer feed efficiency than L pigs.

The breeds were similar in most aspects of production and body composition over both treatments but GOS tended to be slower growing and fatter than LW, with shorter carcasses, thicker backfat, and smaller subcutaneous fat-free hind limbs. Boars were faster growing, leaner and more efficient than gilts, with a higher proportion of bone in the subcutaneous fat-free hind limb and a lower muscle: bone ratio (boars 4·74, gilts 5·28).

For several aspects of carcass composition the potential benefits of the lean types (LW and boars) over the fat types (GOS and gilts) were realized on treatment L but not on H. There was a significant breed × treatment interaction for lean content of hind limb: LW had higher values than GOS on L but both breeds were similar on H. Both LW and boars had significantly less subcutaneous fat than GOS and gilts respectively on treatment L but similar amounts on H.

Data from 1357 boars ad libitum fed on a performance testing scheme were analysed to explore the genetic aspects of voluntary food intake. The heritabilities of food intake, daily gain and food/gain were found to be 0·23, 0·41 and 0·18 respectively. The correlations obtained between gain and intake of 0·63 (phenotypic) and 0·89 (genetic) were typical of those reported for ad libitum feeding but greater than those reported for semi-restricted. Estimates of genetic correlation between gain and efficiency ranged from 0·64 to zero and for the phenotypic correlation from 0·44 to zero and were smaller than those reported for restricted feeding. Correlations between intake and efficiency were highly negative on the phenotypic level but small and of variable size genetically, in contrast to reports of small phenotypic and positive genetic correlations under restriction.

In two experiments, pigs were weaned at 4 to 5 days of age and offered dry diets based on milk proteins and tallow. Live-weight gains between 7 and 28 days of age were 220 g/day with feed conversion ratios of 0·80 when the optimum diets were given.

Expt 1 was a 2 × 2 × 2 factorial with eight pigs per treatment. There were two sources of carbohydrate, lactose and wheat starch, two levels of fat, 40 and 250 g/kg and two levels of crude protein, 140 and 250 g/kg of the diet. There was no significant difference in the performance of pigs when they were fed lactose or wheat starch as the source of carbohydrate. However, the feed intake of the pigs and their weight gains and apparent digestibilities of dry matter and nitrogen were lower when the diets contained 250 g fat/kg than when the diets contained 40 g fat/kg.

In Expt 2 six diets were fed to 12 pigs each. The diets contained 150, 180, 210, 240, 270 or 300 g/kg of crude protein. Weight gains and nitrogen retention showed a positive correlation (r = 0·997) with the dietary nitrogen intake but there was no statistical increase in these parameters above the 270 g crude protein/kg level. The apparent digestibilities of dry matter and nitrogen showed a similar trend. A value of 141 mg nitrogen/day per kg M0·75 was estimated as the metabolic endogenous loss of nitrogen.

Estimates of heritability for 9 litter traits were derived from data on 38 000 Large White and 35 000 Landrace litters by daughter-dam regression (parities 1 to 5) and by a three-level nested half-sib analysis (parities 1 to 3). The regression and half-sib heritability estimates were similar and overall the estimates were quite low, averaging 7% across traits and breeds. This is in general agreement with estimates from two other large-scale European analyses of field data. Some other reports, including lesser experimental material, show rather higher heritability values.

1. Two groups of artificially-reared lambs were used to evaluate electronic equipment which allowed group-housed lambs individual access to their own food supply.

2. Trial group A comprised six lambs in a cross-over design between individual metabolism cages and group-housing with electronic doors to examine the effects of method of housing upon ad libitum food consumption. There were no significant differences in dry-matter intake although it was observed that food consumption was temporarily reduced during the training periods.

3. Trial group B comprised 16 lambs used to test established training techniques and to examine the effects of adaptation to electronic doors upon food consumption and live-weight gain over a period of 50 days. There was a reduced intake of food during days 1 to 7 which resulted in the daily dry-matter intakes and live-weight gains for days 8 to 50 and 15 to 50 being higher (P<0·01) than those for the total period (days 1 to 50). It was concluded that a minimum of 7, and preferably 14, days were required for training lambs and for adaptation to a diet provided through electronic doors.