Growth results of 43 ostrich males and females were used to compile growth parameters of a flock that is representative of Oudtshoorn birds, using the Gompertz model. Growth results comprised 19 recordings of body weight for each individual commencing from 1-day-old to day 520. Individual fits of data to the growth model were exceptionally good, resulting in low CV values of 0·02 and 0·03 for the mean values of all estimates of mature live weight for male and females respectively. The estimated mean mature body weights for the flock were 119·2 kg for males and 122·3 kg for females. Rates of maturing were 9100 and 8500 for males and females respectively which corresponded to ages of 180·83 and 199·2 days at which maximum gain in weight were achieved. None of these parameter estimates differed significantly between sexes. Results in the present study suggested substantial adjustments to growth parameters for Oudtshoorn ostriches published by du Preez, Jarvis, Capatos and de Kock, 1992.

Carcass composition was measured after six generations of divergent selection for lean growth rate on ad-libitum and restricted feeding, lean food conversion and daily food intake in populations of Large White (LW) and Landrace (LR) pigs. There were 161 half-carcass dissections in LW pigs and for LR pigs, a double sampling procedure combined information from 53 half-carcass and 53 hand joint dissections. The performance test started at 30 kg and finished at 85 kg with ad-libitum feeding and after 84 days with restricted feeding, and pigs were slaughtered at the end of the test.

In the LR population, selection for lean growth on restricted feeding increased carcass lean content (605 v. 557 (s.e.d. 19) g/kg), but there were no significant responses in carcass lean content with the selection strategies on adlibitum feeding. Selection for lean food conversion and high lean growth on restricted feeding reduced carcass fat content (201 v. 241 (s.e.d. 14) and 150 v. 218 (s.e.d. 18) g/kg), but selection for high lean growth rate with adlibitum increased carcass fat content (212 v. 185 (s.e.d. 11) g/kg). Responses in carcass composition were not significant with selection on daily food intake.

In the LW population, selection for high lean food conversion or low daily food intake increased carcass lean content (539 v. 494 and 543 v. 477 (s.e.d. 11) g/kg) to a greater extent than selection on lean growth rate (509 v. 475 g/kg). Responses in carcass fat content were equal and opposite to those in carcass lean content. Selection on lean growth rate with ad-libitum feeding increased lean tissue growth rate (LTGR) (491 v. 422 (s.e.d. 23) g/day), but there was no change in fat tissue growth rate (FTGR) (206 v. 217 (s.e.d. 15) g/day). In contrast, FTGR was reduced with selection on lean food conversion (169 v. 225 g/day), but LTGR was not significantly increased (520 v. 482 g/day). Selection for lean growth rate with restricted feeding combined the desirable strategies of lean growth rate on adlibitum feeding and lean food conversion, as LTGR was increased (416 v. 359 (s.e.d. 12) g/day) and FTGR decreased (126 v. 156 (s.e.d. 7) g/day). The preferred selection strategy may be lean growth rate on restricted feeding, which simultaneously emphasizes rate and efficiency of lean growth.

For ad-libitum fed LW pigs, coheritabilities for growth rate, daily food intake and backfat depth with carcass lean content were negative (-0·12, -0·22 and -0·50 (s.e. 0·05), but positive with carcass subcutaneous fat content (0·22, 0·24 and 0·50), when estimated from six generations of performance test data and carcass dissection data in generations 2, 4 and 6.

Plasma very low density lipoproteins (VLDL) of gilts were separated into two sub fractions according to their affinity for heparin. The proportion of VLDL present as subfraction 2 (higher affinity for heparin) varied, according to the genetic line of the pigs, between 0·21 and 0·78 in virgin gilts. The proportions were related to the variation in piglet survival in the same nine genetic lines by a quadratic equation, which predicted that greater than 90% survival to weaning was to be found in piglets born to gilts having between about 0·3 and 0·7 of their VLDL as subfraction 2. This observation suggests a simple measurement that could be used in the selection of sows for a breeding programme. The proportion of subfraction 2 fell throughout pregnancy in each of three genetic lines measured and only returned to pre-pregnant values after weaning: these changes did not correlate with the changes in the lipid composition of plasma VLDL measured during pregnancy and lactation. The findings suggest a role for the VLDL subfractions in controlling the nutrition of the neonatal pig.

A method to obtain linear selection indexes that maximize objectives that involve average profit in one or more generations within a planning horizon based on non-linear profit functions, was derived through application of optimal control theory. The method involves simultaneous optimization of indexes for each generation in the planning horizon. Optimum linear indexes were found to be conform indexes derived from selection index theory, with economic values equal to a weighted sum of partial derivatives of the profit function at the trait means which result in each generation of the planning horizon. Numerical procedures to derive optimum indexes are presented. Methods and properties of alternative strategies for selection witli non-linear profit functions are illustrated for selection on egg weight and rate of lay in poultry. In the example, the additional benefit of selection indexes that maximize cumulative net present value of profit over a planning horizon of10 years was small relative to use of traditional selection procedures. Optimal indexes were also derived with a derivative-free non-linear programming optimizer, with identical results. The latter method also allows incorporation of additional constraints.

Possible extensions of the optimal control methodology to address other problems related to optimization of selection over multiple generations are discussed.

Estimation of genetic parameters for litter size in Danish Landrace and Yorkshire pigs

Twelve sows in good quality unstrawed stalls, three groups of five sows in strawed pens with individual feeding stalls and sows in a 38-sow group in a strawed yard with an electronic sow feeder were compared during the first four parities. They originated from the same source, were about 9 months of age and in the 7th week of their first pregnancy at the start of the experiment and were kept in adjacent rooms in a building, cared for by the same staff and given the same diets at a rate of 2·2 kg/day per animal. No new animals were added to the groups or stalls during the study and animals returned to the same condition after periods in farrowing and service accommodation. Using a wide range of welfare indicators, it was clear that stall-housed sows had more problems than group-housed sows and that tliese problems were worse in the fourth than in the first pregnancy. By the fourth pregnancy, stall-housed sows spent proportionately 0·14 of time showing activities which were clearly stereotypies and much time on activities which were sometimes stereotyped, i.e. ‘drinking’ and rooting or chewing at pen fittings making a total of proportionately 0·50 of time. Comparable figures for group-housed sows were much lower (0·037 and 0·081 in total). Stall-housed sows were also more aggressive than group-housed by the fourth pregnancy and their body weights were lower. There were no differences using physiological or immunological tests or measures of reproductive output. When the two group-housing systems were compared, sows in the electronic feeder system showed more fighting, especially soon after initial mixing, but fewer total agonistic interactions than sows in groups of five during the first pregnancy. Oral stereotypies were slightly higher in small groups, perhaps because of smaller pen space, than in larger groups but much lower than in stalls. By the fourth pregnancy there were few differences between sows in small and large groups and all seemed to have adapted well to the conditions. Evaluation of welfare in different housing systems requires use of a wide range of measures and of long-term studies.

The effects of dietary energy level and added fat were studied by comparative slaughter on 60 primiparous rabbit does in different reproductive states. Nine does were slaughtered immediately after their first parturition (preliminary slaughter group) to estimate initial empty body composition. The 51 remaining does were divided into three groups and given diets differing in digestible energy (DE) content: M (11·28 MJ/kg dry matter (DM); H (12·16 MJ/kg DM); F (11·93 MJ/kg DM, obtained by the inclusion of 25 g/kg of animal fat). Thirty-six does (12 per group) were remated 3 to 4 days after parturition, after which 20 does were concurrently pregnant and lactating (LP) and gave birth a second time. At the second parturition these does were slaughtered with their new-born litters. The non-mated or non-pregnant lactating does (LN) were slaughtered at the same time. All litters from the first parturition were weaned at the 30th day of age.

The diets influenced the DE intake (3·11 v. 3·31 and 3·36 MJ/day, P < 0·05) and the milk production (171 v. 180 v. 191 glday, P < 0·05), respectively for the M, H and F diets. The high-energy diets (H and F) significantly modified the final empty body composition. The loss of body fat was proportionately 0·34, 0·36 and 0·39 of the initial body fat and the loss of energy was proportionately 0·17, 0·19 and 0·21 of the initial body energy in the M, H and F groups respectively (P > 0·05) (average of LP and LN does). The maternal diet significantly influenced the weight of the sucking litters (first parturition) at 20 days (2409 and 2454 v. 2629 g, P < 0·05).

The LP does showed lower DE intake, milk yield (from 10 to 30 days) and litter weaning weights than LN does. Between the first and the second parturition, the LP does had a loss of empty body weight and a negative protein balance (-0·06 of the initial content), while the LN does had an increase in live weight and empty body weight and a positive protein balance (+0·11 of the initial content). Both LP and LN does had a negative energy balance (−0·24 v. −0·25, respectively; P < 0·01).

Intensively reared rabbits are particularly sensitive to heat stress. For this reason it is useful to identify reliable stress indicators to evaluate peculiar stress conditions of the breeding environment.

In order to recognize which changes in biochemical and functional measurements can be utilized as stress indicators, three groups of eight New Zealand White rabbits, of 2·8 kg body weight and 11 weeks of age, were kept in individual cages and submitted to different environmental conditions.

Group 1 was located in a climatic chamber at 33·5 (s.e. 0·5)°C and relative humidity 0·62 (s.d. 0·05) and groups 2 and 3 (control) at 18·0 (s.d. 0·5)°C. Group 1 was given ad libitum a commercially pelleted diet, group 2 was pairfed with group 1, and group 3 was given food ad libitum. For all the groups, at days 0, 1, 6, 12 and 24, the following measurements were made: body weight, rectal temperature, food consumption and plasma glucose, cholesterol, urea, triglycerides, uric acid, and glutamate oxalacetate transaminase, glutamate pyruvate transaminase, thiobarbituric acid-reactive substances, vitamin A and vitamin E, SH-groups and total (peroxil) radical-trapping antioxidant parameter (TRAP).

Food consumption of animals exposed to 33·5 °C was strongly reduced in the 1st day (13·6 v. 161·6 glday); a gradual increase until the end of the trial was then observed (98·8 v. 177·3 gl day). Rectal temperature rapidly increased and remained stable and higher than in the control groups all through the trial (P < 0·01). The major changes in the measurements of the heat stressed animals were a significant increase of the plasma level of vitamin E at days 6, 12, 24 (P < 0·05), and a significant reduction of the plasma concentration of SH-groups and TRAP (P < 0·05).

The results suggest an impairment or overload of antioxidant systems after thermal stress, indicating a reduced resistance to biological and environmental stress factors. The results also indicate that some parameters of antioxidant systems can be used to select a significant stress indicator.

A series of 4 × 4 Latin-square digestibility trials was carried out to determine whether there were any differences between different types of equid in their ability to digest diets containing different levels of fibre and protein. The equids (Thoroughbreds, Highland ponies, Shetland ponies and donkeys) were offered one of four molassed diets in turn and these contained different proportions of alfalfa and oat straw: 1·0:0, 0·67:0·33, 0·33:0·67, 0:1, respectively. The apparent digestibility of dry matter (DM), organic matter (OM), gross energy (GE), crude protein (CP), acid-detergent fibre (ADF) and neutral-detergent fibre (NDF) were estimated. The rate of passage of the different diets was measured using Cr-mordanted fibre (Cr-fibre) and Co-ethylene diamine tetra acetic acid.

All animals digested the components of the high-fibre diets less well than those of the low-fibre diets (P < 0·001 for DM, OM, GE, CP and ADF). Donkeys digested fibre more effectively than the other equids (F < 0·01 for ADF and NDF). The gastro-intestinal transit time of the high fibre diets was significantly less than that for the low fibre diets (P < 0·001) and donkeys retained food residues longer than the other equids (P < 0·01).

Semi-purified diets incorporating 495·4 g/kg crude protein and 72·0 g/kg oil, were used to identify the qualitative requirement of Spams aurata juveniles for thiamin, riboflavin, pyridoxine, niacin and pantothenic acid. Deficiency of these vitamins was associated with poor performance in terms of growth, food efficiency and apparent net protein utilization. All dietary vitamin deficiencies resulted in elevated moisture and a lowering of the lipid content of the carcass. In addition to increased mortality among the fish fed deficient diets, a small number of externally visible changes were observed including food refusal, anorexia and changes of skin colour. At the haematological level, all cases of vitamin deficiency were associated with significant reductions in haematocrit. In general, histological examination revealed that the pancreas of vitamin-deficient animals became atrophic with an accumulation of pigmented granules around this organ while additionally, the normal homogeneity of the liver parenchyma was lost.

To evaluate the ability of the eel to use diets with high carbohydrate content, a comparative study was made by using the rainbow trout, a carnivorous fish, as a reference species. Four isoenergenetic diets (in terms of gross energy) were formulated incorporating different protein/carbohydrate ratios (450/200, 370/300, 290/400 and 210/500 as g/kg dry matter, respectively) and each one was tested in three replicates groups of eels and trout. The data on growth, food conversion and utilization of dietary protein and energy show that the eel has a comparatively greater ability than the rainbow trout for using diets with a high carbohydrate level. Thus it is postulated that higher carbohydrate levels could be used for formulating cheaper diets.

Semi-purified diets were used to determine the nicotinic acid requirement of the gilthead seabream, Sparus aurata. Vitamin losses during food manufacture were minimal resulting in dietary levels which were close to the declared content. Dietary nicotinic acid contents of 52·21 mg/kg and below resulted in sub-optimum growth, reduced food efficiency and poor values for apparent net protein utilization. Diets containing less than 28·67 mg/kg gave a low proportion of carcass lipid concomitant with an elevation in the relative content of carcass moisture. Although gross deficiency symptoms were not observed, a reduced hepatosomatic index and a slightly lower plasma glucose concentration were detected amongst the fish given diets supplemented with nicotinic acid at the level of 25 mg/kg or less. Based upon the results of broken line analysis and data derived by modelling the weight gain of the fish, the nicotinic acid requirement of Sparus aurata fingerlings lies between 63 and 83 mg/kg of diet or 1·57 to 2·07 µg/kg body weight per day.

Using a high protein diet (483 g/kg), two trials were carried out to assess any potential benefit which may result from the supplementation of diets for fingerling and grower class gilthead seabream with pyridoxine at levels which were below, matched and far exceeded the minimum dietary requirement. At the level of supplementation below the minimal requirement (lowest level) the responses from the practical diet almost matched the responses from the diet containing an amount of pyridoxine corresponding to the published minimum requirement for the species and no significant improvement in performance was recorded in response to increasing supplement level. However, despite the absence of a marked effect on overall performance, a small potential for increased activity of alanine aminotransferase was recorded amongst grower class fish given diets containing the lowest supplement. The proximate composition of the grower class fish was unaffected by the level of pyridoxine supplementation though marginal increases in the lipid content of the fingerlings were observed. At the haematological level, haematocrit, total haemoglobin and the plasma concentrations of glucose and protein were also unaffected. However, on the application of an acute stressor (repeated netting), significant alterations in haematocrit and plasma glucose concentration reflecting dietary pyridoxine supplement were recorded.