Twenty-four young female sheep, 12 Galways and 12 Fingalways, were used to study the effects of breed and level of nutrition on pre-puberal plasma luteinizing hormone and progesterone concentrations throughout the oestrous cycle and during the first 35 days of pregnancy. The sheep were spring-born and were housed at the end of July when they weighed approx. 34 kg. Equal numbers of animals from each breed were fed on a concentrate diet either ad libitum or at a restricted level that was slightly above their estimated maintenance requirements. The Fingalways reached puberty 1 month earlier than the Galways (11 October ±4 days v. 10 November ±5 days). The restricted animals tended (P < 0·10) to reach puberty later than those fed ad libitum (1 November ±5 days v. 20 October ±4 days). Breed differences in the mean level of plasma progesterone on any day of the oestrous cycle were not significant. The mean daily plasma progesterone concentration was similar for the animals on the two planes of nutrition throughout the cycle, with the exception of day 11 when those fed ad libitum had a significantly higher level (P < 0·01). Plasma progesterone levels in the pregnant females between 5 and 35 days post mating were generally higher in Fingalways than in Galways and were not influenced by plane of nutrition. Plasma luteinizing hormone levels tended to be higher, during the 7 weeks before puberty, in Fingalways than in Galways and in animals fed ad libitum than in those on the restricted level of feeding.

In populations where generations overlap and initial genetic differences between age groups differ from steady-state values, genetic responses fluctuate in the early years of a selection programme. The degree of deviation of these selection responses from steady-state responses indicates the usefulness of estimates of economic returns calculated more simply using the steady-state value. Here these deviations and their effect on sums of discounted returns are first defined and the models derived then used in numerical analysis. Some problems of definition of these deviations are discussed.

The results showed that deviations from sums of discounted returns calculated using steady-state responses varied from about −1% when starting conditions were similar to steady-state conditions to more than 20% when initial genetic differences between age groups were taken as zero. Increases in discount rate increased the effect of the deviations from uniform response while the effect of changing age structure was unpredictable. As initial genetic differences between age groups increased, deviations were increasingly positive among selection methods which made better use of those differences.

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.

Where genetic differences between age groups change during a selection programme, proportional contributions of each age group to replacements should also change in order to maximize genetic responses to selection. Sums of discounted returns were estimated for such a ‘dynamic’ selection policy and these were compared with those from ‘static’ selection policies in which genetic contributions of different age groups remained unchanged. Four selection methods, two sets of genetic differences between age groups at the outset, three age structures and two discount rates were used.

The results showed that the superiority of the dynamic policy was greatest where genetic differences at the outset differed most markedly from their steady-state values, where discount rates are high and where there are large numbers of age groups and the selection method allows culling in all age groups. Under most conditions initial genetic differences are probably the most important factor. The proportional advantage in sums of discounted returns is variable and generally small within the framework of this study ranging from zero to roughly 8% unless breeding objectives before and during the programme were negatively correlated. In the latter case the proportional superiority of the dynamic policy was much greater.

In an experiment carried out on five farms in 3 years and comprising 1221 annual weight records of adult ewes, an increased level of feedingwas comparedwith feeding according to farming practice. The higher feeding level started 6 weeks before mating andfinishedjust before lambing. Significant effects of feeding level on ewe live weight and body condition, ewe fecundity and the birth and weaning weights of lambs were found.

Ewe fecundity increasedlinearly with ewelive weight at 8 weeks prior t o mating (b=1·05 lambs/kg per 100 ewes), curvilinearly with ewe body condition score at 8 weeks before mating (maximum at score 3·32) and curvilinearly with weight gain from 8 to 2 weeks before mating (maximum at 2·3 kg gain). A 10% range in live weight, condition score and live-weight gain resulted in a predicted fecundity range of 21 lambs per 100 ewes alive at lambing. Changes in weight and condition score during the mating period did not affect ewe fecundity.

(1) Voluntary intake of forage was measured in 31 Scottish Blackface ewes for the last 14 weeks of pregnancy, throughout lactation, and 15 weeks subsequently. During pregnancy 15 ewes were given hay and 16 dried grass (apparent dry-matter digestibilities in vitro were 51 and 69·6% respectively). All ewes were given the same dried grass during lactation and after weaning (digestibilities 75 and 73% respectively). Body fat was estimated from tritiated water space.

(2) Pregnant ewes consumed twice as much digestible dry matter from dried grass (1028 g) as from hay (502 g). Intakes of ewes with twin and single foetuses were similar.

(3) During lactation the mean daily intakes of dried grass were 2278, 2610,2612 and 2722 g dry matter respectively, for ewes that had been given dried grass in pregnancy and had single and twin lambs, and for those that had been given hay and had singles and twins. Differences between dried grass and hay were consistently significant (P < 0·01).

(4) After weaning the intakes declined rapidly but their ranking remained similar.

(5) Lamb birth weights were affected by nutrition during pregnancy, lamb growth rates within twins or singles were not influenced by maternal nutrition during pregnancy or lactation. Differences in ewe intakes during lactation were reflected in ewe body-weight changes.

(6) For all ewes, up to 64% of the variation in intake during lactation could be related to factors prevailing before and at lambing (pregnancy diet, ewe weight and fat content) and during lactation (lamb gain and ewe weight change).

1. Adolescent mice were exposed from 33 to 84 days of age to a warm (30°C) or to one of four cold (15°C, 10°C, 5°C or 1°C) environments. Before and after exposure the mice were kept at a normal mouseroom temperature of 23°C. Controls remained at this temperature throughout. Voluntary food intake, live weight and growth efficiency were individually monitored before, during and after exposure, i.e. from 19 to 112 days of age.

2. Food intake during exposure was linearly related to temperature, ranging from 4 g/day at 30°C to 14 g/day at 1 °C. Intakes differed only slightly between males and females. Food intake at 10°C was 70% above controls. Oxygen consumption in adults at 10°C was 74% above controls.

3. Male growth was unaffected by temperature. Superiority over females (56% at 30°C) diminished at lower temperatures (12% at 1 °C) because females grew 41% faster at 1 °C than at 30°C. Females whose growth was depressed at 30°C, showed compensatory growth on returning to 23°C.

4. Growth efficiency was strongly, but not entirely linearly, related to temperature, and increased approximately three-fold between 1°C and 30°C. Efficiency was maximal at 30°C in males and at 23 °C in females. Males grew 76% more efficiently than females at 30°C and only 12% more efficiently at 1°C.

5. Increased food intake in the cold satisfied energy requirements and allowed females to grow faster.

6. Individual differences in appetite persisted throughout life, but rankings in growth and efficiency changed with age. Food intake was strongly correlated with growth rate in weanlings, but growth rate was always the main determinant of growth efficiency.

7. The variance of adolescent growth rate was unaffected by the treatments.

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.

1. Young adult and adult lactating British Friesian female cattle (heifers and cows) were individually fed ad libitum on perennial ryegrass silage (F) made with an additive of formic acid (3·41 of 85% acid/t fresh grass) or on a silage (FF) made from the same crop with an additive of 9·01/t of a mixture of equal volumes of formic acid and formalin (35% w/w solution of formaldehyde). Silage F was supplemented with a concentrate containing 50% dried grass and 50% barley at a low (L) or high (H) level of feeding; silage FF was supplemented with the same concentrate at the lower level only, either with urea at 2·0% of the silage DM (FFLU) or without urea (FFL).

2. Silage F had a lower pH (P< 0·001) and contained more lactic, acetic and total fermentation acids (P><0·001). The DOMD in vivo of the diet was lower (by up to 3 units) for treatment FFL than for the other treatments (P<0·05 in weeks 17 and 18).

3. Over weeks 4 to 18 of lactation the mean dry-matter intakes (DMI) of silage on treatments FL and FFL were similar, but silage DMI was 12 to 13% greater on treatment FFLU than on FL or FFL (P<0·05). Digestible OM intake was greater with FFLU than with FFL (P<0·01) and with FL (P<0·05).

4. Milk yields did not differ significantly between treatments and metabolic blood profiles were normal.

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 trial compared 50 purebred Canadian Holstein and 46 British Friesian steers. The cattle were reared on a grass/cereal system designed to achieve an overall target live-weight gain of 0·82 kg per day from weaning to slaughter at 18 months of age. The cattle, born i n September 1973, grazed during the summer of 1974 and were slaughtered out of yards from January to July 1975. Equal numbers of each breed were allocated at random to three slaughter weights (477, 500 and 523 kg live weight). The Meat and Livestock Commission measured and classified all carcasses. In addition, a sample was cut according to commercial specifications. There were no significant differences in slaughter age or live-weight gain between the breeds. A significant difference (P < 0·05) in killing-out percentage was found in favour of the British Friesian as was a small (4%) but highly significant difference (P < 0·001) in carcass gain.

The Canadian Holstein carcasses were considerably longer (P < 0·001) with less eye-muscle area (P < 0·001). The British Friesian carcasses contained 0·7% more saleable meat (P < 0·001) and 1% less bone (P < 0·01). There were no significant differences in fat trim. There were large differences in live appearance and carcass classifications, the British Friesians being of superior beef conformation.

Grass silage with a dry-matter (DM) content of 253 g/kg and containing 142 g crude protein and 670 g digestible organic matter/kg DM was offered ad libitum to 56 first- and second-lactation British Friesian cows during the first 75 days post-calving. In addition the animals received supplementary concentrates containing either 95 (T1), 137 (T2), 174 (T3) or 209 (T4) g crude protein per kg fresh weight, with extracted soya bean meal being used as the protein source. All concentrates were offered at equal levels across treatments, the amounts being 8 kg for first- and 10 kg per day for second-lactation animals. The silage DM intakes recorded over the period were 514, 524, 548 and 545 ± 19·9 kg and milk outputs were 1349, 1451, 1533 and 1628 ±40·2 kg for treatments Tl to T4 respectively. The rate of live-weight change and the milk fat, solids-not-fat, protein, lactose and ash contents of the milk were not affected significantly by any of the treatments. Diet digestibilities were determined using three animals per treatment. The digestibility coefficients were for DM 0·738, 0·746, 0·776 and 0·772 ± 0·0088 and nitrogen 0·597, 0·641, 0·707 and 0·727 ±0·0126 for treatments T1 to T4 respectively.

Regressions of progeny growth rate and slaughter age on bull weight for age (400-day) record were estimated from data on 63 Hereford bulls. The bulls had been weight-recorded by the Meat and Livestock Commission and subsequently progeny-tested by the Milk Marketing Board on 1300 crossbred British Friesian steers. Interpretation of the regressions led to estimates of 16 to 35% (± 9 to 17%) for the ‘effective’ heritability of400-day weight. These are lower than the average in the literature and may indicate that farm records with natural rearing of bulls are less reliable than tests with uniform rearing and feeding conditions.

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.

Simple algebraic models of milk yield, live-weight change and food requirement are developed for use in a programmable desk calculator. The unit of time used is a week and of energy a megajoule. An algebraic equation for milk production is used to define potential energy output. An expression using live-weight gain describes the demand for energy for the recovery of weight lost and the requirements of pregnancy. The use of appropriate conversion factors enables the necessary dietary input to be calculated. The model also takes account of restricted feeding by allocating dietary energy to milk production and live-weight gain in proportion to their potential demand. Ten decisions relating to milk yield, live-weight loss and live-weight gain are required by the model.

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.

Milk replacers in which skim milk protein (SMP) was replaced in various proportions by undried or dried fish protein hydrolysate (FPH) were offered twice daily to British Friesian male calves. Various proportions of fish protein and milk protein in the diets were obtained by mixing replacer made from SMP with replacers made from undried and dried FPH respectively. The ratios were: 100 FPH, 0 SMP; 67 FPH, 33 SMP; 33 FPH, 67 SMP; and 0 FPH, 100 SMP. Calves were offered the milk replacers only to a maximum of 5 1 per day until 28 days when concentrates and hay were offered ad libitum. The calves were weaned after 42 days. Feed intake and live-weight gain were recorded for 84 days.

There was a marked decrease in performance to weaning when the milk replacer contained two-thirds or more of the FPH. The FPH-fed calves had lower hay intakes than those fed milk only. Treatment differences in post-weaning live-weight gain reflected mainly differences in concentrate intake. There was no significant difference in live-weight gain nor food efficiency for calves fed either undried or dried FPH in any period to 84 days. The number of treatments for scour was similar for the two groups. However, the calves fed dried FPH had a lower dry-matter intake in the post-weaning period.

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.

The birth weight and growth rate of sucking calves reared by three groups of cows grazing on veld and receiving different amounts of concentrates during winter and the first 8 weeks of lactation were studied over four successive calving seasons. Calves were weaned at either 150 or 240 days. The efficiency of use of concentrates for weaned calf production was calculated.

Calves from cows given most concentrates were heavier (P<0·01) than othei calves at birth, 150 days and 240 days. Milk consumption during the first 98 days of life accounted for most of the variation in pre-weaning growth. Time of weaning had little effect (P<0·05) on birth weight of the next year's calf and although cows in the early- weaning groups produced calves which were the heaviest at 150 days (P>0·05) these calves weighed less than other calves at 240 days (P<0·001). Simple and multiple regression analyses were used to show that birth weight was affected significantly by cow-weight change during winter and these differences were in part independent of treatment and year. Calf birth weight increased as age of dam increased but this was due to increase in weight of cow with age. Within classes, calf birth weight had a significant and positive effect on weight gain after accounting for milk consumption and this was shown to be an effect of sex. Cows given concentrates produced more weight of 240-days-old weaned calf per year than those given none (P<0·01), and late weaning led to the production of more weaned calf per annum than early weaning (P< 0·001) even when allowance was made for differences in concentrate consumption.