The experiment compared four different space allowances for growing pigs housed on fully slatted floors. Space allowance (A m2) was defined in relation to live weight (M kg) of the pigs according to the equation A = kM0·67, using values for the constant (it) of 0·024, 0·027, 0·030 and 0·034. Six replicate pens of 12 pigs were housed on each treatment in a controlled environment building. Food was given ad libitum and from 34 kg until slaughter at 85 kg pigs were individually weighed each week and the pen size was adjusted according to the appropriate equation. Increasing space allowance increased live-weight gain (844, 862, 883, 897 (s.e.d. 14·4) g/day). Differences in killing-out proportion reduced the effect on final carcass weight (63·3, 63·9, 64·1, 64·5 (s.e.d 0·82) kg). Daily food intake was unaffected by treatment but food conversion ratio was significantly poorer at the lowest space allowance (2·70, 2·56, 2·60, 2·59 (s.e.d. 0·043) kg/kg). Economic analyses of the results indicated an adverse effect on profitability of space allowance less than that defined by the equation A(m2) = 0·027 M0·67 (kg). A minimum allowance defined by the equation A (m2) = 0·030 M0·67 is recommended in commercial practice for pigs in fully slatted housing.

Effects of daily food intake (FI) on daily gain (DG), food conversion ratio (FCR), ultrasonic backfat thickness (BF), proportion of lean parts (LP), proportion of fatty parts (FP), lean tissue growth rate (LTGR), fatty tissue growth rate (FTGR) and lean tissue food conversion (LTFC) were investigated in 687 barrows and 98 gilts, slaughtered at a mean live weight of 108 kg and fattened in seven batches. In the range of food intake from about 1·7 to 3·2 kg/day (22 to 42 MJ digestible energy) a continuous distribution of data was available.

Body composition was linearly related to FI. Most regressions of BF and all of LP and of FP on FI were linear, showing fatter animals at higher food intake. For FTGR, BF, LP and FP, parameter estimates based on linear regression were given. Although the response of DG and of LTGR on increasing FI was not always significantly different from linearity, the second degree polynomials indicated diminishing returns in all batches. FTGR had a high linear correlation with FI (0·85 to 0·95), indicating that in the present range of FI a rather fixed proportion of the food was used to deposit fatty tissue.

For DG and LTGR a non-linear model of the type a(FI -fo)b was fitted, where fo was interpreted as maintenance requirement. For FCR and LTFC the corresponding model was FI/(α(FI — fo)b). Both models were preferred over second degree polynomials because of better interpretation of parameters. FCR and LTFC showed minima at about 2·6 and 2·2 kg/day food intake, but especially for FCR the increase at increasing FI was low. Results were not consistent in demonstrating or refuting a plateau in LTGR, which in any event appears to lie near to or beyond ad libitum FI for most pigs.

To determine whether gases generated during the breakdown of accumulated manure in an environmentally regulated building affects the onset of puberty in gilts, 42 crossbred gilts, born from 1 o t 15 September 1985, were reared indoors from 10 to 30 weeks of age on concrete slats over a pit that was drained and refilled with clean water biweekly (clean group). Forty-two gilts were reared over a pit where manure was allowed to accumulate (control group). These two groups had similar feeding, water, floor space, lighting and room temperature. A third group of 42 crossbred gilts was reared from 10 to 30 weeks of age in an open-front building with a concrete apron (outdoor group). Concentration of aerial ammonia in the control environment was three- to five-fold higher than in either the clean or the outdoor environment (P < 0·001). Average daily gain and food conversion efficiency were similar for the two indoor treatment groups, but the outdoor group gained less weight than either indoor group (P < 0·05). At 26 weeks of age all gilts were exposed to mature boars daily for 2 weeks, then every 2nd day for an additional 2 weeks. A greater proportion of gilts in the clean environment attained puberty 7 days (P < 0·05) and 10 days (P < 0·07) after first exposure to boars. These data suggest that odorous gases, such as ammonia, in the air of environmentally regulated buildings may diminish the stimulatory influence of boars on the onset of puberty in gilts.

Thirty-two entire male and 32 female pigs were used to investigate responses to eight concentrations of dietary protein, with constant amino acid composition ranging from 90 to 248 g/kg over different live-weight stages between 20 and 90 kg.

With increasing live weight there was a continuous decline in the concentrations of dietary protein required to support maximum growth and an increasing difference between the sexes in their response to dietary protein. Between 20 and 40 kg live weight sex had no significant effect on growth performance or on the dietary protein concentration for maximum growth (P > 0·05). Over all heavier live-weight stages entire males grew faster and more efficiently than females, and between 20 and 70, 20 and 80, 20 and 90 and between 50 and 90 kg live weight they responded to higher concentrations of dietary protein than females. During the latter stages of growth, the performance of females was also depressed on the two highest-protein diets. This was associated with a significant increase in carcass fat thickness at 90 kg.

Relative growth of length and thickness of femur, tibia, humerus and radius-ulna was studied using data from 320 rabbits from both sexes of two lines (New Zealand White and California). A cross-sectional design was used with slaughter points fixed at weekly intervals from 1 to 20 weeks of age. Carcass length was chosen as independent variable and two models were fitted to the data. Model 1 assumed the existence of one allometric change at some moment of the post-natal development and model 2 of a continuous change of the allometric coefficient throughout the experimental period.

Most of the bone measurement showed allometric changes and in all the cases they were not abrupt but continuous. The theoretical and practical implications of the existence of these changes are discussed. The allometric coefficients of all the bone measurements showed a decreasing rate of change except radius-ulna thickness. While the coefficients for bone lengths were positive tending to isometry, for bone thickness they were always negative.

Forty-three entire males were used to determine the pig's tissue requirements for protein and amino acids from 8·0 to 20·0 kg, and provide information on the capacity of diets formulated with conventional ingredients to contain the same levels and balances of amino acids as ideal protein to supply these nutrients. Seven diets with similar digestible energy (15·9 MJ digestible energy (DE) per kg) and crude protein concentrations from 119 to 232 g/kg (8·7 to 17·3 g lysine per kg) were offered ad libitum between 8·0 and 200 kg live weight. The rate of protein deposition was determined by comparative slaughter. The composition of the protein deposited in the whole empty body was determined from amino acid analyses of pigs killed at 8·0 kg and from the two extreme dietary treatments at 20·0 kg. Growth performance and the rates at which protein and lysine were deposited in the empty body increased linearly with increasing dietary protein concentration up to 187 g/kg and remained relatively constant thereafter. The corresponding dietary protein and lysine intakes required to support maximal protein accretion were 178 g/day (11·7 g/MJ DE) and 13·0 g/day (0·84 g/MJ DE) respectively. Based on the maximal deposition rates for protein (91·8 g/day), and lysine (5·96 g/day) and endogenous protein loss (77middot;6 g/day) estimated from the linear component of the relationship determined between protein deposition and apparent digestible protein intake, the pig's tissue requirements for protein and lysine were only 99·4 g/day (6·5 g/MJ DE) and 6·46 g/day (0·43 g/MJ DE) respectively. This disparity between the pig's tissue protein and amino acid requirements and the dietary levels needed to support these was associated with the fact that the apparent digestibility and biological value of the dietary protein were 0·92 and 0·602 respectively. Apart from small differences in the lysine content of body protein and the methionine: lysine ratio, the average amino acid composition of pigs killed at 8·0 kg, and from the diet of highest protein concentration at 20 kg, was similar to that of ideal protein, indicating that the low utilizability of dietary protein for tissue growth and maintenance was probably associated with low amino acid digestibility and/or availability. The implications of the results with respect to expression of the growing pig's requirements for protein and amino acids are discussed.

Eighteen pregnant red deer hinds were slaughtered at known stages of gestation between 72 and 224 days (term = 233 days). The udder was removed and the gravid uterus was separated into foetal, placental, empty uterus, amniotic fluid and allantoic fluid components. Equations were fitted to the weights of each component to describe the effects of stage of gestation. Hind weight at mating had no significant effect. For the foetal weight (Y, kg) the data were closely fitted by a version of the Gompertz equation,

loge Y = 3·016 — 14·267exp (–0·01138t) – 0·086s

where t is time in days from conception and s is the sex of the foetus (male = −1, female = 1). The weights of the placenta and empty uterus were similarly fitted by versions of the Gompertz equation and mammary tissue by an exponential relationship. However, the weight of (logc) amniotic fluid was bestdescribed by a third degree polynomial, and that of (loge) allantoic fluid by a linear equation.

Using the equations and their first differentials, respectively, estimates were made of mean weights and daily rates of gain at different stages of gestation. These indicated altogether relatively slow growth and low weight of the red deer conceptus. Udder development occurred typically late in pregnancy.

Body weight and food intake were measured at different ages up to 30 weeks in males and 21 weeks in females in lean, fat and commercial lines of broiler chickens given diets of different crude protein content. The lean and fat lines showed no differences in rates of body-weight gain or final body weights but the lean line had consistently lower food intakes. Dietary protein concentration within the ranges studied did not influence final body weights.

Equations derived from a theory of feeding and growth were used along with the data up to 21 weeks of age to calculate mature body weights and various feeding characteristics. These values were compared with those obtained by application of the theory to another set of broiler data. The theory was found to be sufficiently robust to give some consistent interpretations of data from experiments involving considerable differences in time, breed and diet.

The concentrations of dry matter (DM), crude protein (CP), fat and ash were determined for 18 singleton red deer foetuses of known gestational ages within the range 72 to 224 days (term = 233 days) and for their associated placentae and empty uteri. In addition, concentrations of Ca, P, Mg, Na and K were determined for the foetuses. The amniotic and allantoic fluids were analysed for DM, CP and ash content.

Concentrations of all measured components in the foetal fluids increased with foetal age (except for amniotic ash concentration which decreased) and linear regressions were fitted. Concentrations in the empty uterus remained constant. Given the equations previously fitted relating the weight of these tissues t o foetal age, the weights of their chemical constituents could then be calculated at various stages.

Concentrations of all measured components in the foetus increased with foetal age (except for foetal K which remained constant). In the placenta, concentrations of DM and CP tended to increase while those of fat and ash decreased. The actual weights of the chemical constituents were related to both foetal age and foetal weight by further regression analysis in the form of extended Gompertz equations.

Estimates are made of the daily rates of accretion of chemical components in the foetus and adnexa and these provide data against which to assess the additional nutrient demands of pregnancy in the red deer hind.

In ruminants a dynamic state of protein turn-over has been poorly understood although the methodology of measuring the rate of protein turn-over has recently been advanced to a great extent (Waterlow, Garlick and Millward, 1978). Available evidence suggests that ruminants such as sheep and cows are no exception among various mammalian species when whole-body protein synthesis of adult animals is compared on a metabolic body-weight basis (Waterlow et al., 1978; Reeds and Lobley, 1980).

The effects of long-term oral administration of enkephalinase inhibitors (acetorphan and thiorphan) on food and water intake, live-weight gain and food conversion efficiency were investigated in growing rats and mice. In rats, daily drenching with acetorphan (an absorbable prodrug of thiorphan) at 1 mg/kg per day for 8 days did not alter food and water consumption but significantly increased live-weight gain (32·0 (s.d. 5·1) g for control rats v. 40·7 (s.d. 9·1) g for treated rats (P ≤ 0·05 U test) and improved food conversion efficiency (4·37 (s.d. 0·49) g food per g gain for control rats v. 3·70 (s.d. 0·67) g food per g gain for treated rats). In mice, lower doses (0·2 mg/kg per day) of thiorphan and acetorphan given in the drinking water similarly affected live-weight gain (7·7 (s.d. 0·9) g v. 6·0 (s.d. 1·6) g in 3-week-old mice receiving thiorphan and 2·6 (s.d. 0·4) g in 5-week-old mice receiving acetorphan) with a likely improvement in food conversion efficiency. These results suggest that oral administration of enkephalinase inhibitors may alter growth in rodents, probably by affecting the digestive process.

A technique is described for the collection of digestive contents with a glass T-shaped ileal cannula, in rabbits fed ad libitum. Repeated samples of ileal contents were easily obtained by gravity from conscious animals lying in a hammock for 1 h, twice a week, over a period of 2 months. Analysis of the ileal contents showed no diurnal variations in concentrations of crude protein, neutral-detergent fibre, ammonia, and total short-chain volatile fatty acids. The fresh weight output was maximal at 09.00 h and minimal at 03.00 h. The transit time of phenol sulphone phthalein between mouth and ileum was 75 (s.d. 14) min and did not vary according to the time of day when measured (08.00 to 12.00 h, 14.00 to 18.00 h, 20.00 to 24.00 h).

Friesian/Holstein dairy heifers require an average daily live-weight gain of about 0·68 kg/day from birth to calving if they are o t reach a target live weight of 540 kg before first calving at 2 years of age. For autumn- born cattle the diet during their second winter is usually based on silage, hay or straw and the level of supplementation depends on the forage quality. When supplementation is necessary the aim should be to feed a least-cost diet. One possible supplementary food is fodder beet which, if grown without the use of purchased fertilizer (West of Scotland Agricultural College, 1984), can be a relatively cheap source of energy and compares favourably with other crops in yield per ha. In the two experiments reported here fodder beet was used for feeding dairy youngstock. The objective of experiment 1 was to evaluate the substitution of barley by fodder beet in straw-based diets. In experiment 2, fodder beet was fed as a partial substitute for silage.

Long-day photoperiods of 16 h light (L) and 8 h dark (D) stimulate a proportional increase in live-weight (LW) gain of peripubertal Holstein heifers of 0·08 to 0·17 compared with heifers exposed to short days of less than 12 h L per day (Peters, Chapin, Leining and Tucker, 1978; Peters, Chapin, Emery and Tucker, 1980; Petitclerc, Chapin, Emery and Tucker, 1983; Zinn, Chapin and Tucker, 1986). One factor that could account for some of this variation in the magnitude of the growth response to long days is that the previous photoperiod exposure may influence the response to a subsequent different photoperiod (Moore-Ede, Sulzman and Fuller, 1982). For example, exposure to 13L: 11D induced pulsatile activity of serum luteinizing hormone (LH) in ewes previously exposed to 16L: 8D, but reduced serum LH to undetectable levels in sheep previously exposed to 8L: 16D (Robinson and Karsch, 1987). Thus, sheep exposed to identical photoperiods exhibited different responses depending on previous photoperiod exposure.

It has been reported that a purified extract from sheep hypothalami inhibited growth hormone (GH) release in rats. This somatotropin-release-inhibiting factor (SRIF), or somatostatin, is a tetradecapeptide and has been prepared synthetically (Brazeau, Vale, Burgus, Ling, Butcher, Rivier and Guillemin, 1973). In addition, _SRIF has been reported t o inhibit the release of other hormones which have major effects upon growth and metabolism such as insulin (Koerker, Ruch, Chideckel, Palmer, Goodner, Ensinck and Gale, 1974), glucagon (Ruch, Koerker, Carino, Johnson, Webster, Ensinck, Goodner and Gale, 1973) and thyroid stimulating hormone (Vale, Rivier, Brazeau and Guillemin, 1974). Furthermore, SRIF has also been shown to be present in large quantities i n the gastrointestinal tract where it controls the release of many gut hormones (Schusdziarra, Zyzhar and Rouiller, 1980). Somatostatin seems, therefore, to be centrally involved in regulating digestion and absorption of food and the subsequent distribution of the absorbed nutrients into tissues within the body. Its removal from the blood circulation by passive immunization increased GH concentrations in plasma in rats (Arimura and Schally, 1976) and prevented decreases in GH concentration as a result of stress (Arimura, Smith and Schally, 1976). Similarly, removal of SRIF by active immunization has been reported to result in higher plasma GH levels in lambs (Varner, Davis and Reeves, 1980; Spencer, Garssen and Hart, 1983b). However, this increase in circulating GH did not appear to have a constant effect in later studies and resulted in inconclusive effects on sheep growth. Laarveld, Chaplin and Kerr (1986) and Spencer, Garssen and Bergstrom (1983a) observed increased growth with improved food efficiency in crossbred and Dutch moor lambs respectively, immunized against SRIF, whereas Varner et al. (1980) reported a significantly lower growth rate in male Columbia lambs and others (Fitzsimons and Hanrahan, 1984; Galbraith, Wigzell, Scaife and Henderson, 1985; Garssen, Welling and Spencer, 1984) concluded that immunization against SRIF did not affect growth in crossbred lambs. It has also been reported that immuno-neutralization of SRIF can lead to enhanced milk production early in lactation n i goats (Spencer and Garssen, 1985).