The activity ofamylase, maitase, lipase, pepsin, trypsin and chymotrypsin in suckling (15 days of age) and in 1-day weaned (43 days of age) domestic rabbits was assayed and compared with older (90 and 180 days) rabbits. It was found that amylase was active in the pancreas at 15 days (11 580 amylase units (AU) per mg protein) and increased during growth, reaching a maximum level (58 960 AU per mg protein) at 90 days of age. Specific activity (SA) of maitase from the small intestine mucosa varied depending on the intestinal segment and the age of the rabbits: activity in the duodenal mucosa decreased, while in the jejunal and Heal mucosa activity increased, during growth. Lipase SA reached a maximum level in suckling rabbits at the age of 15 days (in gastric mucosa 242 and in pancreas 608 mequiv. liberated oleic acid per mg protein per h, 37°C) and decreased sharply at weaning: in gastric mucosa down to 86 and in pancreas down to 89 mequiv. oleic acid per mg protein per h, 37°C. SA of pepsin remained relatively constant for all the studied categories of rabbits: 38 to 39 nmol tyrosine per mg protein per min, 25°C. Trypsin and chymotrypsin SA reached a peak at about weaning: 1·83 nmol benzoyl-arginyl-ethyl-ester per mg protein per min, 25°C and 40·1 nmol benzoyl-phenyl-naphtyl-ester per mg protein per min, 35·5°C respectively.

The objectives of this study were to investigate reproductive performance and the influence of maternal environment on reproductive performance in two genetic lines of maiden heifers. These were given food and managed in the same way at the Langhill Dairy Cattle Research Centre. The two genetic lines were established in 1973; one has been selected for high combined yield of fat plus protein (selection line; S) and the other has been maintained at around the UK average for genetic merit of yield of fat plus protein (control line; C). Analysis of the reproductive performance of 988 heifers born between 1981 and 1998 showed that S heifers were poorer (all P < 0·05) than C heifers for all reproductive measures: conception at first service (S: 0·64, s.e. 0·02; C: 0·71, s.e. 0·03), interval between first and last service (S: 18·2 days, s.e. 2·2; C: 13·4 days, s.e. 2·2) and number of services per conception (S: 1·49 services, s.e. 0·06; C: 1·39 services, s.e. 0·06). S heifers were also younger at first service than C heifers (474·9 days v. 480·1 days, s.e. 1·9, for S and C respectively; P • 01). Fertility of service sires may have had some influence on these results, but this could not be investigated here, as S heifers were mated only to high merit bulls and C heifers to average merit bulls. However, within genetic line, the yearly downward trend in the average number of services per conception of heifers was significantly different from zero for the S line, but not the C line. There were no statistically significant relationships between conception rates in maiden heifers and their subsequent reproductive performance in first lactation. The effect of maternal environment on the reproductive performance of daughters as maiden heifers was investigated. There were no statistically significant relationships between daughter reproductive performance and dam parity or the feeding system of the dam (either a high or low level of concentrates). Within the limited range of nutritional status of dams during the periods post calving and in early pregnancy, there was no statistically significant effect of maternal nutrition on daughter reproductive performance.

Three diets were given separately, each at four levels of digestible energy (DE) intake, to gilts, castrates and boars growing from 21 to 92 kg live weight. The energy levels were those suggested by the Agricultural Research Council, compared with a 5% increase or 10% or 20% decreases in daily allowance. One diet (ME 18) had 3·0 Meal DE/kg and 18·2% crude protein; the other two (HE 16 and HE 19) had 3·26 Meal DE/kg and 16·1% or 19·3% crude protein.

They were given unchanged throughout the experiment. Responses to change in daily DE intake were not affected by sex or diet, except in shoulder fat thickness. Feed eaten per kg gain did not vary by more than 4% over the intake levels investigated, and no difference was significant. On average, each reduction in daily intake below the ARC+5% allowance led to an increase of 1·2 percentage units of carcass lean and a decrease of 1·3 percentage units of carcass fat.

In comparison with HE 16, the higher protein diet HE 19 gave improved feed conversion efficiency and growth rate, particularly in gilts. It did not cause significant changes in carcass measurements. In comparison with ME 18, HE 19 gave more efficient conversion of DE to weight gain, and faster growth.

Boars required less feed per kg gain and had faster growth rates and leaner carcasses than gilts, which were superior to castrates. There was a high incidence of unpleasant odour in fat from boars, but some was also detected in that from gilts and castrates.

In order to describe the temporal evolution of milk yield (MY) and composition in extended lactations, 21 658 lactations of Italian Holstein cows were analyzed. Six empirical mathematical models currently used to fit 305 standard lactations (Wood, Wilmink, Legendre, Ali and Schaeffer, quadratic and cubic splines) and one function developed specifically for extended lactations (a modification of the Dijkstra model) were tested to identify a suitable function for describing patterns until 1000 days in milk (DIM). Comparison was performed on individual patterns and on average curves grouped according to parity (primiparous and multiparous) and lactation length (standard ⩽305 days, and extended from 600 to 1000 days). For average patterns, polynomial models showed better fitting performances when compared with the three or four parameters models. However, LEG and spline regression, showed poor prediction ability at the extremes of the lactation trajectory. The Ali and Schaeffer polynomial and Dijkstra function were effective in modelling average curves for MY and protein percentage, whereas a reduced fitting ability was observed for fat percentage and somatic cell score. When individual patterns were fitted, polynomial models outperformed nonlinear functions. No detectable differences were observed between standard and extended patterns in the initial phase of lactation, with similar values of peak production and time at peak. A considerable difference in persistency was observed between 200 and 305 DIM. Such a difference resulted in an estimated difference between standard and extended cycle of about 7 and 9 kg/day for daily yield at 305 DIM and of 463 and 677 kg of cumulated milk production at 305 DIM for the first- and second-parity groups, respectively. For first and later lactation animals, peak yield estimates were nearly 31 and 38 kg, respectively, and occurred at around 65 and 40 days. The asymptotic level of production was around 9 kg for multiparous cows, whereas the estimate was negative for first parity.

The effects of concentrate energy source on feeding behaviour and energy utilization, when offered with grass silages of differing intake characteristics, were studied in lactating dairy cows. A total of five silages, which differed in fermentation and intake characteristics, were prepared. Silages A, B and D and silages C and E were harvested from primary regrowths and secondary regrowths respectively of predominantly perennial ryegrass swards. Herbage was ensiled either pre-wilted or unwilted and either untreated or treated with a bacterial inoculant or formic acid based additives. Five concentrates (0s, 25s, 50s, 75s and 100s) were formulated to contain similar concentrations of crude protein, effective rumen degradable protein and metabolizable energy (ME) but using different carbohydrate sources to achieve a wide range of starch concentrations. The silages were offered ad libitum, supplemented with 10 kg concentrates per head per day. In experiment 1, a partially balanced change-over design experiment involving 50 lactating dairy cows was undertaken to examine the effects of concentrate energy source on silage feeding behaviour. Silages A, B, C, D and E were each supplemented with concentrates Os, 25s, 50s, 75s and 100s. Concentrate energy source did not alter (P > 0·05) silage feeding behaviour. The number of meals per day decreased (P < 0·01) as silage dry-matter concentration increased. Experiment 2, a completely randomized experiment involving 18 lactating dairy cows, was undertaken to examine the effects of concentrate energy source on energy utilization with cows offered silages B, C and D. These were supplemented with 10 kg/day of concentrates Os, 50s and 100s. Concentrate energy source had little effect (P > 0·05) on ME intake, energy output or on the efficiency of utilization of ME for lactation (k1). In experiment 3, the effect of concentrate energy source on silage preference was examined in a factorial design experiment involving 12 lactating dairy cows. Silages B, C and D were supplemented with concentrates Os, 50s and 100s. Concentrate energy source did not alter (P > 0·05) silage preference. It is concluded that with silages of differing fermentation and intake characteristics but of similar digestibility, concentrate energy source had no effect on feeding behaviour, silage preference or energy utilization. Furthermore there was no evidence of concentrate energy source by silage type interactions on silage feeding behaviour and preference, or energy utilization.

A total of four diets with different carbohydrate composition were investigated in a 4×4 Latin square design experiment with four Norwegian Coldblooded trotter horses. The objective of the present study was to increase the fermentable fibre content and reduce the starch intake of the total ration obtained by partly substituting mature hay and barley with sugar beet pulp (SBP), a soluble fibre source. The diets investigated were hay only (HAY), hay (85% of dry matter intake (DMI)) and molassed SBP (15% of DMI) (SBP), hay (68% of DMI) and barley (32% of DMI) (BAR), and hay (68% of DMI), barley (26% of DMI) and SBP (6% of DMI) (BAR+SBP). The feeding level was 18.5, 17.3, 15.7 and 15.7 g DM/kg BW per day for the HAY, SBP, BAR and BAR+SBP diets, respectively. Each diet was fed for 18 days followed by 10 days of data collection, where apparent total tract digestibility (ATTD), total mean retention time (TMRT) of ytterbium-labelled hay, water balance, digestible energy (DE) intake and nitrogen balance were measured. An enzymatic chemical dietary fibre (DF) method was used to get detailed information on the composition and ATTD of the fibre fraction. Inclusion of SBP in the diet increased the ATTD of the constituent sugars galactose and arabinose (P<0.01). Feeding the HAY and SBP diets resulted in a lower TMRT owing to a higher DF intake than the BAR and BAR+SBP diets (P<0.01). There was no difference in water intake between HAY and SBP, but faecal dry matter was lower for HAY than the other diets (P=0.017), indicating that water was more tightly bound to fibre in the HAY diet. The diets were iso-energetic and provided enough DE and protein for light to moderate exercise for a 550 kg horse. In conclusion, this study showed that the DF intake had a larger effect on TMRT than partly substituting hay or barley with SBP, and that highly fermentable pectin-rich soluble DF from SBP maintains high nutrient utilization in horses.

Prenatal growth is sensitive to the direct and indirect effects of maternal dietary intake; manipulation can lead to behavioural and physiological changes of the offspring later in life. Here, we report on three aspects of how a high-salt diet during pregnancy (conception to parturition) may affect the offspring’s response to high oral salt loads: (i) dietary preferences for salt; (ii) response to salt and water balance and aldosterone and arginine vasopressin (AVP) concentrations after an oral salt challenge; (iii) concentrations of insulin and leptin after an oral salt challenge. We used two groups of lambs born to ewes fed either a high-salt (13% NaCl) diet during pregnancy (S lambs; n = 12) or control animals born to ewes fed a conventional (0.5% NaCl) diet during pregnancy (C lambs; n = 12). Lambs were subjected to short- (5 min) and long-term (24 h) preference tests for a high-salt (13% NaCl) or control diet, and the response to an oral challenge with either water or 25% NaCl solution were also carried out. Weaned lambs born to ewes fed high salt during pregnancy did not differ in their preference for dietary salt, but they did differ in their physiological responses to an oral salt challenge. Results indicate that these differences reflect an alteration in the regulation of water and salt balance as the metabolic hormones, insulin and leptin, were not affected. During the first 2 h after a single salt dose, S lambs had a 25% lower water intake compared to the C lambs. S lambs had, on average, a 13% lower AVP concentration than the C lambs (P = 0.014). The plasma concentration of aldosterone was higher in the S lambs than in the C lambs (P = 0.013). Results suggest that lambs born to ewes that ingest high amounts of salt during pregnancy are programmed to have an altered thirst threshold, and blunted response in aldosterone to oral salt loads.

Feeding strategies based on the addition of plant lipids rich in polyunsaturated fatty acids (PUFAs) in diets of bovines during the finishing period are common to enhance the nutritional value of meat. However, following rumen biohydrogenations, these FAs could still be metabolised in various tissues/organs involved in the FA metabolism such as the liver and adipose tissues (ATs), thus affecting their subsequent deposition in muscles. In this context, the objective of this study was to characterise the various metabolic pathways of linoleic acid (LA) and α-linolenic acid (ALA) in the liver and ATs (subcutaneous (SC) and inter-muscular (IM)) of Normande cull cows fed a diet supplemented (LR) or not (C) with extruded linseeds and rapeseeds, using the ex vivo incubated tissue slice method. Hepatic uptake of both FAs was higher with the LR than with the C diet (P = 0.02). For the two diets, ALA uptake was higher than that of LA (+46%, P = 0.04). ALA was much more degraded by β-oxidation (>50% of ALA present in cells) than LA (∼27%) with both diets (P = 0.015). Whatever the diet, ALA was not converted into longer and/or more unsaturated FA, whereas about 14% of LA was converted into 20:4n-6. The intensity of the esterification pathway was higher (+70%, P = 0.004) with the LR than with the C diet, for both FAs. Hepatic secretion of ALA as part of the very-low-density lipoprotein particles was lower than that of LA (−58% and −23% for C and LR diets respectively, P = 0.02). In SC and IM ATs, dietary lipid supplementation did not alter metabolic pathways of LA and ALA. They were efficiently taken up by ATs (>68% of FA present in the medium), with uptake being higher for IM than for SC AT (+12%, P = 0.01). Moreover, LA uptake by ATs was higher than ALA uptake (+10.7%, P = 0.027). Both FAs were mainly esterified (>97% of FA present in adipocytes) into neutral lipids (>85% of esterified FA). Around 9.5% of LA was converted into 20:4n-6, whereas only around 1.3% of ALA was converted into 20:5n-3. We concluded that, in our experimental conditions, liver was highly active in ALA catabolism limiting its subsequent deposition in muscles. However, bovine liver and ATs were inefficient at converting ALA into long-chain n-3 PUFA, but actively converted LA into 20:4n-6.

This work aims at the identification of relevant intermediate metabolism enzymes contributing to improved meat production due to genetic selection. A wild rabbit (WR) breed and a highly meat selected breed (New Zealand (NZ) rabbit) were used. Food restriction was used as an experimental condition so as to enhance differences within the metabolic pathways under study. During a period of 30 days, NZ and WR experimental breeds were subjected to, respectively, 40% and 60% ad libitum food restriction leading to 17.7% and 21.1% initial weight. Hepatic glycolytic, lipidic and protein regulatory enzyme activity, transcriptional and metabolite levels were determined. Insulin-like growth factor (IGF-1), triiodothyronine, and cortisol were also evaluated. In the glycolytic pathways, the NZ control rabbits presented a higher phosphofructokinase and pyruvate kinase activity level when compared to the WR, while the latter group showed a higher expression of glycogen synthase, although with less glycogen content. In the nitrogen metabolism, our results showed a lower activity level of glutamate dehydrogenase in WR when subjected to food restriction. Within the lipid metabolism, results showed that although WR had a significantly higher mRNA hepatic lipase, non-esterified fatty acid levels were similar between the experimental groups. NZ rabbits presented a better glycemia control and greater energy substrate availability leading to enhanced productivities in which triiodothyronine and IGF-1 played a relevant role.

The last 10 years have seen a significant expansion in the scope of attempts to manipulate the growth of animals (Buttery, Lindsay and Haynes, 1986). The expansion of interest has been driven by a number of factors, both economic and theoretical. At the economic level the need to develop energetically and economically efficient strategies of animal production has been coupled with a renewed awareness of the implications for human health of excessive intakes of saturated fats. Emphasis then has switched from the maximization of weight gain as an end in itself towards a need to promote protein deposition at any given intake and, at the same time, to reduce the fat content of meat and meat products. These twin objectives might be achieved by one of three strategies: the promotion of protein deposition alone, because at any given rate of weight gain this will tend to minimize the rate of fat deposition (the so-called repartitioning effect); the reduction of fat gain (an approach that has received particularly close attention by those concerned primarily with human obesity); or ideally the simultaneous promotion of protein accretion and depression of that of fat.

Eight multiparous lactating Holstein–Friesian cows were used to evaluate the partitioning of dietary nitrogen (N) from diets based on mixtures of red clover and maize silages in comparison with diets based on ryegrass silage. All cows received 4 kg/day of a standard dairy concentrate with one of four forage treatments in an incomplete changeover design with three 4-week periods. Three treatments were based on mixtures of red clover and maize silage. N intake was altered both by varying the ratio of these silages (40/60 and 25/75 on a dry matter (DM) basis) and by an additional treatment for which the DM intake of the 40/60 mixture was restricted to the level achieved with grass silage. Rumen passage rates were estimated from faecal excretion curves following a pulse oral dose of Dysprosium-labeled silage and urinary excretion of purine derivatives (PD) was used as an index of rumen microbial protein synthesis. Red clover silage mixtures led to significantly increased feed intake (21.5, 20.7 and 15.2 kg DM/day for 40/60 and 25/75 red clover/maize silage mixtures and grass silage, respectively), milk production (25.8, 27.8 and 20.0 kg/day for the same treatments, respectively) and milk component yields, but were without effect on milk fat and protein concentrations. The large increase in the yield of milk (24.5 kg/day) and milk components for the restricted red clover/maize silage treatment, in comparison with the grass silage treatment, was proportionately greater than the increase in DM intake (16.6 kg DM/day). There were no significant treatment effects on diet digestibility, while the higher intakes of red clover silage mixtures were associated with higher rumen passage rates (5.82%, 6.24% and 4.55%/h, respectively). There were significant effects of both N intake and forage source on the partitioning of dietary N between milk and urine. When dietary protein was diluted by the inclusion of maize silage, red clover silage led to increased milk N and reduced urinary N in comparison with grass silage. Improvements in N utilisation may be related to increased dietary starch and/or rumen passage rates leading to increased microbial protein synthesis for these treatments. Urinary excretion of PD was significantly higher for all diets based on mixtures of red clover and maize silages, in comparison with grass silage. Urinary N output was close to literature predictions based on N intake for the diet based on ryegrass silage, but 40 to 80 g/day (25% to 30%) less than predicted for the diets based on the mixtures of red clover and maize silages.

Although dried orange pulp (DOP) may conveniently replace cereals in ruminant diets, few studies have considered similar diet substitution for goats. We hypothesised that DOP could replace cereal-based concentrate in goat diets without detrimental effects on growth performance and carcass quality of suckling kids and milk performance and blood biochemical parameters of dams in early lactation. We also hypothesised that DOP substitution may increase the levels of antioxidants, such as phenolic compounds and vitamin E, in milk and improve its total antioxidant capacity (TAC). Therefore, 44 primiparous Payoya dairy goats were allocated to three experimental groups, each fed a different diet: control (CD, n = 14) based on a commercial concentrate with alfalfa hay as forage; and DOP40 (n = 16) in which 40% and DOP80 (n = 14) in which 80% of the cereal in the concentrate were replaced by DOP. The experiment lasted from the final month of pregnancy to 55 days postpartum. The DOP diets did not affect suckling kids’ carcass quality, but at 28 days, led to improvement in live weight (LW) and average daily gain (ADG) from birth, although no differences were found between DOP40 and DOP80 (for CD, DOP40 and DOP80, LW at 28 days was 8.00, 8.58 and 8.34 kg and ADG was 184, 199 and 195 g/day, respectively). Diet had no significant effect on milk yield (average daily milk yield and total yield at 55 days were 1.66 l/day and 90.6 l, respectively) and commercial and fatty acid composition. Nevertheless, α-tocopherol, total phenolic compound (TPC) and TAC concentration in milk increased with substitution of cereals by DOP (for CD, DOP40 and DOP80, concentration of α-tocopherol was 21.7, 32.8 and 42.3 μg/100 g, TPCs was 63.5, 84.1 and 102 mg gallic acid equivalents/l, and TAC was 6.63, 11.1 and 12.8 μmol Trolox equivalents/ml, respectively). Every plasma biochemistry parameter considered was within reference values for healthy goats; therefore, no pathological effect was detected for these variables due to dietary treatment. However, DOP diets caused a reduction in plasmatic creatine kinase and aspartate aminotransferase, implying reduced oxidative damage to muscles. In conclusion, DOP may be an interesting alternative to cereals in early lactation goat diets for increasing farmers’ income and the healthy antioxidant capacity of milk.

The response of post-pubertal entire male cattle (bulls) to implantation with trenbolone acetate and hexoestrol was studied in two experiments. In experiment 1, eight British Friesian bulls, weighing approximately 359 kg at the beginning of a 90-day experiment, were either sham-implanted or implanted with 45 mg hexoestrol, followed 21 days later with a further implantation of 300 mg trenbolone acetate. In experiment 2, 16 bulls (14 British Friesian and two Simmental < ♂ × (Hereford < 5 × Friesian ♀), weighing approximately 349 kg, were similarly untreated or implanted with 30 mg hexoestrol and 300 mg trenbolone acetate. Treatment with hexoestrol gave a small and non-significant increase in live-weight gain in both experiments. However, live-weight gain and efficiency of conversion of food into live-weight gain were significantly improved in both studies following implantation with trenbolone acetate (P < 0·05). Treated bulls had heavier carcasses and greater mean values for estimated carcass gain (P < 005 in experiment 2). Comparison of mean values for blood metabolites indicated significant differences in concentrations of plasma glucose, free fatty acids and cortisol, and serum total protein, growth hormone, insulin and prolactin. Mean values were significantly lower in treated animals for serum albumin in experiment 2 (P < 001) and for plasma urea in both experiments (P < 0·001; P < 0·05). Treatment with hexoestrol resulted in lower mean concentrations of plasma androgens. These were further reduced following treatment with trenbolone acetate (P < 0·01). The results suggest that the combination of trenbolone acetate plus hexoestrol may improve growth performance, by altering protein metabolism, in post-pubertal entire male cattle. The combination of trenbolone acetate plus hexoestrol appears to have more potent anabolic activity than the endogenous hormones of these animals.

The nutritional effects of varying levels of leguminous leaf meal inclusion were investigated using 40 mixed weaner pigs of average weight 31·4 (s.d. 4·19) kg offered diets which included leguminous leaf meals (Acacia karroo, Acacia nilotica and Colophospermum mopane) over 18 days. The leaf meals were included at 100, 200 and 300 g/kg of dry matter. Leaf meals increased daily live-weight gain (P > 0·05) at low inclusion levels. They were also shown to increase food intake and food conversion ratio. There was an increase in digestibility of dry matter and protein at low inclusion level of leaf meals (P < 0·05), then a decrease in the digestibility as the level of leaf meals increased. Inclusion of leaf meals induced production of proline-rich proteins (molecular weights of 24 600, 54 000, 66 000 and 74 000 Da) in the parotid salivary glands of pigs but not in the mandibular glands (P > 0·05). The activity of hepatic microsomal uridine diphosphate glucuronyl transferase increased significantly (P < 0·05) for pigs offered diets supplemented with A. nilotica and C. mopane but not with A. karroo (P < 0·05). Intestinal parameters (crypt depth, villus height and villus-crypt ratio) were not significantly affected by leaf meal inclusion (P > 0·05) except crypt depth at the proximal position of the small intestine, which decreased with increasing leaf meal levels (P < 0·05).

Heat stress has a significant impact on all livestock and poultry species causing economic losses and animal well-being concerns. Providing shade is one heat-abatement strategy that has been studied for years. Material selected to provide shade for animals greatly influences the overall stress reduction provided by shade. A study was conducted to quantify both the environment and animal response, when cattle had no shade access during summertime exposure or were given access to shade provided by three different materials. A total of 32 Black Angus heifers were assigned to one of the four treatment pens according to weight (eight animals per pen). Each pen was assigned a shade treatment: No Shade, Snow Fence, 60% Aluminet Shade Cloth and 100% Shade Cloth. In the shaded treatment pens, the shade structure covered ~40% of the pen (7.5 m2/animal). Animals were moved to a different treatment every 2 weeks in a 4×4 Latin square design to ensure each treatment was applied to each group of animals. Both environmental parameters and physiological responses were measured during the experiment. Environmental parameters included dry-bulb temperature, relative humidity, wind speed, black globe temperature (BGT), solar radiation (SR) and feedlot surface temperature. Animal response measurements included manual respiration rate (RRm), electronic respiration rate (RRe), vaginal temperature (body temperature (BT)), complete blood count (CBC) and plasma cortisol. The environmental data demonstrated changes proportional to the quality of shade offered. However, the animal responses did not follow this same trend. Some of the data suggest that any amount of shade was beneficial to the animals. However, Snow Fence may not offer adequate protection to reduce BT. For some of the parameters (BT, CBC and cortisol), 60% Aluminet and 100% Shade Cloth offers similar protection. The 60% Aluminet lowered RRe the most during extreme conditions. When considering all parameters, environmental and physiological, 60% Aluminet Shade Cloth offered reductions of BGT, SR, feedlot surface temperature and the best (or equal to the best) overall protection for the animals (RRe, RRm, BT, blood parameters).

Predictions of body composition have been made in 24 baconweight pigs of widely differing fatness, using feed intake and live-weight gain data.

Measurements of feed intake and live weight were made every 7 days throughout the growing period from 25 to 90 kg. After each pig was killed at about 90 kg, one carcass side was physically dissected and the whole empty body was chemically analysed. Multiple regression equations were then computed with the dependent variables being the weights of the physically dissectible and the chemical components. The independent variables were initial live weight, energy intake above maintenance, and live-weight gain.

The residual standard deviations of the regressions as a percentage of the mean weights of the dependent variables were for body lipid, 5·6%, fat-free mass, 3·3%, dissectible fat, 6·1 % and dissectible lean, 4·9 %. The predictions seem at least as good as can be achieved by more sophisticated techniques.

Analysis of the data allowed the efficiency of utilization of energy for protein and lipid deposition to be calculated, and an estimate of the energy costs of maintenance to be made.

The digestibility of horse feeds and rations can be determined using different techniques such as calculations based on the chemical composition, in vivo or in vitro methods. The marker methods overcome difficulties like discomfort for the animals and longer experimental times encountered using the ingesta/egesta method. In field conditions, a natural indigestible marker like acid-insoluble ash (AIA), with no changes in the normal ration, could be a very useful tool for digestibility trials. A group of six standardbred horses was used in a set of seven apparent digestibility trials. The diets were based on a first-cut meadow hay added to three different cereals (barley for trials 1 and 2; oats for trials 3 and 5 and corn for trials 6 and 7), the hay : concentrate ratio being 60 : 40 or 70 : 30 on a dry matter basis. Feedstuffs and faeces were analysed to determine the AIA content, using 2N HCl or 4N HCl technique. No differences about AIA concentration were found between the two methods for means and accuracy in each diet. Digestion coefficients for each diet did not differ with AIA method, even if in some trials interfering factors consistently lowered the overall values. Consequently, the AIA 2N HCl can be considered the easier and cheaper method to state apparent digestibility in field conditions, and a good tool for digestibility trials in horses fed hay-based diets.

Thirteen Blackface and Merino × Cheviot female sheep were shorn and each exposed for a maximum of 10 hours to intense cold (—18° C, 4 m.p.h. wind). Individual exposures were terminated earlier if rectal temperatures fell by 4·5° C. In the first year of the experiment (1963) 11 out of 13 of the sheep were in late pregnancy. There were also 12 control sheep, 9 of them pregnant, which were not subjected to cold treatment. In 1964, 12 of the previously treated sheep were subjected again to similar cold exposures. This time they were unmated and there were no controls.

The cold treatment apparently caused increased variation in gestation length, but the effects on neo-natal lamb mortality were inconclusive.

In 1963 and 1964 there was wide variation between individual sheep in cold tolerance—defined as the ability to maintain rectal temperature during cold exposure. Repeatability for this character was approximately 0·73, suggesting the existence of a genetic component. The average decline in rectal temperature was similar in both years: 3·9·2° C. in 1964. Pregnancy and breed had no detectable effects on cold tolerance.

Skin temperatures on the midside, ear and hind foot (pastern) were measured in 1964. They all declined during cold exposure. Midside skin temperatures typically fell to about 10° C., ear temperatures to about 3° C. and foot temperatures to zero. There were temperature fluctuations due to periodic vasodilation on the ears but the feet generally showed sustained vasoconstriction.

Superior cold tolerance tended to be associated with low mean body skin temperatures and a previous history of live-weight gain. It is suggested that subcutaneous fat deposition may be one factor responsible for improving skin insulation and thereby reducing heat loss in shorn sheep, but direct evidence for this was lacking.

Bone growth patterns and distribution were compared in joints of carcasses from 277 young bulls, progeny of eight sire breeds and two dam breeds, serially slaughtered at 300 kg live weight, 12 and 15 months of age. The growth pattern for bone in a joint was estimated from the allometric equation (Y = aXb). Growth coefficients (b) were homogeneous among breed groups for bone in each joint relative to total side bone indicating that the different breeds followed similar patterns of differential bone growth. Growth impetus of limb bones was lowest in the distal parts, increasing to the proximal regions, with the fore limb showing higher growth impetus than the hind limb. Bones of the whole thoracic region showed a high growth impetus and those of the lumbar region the highest. The cervical vertebrae showed only average growth impetus, maintaining a constant proportion of total bone. Significant sire breed differences were found in the proportion of bone in each joint when adjusted to equal side bone weight but the differences were rather small and probably commercially unimportant. Differences among sire breed groups reflected differences in maturity type, with progeny of Here-ford sires representing early maturity and progeny of Chianina sires the other extreme. Functional association between muscle and bone was not reflected in a similarity of growth patterns, except for the muscles and bones of the limbs.

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.