Twenty-eight high genetic merit and 32 medium genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein) of 43·3 and 1·0 kg respectively, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment consisting of eight treatments. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), while the forage component of the diet was grass silage. Diets were offered ad libitum in the form of a complete diet. Animals remained on these concentrate regimes for a mean of 84·7 days before completing a standard 98-day grazing period. At pasture, cows received either 5·0 or 6·0 kg concentrate daily according to turnout date. There were no significant genotype×nutrition interactions for any of the variables examined during either the indoor feeding or post-turnout grazing periods (P<0·05). Outputs of milk, fat, protein and fat + protein were greater for high merit cows than for medium merit animals (P<0·001). Milk output and milk protein output responses to increasing concentrate proportion were linear for both cow genotypes (P<0·001), while high merit animals showed a linear response in terms of milk fat plus protein output (P<0·01) with these responses being statistically parallel for both merits. High merit cows had a significantly higher DM intake than medium merit animals (P<0·01). With high merit animals, concentrate proportion had little effect on body tissue reserves, while medium merit animals showed a tendency for increased condition score and backfat thickness with increasing concentrate inclusions (P<0·05). In terms of the output of milk and milk constituents during the grazing period, there were no significant residual effects from winter concentrate feed rate (P>0·05), while high merit cows continued to have higher outputs of milk and milk constituents (P<0·001). Body tissue reserves of both genotypes changed little during the grazing period. It is likely that the higher milk yields of the high merit cows can be attributed both to their higher DM intakes and their ability to partition a greater proportion of the nutrients consumed into milk rather than body tissue reserves. Although statistically both high and medium merit cows responded in a similar manner to an increasing proportion of concentrate in the diet, high merit cows did exhibit a 49% greater fat plus protein yield response during the indoor period, compared to animals of medium genetic merit, perhaps hinting at the existence of a genotype×nutrition interaction.

An experiment was carried out in Northern Ireland in 1994 to examine the effects of ensiling grass on the partitioning of nutrients between lean and fat deposition in lambs using the comparative slaughter technique. The six treatments consisted of: (1) unsupplemented grass silage; (2) grass silage supplemented with concentrates, concentrates constituting 250 g/kg total dry matter intake (DMI); (3) grass silage supplemented with concentrates, concentrates constituting 500 g/kg total DMI; (4) unsupplemented grass which had been conserved by freezing; (5) pre-frozen grass supplemented with concentrates, concentrates constituting 250 g/kg total DMI, and (6) pre-frozen grass supplemented with concentrates, concentrates constituting 500 g/kg total DMI. A total of 84 Dutch Texel×Greyface (Border Leicester×Blackface) lambs, consisting of 42 males which were initially 35 (s.d. 4·8) kg liveweight and 42 females which were 33 (S.D. 2·6) kg liveweight, were used. The silage was well preserved as indicated by its low pH (3·8), low concentration of ammonia (60 g/kg total nitrogen) and high concentration of lactic acid (129 g/kg DM). The grass had a higher pH (5·2) and higher WSC concentration (129 g/kg DM) and lower concentrations of lactic (33 g/kg DM) and acetic acids (6 g/kg DM). Ensiling had no significant effect (P>0·05) on empty body and carcass weight gains. Animals offered unsupplemented silage had significantly lower protein (P<0·001) concentration in the carcass gain and significantly higher lipid and energy (P<0·001) concentrations than animals offered unsupplemented frozen grass. However, there was no effect of forage type on chemical composition of carcass gains when 50% forage was offered. It is concluded that ensiling had no effect on empty body or carcass weight gains, but did increase carcass fatness when unsupplemented forages were offered.

The current study was to determine the effects of growth hormone-releasing peptide ([His1, Lys6]-GHRP) on growth performance and carcass traits in pigs, and to determine whether the results were comparable to those of recombinant porcine growth hormone (r-PGH) treatment. Thirty Landrace and Yorkshire pigs (40–45 kg) were randomly divided into three groups, each group consisted of two boars, five gilts and three barrows. Peptides were administered daily by intramuscular injection with the following schemes and dosages: Group A ([His1, Lys6]-GHRP, 200 μg/day in 0·5 ml saline), Group B (r-PGH, 3 mg/day in 0·6 ml saline), and Group C (sterilized physiological saline, 0·5 ml/day). [His1, Lys6]-GHRP caused significant improvements both in pig growth and carcass traits. The average daily gain (ADG) and feed efficiency of the [His1, Lys6]-GHRP treated group were higher than those of the control, but less than with the r-PGH treatment. The net increase in the ADG by [His1, Lys6]-GHRP was c. 14%, and was 23% by r-PGH (both P<0·01). The feed efficiency was improved 17% by [His1, Lys6]-GHRP (P<0·01) and 20% by r-PGH (P<0·01). On the other hand, the back-fat thickness in both [His1, Lys6]-GHRP and r-PGH treated groups (1·76±0·041 cm and 1·72±0·040 cm, respectively) was considerably less (P<0·05) than that of the control group (1·81±0·040 cm). In addition, the lean cuts percentage and the rib longissimus muscle area were comparable in the [His1, Lys6]-GHRP and r-PGH treatments (lean cuts percentage: 57±2·0% and 57±1·5%, respectively; rib longissimus muscle area: 32·8±0·91 cm2 and 32·9±1·10 cm2, respectively), and both were significantly (P<0·05) greater than those of the control group (lean cuts percentage: 53±1·5%; rib longissimus muscle area: 28·3±1·61 cm2). In conclusion, [His1, Lys6]-GHRP appeared to be a promising tool for controlling carcass fat in pigs.

Nitrogen (N) inputs and outputs were measured over 3 years in a trial with four farmlets (each with 16 randomly-allocated 0·4 ha paddocks) on permanent white clover/ryegrass pastures which were grazed throughout the year by dairy cows near Hamilton, New Zealand. Three farmlets were stocked at 3·3 cows/ha and received nominal rates of N fertilizer (urea in 8–10 split applications) of 0, 200 or 400 kg N/ha per year. A fourth farmlet with 4·4 cows/ha received 400 kg N/ha per year and was supplemented with maize grain during the first two years.

Nitrogen balances were calculated, with [sum ]N inputs[ape ][sum ]N outputs. Annual inputs from N2 fixation were 99–231 kg N/ha in the 0 N farmlet, but declined to 15–44 kg N/ha in the 400 N farmlets. The main N outputs (in kg N/ha per year) were in milk (72–126), nitrate leaching (20–204), and transfer of N via cow excreta from pastures to lanes and milking shed (54–92). Gaseous losses by denitrification (3–34) and volatilization (15–78) were smaller than the other N outputs but increased significantly with N fertilizer application. In the maize-supplemented farmlet, N outputs in milk were 31% higher than in the corresponding non-supplemented 400 N farmlet, whereas leaching losses averaged 17% lower during the 2 years of supplementation.

In the N-fertilized farmlets, estimated N balances were influenced by inclusion of the transitional N processes of immobilization of fertilizer N into the soil organic N pool (estimated using 15N at 42–94 kg N/ha per year) and the contribution from mineralization of residual clover-fixed N in soil not accounted for in the current estimates of N2 fixation (estimated at up to 70% of measured N2 fixation or 46 kg N/ha per year). However, these processes were counteracting and together were calculated to have only a small net effect on total N balances.

The output of N in products (milk, meat and feed) relative to the total N input averaged 26% in the 400 N farmlets, and is compared to that measured for commercial intensively-managed dairy farms in England and the Netherlands (14–20%). The 0 N farmlet, which was reliant on N2 fixation as the sole N input, was relatively very N-efficient with the milk production being 83% of that in the 400 N farmlet (at 3·3 cows/ha) and the N output in products relative to total N input averaging 52%.

An experiment was conducted in the semi-arid temperate highlands of central Mexico (1994–95) with 12 adult, female non-pregnant, non-lactating, crossbred Nubian goats to determine the effects of 36 weeks of feed restriction on body weight, carcass composition and blood concentrations of glucose and hormones (insulin, triiodothyronine [T3] and tetraiodothyronine [T4]). After a 9-week feed intake, liveweight and body condition stabilization period, the animals were divided into three groups and individually offered either 100, 80 or 60% of their observed average daily consumption. Feed intake was measured daily, liveweight weekly, and blood-serum glucose and hormone concentrations every 4 weeks. At the end of the feeding experiment, the animals were slaughtered, and the carcasses and viscerae weighed. Liver and muscle samples were obtained and chemically analysed. Insulin and T4 did not differ between treatments (P>0·05). Final liveweight; blood-serum glucose and T3; carcass yield; muscle tissue dry matter, fat, RNA and RNA:protein ratios; hepatic tissue protein, RNA:DNA and protein:DNA ratios decreased, while liver and muscle DNA increased with restriction (P<0·05). These results suggest that capacity of goats to adapt to long term undernutrition and the importance of hepatic and muscle tissues as sources of metabolic energy.

Sixty Holstein/Friesian dairy cows, 28 of high genetic merit and 32 of medium genetic merit, were used in a continuous design, 2 (cow genotypes)×4 (concentrate proportion in diet) factorial experiment. High and medium merit animals had Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 43·3 kg and 1·0 kg respectively. Concentrate proportions in the diet were 0·37, 0·48, 0·59 and 0·70 of total dry matter (DM), with the remainder of the diet being grass silage. During this milk production trial, 24 of these animals, 12 from each genetic merit, representing three animals from each concentrate treatment, were subject to ration digestibility, and nitrogen and energy utilization studies. In addition, the efficiency of energy utilization during the milk production trial was calculated.

There were no genotype×concentrate level interactions for any of the variables measured (P>0·05). Neither genetic merit nor concentrate proportion in the diet influenced the digestibility of either the DM or energy components of the ration (P>0·05). When expressed as a proportion of nitrogen intake, medium merit cows exhibited a higher urinary nitrogen output and a lower milk nitrogen output than the high merit cows. Methane energy output, when expressed as a proportion of gross energy intake, was higher for the medium than high merit cows (P<0·05), while urinary energy output tended to decrease with increasing proportion of concentrate in the diet (P<0·05). In the calorimetric studies, neither heat energy production, milk energy output and energy retained, when expressed as a proportion of metabolizable energy intake, nor the efficiency of lactation (kl), were affected by either cow genotype or concentrate proportion in the diet (P>0·05). However when kl was calculated using the production data from the milk production trial the high merit cows were found to have significantly higher kl values than the medium merit cows (0·64 v. 0·59, P<0·05) while k l tended to fall with increasing proportion of concentrate in the ration (P<0·05). However in view of the many assumptions which were used in these latter calculations, a cautious interpretation is required.

Intake, digestion and growth were examined in young Merino×Border Leicester wether sheep held for 44 days in either cool (13–15°C, thermal humidity index 56–58) or hot (32–40°C, 50–70% relative humidity, thermal humidity index minimum 83–84, maximum 83–88) environments. The sheep were offered diets of medium quality hay ad libitum alone (Con) or supplemented with either 22 g air-dry/kg metabolic liveweight (W0·75) of barley grain fortified with urea and sulphur (Bar/N) or 10 g air-dry/kg W0·75 of fishmeal (FM). Intake of the Con diet by the sheep in the cool environment was high at 79 g DM/kg W0·75 per day. Sheep in the hot environment had higher rectal temperatures and higher respiration rates (40·1°C v. 39·2°C, 196 v. 56 respirations/min respectively, P<0·01). The hot environment reduced (P<0·05) total dry matter (DM) intake, estimated metabolizable energy (ME) intake, liveweight (LW) gain and nitrogen (N) balance. The provision of supplements did not change total DM intake, but increased (P<0·05) organic matter digestibility, estimated ME intake, LW gain and N balance. Wool growth was increased much more by the FM than by the Bar/N supplement, indicating that the supply of absorbed amino acids was increased substantially by the FM supplement. Neither voluntary intake nor productivity were influenced by any interactions between the thermal environments and the balance of nutrients provided by the diets. In conclusion, in these young sheep consuming a high intake of a medium quality roughage diet, moderate heat stress reduced intake and growth but did not affect the relative responses of the sheep to supplements providing principally fermentable ME or a similar amount of fermentable ME and additional metabolizable protein.

The potential use of faecal n-alkanes for estimation of intake and diet composition over periods of 1–2 days was assessed in two experiments. The aim was to determine the accuracy with which intake and diet composition could be estimated by characterizing faecal excretion of n-alkanes following a discrete dose as opposed to steady state kinetics used in previous work.

In the first experiment, 16 sheep were fed mixtures of spinach (rich in C31-alkane) and cabbage (rich in C29-alkane) in known proportions and amounts for two days. Artificial n-alkanes (C28- and C32-alkane) were dosed on four occasions during this time. Total intakes were controlled at 0·2, 0·3, 0·4 or 0·5 kg dry matter (DM) per day and nominal amounts of spinach offered (as a proportion of the total diet) were 0·00, 0·15, 0·30 and 0·45. Each sheep received a unique combination of intake and dietary proportions (four intake rates×four proportions). Sheep were fed fresh grass (timothy, Phleum pratense) before and after feeding spinach and cabbage. Sequential rectal grab samples of faeces were collected at regular intervals and total faecal collections were carried out over 144 h from the start of the spinach/cabbage feeding period to obtain samples for n-alkane analysis. In the second experiment, fresh grass was sprayed with two combinations of artificial n-alkanes (C24- and C32- or C28- and C36-alkane) and fed to 16 sheep over a 24 h period. Each sheep received one of four intake rates (0·8, 1·0, 1·2 or 1·4 kg DM/day) and, within intake rates, each sheep received one of four different proportions of the herbage sprayed with the combinations of n-alkanes (0·2, 0·4, 0·6 or 0·8), in a similar fashion to the first experiment. In order to estimate intake, C26- and C34-alkanes were dosed at the start of the feeding period. Faecal sampling procedures were the same as those in the first experiment.

Different parameters of faecal excretion curves of dosed and natural n-alkanes were used to estimate dietary proportions and intake. Parameters tested included area under the excretion curve and curve maximum. Dietary proportions were calculated using an iterative minimization procedure employing faecal and herbage n-alkane concentrations. Intakes were estimated using ratios of dosed:natural faecal n-alkanes.

The best estimates of dietary proportions were obtained using faecal concentrations at a single point in time in both experiments (>80% variation explained for regressions of estimated v. actual proportions). Intake estimates required the calculation of the area under the excretion curve to obtain acceptable estimates (70–90% variance explained for regressions of estimated v. actual intakes in Expt 2). The experiments demonstrate that precise estimates of diet composition can be obtained using single faecal samples following consumption of simple herbage mixtures over 24–48 h. Intake may also be estimated using this technique provided that a series of faecal samples are collected over 4–5 days following the period of ingestion.

Effects of dietary energy and protein supply on liveweight (LW) gain and gain of protein, fat and ash in the carcass, and weight and gain of non-carcass organs were determined in 118 weaned crossbred lambs from two nutritional histories at Camden, NSW in 1991. Half of the lambs were fed to achieve and maintain LW at 35 kg (LOW group) and half of the lambs were fed ad libitum until they attained 50 kg LW (HIGH group), during a preliminary period of 126 days. In the subsequent experimental period, lambs were allocated to treatments providing 500, 800, 1200 or 1500 g/day of pelleted diets (123 g crude protein, 10 MJ ME/kg dry matter). Diets at each intake contained either 0, 30, 60 or 90 g of formaldehyde-treated casein (rumen escape protein, REP). This resulted in an experiment comparing LOW and HIGH group lambs at four energy intakes, within which were four rates of inclusion of REP. During the 90-day experimental period, LOW group lambs had higher rates of gain of LW, carcass weight and all non-carcass components than did HIGH lambs (P<0·001). At any rate of carcass gain, LOW lambs contained a significantly lower proportion of fat in carcass gain than did HIGH lambs (P<0·05). After adjustment to a common carcass weight, the carcass of LOW lambs contained a significantly lower mass of fat than did that of HIGH lambs at slaughter (P<0·05).

Carcass fat gain in the experimental period was not affected by LW at the start of that period or by nutritional history once initial LW was accounted for as a covariate. Data were consistent with fat deposition being principally controlled by energy intake over the immediate pre-slaughter period. In contrast, responses to energy intake in the rate of gain of carcass muscles, ash, liver, head and feet and gut tissue were significantly greater in lambs of LOW compared to HIGH nutritional history. A significant component of this effect of nutritional history was attributable to LW differences between LOW and HIGH lambs; however, nutritional history still had a significant effect on these parameters once initial LW was accounted for as a covariate. Nutritional history may also have modified carcass composition by changing the partial efficiency of use of available energy for protein deposition without changing the partial energetic efficiency of fat deposition.

In order to learn more about the digestibility, breakdown when eaten and physical structure of stovers and straws, seven diets were compared in one experiment and eight in another. The diets in the first experiment were: the upper and lower parts of lucerne (Medicago sativa) hay, the leaves, upper stem and lower stem of maize (Zea mays) stover and the leaves and stem of sorghum (Sorghum vulgare) stover. The diets in the second experiment were: the upper and lower parts of lucerne hay, the leaves, stems and whole stover of millet (Setaria italica), wheat (Triticum aestivum) straw, rice (Oryza sativa) straw and sweet potato (Ipomoea batatas) haulm. The diets were examined for in vitro digestibility in three forms: milled, chopped (1 cm lengths) and chewed (by cattle). The lengths and widths of the chewed particles were recorded in both experiments. Aspects of the morphology and vascular structure of plant parts of the diets and of chewed particles were recorded in the second experiment.

The in vitro digestibility of chopped or chewed plant material was lower (by 11 and 12 percentage units, respectively, on average) than that of milled material. The difference between chewed and milled material in in vitro digestibility was smaller with leaves (5 percentage units, on average) than with stems (18 percentage units, on average) in maize, sorghum and millet. Digestibility of chewed material was similar to or lower than that of chopped material, except with the leaves of maize, sorghum and millet. Millet stover had higher in vitro digestibility than wheat straw or rice straw, whether the diet was milled, chopped or chewed.

The thinnest stem internode vascular bundles recorded (0·14 mm) were in wheat. The percentage of stem internode cross-sectional area occupied by vascular bundles was in the range 6–8 for lucerne, millet, wheat and rice. The mean numbers of veins or vascular bundles per chewed particle were in the range 6–23. The mean length of the chewed particles varied from 10 mm with the upper stem of maize to 18 mm with sorghum stem and maize leaves. The mean width of the chewed particles varied from 1·8 mm with rice straw to 5·4 mm with maize leaves.

It is suggested that the low digestibility of mature plant tissue such as stovers and straws is not particularly due to thick vascular strands or to a high proportion of vascular tissue, but rather to a high proportion of cell wall and incomplete and delayed access by rumen microorganisms to much of the cell wall.