Observations on duration of the period of receptivity in two groups of Milking Criollo, one of Jersey and one of Brahman cows are presented. After one or two oestrus periods measured without service the cows were bred naturally in the case of Jerseys, Brahmans and one group of Milking Criollos. In the other group of Milking Criollos, artificial insemination was used. The period of receptivity was shortened after natural service by 8·7 hours in Milking Criollo and by 4·1 hours in Brahman cows. No shortening of oestrus occurred in the Jerseys and no significant shortening in artificially inseminated Milking Criollos.

Nine of the cows under observation (and seven other cows with some Zebu blood) allowed only one service by the bull.

1. All-concentrate diets containing four different levels of Peruvian (anchovy) fish meal and varying in crude protein content from 14·8% to 21·7% in dry matter were given ad libitum to 8 early-weaned Friesian calves over a live-weight range of 60–100 kg.

2. Nitrogen retention was significantly higher on diets containing 21·7% and 19·4% crude protein in dry matter than on diets with 16·8% and 14·8% crude protein. Nitrogen retention as a percentage of dietary intake appeared to be less on the diet with 21·7% crude protein in dry matter than on the other diets.

3. From these data it was calculated that the digestible crude protein requirement for a calf of 82 kg. live-weight gaining at 909 g. daily is between 270 and 340 g.

Two prototype two-tiered pens were constructed for fattening pigs. The pens consisted of a solid or porous upper floor located 0-8 m above a slatted lower floor, with a short ramp joining the two levels. Food was available only on the upper level and water only on the lower. Eleven groups, each of 15 to 18 pigs were housed in the two-tiered pens for 8 weeks, starting at 10 weeks of age, while matched control groups were housed in a conventional pen offering the same amount of total floor space. During the 1st week, some pigs were slow to adapt to the two-tiered system and average weight gain was lower than in the control pen. Over the 8 weeks, however, weight gain and food conversion ratios were very similar in the two pen types. The animals made effective use of the two levels, and kept the upper level free from dung. Physical condition of pigs in the two-tiered pen was as good as, or better than, that of the controls. The two-tiered design offers several potential advantages in terms of animal production and behavioural problems.

In the analysis of the causes of variation between cows of a given breed in milk production, differences between herds pose some difficult problems. The nature of this variation is of importance from several points of view in the discussion of breed improvement. The situation is complicated by the fact that the herds of any breed type do not form a uniform group but can be classified roughly into a sort of ‘social structure’ (Robertson and Asker, 1951). The discussion of variation between all herds of a given breed type can then be broken down into the variation between strata and that between herds in the same stratum. From the analysis of production data from herds using artificial insemination (Robertson and Rendel, 1954; Korkman, 1953) there is evidence that the genetic component is a small proportion of the total variance in these herds; and also that in Great Britain the genetic difference in yield between the dominant group of herds (which provide many of the bulls used in A.I.) and the herds using A.I. is small. This is in agreement with studies on breed structure. In this paper we shall discuss the genetic differences between members of the small group of important herds which dominate each breed. These usually supply a high proportion of the bulls used. If we have good estimates of the breeding values of such bulls from the production records of their progeny, we can then examine the different breeding herds according to the breeding value of the bulls bred in them. Evidence of this type has been presented for Jersey bulls in New Zealand (Castle, 1952) but without statistical analysis of the results, although inspection suggests that there are definite differences between studs.

Leptin is thought to act on the central nervous system as an important regulator of food intake and body weight in mice. To examine the actions of leptin in sheep, we injected recombinant mouse leptin into the lateral cerebral ventricle of ewes. Six ewes were intracerebroventricularly cannulated and given free access to forage and water. The ewes were injected with phosphate-buffered saline (PBS) as a vehicle for 5 days through the cannula and then with PBS + leptin for 7 days consecutively. Although food intake and body weight did not change during PBS injection, the administration of leptin decreased food intake and body weight. Plasma glucose levels decreased and plasma non-esterified fatty acid levels increased on the last few days of leptin administration. Approximately 2 weeks after normal food intake was recovered, the amount of diet was individually reduced in accordance with the recorded food intake during the leptin administration in each sheep. During food restriction, body weight and plasma metabolite concentrations were similarly changed as during the leptin-administration period. These results indicate that leptin decreases food intake in sheep. Moreover, it is likely that the changes in body weight and plasma metabolites were mainly induced by the suppression of food intake during leptin injection.

Straw possesses many characteristics that make it attractive to pigs and can therefore be effective in preventing negative penmate-directed behaviours. However, straw is difficult to handle in current vacuum slurry systems under most commercial conditions and can therefore only be used in limited amounts. To occupy pigs effectively, straw must remain attractive to pigs throughout the whole day; hence, have a certain degree of novelty. We investigated the penmate-directed behaviour of liquid-fed growing pigs in a production herd, assigned to five experimental treatments: 1×25, 1×50, 1×100, 2×50 and 4×25 g of chopped straw/pig per day, with 20 replicates of each treatment (pen was regarded as experimental unit). Behaviour was observed at two different growth stages; ~40 and 80 kg live weight of the pigs. Activity and exploratory behaviour directed at penmates, straw, pen components and the slatted floor were registered continuously for 15 min of each hour during day time (0600 to 2200 h) by use of video observation of three focal pigs per pen. The pigs were active for about one-third of the day corresponding to ~5 h/day. Of the active time, an average of 7% (35 min) was spent on penmate-directed behaviour. The pigs were more active and increased their straw-directed behaviour when provided with 100 g straw/pig per day compared with 25 and 50 g (P<0.001). However, penmate-directed behaviour was not reduced with an increased amount of straw (P>0.05), and there was no effect on pigs’ behaviour when straw provision was increased per day (P>0.05). Pigs became less active and reduced their straw-directed activities when their weight increased from 40 to 80 kg live weight (P<0.001), but the amount of penmate-directed behaviour was similar (P>0.05). Further, the residual straw results indicated that perhaps a more frequent straw provision could help establish a more even level of fresh available straw during the day. However, the frequent straw provision did not occupy pigs more than one daily allocation did. In conclusion, there was no difference in penmate-directed behaviour of the pigs when given 25 or 50 g of straw/pig per day compared with 100 g of straw/pig per day, nor were there any difference when 100 g of straw/pig per day was provided more frequently.

Employing practical-type diets containing graded levels of all-rac-α-tocopheryl acetate (0, 5, 15, 30, 45, 60, 75 or 100 mg/kg), the quantitative requirement for a-tocopherol by juvenile African catfish (Clarias gariepinus Burchell) was investigated. Diets, defined with respect to selenium, fatty acid and ascorbate inclusion, were offered for 12 weeks during which catfish grew from 10 g to 120 g. Dietary regime had no significant effect on growth (P > 0·05), although haematocrit values increased with increasing tocopherol dose above 15 mg/kg (assayed) (R2 = 0·71, P < 0·05). Tissue accretion of the vitamin increased concomitant with dietary dose (P < 0·001). Employing a colorimetric assay for thiobarbituric acid reactive substances (TBARS) it was evident that concentration ofTBARS in muscle and liver reflected tissue oxidation status, in that elevated dietary vitamin E resulted in decreased assayed TBARS (P < 0·05). By broken-line analysis the requirement for this species to suppress lipid peroxidation was estimated as 30 to 40 mg all-rac-a-tocopheryl acetate per kg dry diet and this agrees with published requirements of many fish species.

1. An experiment is described in which the individual feed intakes of 16 cows under winter housing conditions in yards, during the transition to spring grazing and on. summer grazing, were determined by faecal indexdigestibility methods. The influence of quality of feed before calving on intake and subsequent performance and the influence of pasture quality and availability on feed intake were included in the study.

2. The provision of a diet of 67% organic matter digestibility, either as high quality hay or as low quality hay with concentrates, increased feed intake before calving when compared with a diet of low quality hay (digestibility 62%) alone. Compared with previous lactation yields the better diets were associated with the maintenance of milk yield, while the low quality hay diet before calving was associated with a 10%, but non-significant, reduction in milk yield.

3. There was a marked rise in faecal output and digestible organic matter (DOM) intake after calving. During lactation, and especially on pasture, faecal output and DOM intake were both correlated with milk yield and metabolic live-weight. Total DOM intake was lower when the availability of feed was restricted and increased when feed was readily available; this increase was associated with a high maintenance requirement.

4. When herbage with OM digestibility of 74–82% was consumed, faecal output rose with decreasing digestibility, but DOM intakes were relatively constant. Provided that efficient utilisation can be achieved, total utilisation per acre might be increased if herbage were grazed at the lower end of this range of digestibility.

Segregation analyses were applied to data from an experimental sheep flock to investigate the presence of a major gene affecting litter size. The data set contained 14 years of litter size data, with up to five parities per ewe, from Cheviot sheep carrying the putative Thoka fecundity gene from Icelandic sheep. Segregation analyses were performed using a Markov chain Monte Carlo method implemented using Gibbs sampling. Uniform priors were initially used for estimating variance components, the gene effect and fixed effects in the data. Genotypes in the base generation were assumed known based on the use of the imported Icelandic donor semen from the founder rams. The use of alternative priors (naïve and inverse-gamma distributions) for the variance components did not significantly affect the results, demonstrating the data to be sufficiently powerful for the analyses used. Segregation analyses detected a major gene for litter size in the Thoka Cheviot flock increasing litter size by 0·70 lambs per ewe lambing for a single copy of the gene. When the analysis was repeated without fixing the genotypes in the base population, the analyses predicted a different genotype than that previously used for one of the founder rams and suggested the major gene to be segregating in the Cheviot founder animals prior to the introduction of the Thoka rams. A liability threshold analysis was also applied to the data. As identified in other studies, the threshold analysis overestimated the heritability, but the estimated major gene effect was not significantly different from other analyses. The results confirm the segregation of the Thoka gene in a Cheviot flock and highlight the statistical method as a useful tool for identifying carrier animals to be used for future matings.

1. An experiment was conducted with dairy cows over two grazing seasons to investigate the feasibility of fixed rotational grazing. Each year a comparison was made between treatment A, which consisted of four equal paddocks grazed for 1 week and rested for 3, and treatment B, which contained five paddocks grazed for 1 week and rested for 4. The influence of the length of the rest periods on output per hectare and per cow was measured. Within each paddock approximately one-seventh of the area was allocated daily to each treatment group, there were no back fences and the paddocks were not topped or harrowed. Stocking rates were identical on both treatments at all times at 6·2 cows per ha throughout 1964; 7·1 cows per ha for weeks 1·9 inclusive and 6·2 cows per ha for weeks 10·20 inclusive in 1968. The fertilizer nitrogen applied (282 kg/ha) was equivalent to a daily rate of 2·02 kg/ha. The feed intake of each cow was measured on three occasions during 1967 and four in 1968.

2. Differences between treatments in outputs per ha were small and on average about 13 000 kg milk and 890 cow grazing days were produced per ha during the 20-week experimental period.

3. Differences between treatments A and B in herbage intake, milk production, milk composition and live-weight change were not statistically significant.

4. When 3·6 kg of a supplementary concentrate was given to some cows, positive responses in milk production, milk composition and live-weight change were found, but the value of the extra milk produced was less than the cost of the concentrate.

Reduction of the CP content in the diets of piglets requires supplementation with crystalline essential amino acids (AA). Data on the leucine (Leu) and histidine (His) requirements of young pigs fed low-CP diets are limited and have primarily been obtained from nonlinear models. However, these models do not consider the possible decline in appetite and growth that can occur when pigs are fed excessive amounts of AA such as Leu. Therefore, two dose-response studies were conducted to estimate the standardised ileal digestible (SID) Leu : lysine (Lys) and His : Lys required to optimise the growth performance of young pigs. In both studies, the average daily gain (ADG), average daily feed intake (ADFI) and gain-to-feed ratio (G : F) were determined during a 6-week period. To ensure that the diets had sub-limiting Lys levels, a preliminary Lys dose-response study was conducted. In the Leu study, 60 35-day-old piglets of both sexes were randomly assigned to one of five treatments and fed a low-CP diet (15%) with SID Leu : Lys levels of 83%, 94%, 104%, 115% or 125%. The His study used 120 31-day-old piglets of both sexes, which were allotted to one of five treatments and fed a low-CP diet (14%) with SID His : Lys levels of 22%, 26%, 30%, 34% or 38%. Linear broken-line, curvilinear-plateau and quadratic-function models were used for estimations of SID Leu : Lys and SID His : Lys. The minimum SID Leu : Lys level needed to maximise ADG, ADFI and G : F was, on average, 101% based on the linear broken-line and curvilinear-plateau models. Using the quadratic-function model, the minimum SID Leu : Lys level needed to maximise ADG, ADFI and G : F was 108%. Data obtained from the quadratic-function analysis further showed that a ±10% deviation from the identified Leu requirement was accompanied by a small decline in the ADG (−3%). The minimum SID His : Lys level needed to maximise ADG, ADFI and G : F was 27% and 28% using the linear broken-line and curvilinear-plateau models, respectively, and 33% using the quadratic-function model. The preferred model to estimate the His requirement was the curvilinear-plateau model. However, a 10% reduction in the SID His : Lys level was associated with an 11% reduction in the ADG. In conclusion, the SID Leu : Lys level needed to maximise growth was 108% when using the quadratic-function model as the best-fitting model. The minimum SID His : Lys level required to optimise growth was 28% when using the curvilinear-plateau model as the best-fitting model.

The way the pH falls post-slaughter has an impact on meat quality. Pork longissimus muscles (n=48) were sorted in fast- (FG) (n=15) and normal glycolysing (NG) (n=33) muscles according to the post-slaughter pH 45 min values (FG<6.0; NG>6.0). FG muscles (5.84±0.04) compared with NG muscles (6.27±0.04) were accompanied with higher temperature, electrical conductivity, lightness and yellowness, and reduced grill loss and shear force values (P<0.05), but there were no pH-dependent changes of the drip loss and redness results. FG muscles had higher (P<0.05) percentages of fast-twitch glycolytic and lower proportions of fast-twitch oxidative and slow-twitch oxidative (P<0.05) muscle fibres. The study confirms the relationship of pH value to meat quality and muscle fibre characteristics also showing that pH values have no impact on intrinsic mitochondrial respiratory function.

In order to investigate the effect of different levels of oral glucose supplementation and/or reproductive method on productive and reproductive performance of New Zealand White (NZW) doe rabbits in the tropic, 36 bucks and 120 doe NZW rabbits were equally divided among four treatment groups (n = 9 bucks + 30 does). The treatments consisted of supplementing drinking water with 0 (control), 2.5, 5 and 10 g glucose/l, respectively. To study the effect of reproduction method (natural v. artificial), each group was divided into two sub-groups (naturally mated and artificially inseminated) with the same bucks of the same treatment group. Glucose supplementation at 5 or 10 g/l of water increased (P < 0.01) litter weight at birth and at weaning, and litter weight gain during the 4 weeks. However, glucose supplementation at 2.5 or 5.0 g/l water decreased (P < 0.01) feed consumption from 7 to 14 days after delivery. Glucose supplementation at 2.5 g/l water did not affect productive and reproductive performance of rabbits. Artificially inseminated does had higher daily litter weight gain between 21 and 28 days post partum. Artificially inseminated group had better milk conversion during the 1st and 4th week as compared to naturally mated groups. Compared with the control group, the economic efficiency and performance index of NZW rabbits was significantly improved by 5 g glucose supplementation under tropic condition.

Genetic analyses were carried out on Nematodirus spp. egg counts (NEM) of lambs from a set of Romney breeding lines. The lines had been under selection for 22 seasons (1979 to 2000) for divergence in resistance to infection by strongyle nematodes other than NEM, using faecal egg count (FEC) as the selection criterion. Heritabilities and genetic correlations for NEM were estimated using residual maximum likelihood procedures. Correlated responses in NEM were also determined. Heritability estimates for loge(NEM + 100) in lambs at 4 months of age (NEM1) or 6 months of age (NEM2) were 0·15 (s.e. 0·03) and 0·26 (s.e. 0·04) respectively (c.f. 0·28 (s.e. 0·02) and 0·35 (s.e. 0·02) for loge(FEC + 100)). The genetic correlation between loge(NEM1 + 100) and loge(NEM2 + 100) was 0·85 (s.e. 0·08), while the genetic correlations between measurements of loge(NEM + 100) and loge(FEC + 100) on both sampling occasions had a weighted average of 0·43, with estimates ranging from 0·30 (s.e. 0·08) to 0·52 (s.e. 0·07). Divergence in loge(NEM + 100) between the high and low FEC lines, estimated over both sampling times combined, was 1·07 phenotypic standard deviations, compared with 3·6 phenotypic standard deviations for loge(FEC + 100). Expressed in terms of back-transformed eggs per g, the high and low FEC lines differed by factors of 7·6 and 32·2 for NEM and FEC, respectively. The results support earlier parasitological data indicating that the genetic mechanisms in sheep which are responsible for resistance to other strongyle nematodes probably also influence resistance to Nematodirus infection.

The effect of body condition on hypothalamic and pituitary function in post-partum suckled beef cows was studied. Thirty-eight Blue-Grey cows were calved at a body condition score of either 2·35 (L) or 2·80 (H), fed to maintain live weight and body condition thereafter and ovariectomized at either 5 or 9 weeks post partum. The H cows had higher LH pulse frequencies before ovariectomy (0·36 v. 0·28 pulses per h; P < 0·05) and 15 days after ovariectomy (0·86 v. 0·72 pulses per h; P < 0·01), indicating a direct effect of body condition on GnRH release from the hypothalamus. Body condition had no effect on the ability of the pituitary to release LH in response to a physiological dose (2·5 u.g) of GnRH in entire or ovariectomized cows at 5 or 9 weeks post partum. The magnitude of the increase in circulating levels of LH following GnRH injection was greater at 9 weeks compared with 5 weeks post partum (2·23 v. 1·73 u.g/1; P < 0·001) in entire cows, but there was no difference between 5 and 9 weeks in ovariectomized cows. Following ovariectomy there was a 2·5-fold increase in LH pulse frequency within 15 days and LH pulse frequency approached 1 pulse per h in all treatments groups. It is concluded that both the hypothalamus and the pituitary are capable of functioning normally by 5 weeks post partum in suckled beef cows, that the pulsatile release of GnRH from the hypothalamus is inhibited, possibly due to a very high sensitivity to oestradiol, and that the sensitivity of the pituitary to the negative feedback effect of oestradiol may decrease with time post partum.

In each of two experiments, 36 3 to 5-day-old dairy calves (male and female), were allotted to one of three groups: warm housing, milk feeding in teat-buckets twice a day (group 1); warm housing and computer-controlled milk feeding (group 2); and cold housing and computer-controlled milk feeding (group 3). The experiments were conducted from September until February. The daily gain in the first 4 weeks was lower for the calves in group 3 in both experiments and for calves in group 2 in experiment 2 because of lower food intake in this period. This was compensated for by an increased gain later. In spite of the different method of milk feeding, the activity rhythm was nearly equal among groups, but at week 6 and 10 the calves in group 1 spent more time with the head over the feeding table than the calves in the two other groups. The number of unrewarded visits per calf to the milk feeding station decreased from over 30 at week 4 to around 20 shortly before weaning. The frequency of sucking/licking pen-mates was almost negligible in all groups. In order to reduce the heat loss, the frequency of calves lying with body contact clearly increased by decreasing ambient temperature in cold housing.

The objective of this work was to determine the rumen fermentation characteristics of maize land races used as forage in central Mexico. In vitro gas production (ml per 200 mg dry matter (DM)) incubations were carried out, and cumulative gas volumes were fitted to the Krishnamoorthy et al. (1991) model. The trial used a split-plot design with cultivation practices associated with maize colour (COL) as the main plot with three levels: white, yellow and black maize; growing periods (PER) were the split plots where PER1, PER2 and PER3 represented the first, second and third periods, respectively and two contrasting zones (Z1=valley and Z2=mountain) were used as blocking factors. The principal effects observed were associated with the maturity of the plants and potential gas production increased ( P<0·05) in stems (PER1=51·8, PER2=56·3, PER3=58·4 ml per 200 mg DM) and in whole plant (PER1=60·9, PER2=60·8, PER3=70·9 ml per 200 mg DM). An inverse effect was observed with fermentation rates in leaves ( P<0·01) with 0·061, 0·053 and 0·0509 (per h) and in whole plant ( P<0·05) with 0·068, 0·057, 0·050 (per h) in PER1, PER2 and PER3 respectively. The digestibility of the neutral-detergent fibre (NDF) decreased with maturity especially in leaves ( P<0·05) with values of 0·71, 0·67 and 0·66 g/kg; in rachis ( P<0·01) 0·75, 0·72, and 0·65 in PER1, PER2 and PER3 respectively. The NDF content in leaves in leaves (668, 705 and 713 g/kg DM for PER1, PER2 and PER3, respectively), stems (580, 594 and 644 g/kg DM) and, husk (663, 774 and, 808 g/kg DM) increased ( P<0·05) with increasing plant maturity, rachis were significantly different between periods ( P<0·01). The structure with the best nutritive characteristics was the husk, because it had the lowest fibre contents, especially in acid-detergent lignin, with values of 22·6, 28·6 and 37·6 g/kg DM in PER1, PER2 and PER3, respectively.

Four groups of Scottish Blackface ewe lambs were reared in the period 11–52 weeks old under different regimes. The regimes differed in the age of the lambs at which they were separated from their dams and whether having been separated they were together in a field and/or penned together n i a sheep shed.

These regimes caused differences in social behaviour among the four groups and also resulted in the groups adopting different parts (home ranges) of an enclosed 350 acre hill pasture. The various home ranges within the pasture are dissimilar environments and it is argued that home range and method-of-rearing effects will be confounded making statistical comparisons between the different rearing treatments impossible.

Investigations utilizing a total number of 3998 farrowings from 1558 sows on two farms have shown a frequency of puerperal diseases (periparturient hypogalactia syndrome=PHS) of 32·7% and 27·0% respectively with significant differences between gilts and sows. Sows without PHS after farrowing (farm A) had a lower frequency of animals without oestrus after weaning of the piglets (0·3 V. 1·1%), a lower rate of late onset of oestrus (3·4% V. 5·9%, P<0·05), fewer sows had abortions (0·9 V. 2·3%, P<0·05) and a lower mortality rate (1·2 V. 4·1%, P<0·05) compared with sows which contracted puerperal diseases. The return rate was significantly lower in sows without PHS (12·4%, 16·1% in herds A and B) when compared with sows with puerperal diseases (15·8%, 21·7%, P<0·05). Also, the litter size of live born piglets was lower in sows with PHS when compared with healthy sows (farm A: 10·42 V. 10·66, P>0·05; farm B: 10·44 V. 10·80, P<0·05)

Finding ways of increasing the efficiency of production systems is a key issue of sustainability. System efficiency is based on long-term individual efficiency, which is highly variable and management driven. To study the effects of management on herd and individual efficiency, we developed the model simulation of goat herd management (SIGHMA). This dynamic model is individual-based and represents the interactions between technical operations (relative to replacement, reproduction and feeding) and individual biological processes (performance dynamics based on energy partitioning and production potential). It simulates outputs at both herd and goat levels over 20 years. A farmer’s production project (i.e. a targeted milk production pattern) is represented by configuring the herd into female groups reflecting the organisation of kidding periods. Each group is managed by discrete events applying decision rules to simulate the carrying out of technical operations. The animal level is represented by a set of individual goat models. Each model simulates a goat’s biological dynamics through its productive life. It integrates the variability of biological responses driven by genetic scaling parameters (milk production potential and mature body weight), by the regulations of energy partitioning among physiological functions and by responses to diet energy defined by the feeding strategy. A sensitivity analysis shows that herd efficiency was mainly affected by feeding management and to a lesser extent by the herd production potential. The same effects were observed on herd milk feed costs with an even lower difference between production potential and feeding management. SIGHMA was used in a virtual experiment to observe the effects of feeding strategies on herd and individual performances. We found that overfeeding led to a herd production increase and a feed cost decrease. However, this apparent increase in efficiency at the herd level (as feed cost decreased) was related to goats that had directed energy towards body reserves. Such a process is not efficient as far as feed conversion is concerned. The underfeeding strategy led to production decrease and to a slight feed cost decrease. This apparent increase in efficiency was related to goats that had mobilised their reserves to sustain production. Our results highlight the interest of using SIGHMA to study the underlying processes affecting herd performance and analyse the role of individual variability regarding herd response to management. It opens perspectives to further quantify the link between individual variability, herd performance and management and thus further our understanding of livestock farming systems.