Seasonal reproduction patterns are typically observed in small ruminants and are a major limitation for production efficiency in most meat- and dairy-type production systems. Indeed, selection for reduced seasonality could be an appealing strategy for the small ruminant industry worldwide, although its genetic background has been poorly analyzed. One of the main limitations relied on the availability of appropriate analytical tools to cope with the circular (i.e. year-round) pattern of lambing and kidding data. The recent development of a heteroskedastic circular mixed model provided the statistical tool to go deeply into the knowledge of seasonality in small ruminants. In this study, 26 005 lambing distribution records from 4764 Ripollesa ewes collected in 20 purebred flocks were analyzed. The model accounted for systematic (lambing interval and ewe age), permanent environmental (flock-year-season and ewe) and additive genetic sources of variation influencing both mean and dispersion pattern (i.e. heteroskedasticity). Systematic effects suggested that first-lambing ewes and short lambing intervals delayed lambing date (~30 days) and increased dispersion of the lambing period. Nevertheless, this was partially compensated by ewe age, given that youngest females tended to concentrate the lambing peak. Flock-year-season, permanent ewe and additive genetic sources of variation reached moderate variance components for direct (and residual) effects on lambing distribution, they being 0.119 (0.156), 0.092 (0.132) and 0.195 (0.170) radians2, respectively. Moreover, all 95% credibility intervals were placed far from the null estimate. Covariances between direct and residual effects where high and positive for additive genetic (posterior mean, 0.814) and permanent ewe effects (posterior mean, 0.917), whereas it was not relevant for flock-year-season. Selection for direct additive genetic effects should be able to advance or delay the lambing peak, whereas selection applied on residual additive genetic effects should increase or reduce seasonality (i.e. concentrate or flatten the lambing peak). Moreover, the positive and relevant genetic covariance between direct and residual effects also suggested correlated genetic responses. As example, genetic selection for earlier lambing peaks must also reduce seasonality, whereas selection for narrower lambing seasons may originate a delay in the lambing peak. These results must be viewed as the first attempt to analyze systematic, environmental and genetic sources of variation of lambing distribution within the circular paradigm, they providing a reliable characterization of these effects within the context of an heteroskedastic model.

Over a 15-year period 1011 calving intervals from 187 Brahman (B) cows and 687 calving intervals from 146 Santa Gertrudis (SG) were examined. Year of calving significantly affected intervals in both breeds. Season of calving and parity of dam were both important in SG. Longer intervals were seen in B than SG (437 v. 406 days). Repeatability of calving interval was low (< 0·02). The average life-time calving interval was significantly related to total calf production in that cows with shorter mean intervals had more calves in their lifetime.

Knowing how energy intake is partitioned between maintenance, growth and egg production (EP) of birds makes it possible to structure models and recommend energy intakes based on differences in the BW, weight gain (WG) and EP on commercial quail farms. This research was a dose-response study to re-evaluate the energy partition for Japanese quails in the EP phase, based on the dilution technique to modify the retained energy (RE) of the birds. A total of 300 VICAMI® Japanese quail, housed in climatic chambers, were used from 16 weeks of age, with averages for BW of 185 g and EP of 78%, for 10 weeks. To modify the RE in the bird’s body, a qualitative dilution of dietary energy was used. Ten treatments (metabolisable energy levels) were distributed in completely randomised units, with six replicates of five quails per experimental unit. Metabolisable energy intake (MEI), egg mass (EM) and RE were expressed in kJ/kg0.67. The utilisation efficiency (kt) was estimated from the relationship between RE and MEI. The metabolisable energy for maintenance was given by RE = 0. The net energy requirement for WG was obtained from the relationship between RE in the BW as a function of the BW. The utilisation efficiency for EP (ko) was obtained from the relationship between EM and RE corrected MEI for maintenance and WG. Based on these efficiencies, the requirements for WG and EM were calculated. The energy intake by Japanese quails was partitioned according to the model: MEI = 569.8 × BW0.67 + 22 × WG + 13 × EM. The current study provides procedures and methods designed for quails as well as a simple and flexible model that can be quickly adopted by technicians and poultry companies.

Records on total of 1746 calvings of principally Milking Criollos and their crosses were collected between 1972 and 1990 at the experiment station of the Mexican Association of Animal Production on the Gulf Coast of Mexico. Traits of interest were 305-day milk yield, days in lactation, number of services per lactation (raised to power 1/2), age at first calving and lifetime milk yield. Data were analysed by restricted maximum likelihood (REML) under an individual animal model based on 584 animals of which 146 were female ancestors and 35 were male ancestors. Heritabilities of 305-day milk and age at first calving were 0·17 and 0·07, respectively, but heritabilities of other traits were close to zero. Genetic trend in the Milking Criollos for 305-day milk was small and not significant (0·76 (s.e. 2·38) kg/year). Of crosses with Criollo sires, those involving Holstein and Canadienne breeding had highest 305-day and lifetime milk yields and those involving Brown Swiss and native Mexican (mostly Oaxaca) had lowest yields. Jersey crosses were intermediate for 305-day yield. The F1 Criollo × Jersey cross had highest lifetime yield, but backcrosses involving Jersey breeding were poor for lifetime milk. Additive breed effects for Jersey and Canadienne, relative to Milking Criollo, were 88 (s.e. 91) and 227 (s.e. 74) kg 305-day milk, respectively. Heterosis was 144 (s.e. 55) kg (11·6%) for 305-day milk, 16–4 (s.e. 9·6) (5·0%) for days in milk, −0·107 (s.e. 0–042) (7·7%) for number of services per lactation raised to power 1/2, −25·6 (s.e. 41·4) days (2•3%) for age at first calving and 1789 (s.e. 664) kg (60·0%) for lifetime milk. A plan was designed to develop a nucleus breeding scheme utilizing multiple ovulation and embryo transfer technology (MOET) for the genetic improvement of the Milking Criollo breed in Mexico.

Eighty calves of both sexes, 4 months of age, of two lines, differing in genetic merit for fat plus protein production by 70 kg per 305-day lactation, were given one of four diets differing in protein content to give an estimated range of protein intakes from 299 to 530 g/day. After 21 days the calves were fasted for 72 h. Samples of blood were taken before and after feeding in the morning and afternoon prior to fasting, seven further samples were taken throughout the fast and five samples were taken ranging from 0·5 to 7·5 h after food was re-introduced. The samples were analysed for concentrations of urea, free fatty acids (FFA), glucose, triglyceride and f5-hydroxybutyrate.

No association between metabolite concentrations and predicted breeding value (PBV) were found at any stage of the trial except for the effect of feeding on FFA concentration, the rate of increase of FFA during the fast and its ultimate concentration. These associations with FFA depended on the sex of the calf and were either absent or less marked in males. The results strengthen the possibility that FFA concentrations during fasting are related to PBV in females, and that sexual dimorphism may explain differing conclusions amongst previous trials.

The magnitude of the estimate of coheritability of urea concentration during fasting with PBV, pooled across experiments, is reduced from -0·193 to -0·066 (s.e. 0·037) by inclusion of these results. However, heterogeneity between experiments is evident and remains to be explained. This suggests that urea concentrations are not consistent predictors of genetic merit and cannot be considered to be reliable for use in practice.

This study examined whether a prolonged anoestrus had any long-term effect on subsequent fertility of cows and estimated the relationship between repletion and resumption of reproductive activity. Twelve low body-condition, non-milking, non-cycling (depletion state) F1 crossbred dairy cows (Friesian × Boron and Simmental × Boran) were stratified to two diets (H: natural grass hay offered ad libitum and mineral lick +3 kg concentrate, and H + P: H + 7 h/day natural pasture grazing) according to parity, body weight, body condition score and calving intervals. Daily dry-matter intake was similar between cows on the two diets, but total intake of nitrogen was proportionately about 0·10 greater for cows with access to pasture. The calculated metabolizable energy intake was more than twice the estimated maintenance requirement for cows on both diets. Live weights increased from depletion to ovulation, to oestrus and to conception, but were not significantly different between cows on both diets. Body condition score increased from depletion time to first oestrus and to repletion and was greater for H + P than for H cows at first oestrus and at conception. After an average of 45 days of repletion, cows were already ovulating with no significant differences between cows on either diet. Days to onset of oestrus were 83 and 44 days for diet H and H + P, respectively. Time to conception was similar between coivs on both diets. Conception occurred when cows on H and H + P diets had recovered proportionately 0·51 and 0·58 of their live-weight and 0·84 and 1·27 of their body condition loss, respectively. Interval to repletion weight was 178 and 139 days for cows on the H and H + P diet, respectively. Cows subjected to an exceptionally long depletion period were able to resume ovarian cyclic activity and to conceive in less than 3 months when given twice maintenance requirements. These results have important management implication for on-farm situations in the tropics where fluctuations of food availability and quality occur.

Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged about 5 months, were divided on the basis of live weight such that group G1 contained the 16 lightest lambs and group G2 the 16 heaviest lambs. Lambs in group G1 were subdivided equally at random to be either sham-implanted controls (group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (OE) (group T1) at 24 kg initial live weight. Lambs in group G2 were also subdivided into two groups (C2 and T2) and similarly treated approximately 1 month later at 37 kg initial live weight. Animals were offered ad libitum, a diet containing an estimated 12·5 MJ metabolizable energy and 140 g crude protein per kg dry matter. The experimental treatments lasted for 60 days.

Samples of pre-heparin plasma were analysed for free fatty acid (FFA) and triglycerides (TG). Post-heparin plasma was analysed for lipoprotein lipase (LPL) activity. Samples of subcutaneous (SCAT), perinephric (PNAT), mesenteric (MAT) and intermuscular (IMAT) adipose tissue, liver and muscle, taken immediately post mortem, were analysed for total lipid concentration and fatty acid composition. Comparisons were made for the main effects of hormonal treatment and live weight.

Plasma FFA concentrations in heavier lambs (group G2) were significantly higher than in group G1 from week 1 pre-implantation to week 3 post implantation. Compared with group G1, animals in group G2 had significantly higher plasma TG concentrations at weeks 1, 2, 5 and 8 when data was analysed using pre-implantation values as covariates. The lipid concentration was lower in group G1 than in group G2. In group G1 compared with group G2 there were greater proportions of C12:0 and C18:2 in SCAT and C16:1 in PNAT and lesser proportions of C18:0 in SCAT and PNAT.

Significant effects due to hormonal treatment were recorded for plasma TG at weeks 1, 5, 6, 7 and 8 mainly due to increases in group T1 compared with group C1. Hormonal treatment increased the proportions of C12:0, C15:0, C16:1 and C18:1 in SCAT and C16:1 and C18:1 in IMAT; reduced the proportions of C16:0 and C18:0 in SCAT and C18:0 in MAT and IMAT and reduced the ratio of saturated to unsaturated fatty acids in SCAT and IMAT and to a lesser extent in MAT.

A genotype-environment interaction experiment was carried out on a total of 140 pigs. Three genotypes, produced by mating an inbred boar of each of the Large White, Landrace and Wessex Saddleback breeds to Large White sows, were fattened on conventional rations and on a high growth ration with 10% fat and growth promoting additives.

The high growth ration increased growth rate by 34% and improved food conversion ratio by 26% and gave a higher dressing-out percentage, but produced shorter and fatter carcasses. No significant genotype-environment interactions were found for growth rate or food conversion. A significant interaction was found for streak thickness but not for other carcass measurements.

An on-farm study was conducted over a 12-year period (1979 through 1990) at four locations in the subhumid zone of Nigeria to estimate levels of performance of Bunaji cattle and to examine factors affecting productivity in these production systems. Average weight at birth, at 9 months and at 12 months were 19·6 kg, 76·2 kg and 93·1 kg, respectively. Average daily gain between birth and 9 months was 211 g/day. The corresponding figure between 9 months and 12 months was 176 g/day. Cumulative calf mortality at 9 months and at 12 months were proportionately 0·14 and 0·15, respectively. Mean age at first calving was 62·5 months while interval between consecutive calvings averaged 22·5 months. Mean daily milk offtake was 510 ml. Mean length of offtake period varied substantially between locations ranging from 339 days in Kurmin Biri to 425 days in Madauchi. Lactation milk offtake was estimated at between 200 and 260 I. Peri-urban Madauchi had the highest daily milk offtake, the longest milk extraction period but the poorest calf growth and survival rates. Locations with low milk offtake had superior calf performance both in terms of growth and survival. Calves born in late wet and early dry seasons had superior growth and survival rates. Most calvings occurred in the dry season mainly because of the effect of season on conception rates. There was a tendency towards improved productivity on a per-animal basis over the years. This ivas so for age at first calving, calving interval, calf survival and milk offtake. Improved reproductive performance provided opportunity for higher offtakes. However, growth between 9 months and 12 months and weight at 12 months declined during the study period.

1. A growth trial was carried out using 24 British Friesian steers given diets containing (1) 100%, (2) 60%, (3) 40% and (4) 0% concentrates and chopped dried grass up to 100%.

2. Daily dry-matter intake was significantly lower for steers on Treatment 1 than for steers on the other three treatments.

3. Rate of live-weight gain declined from 1·18 to 0·88 kg/day and carcass gain from 625 to 430 g/day between steers on Treatments 1 and 4.

4. Killing-out percentage dropped from 55·3% (1) to 51·9% (4) and the 8th-10th rib from steers on Treatments 3 and 4 contained significantly more crude protein and less ether-extractable matter than ribs from steers on Treatments 1 and 2.

Although sheep are known to be seasonal breeders and give birth in winter, not all of them follow this trend. A few breeds can be mated and give birth all year round, meaning that mothers and neonates will have to face contrasting climatic conditions. The aim of this study was to test whether lambing season affects maternal and neonatal behaviors in D’man sheep. During four different lambing seasons (winter, autumn, summer and spring), periparturient ewes (n = 111) and their lambs (n = 213) were kept under 24-h-video surveillance in order to record postpartum behaviors. Mother-young preference was tested around 48 h after parturition. Lamb vigor was studied by the determination of birth weight, early postnatal behavior and rectal temperature at birth and 48 h later. Litter expulsion time was not affected by lambing season, but birth weight was biased against summer and winter born lambs. Ewes provided a higher intensity of care to their offspring in winter: latency for grooming was shorter and time spent grooming was longer compared to lambing in spring and summer (P = 0.01 in all cases). On the other hand, lambs were the most active in spring as they were faster to extend their hind legs (P = 0.01), stand up (P = 0.04) and reach the udder (P = 0.04). Rectal temperature at 48 h was affected by season of birth (P < 0.001) with higher values observed in summer. Glycemia variation between birth and 48 h was the lowest in spring born lambs and plasma levels increased less in spring born lambs than in winter (P < 0.0001), autumn (P < 0.0001) and summer born lambs (P < 0.0001). In the choice test, mothers clearly preferred their own young and no season effect was detected except that in the first minute of the test they spent less time near their own young in winter than in the other seasons (P = 0.04). Lambs also chose their mother successfully without any major effect of the season however, but winter born lambs were the least vocal (P = 0.01). Overall, this study show that maternal care, lamb behavior and vigor vary lightly according to seasons, albeit not in a consistent manner. In conclusion, a season is no more detrimental than another for the onset of mother-young relationships.

In reporting on the Charolais importation of 1962, Edwards et al. (1966) noted different average growth rates of calves born at different times of the year: spring born calves for instance were slowest at 1·67 lb/day and autumn born calves fastest at 1–80 lb/day. The Beef Recording Association (1967) has also reported that growth rates for castrated males in commercial intensive cereal feeding beef lots consistently reflected seasonal effects on growth. In both cases the data were derived under conditions which did not permit detailed investigation of seasonal changes in the growth curve.

The relative importance of the breed of lamb and the breed of dam in determining the copper status of the lamb until 24 weeks of age was investigated by transferring embryos within and reciprocally between Scottish Blackface and Welsh Mountain ewes. A diet low in Cu (2·4 mg/kg dry matter (DM) was fed both to the ewes from mating onward and subsequently to their lambs.

At birth, lambs with Welsh dams had greater concentrations of Cu in their livers than lambs with Blackface dams. This difference, although reduced, still remained at 9 weeks of age (weaning), when lambs with Welsh dams also had greater concentrations of Cu in plasma.

By 24 weeks of age, Welsh lambs, irrespective of their dams' breed, had greater concentrations of Cu in both liver and plasma than Blackface lambs, although the average Cu concentration in the liver was below 10 mg/kg DM in both breeds.

Results are also given for concentrations of Cu in kidney, brain and milk.

The experiment suggests the importance of maternal breed in determining the susceptibility, both of the foetus and of the young lamb to problems associated with Cu deficiency.

1. Three measurements on both sides of 15 carcasses and 5 additional measurements on bot h sides of 6 carcasses were taken in duplicate by 3 observers working independently. The carcasses, which ranged in weight from 520 to 884 lb., were measured from 2 to 6 hr. after slaughter while on the hook in the chill-room of a slaughter-house.

2. Length of body and loin were the measurements which could be taken the most consistently, whereas the 2 depth measurements and the length of tibia were the least repeatable.

3. For 2 measurements, there were marked differences between observers i n the average differences between sides. In all carcass investigations, measurements should be taken on both sides and averaged.

4. For all measurements, except the length of body and loin, there were differences in the average values found by the 3 observers.

5. It is suggested that to achieve a satisfactory degree of repeatability, slight redefinition and clarification of the points of reference is required for some measurements, whereas others may have to be discarded.

We examined short- and long-term effects of high milking frequency (HMF) for the first 21 days of lactation. The study included 122 Israeli Holstein cows – 32 pregnant heifers, 40 cows in second lactation and 50 cows in >second lactation. Heifers were paired according to predicted transmitting ability and cows according to energy-corrected milk (ECM) production, age, days in milk and expected calving date. Thin cows (body condition score <2.75) were not included. One cow from each pair was arbitrarily allocated to a control group milked three times daily (3× milking cows) and the counterpart to an experimental group milked six times daily for the first 21 days of lactation and then three times daily for the rest of the lactation (6× milking cows). During the first 21 days of lactation, 6× milking cows produced 9.3 kg more milk (26.5%) and 7.16 kg more ECM (19%) than the 3× milking cows. The higher milk production persisted throughout the entire lactation (305 days), as reflected by treatment×age interaction showing higher milk production for the first and second (7%) but not >second lactation cows relative to their control counterparts (−0.37%); ECM production was also higher in 6× milking first and second lactation (7.6% and 5%, respectively) but not for >second lactation cows. Furthermore, HMF had long-lasting effects, expressed as significantly higher milk production through the succeeding lactation in the previous first lactation cows (10%); a tendency toward significance in the second lactation cows relative to the controls (4.7%), but a deleterious effect on the >second lactation cows, reflected by lower milk production (−5.25%) than in controls; similar patterns were found for the ECM. For the entire 305 days of lactation, fat and protein yields were higher for first and second lactation cows, whereas protein yield for >second lactation cows was lower in the 6× milking v. control group. Given that HMF during the first 21 days of first or second lactation increases milk and ECM yields throughout the concurrent and successive lactation with no adverse effect on energy balance, mastitis, metabolic diseases or reproduction, it seems to be economically beneficial. However, caution should be paid for >second lactation cows due to absence of significant effect in the entire of the first HMF applied lactation and the deleterious effect in the succeeding lactation.

Each individual in the population has a distinct maximum growth potential, and the growth curve may vary depending on the response to nutrient intake, growth phase and variability among animals. The present study aimed to (1) model weight gain (WG) response to methionine+cystine (Met+Cys) supply using different mathematical functions, (2) identify functions that better fit the growth responses of pullets, (3) determine the Met+Cys requirements that maximize WG based on breeding standards and (4) partition the Met+Cys requirements for WG and maintenance. Three trials were performed using 1448 laying-type pullets. We adopted a completely randomized design with eight treatments and six replicates. The first trial (2 to 6 weeks, P1) used 15 pullets per experimental unit. The second and third trials (8 to 12 weeks, P2; 14 to 18 weeks, P3) were used eight pullets per replicate. The Met+Cys levels were obtained using a dilution technique. The mathematical functions used to describe WG responses to Met+Cys intake were broken line, broken line with curvilinear ascendancy, Michaelis–Menten, saturation kinetics and three logistic and three exponential models. Models were selected using the Bayesian information criterion and evaluated by residual analysis. It was possible to model the responses using the studied functions. The best functions were obtained by logistic and sigmoidal models in P1 and P2, and with the broken line by the curvilinear ascendancy model in P3. The Met+Cys intake that determined the maximum potential for WG (WGmax) in P1, P2 and P3 were 313, 381 and 318 mg/day, respectively. The Met+Cys requirements for WG were 20, 22 and 27 mg/g, and for maintenance were 214, 53 and 30 mg/kgBW0.75 for P1, P2 and P3, respectively.

A study was made of the levels of oestrous activity of two indigenous breeds of sheep (Somali and Nandi) and three exotic breeds of sheep (Merino, Karakul and New Zealand Romney Marsh) over a period of 3 years, in an equatorial environment. Breed was the only significant source of variation for the length of the oestrous cycle (P < 0·01). The mean lengths of the oestrous cycle were 17·2 (s.d. 3·21), 17·5 (s.d. 2·24), 17·9 (s.d. 2·99), 17·5 (s.d. 2·57) and 16·5 (s.d. 3·41) days for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively.

The mean percentage of ewes of the different breeds showing oestrus in 20-day periods were 69·8 (s.d. 22·57), 49·9 (s.d. 18·67), 63·4 (s.d. 25·70), 79·2 (s.d. 20·30) and 33·2 (s.d. 23·50) % for the Somali, Nandi, Merino, Karakul and Romney Marsh breeds, respectively. Time-series analysis did not detect any evidence of seasonal variation in oestrous activity, although there was an indication that the Merino and Romney Marsh breeds showed a marked increase in oestrous activity following, the introduction of rams. It was concluded that the variation in level of oestrous activity was short term and random.

1. The effects of supplementing diets containing 10% or 17% crude protein wheat, vitamins and minerals with the limiting amino acids were studied with growing Large White x Landrace pigs. Performance was measured in terms of growth rate, feed conversion, carcass measurements, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.

2. With diets based on wheat containing 17% crude protein, a lysine supplement gave a slightly higher growth rate and a slightly lower feed conversion ratio than when fish meal and meat meal was the supplement.

3. With diets based on wheat containing 10% crude protein, performance was significantly poorer when the diet was supplemented with the four most limiting amino acids (lysine, threonine, valine, methionine) than with fish meal and meat meal. Meat meal and soya bean meal appeared to be a good source of the limiting amino acids, other than lysine, when added to a diet based on wheat containing 10% crude protein.

4. Eye-muscle area was lower and backfat thickness greater when diets based on wheat containing 10% crude protein were unsupplemented or supplemented with lysine than when they were supplemented with protein or with the four most limiting amino acids. However, no significant differences in backfat thickness were obtained between similar comparisons when the wheat contained 17% crude protein.

The use of antibiotics as performance enhancers in animal feeding is declining, so Lippia gracilis Schauer essential oil (LGSEO) could be used as a potential substitute for the conventionally used growth promoters. The LGSEO contains components such as carvacrol and thymol, which kill and/or control pathogenic bacteria, increase population of beneficial organisms, act against oxidative processes and onto nutrient digestibility and absorption. The aim of this study was to investigate the action and the effects of LGSEO as a growth promoter in the diet of Japanese quail by examining their productive performance, intestinal microbiology, blood biochemical parameters, hepatic thiobarbituric acid reactive substances (TBARS) content and intestinal gene expression. A total of 252 two-day-old quail (Coturnix coturnix japonica) were assigned to 3 treatments in 7 replicates, using 12 birds per experimental unit. The treatments consisted of a basal diet, basal diet + LGSEO at 400 mg/kg of diet and basal diet + chemical antimicrobial (bacitracin methylene disalicylate) at 500 mg/kg of diet. The experimental period was 34 days. The highest feed intake (P < 0.01) was found in the group receiving the conventional antimicrobial, whereas the best feed conversion (P < 0.01) was shown by the animals receiving LGSEO. Escherichia coli growth was restricted in the quail receiving the growth promoters. Salmonella spp. growth was controlled by the treatment containing the conventional antimicrobial. There was no difference between the treatments (P > 0.05) for the concentration of aspartate aminotransferase and alanine aminotransferase enzymes in the blood or hepatic TBARS content. Birds receiving negative-control treatment exhibited a higher expression of sodium-glucose cotransporter (SGLT1), while those receiving the treatment with essential oil showed lower catalase (CAT) and glutathione peroxidase (GPX7) expressions compared to the conventional antimicrobial and control groups, respectively. Lippia gracilis Schauer essential oil is a powerful performance enhancer for Japanese quail by virtue of its abilities to improve their intestinal environment, balance the microbial population and reduce energy expenditure for oxidative processes.

Previous studies examining the effect of age on gilt reproduction have generally failed to discriminate between chronological (i.e. days) and physiological age (i.e. number of oestrous cycles experienced) and the importance of each factor remains unclear in the pig. The present investigation tested the hypothesis that the physiological age at which gilts are bred in a dynamic service system (DSS) affects their reproductive behaviour and performance. A hundred and ninety gilts were randomly allocated between two treatments. They were introduced into the service pens of a DSS to be bred at the same age (215 days) but either at second (2H; no. = 96) or third (3H;no. = 94) post-pubertal heat period. The sexual behaviour of half of them was continuously recorded over a 13-week period and reproductive data from all the gilts were collected. Gilts of 2H treatment were significantly heavier at entry into the service pens (123 v. 119 kg; P < 0·05) than 3H gilts, but there was no significant difference in their backfat thickness. Treatment failed to affect the quality and frequency of mating attempts (MAs) gilts received or oestrus duration. Conception rate to first oestrus in the DSS (82%) was not affected by treatment. Litter size and number of piglets born alive was similar for 3H and 2H gilts (12·0 v. 11·7, s.e.d. 0·40 and 11·5 v. 11·0, s.e.d. 0·4 respectively; all P > 0·05). It is concluded that the reproductive behaviour and performance of gilts that had experienced either two or three oestrous cycles prior to mating at a constant age does not differ significantly in a DSS. More studies are needed in order to clarify the possible interactive influence of repeated and frequent services, which are common in a DSS, on gilt reproduction.