High body condition score combined with a reduced lambing to ram introduction interval improves the short-term ovarian response of milking Lacaune ewes to the male effect.

The male effect is an effective natural technique to induce off-season ovulation and ultimately mating or artificial insemination in small ruminants. It constitutes an alternative to hormonal treatments in conventional breeding systems and, to shift and organise the yearly production cycle, is currently the only solution complying with European organic standards. However, its associated performances are still heterogeneous, both in terms of the global response and the extent of reproductive synchronisation of the females, due to complex interactions with environmental factors that limit its use on commercial farms. This study was carried out on a French organic farm under commercial conditions to investigate, in the field and across five consecutive years, the main parameters affecting the early ovarian response to a ram effect on Lacaune dairy ewes. While the within-year binary logistic regressions yielded contrasting results, the cross-year mixed-effect binary logistic regression models clearly showed that parameters associated with the nutritional state of the animals have a profound influence on the ovarian response of the ewes. Indeed, the probabilities of a spontaneous resumption of ovarian activity before the ram effect and of an early ovarian response to the ram effect were positively associated with the body condition score, total milk production and the age of the animals, while being negatively associated with the milk production level at the 3rd milk recording. The probabilities of a spontaneous resumption of ovarian activity before the ram effect were positively associated with the interval between lambing and the introduction of the rams. Altogether, these results indicate that the ovarian performances in response to a male effect follow a bell-curve pattern with optimal performances depending upon a complex combination between photoperiodic and nutritional cues. Regarding these latter, this study highlights the major contribution of body reserves and energy balance dynamics.

An assessment of Walk-over-Weighing to estimate short-term individual forage intake in sheep.

The main limitation for determining feed efficiency of freely grazing ruminants is measurement of daily individual feed intake. This paper describes an investigation that assessed a method for estimating intake of forage based on changes in BW of ewes. A total of 24 dry and non-pregnant Romane ewes (12 hoggets, HOG; mean±SD 51.8±2.8 kg BW; body condition score (BCS) 2.6±0.2; and 12 adults, ADU; 60.4±8.5 kg BW; BCS 2.7±0.8) were selected for the study and moved from their rangeland system to a confined pen with controlled conditions and equipped with individual automatic feeders. The experiment lasted for 28 days (21 days adaptation and 7 days feed intake measurement). Ewes were fed hay and trained to use the electronic feeders (one feeding station per ewe) in which actual daily intake (H intake24) was measured. The pens were designed to maximize movement of trained ewes through an automated Walk-over-Weighing device, by using water and mineral salts as attractants. Total individual intake of hay measured in the automatic feeder at each meal (H intake) was compared with indirect estimates of feed intake determined using differences in the BW of the ewes (∆BW) before and 1 h following morning and afternoon feeding at fixed times. The BW, BCS, H intake, H intake24, as well as plasma non-esterified fatty acids (NEFA), glucose and insulin profiles were determined. The BW was higher in ADU v. HOG but BCS was not affected by parity. The H intake24 was affected by day of experiment as a consequence of reduced availability and intake of water on one day. Plasma glucose, NEFA and insulin were not affected by parity or day of experiment. The H Intake was and ∆BW tended to be higher in the morning in HOG, whereas H intake was and ∆BW tended to be higher in ADU at the afternoon meal. Irrespective of parity or feeding time, there was very strong correlation (r 2=0.93) between H intake and ∆BW. This relationship confirms that our indirect method of estimating individual forage intake was reliable within the strictly controlled conditions of the present experiment. The method appears suitable for use in short-term intensive group feeding situations, and has potential to be further developed for longer-term forage intake studies, with a view to developing a method for freely grazing ruminants.

An automated method for the evaluation of ram libido in real mating conditions.

We investigated if sexual behaviour of rams can be assessed with an electronic Alpha-Detector (AD) which automatically records mounts of mating rams. To evaluate the rams' libido (i.e. all sexual activities), we used six intact and six vasectomised rams in pen tests in three different seasons (late spring, autumn and early spring). The pen tests consisted of 30-min visual observations of each ram placed in a group of six Merino ewes (three ewes in oestrus and three ewes not in oestrus). In the pen tests, sexual behaviour was recorded and divided into two categories: pre-copulatory and copulatory. For validation purposes, during the pen tests the 12 rams were equipped with the AD and the number of times the 18 oestrous ewes were mounted were counted over a period of 3 days. Of the 1191 mounts visually identified in the six 30-min sessions, 1026 were recorded automatically by the AD (i.e. 94%). The paddock test is an automated method consisting of the same rams wearing an AD and placed in a flock of ~250 Merino ewes on two occasions (late spring (spring 1) and early spring of the following year (spring 2)), their copulatory activities were automatically recorded over a 5-day period. The results of the pen tests in the three seasons revealed no difference between the two types of rams (breeding v. detecting rams). Based on live observations high correlations (r=+0.81, P<0.003 for breeding and r=+0.76, P<0.02 for detecting rams) were found between pre-copulatory and copulatory behaviours. The libido of the two types of rams measured in pen tests showed high repeatability across the three seasons (83 and 75%, P<0.05 for copulatory and pre-copulatory behaviours, respectively). When measured automatically in paddock tests over two consecutive springs, even higher repeatability was observed in both breeding (94%; P<0.01) and detecting rams (97%; P<0.004) in the number of mounts. In addition, high correlations (+0.89

Polyethylene glycol marker measured with NIRS gives a reliable estimate of the rangeland intake of grazing sheep.

Polyethylene glycol (PEG) measured with NIRS is known to be a valuable faecal marker when used in indoor experiments. In order to verify whether it can be used at pasture, an experiment was conducted with two trials. In trial 1, six Romane breed adult dry ewes placed in metabolism cages were fed daily with natural, freshly cut rangeland from a fertilised or unfertilised paddock for 6 weeks. Three ewes did not receive PEG and the three others were dosed with 10 g of PEG in solution form once daily until the end of the experiment to measure in vivo dry matter digestibility and PEG recovery rate for each forage quality. At the same time (trial 2), 15 ewe lambs and 14 lactating adult ewes suckling one or two lambs were allowed to graze together on the same herbage as that cut for indoor ewes. All animals were initially equipped with faecal bags emptied twice daily for collecting total faeces, and eight ewe lambs and seven adults were dosed once daily with 10 g of PEG. Faecal grab samples were collected for 4 to 5 days for each forage quality grazed. Indoor trial 1 showed that PEG had no effect on dry matter intake (DMI) or on digestibility. PEG recovery rates measured on fertilised (77.7%) and unfertilised (82.1%) forage were not different (P>0.05). PEG recovery rates measured at pasture did not differ (P>0.05) between pasture quality and animal type with an average value of 68.9%. Faecal output measured with bags or estimated with PEG and calculated DMI were not different (P>0.05) when PEG recovery rate measured at pasture was used. Conversely, using indoor PEG recovery values, significantly (P<0.05) or tended to overestimate faecal output. In conclusion, PEG could be used as a faecal marker administered at a minimal dose of 1% of DMI with a recovery rate measured under pasture conditions for pasture intake measurements on a group of animals at the same physiological stage but not for individual measurements.

The effects of parity, litter size, physiological state, and milking frequency on the metabolic profile of Lacaune dairy ewes.

Effects of parity (primiparous, PRIM vs multiparous, MULT) and litter size (singletons, SING vs twins, TWIN) on metabolic profiles from 1 wk before lambing to the end of lactation were studied in 48 Lacaune dairy ewes reared in confinement during most of the year and grazed on improved pastures at the end of lactation (summer). Another group of 48 ewes was incorporated during the milking period (ie, from 1 wk after weaning), to measure the effects of milking frequency (1 vs 2 milkings per day) on intake, milk production and composition, and body energy usage. Thus, in a 2 × 2 × 2 factorial design, ewes (n = 96) were allocated to homogeneous groups according to body weight (BW) and body condition score (BCS) and were monitored from late pregnancy to late lactation as a function of parity (PRIM, n = 48; MULT, n = 48), litter size (LSi) (SING, n = 40; TWIN, n = 56) and daily milking frequency (FREQ; milked once, ONE; n = 48; or twice, TWO; n = 48). Individual BW, BCS, plasma metabolites, and metabolic hormones were measured regularly (ie, 9 consecutive sampling dates). The BW was higher in MULT but no differences because of LSi or FREQ were detected at the intra-parity group level. The BCS was higher in MULT and in ewes with SING throughout the experiment. The latter was related to the demands for body reserves mobilization, as expressed by higher nonesterified fatty acids and ß-hydroxybutyrate concentrations in ewes with TWIN from late pregnancy to weaning (35 d postpartum) in both PRIM and MULT ewes. This was consistent with higher insulin in MULT and higher triiodothyronine, leptin and insulin-like growth factor 1 in ewes with SING during this period. Differences in energy balance because of FREQ were evident after interpretation of plasma nonesterified fatty acids, glucose, insulin, and leptin concentration during the milking period. At similar feed intakes, ewes in ONE were in positive balance with regard to TWO. Overall, clear effects of parity, LSi, physiological states, and FREQ on metabolic profiles were found because of differences in nutrient partitioning when combining these experimental factors. Without considering FREQ, changes in metabolic measures in milking period were marginal compared with the periparturient adjustments performed until weaning to compensate energy deficiencies.

Polyethylene glycol compared with ytterbium oxide as a total faecal output marker to predict organic matter intake of dairy ewes fed indoors or at pasture.

Several external markers can be used for estimating total faecal output in view of assessing ruminant intake at pasture. Among them, ytterbium (Yb) has been used for many years in various conditions. Polyethylene glycol (PEG) is a promising external marker because it can be rapidly determined using near-infrared spectroscopy (NIRS). The study consisted of 24 adult lactating dairy ewes over three periods (P1, P2 and P3), fed with three different diets: P1, total mixed ration (TMR); P2, Italian ryegrass (IRG); and P3, pasture. After an adaptation period, the ewes were administered a daily dose of ytterbium oxide (0.35 g/day) and PEG (20 g/day) for 2 weeks. During the last week, the daily organic matter intake (OMIOBS) was measured. Faecal samples were collected at milking time (0800 and 1600 h) to determine marker content, using only samples collected in the morning (PEGm) or by averaging samples (Yb, PEGma). Faecal marker content made it possible to assess total faecal output, either using the two recovery rates for PEG (0.98 or 0.87) or not. The OMIOBS was assessed on the basis of total faeces estimated with Yb (OMIYb) or PEG (OMIPEG), and the digestibility was calculated on the basis of feed analysis. With total TMR (P1), the OMIPEG, corrected with recovery rate (OMIPEGm98) or not corrected (OMIPEGm) was 2.40 kg/day and 2.50 kg/day, respectively, and was not different (P>0.05) from OMIOBS (2.51 kg/day), whereas OMIYb was lower (2.14 kg/day) (P<0.001). With IRG (P2), OMIPEGm98 (1.67 kg/day), OMIPEGm87 (1.51 kg/day) and OMIYb (1.59 kg/day) were not different (P>0.05) from OMIOBS (1.57 kg/day). With pasture (P3), the OMIPEGm (1.54 kg/day) and OMIPEGm98 (1.48 kg/day) were not different (P>0.05) from the OMI assessed from the biomass measurement (1.52 kg/day). The OMIYb (1.36 kg/day) was lower (P<0.05) but not different from OMIPEGm98 and OMIPEGm87. Spearman's rank correlation between OMIOBS and other OMIs (predicted with Yb or PEG P1 and P2) showed that it is possible to rank animals using PEG when there is a sufficiently wide range of OMIOBS (1.65 to 2.8 kg/day in P1) but not within a narrower range (1.47 to 1.72 kg/day in P2). In conclusion, the present study confirms that PEG is a valuable external faecal marker, easy to prepare (solution), administer and determine (NIRS). It can be used to assess intake with numerous animals at pasture, but only for groups, and not to quantitatively estimate individual OMI.

Circannual body reserve dynamics and metabolic profile changes in Romane ewes grazing on rangelands.

Throughout an entire year, 41 Romane ewes reared in an extensive rangeland were used to investigate temporal changes in body reserves (BRs) and profiles of related metabolites and metabolic hormones. Ewes were allocated to homogeneous groups according to BW and BCS and were distributed by parity (primiparous [PRIM], n = 21; multiparous [MULT], n = 20) and litter size (LSi; lambing singletons [SING], n = 21 or TWINS, n = 20). The feeding system was based on rotational grazing of rangeland paddocks and progressive supplementation with hay, silage, and barley at late pregnancy during the winter. Individual BW, BCS, plasma NEFA, ß-hydroxybutyrate (ß-OHB), glucose, insulin, leptin, and triiodothyronine (T3) were monitored at -56, -12, 8, 49, 76, 107, 156, 195, 216, 246, and 301 d relative to lambing. The BR mobilization was observed from late pregnancy to the end of suckling and varied as a function of the ewe energy balance but also because of transitions from fertilized to native rangeland paddocks and by supplementation. Contrarily, BR accretion occurred from weaning, during the dry-off, and until the start of the next pregnancy. Lipolysis was well reflected by NEFA, ß-OHB, and T3 kinetics. Mean BW (but not mean BCS) was affected by parity (MULT > PRIM), whereas both BW and BCS were influenced by LSi (SING > TWINS) but only for MULT. The most drastic BW loss was observed during the mid-suckling period (49 d in milk [DIM]) in all ewes. The lack of effects of LSi in PRIM but not in MULT was also evident in the majority of blood plasma kinetics, which were affected (P < 0.0001) by physiological stage in all ewes. A tendency to ketosis (ß-OHB) was found in ewes nursing TWINS around lambing, irrespective of parity. Glucose concentrations were greater during suckling and dry-off, and a peak (0.96 ± 0.05 g/L) was attained at 156 DIM in MULT nursing TWINS. The highest plasma leptin concentration was observed during the start and the middle of the next pregnancy in MULT (107-216 DIM; 9.6 ± 0.44 ng/mL). In all ewes the physiological stage affected T3, which was affected by LSi just in MULT (from late pregnancy, MULT by SING > MULT by TWINS; 99.91 vs 85.52 ng/dL) and during suckling (111.7 ± 4.18 ng/dL). Lamb BW was affected at birth and weaning by parity (MULT > PRIM) and LSi (SING > TWINS). Overall, temporal changes in BR were directly affected by the transition of physiological states and feeding levels, whereas individual responses were predetermined by parity. In MULT, the reactivity and magnitude of response was influenced by LSi. The whole set of parameters allowed us to detect sensitive and critical periods throughout the entire annual cycle. We thus identified opportunities for improved nutritional management, for example, during physiological states usually underestimated such as early and mid-pregnancy. This work indicates the applicability of long-term studies about BR dynamics in ruminants as a potential component contributing to farm economic resilience.

A method for estimating dry forage intake by sheep using polyethylene glycol as a faecal marker measured with NIRS.

In experiments based on ruminants' individual dry matter intake (DMI) assessment, several external markers can be used to estimate faecal output when total faeces collection is not possible. However, preparation of the markers to be administered and analytical procedures used for marker content determination are time-consuming thus strongly limiting the number of animals involved in the experiments. In this paper, polyethylene glycol (PEG, molecular weight 6000 da) was tested as a faecal marker. Four trials were conducted on dry, non-lactating ewes kept in digestibility crates that allowed individual measurements. The overall experiment was designed to assess the major factors that could lessen the effectiveness of this method, assuming that the use of grab samples of faeces is sufficient. Trial 1 was designed to test two levels of PEG (20 and 40 g/day) administered in two equal amounts. Trial 2 was designed to test the effect of either a single morning (0800 h) dose (20 g/day) or a twice daily administration (0800 and 1600 h) of the same fractionated dose. Trial 3 was designed to test a 20 g/day dose of PEG administered once daily to ewes fed with hays of different qualities: medium (MH) and low (LH). In trial 4, a lower dose of PEG (10 g/day) was administered once a day to ewes fed with fresh oat-vetch forage. It was demonstrated that PEG could be precisely estimated (average prediction error = 3.47 g/kg) with near-infrared reflectance spectroscopy (NIRS). On the basis of the four trials, it has been proved that PEG administration (20 and 40 g/day) did not significantly affect the DMI of ewes fed dry diets (trials 1, 2 and 3), whereas there was an unexpected increase of DMI for ewes fed exclusively with green feed (trial 4) without DM digestibility modification. Providing PEG as a single dose (0800 h) or split into two equal parts (0800 and 1600 h) did not alter the estimated DMI. Considering the interest of grab sampling, there were clear variations of PEG in faeces with higher concentrations observed at 0800 and 1600 h and lower concentrations at 1400 h. Consequently, with PEG (measured with NIRS) administered once and using the grab sampling procedure (morning collection), it is possible to estimate the DMI of dry feeds with good accuracy. For green feeds, more research is needed as the estimated results are still highly variable.

Sustainability of ruminant agriculture in the new context: feeding strategies and features of animal adaptability into the necessary holistic approach.

There are numerous recent studies highlighting sustainability problems for the development of ruminant production systems (RPS) while facing increasing human food necessities and global climate change. Despite the complexity of the context, in our view the main objectives of the ruminants' physiologist should be convergent for both industrialized (IC) and developing countries (DC) in a common and global strategy of advancing knowledge. In DC, this means improving the efficiency of RPS, taking into account the unique possibility of using rangelands. For IC settings, RPS should be revisited in terms of autonomy and environment- friendly feeding and managing practices. Assuming that competition for feed/food use is still a crucial criterion, future ruminant feeding systems (FeSyst) should preferably focus on lignocellulosic sources. According to biome distributions, and the recent increases in volumes of crop residues and their by-products, the annually renewed volumes of these biomasses are considerable. Therefore, we need to redesign our strategies for their efficient utilization at the local level. For this purpose, digestion processes and rumen functioning need to be better understood. The renewed vision of ruminal digestion through the reduction of greenhouse gas emissions is also a key aspect as it is an environmental demand that cannot be ignored. With regard to other ruminants' physiological functions, accumulated knowledge could be mobilized into an integrative approach that puts forward the adaptive capacities of animals to face variability in quantity and quality of supplied feeds. Basically, the reduction of inputs that were traditionally used to ensure FeSyst will need more flexible animals. In that sense, the concepts of homeostasis and teleophorhesis need to be updated and adapted to domestic species and breeds that were until now largely excluded from the dominant productive systems. In conclusion, a more holistic approach of research targets is required in which physiological functions and farmers' practices must converge and respond to each particular situation in an integral, dynamic and flexible conceptual perspective. From a scientific point of view, both for ICs and DCs, a broader range of experimental scenarios should be explored in order to arrive at innovative practices and solutions that respect environmental, ethical and economical issues. The clear challenge is to in evaluate the sustainability of RPSs. This includes, in our opinion, a strong interaction with other disciplines (multi- and trans-disciplinary conception), thus structuring new relevant indicators for the evaluation sustainability.

Rangeland utilization in Mediterranean farming systems.

In the countries surrounding the Mediterranean basin, most of the semi-natural grazing lands are covered by rangelands. Rangelands can be defined as highly heterogeneous natural vegetation communities with high conservation value, growing in harsh environments (poor soils, unfavourable climatic conditions). In the recent socio-economic context, traditional livestock grazing practices that enabled one to reconcile rangeland preservation and animal production no longer apply, especially because they require labour that has become scarce and costly. The consequence is rangeland degradation, due to underutilization in Southern Europe, and overutilization in Northern Africa. We analysed issues raised by rangeland utilization in livestock farming systems of the Mediterranean basin. Based on a review of the scientific literature about rangeland utilization in this area, we argue that the best way to reconcile animal production and rangeland preservation would be to promote management practices allowing animals to express their adaptative capacities in feeding behaviour and productive response. In order to propose management practices adapted to extensive and simplified systems, we conclude that research efforts should focus on: (i) proposing a functional characterization of vegetation heterogeneity at the scale of the vegetation community, (ii) validating the criteria determining animals' foraging behaviour on Mediterranean rangelands, (iii) developing and using simulation models to test management strategies against seasonal and long-term variability in climatic conditions and (iv) evaluating the potential of modern technologies for improving rangeland utilization.

Postcalving factors affecting conception risk in Holstein dairy cows in tropical and sub-tropical conditions.

The objective was to identify postpartum risk factors between nutritional imbalance and health disorders affecting first-service conception risk (FSCR) in 21 commercial Holstein herds in Reunion Island. Multivariate logistic-regression models including herd as a random effect were used to analyze the relationship between FSCR and energy status, nitrogen status, hepatic function, mineral deficiencies, and postpartum health disorders. Two models (A and B) were built on two subsets of data (n=446 and n=863) with risk indicators measured during the first month of lactation and around time of first service, respectively, adjusted for season, breed, parity, origin, milk yield, calving to first service interval (CS1), and type of estrus (spontaneous vs. induced). The averaged conception risk was 0.266+/-0.015 (n=913) (mean+/-S.E.M.). In both models, FSCR was decreased by CS1 < or = 60 d and induced estrus. In model A, FSCR was decreased (p<0.05) for cows with mean cumulative 100 d daily milk yield < or =23 kg/d and >27 kg/d, with losses of body condition score >1.5, and with retained placenta. In model B, FSCR was decreased (p<0.05) for cows inseminated during wet season, previously raised out of the farm as nulliparous, with blood magnesium concentration < or =0.9 mmol/L, and for high-yielding cows (100 d milk yield > 27 kg/d) with glutamate deshydrogenase>17 UI/L. Hence, high-body-lipid mobilization during the first month of lactation was a strong nutritional predictor of low FSCR together with liver damage in high-yielding cows. Interestingly, our models revealed that infertility is better related to nutritional factors than to postpartum health disorders occurrence.

Suitability of electronic mini-boluses for early identification of lambs.

Three types of ceramic mini-boluses, B1 [13.8 g; 10.5 x 51.0 mm (o.d. x length)], B2 (16.2 g; 12.2 x 42.2 mm), and B3 (20.1 g; 11.2 x 56.4 mm), were used to electronically identify as soon as possible after birth a total of 545 lambs of 3 breeds: Ripollesa (meat breed, n = 274), Manchega (dairy breed, n = 129), and Lacaune (dairy breed, n = 142). Boluses were administered by a trained operator using a balling gun or directly by hand. Lambs were also identified with 2 types of plastic ear tags in the left (temporary, 1.5 g) and the right (permanent, 4.1 g) ears. Lamb and identification device performances were checked during suckling (to wk 5 or 7) and fattening. At 24 kg of BW, lambs were slaughtered (n = 385) or kept for breeding (n = 144). No differences in performance were observed between the 2 dairy breeds, and their data were pooled. Minimum BW for bolus administration was lower in dairy than in meat lambs (P < 0.001). Across breeds, B1 and B3 did not differ in lamb age (27 d) and weight (9.2 kg) at administration, but B2 required older and heavier lambs (33 d and 11.1 kg; P < 0.01). Boluses did not affect lamb performance, but final readability at slaughter differed between B1 and B2 (97.7 and 95.2%, respectively) and B3 (100%), and between ear tags (temporary, 98.1; permanent, 100%). Bolus recovery was 100% in all cases, but the proportion of boluses found in the reticulum varied among bolus type (83.3 to 93.8%; P < 0.05). Three B1 (2%) were recovered from the abomasum. In a second experiment, effects of the intermediate mini-bolus (B2) on diet digestibility were evaluated. Digestibility of control and bolus-administered, Manchega ram lambs (14.9 kg of BW; n = 8) fed ad libitum with 2 pelleted concentrates and barley straw was assessed in digestibility crates. Feed intake and nutrient digestibility were measured in four 21-d periods, during which lambs received the 2 diets consecutively. No differences in intake, growth performance, or nutrient digestibility were observed between control and bolused lambs. In conclusion, the B3 mini-bolus proved to be an efficient device for identification of lambs before weaning (recommended age, >4 wk; recommended BW, >10 kg), allowing a reliable traceability of dairy and meat lambs until slaughter.

Effects of small ruminal boluses used for electronic identification of lambs on the growth and development of the reticulorumen.

Fifty-four male lambs were used to study the effects of two types of small electronic boluses on the dimensions and epithelial characteristics of their reticulorumen. Newborn lambs were assigned according to bolus type and age of application to the following treatments: 1) control (C, n = 21), without bolus; 2) mini (M, n = 21), identified with a 9.3 x 37.4-mm, 5.2-g bolus during the first week after birth; and 3) small (S, n = 12), identified with a 15.0 x 39.1-mm, 20-g bolus after weaning at wk 5, when lambs weighed more than 12 kg. After weaning, lambs were given ad libitum access to concentrate and barley straw. Six lambs were euthanized at the start of the experiment to measure initial reticulorumen characteristics. Ten lambs (five from M and five from C treatments) were slaughtered at weaning and 24 (eight per treatment) were slaughtered when they reached 24 kg. After bolus recovery, the reticulorumen was emptied and filled with polyurethane foam to obtain reticulorumen casts. Weight of the emptied reticulorumen and volume of the casts were measured. Four representative lambs from each treatment were also slaughtered at 24 kg, and their reticulorumen used to evaluate papillae size, number of dead cells, and degree of keratinization of both the reticulum wall and the rumen wall epithelia. Weight at weaning (13.8 kg), age at the end of fattening (65 d), and mortality rate (4%) did not differ among treatments. Retention rate for M and S boluses was 82.4 and 100%, respectively. Fresh weight and volume of the reticulorumen did not differ among treatments at weaning (130 g and 1,679 mL) or at the end of the fattening period (640 g and 5,931 mL). Lambs in the M treatment had greater (P < 0.05) rumen papillae size and lower (P < 0.10) keratinization than C lambs; values in the S lambs were intermediate between M and C lambs. Neither the M nor S type of bolus affected dimensions of the reticulorumen, but the earlier presence of M boluses induced a greater papillae size, with no negative effects on health and fattening performances of young lambs.

Plasma leptin concentration in adult cattle: effects of breed, adiposity, feeding level, and meal intake.

An ovine-specific RIA, shown to be reliable for bovine leptin determination, was used to study the effects of breed, body fatness, feeding level, and meal intake on plasma leptin level in adult cattle. Eighteen fat Charolais, fat Holstein, and lean Holstein adult cows were either well-fed (130% of maintenance energy requirements [MER]) or underfed (60% of MER) for 3 wk. The breed tended to have a small effect on plasma leptin level, which was decreased by 70% (P < 0.05) in lean compared to fat Holstein cows. A strong curvilinear relationship was found between mean adipocyte volume and plasma leptin concentrations in well-fed (r = +0.95) and underfed (r = +0.91) cows. Underfeeding caused a significant decrease in plasma leptin levels from 8.0+/-3.1 to 6.1+/-2.3 ng/mL (P < 0.01). Nine adult Holstein cows initially fed at 130% of MER (control) were underfed to 21% of MER for 7 d, and five of them were refed to 237% of MER for 21 d. Plasma leptin measured 1 h before meal distribution was decreased from 5.9+/-0.4 to 3.8+/-0.2 ng/mL (P < 0.01) by underfeeding and increased to reach 8.8+/-1.0 ng/mL (P < 0.01) after refeeding. It was positively related to plasma glucose (r = +0.52, P < 0.01) and negatively related to plasma NEFA (r = -0.67, P < 0.001). Plasma leptin measured 4 h after meal distribution was positively related to feeding level and to plasma 3-OH-butyrate (r = +0.61, P < 0.005) and negatively related to plasma NEFA (r = -0.56, P < 0.01). Differences between pre- and postprandial leptin concentrations showed a decrease after meal intake in control and well-fed cows (-7 and -19%, P < 0.01, respectively) and an increase in underfed cows (+12%, P < 0.01). Leptin response to meal intake was positively related to glucose response (r = +0.66, P < 0.001) and negatively related to 3-OH-butyrate response (r = -0.78, P < 0.001). By using the "multispecies" commercial RIA, leptin concentrations were lower and we observed similar physiological responses, although less related to other hormones or metabolites. These data provide evidence, first, that a specific RIA for ruminant leptin determination is necessary to better understand leptin regulation, and second, that plasma leptin is strongly related to adipose cell size and positively related to feeding level in adult cattle, and that an effect of meal intake could be mediated by glucose and(or) ketone bodies.

Effects of photoperiod and feeding level on adipose tissue and muscle lipoprotein lipase activity and mRNA level in dry non-pregnant sheep.

The aim of the present study was to investigate the effects of photoperiod and feeding level on lipid metabolism in ovine perirenal and subcutaneous adipose tissues (AT) and in skeletal and cardiac muscles. Twenty dry non-pregnant ovariectomised ewes were divided into two groups and subjected to either 8 h or 16 h light/d, and underfed at 22 % energy requirements for 7 d. Half of the ewes in each group were slaughtered and the remaining ewes were refed at 190 % energy requirements for 14 d, until slaughtering. Refeeding increased (2.6-4.3-fold) malic enzyme (ME), fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH) and glycerol-3-phosphate dehydrogenase (G3PDH) activities in subcutaneous AT as well as lipoprotein lipase (LPL) activity in perirenal (3.5-fold) and subcutaneous (10-fold) AT and to a lesser extent (1.4-fold) in the skeletal longissimus thoracis and cardiac muscles. Moreover, variations of LPL mRNA level followed variations of LPL activity: refeeding increased perirenal AT- and cardiac muscle-mRNA levels (7.4- and 2-fold respectively). The main finding of this study is that, for a given level of food intake, long days (compared with short days) increased the LPL activity in the longissimus thoracis muscle and, in refed ewes, the activities of LPL and ME in subcutaneous AT. Furthermore, long days increased LPL mRNA level in cardiac muscle and perirenal AT. Thus, our results show that there are direct effects of photoperiod on sheep AT lipogenic potential, as well as on muscle LPL activity, which are not caused by changes in nutrient availability.

Modelling reproduction in farm animals: a review.

During the last few decades, our knowledge of the biology of the reproductive system has improved significantly and also become more quantitative. In parallel, there has been an increase in the development of mathematical models, as both research tools and management tools, that can integrate our knowledge of reproductive events and then attempt to predict reproductive efficiency. This review considers these modelling approaches according to the level of organization that they address, from representation of the dynamic functions of the reproductive axis to the prediction of reproductive performance of a flock or herd. We emphasize the contribution of modelling to the exploration and understanding of a complex system-a system that responds to a host of internal regulatory mechanisms as well as to an array of external factors such as nutrition, photoperiod and sociosexual signals. To date, models have proven useful for depicting the kinetics of some of the endocrine signals that are implicated in perturbations of the reproductive axis and they have also been successful in the exploration of ovarian dynamics during the oestrous cycle. However, two areas are still largely unexplored by biomathematical models: the dynamic links between the different stages of the reproductive life of an animal, and mechanistic influences of environmental factors on the reproductive axis.

Leptin in ruminants. Gene expression in adipose tissue and mammary gland, and regulation of plasma concentration.

This paper reviews data on leptin gene expression in adipose tissue (AT) and mammary gland of adult ruminants, as well as on plasma leptin variations, according to genetic, physiological, nutritional and environmental factors. AT leptin mRNA level was higher in sheep and goat subcutaneous than visceral tissues, and the opposite was observed in cattle; it was higher in fat than in lean selection line in sheep; it was decreased by undernutrition and increased by refeeding in cattle and sheep, and not changed by adding soybeans to the diet of lactating goats; it was increased by injection of NPY to sheep, and by GH treatment of growing sheep and cattle. Insulin and glucocorticoids in vitro increased AT leptin mRNA in cattle, and leptin production in sheep. Long daylength increased AT lipogenic activities and leptin mRNA, as well as plasma leptin in sheep. Mammary tissue leptin mRNA level was high during early pregnancy and was lower but still expressed during late pregnancy and lactation in sheep. Leptin was present in sheep mammary adipocytes, epithelial and myoepithelial cells during early pregnancy, late pregnancy and lactation, respectively. Plasma leptin in cattle and sheep was first studied thanks to a commercial "multi-species" kit. It was positively related to body fatness and energy balance or feeding level, and decreased by beta-agonist injection. The recent development of specific RIA for ruminant leptin enabled more quantitative study of changes in plasma leptin concentration, which were explained for 35--50% by body fatness and for 15--20% by feeding level. The response of plasma leptin to meal intake was related positively to glycemia, and negatively to plasma 3-hydroxybutyrate. The putative physiological roles of changes in leptin gene expression are discussed in relation with published data on leptin receptors in several body tissues, and on in vivo or in vitro effects of leptin treatment.

Effects of underfeeding and refeeding on offals weight in the Barbary ewes.

The influence of long-term (161 days) underfeeding and refeeding (154 days) on the weight of offal components, and digestive content, was studied in 26 adult Barbary ewes. Effects on the protein and mineral content of offals were also measured. Animals were split in three groups: one was fed hay at maintenance level (M), another also received vetch-oat hay to cover 0.2 of maintenance energy requirements (L), and the third one was fed at 0.2 of maintenance requirements during 161 days, then refed at 1.3 times of energy requirements with a diet of hay and barley grain (LH) during 154 days. Underfed animals body weight (BW) at slaughter was 31kg. Animals of groups M and LH were slaughtered at similar BW (50kg). Underfeeding reduced empty BW by 38% and the weight of most metabolically active organs: skin (40%), blood (31%), rumen (34%) and liver (19%), but not others (small intestine). Total offals weight was reduced by 27%. Overfeeding of previously underfed animals (LH) induced a significant increase in liver weight in comparison to M group (18%), owing to a higher nutrient supply. The amount of protein in offals and their fat-free weight were decreased by underfeeding, whereas the amount of minerals was significantly modified only in components rich in bone. These results showed that splanchnic organ mass decreases with underfeeding which leads to energy requirements decrease and contributes towards resistance of Barbary ewes to harsh food conditions.

Plasma leptin determination in ruminants: effect of nutritional status and body fatness on plasma leptin concentration assessed by a specific RIA in sheep.

A specific leptin RIA was developed to assess concentrations of leptin in ovine plasma, and was shown to be efficient with bovine and caprine plasma. A specific, high-affinity antibody was generated against recombinant ovine leptin which, when used in a competitive leptin RIA, provided valid estimates of linearity (r=+0.989-0.998), recovery (102%), repeatability (13%) and limit of sensitivity (0.83 ng/ml for 100 microl sample size). Serial dilutions of five ovine, bovine or caprine plasma samples showed good linearity and parallelism with the recombinant ovine leptin standard curve. A comparison of this RIA was made with a commercial 'multi-species' RIA kit using 56 ovine plasma samples. Major differences were found in assay sensitivity. Non-lactating, non-pregnant, ovariectomized ewes were fed a ration for 65 days which provided 90+/-9% (control; n=12) or 39+/-2% of maintenance energy requirements (underfed; n=16) in order to analyse the respective effects of body fatness (estimated by either an in vivo dilution technique or body condition scoring) and of nutritional status on plasma leptin concentration. There was a significant positive correlation between body fatness or body condition score and plasma leptin levels (r=+0.68, P<0.001 or r=+0.72, P<0.001 respectively). When concentrations of leptin were assessed over time, underfed ewes exhibited a dramatic reduction in plasma leptin values (-56%, P<0.001). These data provide strong evidence that, in sheep, the variations in plasma concentrations of leptin are related to variations in body fatness (35%) and, to a lesser extent, in nutritional status (17%).