Reproductive robustness differs between generalist and specialist maternal rabbit lines: the role of acquisition and allocation of resources

[EN] Background: Farm animals are normally selected under highly controlled, non-limiting conditions to favour the expression of their genetic potential. Selection strategies can also focus on a single trait to favour the most specialized animals. Theoretically, if the environment provides enough resources, the selection strategy should not lead to changes in the interactions between life functions such as reproduction and survival. However, highly specialized farm animals can be required for breeding under conditions that differ largely from selection conditions. The consequence is a degraded ability of specialized animals to sustain reproduction, production and health, which leads to a reduced lifespan. This study was designed to address this issue using maternal rabbit lines. A highly specialized line with respect to numerical productivity at weaning (called V) and a generalist line that originated from females with a long reproductive life (called LP) were used to study the strategies that these lines develop to acquire and use the available resources when housed in different environments. In addition, two generations of line V, generations 16 and 36, were available simultaneously, which contributed to better understand how selection criteria applied in a specific environment changed the interplay between functions related to reproduction and survival. Results: We show that, under constrained conditions, line LP has a greater capacity for resource acquisition than line V, which prevents excessive mobilization of body reserves. However, 20 generations of selection for litter size at weaning did not lead to an increased capacity of nutrient (or resource) acquisition. For the two generations of line V, the partitioning of resources between milk production, body reserves preservation or repletion or foetal growth differed. Conclusions: Combining foundational and selection criteria with a specific selection environment resulted in female rabbits that had a different capacity to deal with environmental constraints. An increased robustness was considered as an emergent property of combining a multiple trait foundational criterion with a wide range of environmental conditions. Since such a strategy was successful to increase the robustness of female rabbits without impairing their productivity, there is no reason that it should not be applied in other livestock species.The authors thank Juan Carlos Moreno Pardo, Luis Rodenas Martinez and Eugenio Martinez Paredes for their technical support, and Doctors Manuel Baselga Izquierdo, Enrique Blas Ferrer and Concha Cervera Fras for their valuable comments in the first version of this work. 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Progesterone profiles around the time of insemination do not show clear differences between of pregnant and not pregnant dairy cows

In this study, features of progesterone profiles were examined in relation to the outcome of insemination. Three groups of estrous cycles were analyzed: resulting in pregnancy, not resulting in pregnancy and resulting in lost pregnancy. The aim of the study was to identify a complex of progesterone profile features associated with successful insemination. The features used were (1) from the estrous cycle preceding the artificial insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone, luteal phase peak, pre-estrus maximum rate of decline in progesterone and the length of follicular and luteal phase and (2) from the estrous cycle following insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone and days from estrus to post-estrus maximum rate of increase in progesterone. A discriminant analysis did not reveal clear differences between the groups. However, the analysis correctly classified 75% of true pregnant cows. Conversely, only 60% of not pregnant animals were classified as such by the discriminate analysis. Individual analysis of progesterone profile features in pregnant and not pregnant groups of estrous cycles showed that a shorter follicular phase preceding insemination is associated with proper timing of post-ovulatory luteinisation and therefore is more likely to result in pregnancy

Energy balance of individual cows can be estimated in real-time on-farm using only frequent liveweight measures even in the absence of body condition score

Existing methods for estimating individual dairy cow energy balance typically either need information on feed intake, that is, the traditional input-output method, or frequent measurements of BW and body condition score (BCS), that is, the body reserve changes method (EBbody). The EBbody method holds the advantage of not requiring measurements of feed intake, which are difficult to obtain in practice. The present study aimed first to investigate whether the EBbody method can be simplified by basing EBbody on BW measurements alone, that is, removing the need for BCS measurements, and second to adapt the EBbody method for real-time use, thus turning it into a true on-farm tool. Data came from 77 cows (primiparous or multiparous, Danish Holstein, Red or Jersey) that took part in an experiment subjecting them to a planned change in concentrate intake during milking. BW was measured automatically during each milking and real-time smoothed using asymmetric double-exponential weighting and corrected for the weight of milk produced, gutfill and the growing conceptus. BCS assessed visually with 2-week intervals was also smoothed. EBbody was calculated from BW changes only, and in conjunction with BCS changes. A comparison of the increase in empty body weight (EBW) estimated from EBbody with EBW measured over the first 240 days in milk (DIM) for the mature cows showed that EBbody was robust to changes in the BCS coefficients, allowing functions for standard body protein change relative to DIM to be developed for breeds and parities. These standard body protein change functions allow EBbody to be estimated from frequent BW measurements alone, that is, in the absence of BCS measurements. Differences in EBbody levels before and after changes in concentrate intake were calculated to test the real-time functionality of the EBbody method. Results showed that significant EBbody increases could be detected 10 days after a 0.2 kg/day increase in concentrate intake. In conclusion, a real-time method for deriving EBbody from frequent BW measures either alone or in conjunction with BCS measures has been developed. This extends the applicability of the EBbody method, because real-time measures can be used for decision support and early intervention

Disentangling the dynamics of energy allocation to provide a proxy of robustness in fattening pigs

International audienceAbstract Background There is a growing need to improve robustness characteristics in fattening pigs, but this trait is difficult to phenotype. Our first objective was to develop a robustness proxy on the basis of modelling of longitudinal energetic allocation coefficient to growth for fattening pigs. Consequently, the environmental variance of this allocation coefficient was considered as a proxy of robustness. The second objective was to estimate its genetic parameters and correlation with traits under selection as well with phenotypes routinely collected on farms. A total of 5848 pigs, from Piétrain NN paternal line, were tested at the AXIOM boar testing station (Azay-sur-Indre, France) from 2015 to 2022. This farm was equipped with automatic feeding system, recording individual weight and feed intake at each visit. We used a dynamic linear regression model to characterize the evolution of the allocation coefficient between cumulative net energy available, estimated from feed intake, and cumulative weight gain during fattening period. Longitudinal energetic allocation coefficients were analysed using a two-step approach, to estimate both its genetic variance and the genetic variance in the residual variance, trait LSR. Results The LSR trait, that could be interpreted as an indicator of the response of the animal to perturbations/stress, showed low heritability (0.05±0.01). The trait LSR had high favourable genetic correlations with average daily growth (−0.71±0.06) and unfavourable with feed conversion ratio (−0.76±0.06) and residual feed intake (−0.83±0.06). The analysis of the relationship between estimated breeding values (EBV) LSR quartiles and phenotypes routinely collected on farms shows the most favourable situation for animals from quartile with the weakest EBV LSR, i.e ., the most robust. Conclusions These results show that selection for robustness based on deviation from energetic allocation coefficient to growth can be considered in breeding programs for fattening pigs

Priming the dairy cow for lactation:A review of dry cow feeding strategies

International audienceThis paper reviews important aspects of dry cow feeding with emphasis placed on the preparation of the cow for the subsequent lactation. A number of feeding strategies, which have been proposed in recent years, are examined, alongside considerations of the effects of dry period length, levels of body reserves at calving and parity. A number of studies have reported the effect of varying the length of the dry period (in the range 0 to 70 days) on subsequent production and health. An 8 week dry period seems optimal though this should be adjusted to allow for the body condition score of cows at drying off. Avoiding extremes of body condition score at calving is desirable, so condition should be monitored throughout the lactation cycle. Attempting to achieve large changes in body reserves in the dry period has been associated with increased problems postpartum. The feeding strategies that are reviewed are strategies to decrease body mobilisation, prime for body mobilisation, prime the rumen for increased intake, prime for milk protein production and prime for calcium mobilisation and absorption. These strategies are also evaluated relative to their biological basis and reported physiological effects. Feeding high starch feeds in the latter part of the dry period was found not to provide clear benefits in terms of decreasing early lactation body mobilisation or increasing early lactation intake. Strategies aimed at priming the cow for the increased mobilisation of body lipid and body calcium that occurs in early lactation appear more favourable both from the point of view of making biological sense and from the available results reviewed.Préparation des vaches laitières à la lactation : bilan des stratégies d'alimentation des vaches taries. Cet article passe en revue les aspects importants de l'alimentation des vaches taries en mettant l'accent sur la préparation de la vache à la lactation suivante. Plusieurs stratégies d'alimentation proposées au cours des dernières années sont examinées, dans le même temps que des considérations portant sur les effets de la durée de la période sèche, du niveau des réserves corporelles au vêlage et du rang de lactation. Un certain nombre d'études ont montré que le fait de faire varier la durée de la période sèche (dans une plage de 0 à 70 jours) avait un effet sur la production et la santé lors de la lactation suivante. Une période sèche de 8 semaines semble optimale, quoiqu'elle doive être ajustée en tenant compte de la note d'état corporel des vaches au moment du tarissement. Il est préférable d'éviter des notes extrêmes au vêlage ; l'état corporel devrait donc être surveillé tout au long du cycle de lactation. Les tentatives de vouloir effectuer de grandes modifications du niveau des réserves corporelles pendant la période sèche ont été associées à une augmentation des problèmes postpartum. Les stratégies d'alimentation exposées ici ont pour objectif de : diminuer les mobilisations corporelles, préparer à la mobilisation des constituants de l'organisme, préparer le rumen à l'augmentation de l'ingéré, préparer à la production de protéines du lait, et préparer à la mobilisation et à l'absorption du calcium. Ces stratégies sont aussi évaluées sur leurs bases biologiques et leurs effets physiologiques mentionnés. Il n'a pas été mis en évidence que le fait de nourrir les animaux en fin de période sèche avec des aliments à haute teneur en amidon apportait des avantages clairs en terme de diminution de la mobilisation des réserves corporelles ou de l'augmentation de l'ingestion en début de lactation. Les stratégies visant une préparation accrue de la vache à la mobilisation des réserves lipidiques et calciques intervenant en début de lactation apparaissent plus favorables, tant du point de vue du sens biologique que des résultats disponibles étudiés

Fitting the model to Dry Matter Intake (DMI) and Milk Fat Content (MFC) in goats before, during and after a 2 days nutritional challenge (grey rectangle).

<p>Data (observed values ± SE) are expressed as fold changes. The inverse of DMI is illustrated since DMI is decreasing during the challenge. Stiffness (K) and resistance to change (C) parameters of the model were fitted on the mean of the DMI (K = 0.04, C = 0.06) and MFC (K = 0.72, C = 0.97) measures.</p