Pauline Martin

The late age at first calving from the French Charolais breeds is associated with both economic and environmental costs which could be partly mitigated by improving the sexual precocity of heifers. This study investigates the environmental and genetic determinism of age at puberty (AP) in this breed and characterize the relationships between sexual precocity and pre- and post-weaning performance. A total of 650 Charolais heifers, raised on two different farms and born over a 4-year period were used. Puberty was determined by progesterone assay and growth was followed up to 2 years of age, ending with a feed efficiency trial. Mean AP was 16.7 months. Heifers born in spring were more precocious than those born in winter. Age at puberty was moderately heritable (0.21 ± 0.08). It was unfavorably genetically correlated with birthweight (0.30 ± 0.21) but favorably with growth before weaning (−0.30 ± 0.23). A trend for a positive genetic relationship between feed efficiency and AP (0.40 ± 0.44) was observed. Overall, a good strategy to improve sexual precocity in French Charolais cows could be to prioritize spring birth season and good rearing conditions for heifers, while selecting for reduced birth weight and increased growth rate.

Genetic selection to reduce methane (CH₄) emissions is a promising solution for reducing the environmental impact of dairy cattle production. Before such a selection program can be implemented, however, it is necessary to have a better understanding of the genetic determinism of CH₄ emissions and how this might influence other traits of interest. In this study, we performed a genetic analysis of 6 CH₄ traits predicted from milk mid-infrared spectra. We predicted 4 CH₄ traits in g/d (MeP, calculated using different prediction equations), one in g/kg of fat- and protein-corrected milk (MeI), and one in g/kg of dry matter intake (MeY). Using an external data set, we determined these prediction equations to be applicable in the range of 70 to 200 DIM. We then estimated genetic parameters in this DIM range using random regression models on a large data set of 829,025 spectra collected between January 2013 and February 2023 from 167,514 first- and second-parity Holstein cows. The 6 CH₄ traits were found to be genetically stable throughout and across lactations, with average genetic correlations within a lactation ranging from 0.93 to 0.98, and those between lactations ranging from 0.92 to 0.98. All 6 CH₄ traits were also found to be heritable, with average heritability ranging from 0.24 to 0.45. The average pairwise genetic correlations between the 6 CH₄ traits ranged from -0.15 to 0.77, revealing that they are genetically distinct, including the 4 measurements of MeP. Of the 6 traits, 2 measures of MeP and MeI did not present antagonistic genetic correlations with milk yield, fat and protein contents, and SCS, and can probably be included in breeding goals with limited impact on other traits of interest.

Residual feed intake is viewed as an important trait in breeding programs that could be used to enhance genetic progress in feed efficiency. In particular, improving feed efficiency could improve both economic and environmental sustainability in the dairy cattle industry. However, data remain sparse, limiting the development of reliable genomic evaluations across lactation and parity for residual feed intake. Here, we estimated novel genetic parameters for genetic residual feed intake (gRFI) across the first, second, and third parity, using a random regression model. Research data on the measured feed intake, milk production, and body weight of 7,379 cows (271,080 records) from 6 countries in 2 continents were shared through the Horizon 2020 project GenTORE and Resilient Dairy Genome Project. The countries included Canada (1,053 cows with 47,130 weekly records), Denmark (1,045 cows with 72,760 weekly records), France (329 cows with 16,888 weekly records), Germany (938 cows with 32,614 weekly records), the Netherlands (2,051 cows with 57,830 weekly records), and United States (1,963 cows with 43,858 weekly records). Each trait had variance components estimated from first to third parity, using a random regression model across countries. Genetic residual feed intake was found to be heritable in all 3 parities, with first parity being predominant (range: 22-34%). Genetic residual feed intake was highly correlated across parities for mid- to late lactation; however, genetic correlation across parities was lower during early lactation, especially when comparing first and third parity. We estimated a genetic correlation of 0.77 ± 0.37 between North America and Europe for dry matter intake at first parity. Published literature on genetic correlations between high input countries/continents for dry matter intake support a high genetic correlation for dry matter intake. In conclusion, our results demonstrate the feasibility of estimating variance components for gRFI across parities, and the value of sharing data on scarce phenotypes across countries. These results can potentially be implemented in genetic evaluations for gRFI in dairy cattle.

Dans un contexte économique et environnemental où l’élevage est de plus en plus questionné, la précocité, l’efficience alimentaire et la résilience sont devenus des points d’intérêt majeurs de par leur rôle potentiel pour améliorer l’efficience globale des élevages. Pour explorer ces caractères et les liens qui les unissent dans les systèmes allaitants, une expérimentation de grande envergure a été menée entre 2011 et 2021 sur 650 femelles charolaises. Cette expérimentation se découpait en trois périodes que les animaux effectuaient successivement : l’étude de la précocité sexuelle et de développement, l’étude de l’efficience alimentaire au travers de l’ingéré résiduel à deux ans, puis l’étude de la réponse à un challenge alimentaire (composé d’une phase de restriction et d’une phase de récupération) au cours de la lactation. Cet article regroupe l’ensemble des résultats obtenus. Si la précocité sexuelle définie par l’âge à la puberté est fortement liée à l’environnement (conduite, alimentation…) et notamment à la saison de naissance, l’héritabilité du caractère est néanmoins modérée (0,21 ± 0,08). Elle est également corrélée génétiquement avec un petit poids à la naissance et une forte croissance pré-sevrage. L’efficience alimentaire des animaux de deux ans est peu héritable (0,09 ± 0,08) mais corrélée favorablement avec la précocité. Face au challenge alimentaire, les vaches ont des réponses équilibrées entre perte de production laitière et mobilisation de réserves corporelles mais cette réponse moyenne de la race cache des disparités entre individus. Enfin, les génisses les plus efficientes présentaient des productions laitières amoindries une fois en lactation par rapport à leurs homologues inefficientes (jusqu’à − 0,7 kg de lait par jour en milieu de lactation soit environ 10 % de moins), ainsi que des retours en chaleurs plus long dans le cadre de la restriction alimentaire. Ces résultats promeuvent l’importance de considérer l’efficience sur le long terme en prenant en compte ses différentes composantes et de ne pas réaliser une sélection génétique sur une efficience alimentaire mesurée sur un moment court et unique pendant la phase de croissance.

Dans le contexte actuel de forts coûts des intrants alimentaires et d’impact des productions bovines sur le changement climatique, l’efficience alimentaire apparaît comme un levier d’action pour la durabilité économique et environnementale de l’élevage allaitant. De plus, la valorisation par les bovins d’aliments cellulosiques, non éligibles à l’alimentation humaine et favorisant un maintien des prairies et des services environnementaux associés, représente également un enjeu majeur, en particulier dans les régimes d’engraissement des jeunes bovins. Dans l’objectif d’étudier les déterminants, aussi bien physiologiques que génétiques, de l’efficience alimentaire des bovins allaitants tout en prenant en compte le fait que la filière allaitante repose sur différents types d’animaux (jeunes bovins à l’engraissement mais également mères allaitantes et génisses de renouvellement) et différents types d’alimentation, un vaste programme de recherche a été mené. Intitulé BEEFALIM 2020, celui-ci s’est étalé entre 2013 et 2021 et a permis la production de nombreuses connaissances scientifiques. Cet article introductif présente la structure et les objectifs de BEEFALIM 2020, décrit les dispositifs expérimentaux utilisés et reprend les principaux enseignements du programme en préambule aux trois articles scientifiques qui en rapportent les résultats dans le détail.

After calving, high-yielding dairy cows mobilize body reserves for energy, sometimes to the detriment of health and fertility. This study aimed to estimate the genetic correlation between body weight loss until nadir and daily milk production (MY24) in first- (L1) and second-lactation (L2) Holstein cows. The data set included 859,020 MY24 records and 570,651 daily raw body weight (BWr) phenotypes from 3,989 L1 cows, and 665,361 MY24 records and 449,449 BWr phenotypes from 3,060 L2 cows, recorded on 36 French commercial farms equipped with milking robots that included an automatic weighing platform. To avoid any bias due to change in digestive content, BWr was adjusted for variations in feed intake, estimated from milk production and BWr. Adjusted body weight was denoted BW. The genetic parameters of BW and MY24 in L1 and L2 cows were estimated using a 4-trait random regression model. In this model, the random effects were fitted by second-order Legendre polynomials on a weekly basis from wk 1 to 44. Nadir of BW was found to be earlier than reported in the literature, at 29 d in milk, and BW loss from calving to nadir was also lower than generally assumed, close to 29 kg. To estimate genetic correlations between body weight loss and production, we defined BWL5 as the loss of weight between wk 1 and 5 after calving. Genetic correlations between BWL5 and MY24 ranged from -0.26 to 0.05 in L1 and from -0.11 to 0.10 in L2, according to days in milk. These moderate to low values suggest that it may be possible to select for milk production without increasing early body mobilization.

Body condition score (BCS) offers a good estimate of the amount of stored fat on the body, and its variations can be used as a proxy for energy balance. Many countries have implemented a genomic evaluation of BCS, including France, where estimated breeding values are based on an individual BCS determination during the first lactation. In this article, we investigate the degree to which this genomic estimated breeding value based on a single phenotype record per cow might reflect different profiles of body reserves throughout lactation and be used to predict, and perhaps limit, their mobilization during early lactation. We also investigate whether selection on BCS affects other traits. A data set including 686 lactations of 435 Holstein cows from 3 experimental farms not used in the reference population for genomic evaluation was used to estimate the effects of the BCS direct genomic value (iBCS) on BCS, body weight, feed intake, milk production, and fat and protein contents throughout the lactation period. For each trait, the model included different iBCS regressions and an effect of the direct genomic value of the trait itself when available. It thus appeared that cows with a positive iBCS always had a higher BCS than negative iBCS cows, whatever the lactation stage, and that this difference increased during the first 6 mo to reach a difference of 0.8 point. A similar effect was seen regarding body weight, but it was the opposite for milk production, with negative iBCS cows producing slightly more milk (difference of about 3% over lactation). Feed intake increased slightly faster at the beginning of lactation for cows with positive iBCS. Therefore, iBCS is a promising tool that could help to limit intense mobilization during early lactation. Should feed efficiency be included in the breeding goal, greater attention should be paid to BCS to avoid further body mobilization in early lactation.