Resumen de la Comunicación Oral presentada al: 71st Annual Meeting of the European Federation of Animal Science (EAAP). Farming for carbon neutral livestock systems. 1-4 de diciembre. Virtual meeting (2020)., Projects EUSMARTER & JCyL CSI276P18, FEDER and ESF.

5 páginas, 1 tabla, 1 figura.-- Trabajo presentado al: 12th World Congress on Genetics Applied to Livestock Production (WCGALP), R.F. Veerkamp and Y. de Haas (Eds), Wageningen Academic Publishers (Holanda), #717, pages 2956-2959. Róterdam (Holanda). 3-8 de julio de 2022., Feed costs constitute a substantial portion of livestock production costs; therefore, improving
feed efficiency (FE) is a major research topic nowadays. However, obtaining individual FE
records in commercial populations requires specialized infrastructure. This research aimed to
study the association between milk fatty acids (MFA) and FE in Assaf dairy sheep to
determine potential MFA biomarkers for FE. Individual feed conversion ratio (FCR) of 39
ewes were estimated. Spearman correlation, regression, and orthogonal partial least squares
were then used to analyze the relationship between FE and a profile of 101 MFA. We
identified 33 MFA significantly associated with the FCR. These MFAs achieved a predictive
performance of 0.82 for the FCR, and were successfully used to identify the most and least
feed efficient animals. Thus, we propose a list of potential biomarkers to validate as an easyto-
measure phenotype for FE trait in a larger population., This project has received funding from the European Union's Horizon 2020 research and
innovation program under grant agreement No 772787 (SMARTER)., Peer reviewed

Trabajo presentado a las: XX Jornadas sobre Producción Animal AIDA, p. 144. 13-14 junio. Zaragoza (España)., Proyectos PID2020-113441RB-I00 (MCIN/AEI, España) y SMARTER (H2020 #772787,
UE) y contrato predoctoral PRE2021-098235 (MCIN/AEI, España y Fondo Social Europeo)., Peer reviewed

Trabajo presentado a las: XX Jornadas sobre Producción Animal AIDA, p. 145. 13-14 junio. Zaragoza (España)., Proyectos PID2020-113441RB-I00 (MCIN/AEI, España) y SMARTER (H2020 #772787,
UE) y contrato predoctoral PRE2021-098235 (MCIN/AEI, España y Fondo Social Europeo)., Peer reviewed

Trabajo presentado a las: XX Jornadas sobre Producción Animal AIDA, p. 167. 13-14 junio. Zaragoza (España)., Proyectos PID2020-113441RB-I00 (MCIN/AEI, España) y SMARTER (H2020 #772787,
UE) y contrato predoctoral PRE2021-098235 (MCIN/AEI, España y Fondo Social Europeo)., Peer reviewed

Trabajo presentado al: 11th International Symposium on the Nutrition of Herbivores (ISNH), P58. Florianópolis (Brasil). 4-8 de junio., In the current scenario of climate change and economic instability, it can be expected that livestock will increasingly face nutrition-related
challenges. Resilience (understood as the ability of an animal to revert quickly to high production and health status in response to a perturbation)
would therefore be of great importance. However, animal breeding is still focused on higher production or, at best, higher feed
efficiency (FE). Yet, it is uncertain whether improving FE could detrimentally affect resilience, particularly in small dairy ruminants. This
experiment was carried out to examine the relationship between resilience and FE; namely, to compare the variation in some blood
metabolites in dairy ewes phenotypically divergent for FE and subjected to an acute nutritional challenge. First, to estimate FE, we used
40 Assaf ewes fed a TMR ad libitum, and measured individual dry matter intake and milk yield daily over 3 weeks. Feed efficiency was calculated
as the difference between the actual and predicted intake estimated through net energy requirements for maintenance, production
and weight change. Then, after selecting two groups of FE ewes: higher (H-FE; n = 9) and lower (L-FE; n = 9) efficient ewes, they were subjected
to a nutritional challenge. The trial consisted of three periods: the pre-challenge (when animals were fed TMR ad libitum), the challenge
(lasting for 3 days, when the TMR was withdrawn and the ewes were only fed wheat straw) and the post-challenge (lasting for
10 days, when animals were fed again TMR ad libitum). At the end of each period, blood samples were collected (before milking and feed
administration) and the serum was analyzed for glucose, non-esterified fatty acids (NEFA) and b-hydroxybutyrate (BHB) concentrations
during the trial. The data were subjected to repeated measurements analysis, with animals nested within the group. The results showed
that glucose levels tended to be marginally greater in H-FE than L-FE (P = 0.058), and dropped significantly (P < 0.001) due to the underfeeding.
Surprisingly, pre-challenge levels were not recovered on day 10 post-challenge. No differences between groups were detected for
NEFA concentrations, which sharply increased during the straw challenge and showed the lowest values in the post-challenge period
(P < 0.001). Regarding BHB, higher levels due to feed deprivation were only observed in the H-FE group (Group Period interaction,
P = 0.022). This could derive from a greater tissue mobilization and might have prevented a stronger drop in glycaemia in these more efficient
ewes. Results on blood serum metabolites may suggest that selection for high FE dairy ewes would not negatively influence their
resilience, as more (H-FE) and less (L-FE) efficient ewes responded to and recovered from the acute nutritional challenge similarly, Projects PID2020-113441RB-I00 (MCIN/AEI, Spain) and SMARTER (H2020 #772787, European Union), and predoctoral
grant PRE2021-098235 (MCIN/AEI, Spain)., Peer reviewed