BUSCADOR RECOLECTA

Agencia Estatal de Investigación (AGL2017-87812-R y PID2020-113441RB-I00). Cofinanciación FEDER.
A. Della Badia: contrato predoctoral FPI (PRE2018-086174) del MICINN. Cofinanciación Fondo Social Europeo., Peer reviewed

Trabajo presentado al: 73rd Annual Meeting of the European Federation of Animal Science (EAAP). The coexistence of wildlife and livestock. 4-9 de septiembre de 2022. Oporto (Portugal)., Project PID2020-113441RB-I00, MCIN/AEI; grant PRE2018-086174, MCIU/AEI/FSE, EU., Peer reviewed

Trabajo presentado al: 73rd Annual Meeting of the European Federation of Animal Science (EAAP). The coexistence of wildlife and livestock..4-9 de septiembre de 2022. Oporto (Portugal)., Project PID2020-113441RB-I00, MCIN/AEI; grant PRE2018-086174,
MCIU/AEI/FSE, EU., Peer reviewed

Trabajo presentado al: Joint Seminar of the FAO CIHEAM Networks on Pasture and Forage Crops and on Sheep and Goat Nutrition. Alternative feed resources and their management for transiting towards a sustainable ruminant production, p. 93. Catania (Italia). 27-29 de septiembre., Authors acknowledge support by PID2020-113441RB-I00 (MCIN/AEI), AGL2017-87812-R
(MINECO/AEI/FEDER, EU) and PRE2018-086174 (MCIU/AEI/FSE, EU)., Peer reviewed

Trabajo presentado al: Joint Seminar of the FAO CIHEAM Networks on Pasture and Forage Crops and on Sheep and Goat Nutrition. Alternative feed resources and their management for transiting towards a sustainable ruminant production, p. 94. Catania (Italia). 27-29 de septiembre., Authors acknowledge support by PID2020-113441RB-I00 (MCIN/AEI), AGL2017-87812-R
(MINECO/AEI/FEDER, EU) and PRE2018-086174 (MCIU/AEI/FSE, EU)., Peer reviewed

Trabajo presentado al: Joint Seminar of the FAO CIHEAM Networks on Pasture and Forage Crops and on Sheep and Goat Nutrition. Alternative feed resources and their management for transiting towards a sustainable ruminant production, p. 33. Catania (Italia). 27-29 de septiembre., Project PID2020-113441RB-I00 (MCIN/AEI) and grant PRE2018-086174 (MCIU/AEI/FSE, EU).

Trabajo presentado al: Joint Seminar of the FAO CIHEAM Networks on Pasture and Forage Crops and on Sheep and Goat Nutrition. Alternative feed resources and their management for transiting towards a sustainable ruminant production, p. 46. Catania (Italia). 27-29 de septiembre., Project PID2020-113441RB-I00 (MCIN/AEI) and grant PRE2018-086174 (MCIU/AEI/FSE, EU).

This work forms part of the PID2020-113441RB-I00 project, funded by the Spanish Research State Agency (MCIN/AEI/10.13039/501100011033). The preliminary phase of the study (for feed efficiency estimation) was funded by the SMARTER project through the Horizon 2020 research and innovation program of the European Commission (Grant Agreement No. 772787). E. Barrio benefited from a FPI predoctoral contract (PRE2021-098235) funded by the Spanish Research State Agency (MCIN/AEI/10.13039/501100011033) and by the European Social Fund (“ESF Investing in your future”)., Peer reviewed

10 páginas, 1 tabla, 2 figuras., As higher feed efficiency in dairy ruminants means a higher
capability to transform feed nutrients into milk and milk components, dierences
in feed efficiency are expected to be partly linked to changes in the physiology
of the mammary glands. Therefore, this study aimed to determine the biological
functions and key regulatory genes associated with feed efficiency in dairy sheep
using the milk somatic cell transcriptom, This research was funded by the Junta de Castilla y León
(JCyL, Spain; project CSI276P18) and the Spanish Research
State Agency (Agencia Estatal de Investigación, Spain; project
PID2020-113441RB-I00 and MCIN/AEI/10.13039/501100011033).
Cofunding by the European Regional Development Fund
(ERDF/FEDER) is also acknowledged. Research activities for the
University of Leon were funded by the SMARTER project through
the H2020 research and innovation program of the European
Commission (Grant Agreement No. 772787)., Peer reviewed

14 páginas, 6 figuras., Enhancing the ability of animals to convert feed into meat or milk by optimizing feed efficiency (FE) has become a priority in livestock research. Although untargeted metabolomics is increasingly used in this field and may improve our understanding of FE, no information in this regard is available in dairy ewes. This study was conducted to (1) discriminate sheep divergent for FE and (2) provide insights into the physiological mechanisms contributing to FE through high-throughput metabolomics. The ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q/TOF-MS) technique was applied to easily accessible animal fluids (plasma and milk) to assess whether their metabolome differs between high- and low-feed efficient lactating ewes (H-FE and L-FE groups, respectively; 8 animals/group). Blood and milk samples were collected on the last day of the 3-wk period used for FE estimation. A total of 793 features were detected in plasma and 334 in milk, with 100 and 38 of them, respectively, showing differences between H-FE and L-FE. The partial least-squares discriminant analysis separated both groups of animals regardless of the type of sample. Plasma allowed the detection of a greater number of differential features; however, results also supported the usefulness of milk, more easily accessible, to discriminate dairy sheep divergent for FE. Regarding pathway analysis, nitrogen metabolism (either anabolism or catabolism) seemed to play a central role in FE, with plasma and milk consistently indicating a great impact of AA metabolism. A potential influence of pathways related to energy/lipid metabolism on FE was also observed. The variable importance in the projection plot revealed 15 differential features in each matrix that contributed the most for the separation in H-FE and L-FE, such as l-proline and phosphatidylcholine 20:4e in plasma or l-pipecolic acid and phosphatidylethanolamine (18:2) in milk. Overall, untargeted metabolomics provided valuable information into metabolic pathways that may underlie FE in dairy ewes, with a special relevance of AA metabolism in determining this complex phenotype in the ovine. Further research is warranted to validate these findings., This work was supported by the Junta de Castilla y León (JCyL, Spain; project CSI276P18)
and Spanish Research State Agency (MCIN/
AEI/10.13039/501100011033, project PID2020-
113441RB-I00). Cofunding by the European Regional
Development Fund (ERDF/FEDER) is also acknowledged. The authors thank C. León Canseco (University
Carlos III of Madrid, Spain) and H. Marina (University
of León, Spain) for helpful assistance with metabolomics data analysis. The authors have not stated any
conflicts of interest., 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. 166. 13-14 junio. Zaragoza (España)., PID2020-113441RB-I00 (MCIN/AEI) y PRE2018-086174 (MCIU/AEI/FSE, UE), 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

13 páginas, 6 tablas, 2 figuras., Selection of dairy sheep based on production levels has
caused a loss of rusticity, which might compromise their
future resilience to nutritional challenges. Although
refocusing breeding programs toward improved feed efficiency
(FE) is expected, more-efficient ewes also seem
to be more productive. As a first step to examine the
relationship between FE and resilience in dairy sheep,
in this study we explored the variation in the response
to and the recovery from an acute nutritional challenge
in high-yielding Assaf ewes phenotypically divergent for
FE. First, feed intake, milk yield and composition, and
body weight changes were recorded individually over
a 3-wk period in a total of 40 sheep fed a total mixed
ration (TMR) ad libitum. Data were used to calculate
their FE index (FEI, defined as the difference between
the actual and predicted intake estimated through net
energy requirements for maintenance, production, and
weight change). The highest and lowest FE ewes (H-FE
and L-FE groups, respectively; 10 animals/group) were
selected and then subjected to the nutritional challenge
(i.e., withdrawing the TMR and limiting their diet only
to the consumption of straw for 3 d). Afterward, sheep
were fed again the TMR ad libitum. Temporal patterns
of variation in performance traits, and ruminal fermentation
and blood parameters were examined. A good
consistency between FEI, residual feed intake, and feed
conversion ratio was observed. Results supported that
H-FE were more productive than L-FE sheep at similar
intake level. Average time trends of milk yield generated
by a piecewise model suggest that temporal patterns of
variation in this trait would be related to prechallenge
production level (i.e., H-FE presented quicker response
and recovery than L-FE). Considering all studied traits,
the overall response to and recovery from underfeeding
was apparently similar or even better in H-FE than
in L-FE. This would refute the initial hypothesis of a poorer resilience of more-efficient sheep to an acute
underfeeding. However, the question remains whether a
longer term feed restriction might impair the ability of
H-FE ewes to maintain or revert to a high-production
status, which would require further research., This work forms part of the PID2020-113441RB-I00
project, funded by the Spanish Research State Agency
(MCIN/AEI/10.13039/501100011033). The preliminary
phase of the study (for feed efficiency estimation)
was funded by the SMARTER project through the
Horizon 2020 research and innovation program of the
European Commission (Grant Agreement No. 772787).
E. Barrio benefited from a FPI predoctoral contract (PRE2021-098235) funded by the Spanish Research
State Agency (MCIN/AEI/10.13039/501100011033)
and by the European Social Fund (ESF Investing in
your future). The authors have not stated any conflicts
of interest., Peer reviewed

El trabajo: "Individual differences in responsiveness to diet-induced milk fat depression in dairy sheep and goats", ha sido presentado en parte en las XIX Jornadas sobre Producción Animal AIDA. 1-2 de junio de 2021. Zaragoza (España)., El trabajo: "Susceptibility to milk fat depression in dairy sheep and goats: individual variation in ruminal fermentation and biohydrogenation", ha sido presentado en parte en las XIX Jornadas sobre Producción Animal (AIDA). 1-2 de junio de 2021. Zaragoza (España) y en parte en FAO-CIHEAM Joint Seminar of Network on Pasture and Forage Crops and on Sheep and Goat Nutrition. 27-29 de septiembre de 2022. Catania (Italia)., El trabajo: "Analysis of factors predisposing dairy ewes to diet-induced milk fat depression", ha sido presentado en parte en las XX Jornadas sobre Producción Animal (AIDA) 13-14 de junio de 2023. Zaragoza (España) y en parte en American Dairy Science Association (ADSA) Annual Meeting. 25-28 de junio de 2023. Ottawa, (Canada)., [ES] La suplementación de la dieta del ganado lechero con lípidos de origen marino permite modular el perfil de ácidos grasos (AG) de la leche y aumentar el contenido de ciertos lípidos bioactivos, potencialmente saludables para los consumidores. Desafortunadamente, produce el síndrome de baja grasa en la leche (MFD, por las siglas en inglés de milk fat depression), que se caracteriza por una inhibición de la síntesis de grasa en la glándula mamaria. Durante mucho tiempo se pensó que las vacas sufrían MFD, mientras que las ovejas y las cabras eran tolerantes, pero posteriormente se demostró que el ovino y el caprino, al igual que el vacuno, desarrollan este síndrome cuando su dieta se suplementa con lípidos marinos. Además, se ha visto que los animales pueden mostrar grados individuales muy diferentes de depresión de la grasa láctea, lo que podría explicar algunas contradicciones en la literatura. Dado que el efecto antilipogénico de ciertos ácidos grasos (AG) es el origen más probable de la MFD, la caracterización del perfil de AG en la leche de los animales que muestran diferentes grados de MFD podría ser útil para comprender la base fisiológica de las diferencias en la intensidad del síndrome. Analizar si ciertos rasgos fenotípicos pueden predeterminar la respuesta individual también sería relevante para cumplir este objetivo. Sin embargo, la información sobre estos aspectos es aún escasa, no sólo en ovino y caprino sino en rumiantes en general.
Por todo ello, en el capítulo I de esta tesis se compararon las divergencias en la respuesta individual en términos de severidad del síndrome de MFD en ovino y caprino en lo que respecta al rendimiento productivo y el perfil lipídico de la leche, lo que permitiría, por una parte, detectar variaciones interespecíficas y, por otra, basándose especialmente en las respuestas comunes, avanzar en el conocimiento de la MFD., Un segundo objetivo fue analizar si algunos rasgos fenotípicos de las cabras y ovejas (en concreto, su rendimiento productivo y composición de AG de la leche) pueden predeterminar una mayor tolerancia o susceptibilidad individual a la MFD. Para cumplir ambos objetivos, se realizó una prueba experimental con 25 cabras de raza murciano-granadina y 23 ovejas de raza assaf que fueron alimentadas con una ración completa mezclada sin suplementación lipídica, durante 3 semanas (periodo Control). A continuación, todos los animales recibieron la misma dieta basal suplementada con un 2% de aceite de pescado (FO) durante 5 semanas adicionales (periodo MFD). Finalizado este segundo periodo, y en función de la caída de la concentración de grasa láctea inducida por el FO, se seleccionaron los 5 animales con una respuesta más marcada (RESPON+) y los 5 cuya respuesta fue más leve (RESPON−) dentro de cada especie (20 en total). Al final de cada periodo se examinó la producción y composición de la leche, incluido un perfil detallado de los AG. De acuerdo con el diseño experimental, hubo diferencias sustanciales en la concentración y producción de grasa láctea entre RESPON+ y RESPON−, pero no se detectó ninguna interacción significativa con el efecto de la especie. La caída media de la concentración y la producción de grasa fue del 26% en RESPON+ y del 6% en RESPON−. Los resultados del estudio no permitieron sugerir que la respuesta a la MFD esté claramente predeterminada ni por los parámetros productivos estudiados ni por el perfil de AG de la leche, pero podría existir cierta relación con el balance energético. Además, la variación individual en la susceptibilidad a la MFD en ovejas y cabras también podría estar relacionada con cambios en la concentración láctea de ciertos AG con efecto potencialmente antilipogénico, como el trans-10 18:1 y el cis-9 16:1, mientras que el trans-10,cis-12 CLA sólo tendría un papel secundario en la intensidad del síndrome. Las variaciones en la producción molar de AG de novo y preformados sugieren diferencias relevantes en los mecanismos responsables del desarrollo de la MFD en RESPON+ y RESPON−, con variaciones entre ovino y caprino sólo en los individuos más tolerantes., A partir de estos resultados, se hacía necesario ampliar la investigación para avanzar en el conocimiento de los mecanismos que determinan la mayor o menor sensibilidad a la MFD. Por ello, basándose en que el perfil de AG de la leche sólo se examina en la grasa que ha sido secretada con éxito, lo que puede no ser una representación exacta de los AG que se forman en el rumen y llegan a la glándula mamaria, planteamos que las diferencias individuales podrían detectarse más fácilmente en el fluido ruminal que en la leche. Esta hipótesis, aplicable tanto a las ovejas como a las cabras, fue la base del trabajo presentado en el capítulo II. En el mismo, se partió de los mismos animales seleccionados en la prueba descrita en el capítulo anterior y se investigó si los procesos de fermentación y biohidrogenación ruminal podrían predeterminar su mayor tolerancia o susceptibilidad a la MFD, y si la gravedad del síndrome depende exclusivamente de la respuesta a la dieta. Los parámetros de fermentación ruminal y los perfiles de AG se examinaron en muestras de líquido ruminal recogidas al final de cada periodo experimental (Control y MFD). En general, la variación individual en el grado de MFD en las ovejas y las cabras no pareció estar predeterminada por rasgos relacionados con la fermentación y la biohidrogenación ruminal, incluidos los AG que sirven como biomarcadores de la microbiota. En cuanto a las diferencias en la respuesta al FO, los resultados sugieren que no hay relación entre la susceptibilidad a la MFD y la concentración de los isómeros C18, C20 y C22 con un doble enlace trans-10. Los resultados también descartarían que variación individual en el grado de MFD se explique por una menor disponibilidad mamaria de acetato y 18:0 de origen ruminal, dada la ausencia de diferencias entre RESPON+ y RESPON−. Sin embargo, el contenido de AG insaturados aportados por el aceite marino (por ejemplo, cis-9 16:1, cis-11 18:1 y 20:5n-3) fue mayor en el rumen de las ovejas y cabras RESPON+ que en las RESPON−. Por lo tanto, aunque se necesita más investigación, cabe especular que la extensión de la biohidrogenación de estos AG podría estar asociada con la tolerancia o susceptibilidad a la MFD., Por último, y centrándose en el ovino (por ser la especie en la que se disponía de más datos), se planteó profundizar, mediante un metanálisis, en la identificación de rasgos fenotípicos de las ovejas, tanto de rendimiento productivo como de composición lipídica de la leche, que pudieran predisponer a cambios más o menos intensos en la síntesis de grasa láctea cuando se usan lípidos marinos para mejorar su perfil. Así, en el tercer estudio (presentado en el capítulo III) se recogieron los datos iniciales de rendimiento productivo y perfil de AG de la leche de 10 experimentos, en los que 160 ovejas assaf fueron alimentadas con 16 dietas que incluían FO o microalgas marinas durante 3-5 semanas. La caída de la concentración y producción de grasa láctea se calculó de 3 formas: cambio absoluto (valor final – valor inicial), cambio relativo (como porcentaje del valor inicial) y cambio potencial (relativo a la máxima MFD esperada, asumiendo que la grasa láctea no podría caer por debajo del 3%). Se utilizaron análisis de tipo bi- y multivariante para explorar la relación del rendimiento productivo y el perfil de AG de la leche con la predisposición a sufrir MFD. Según el primer tipo de análisis, existiría una relación lineal entre la concentración inicial de grasa láctea y los cambios absoluto (R2 = 0,46; R2 parcial de 0,08), relativo (R2 = 0,39; R2 parcial de 0,06) y potencial en el contenido de grasa de la leche durante la MFD (R2 = 0,17; R2 parcial = 0,03). Así, en ovejas que reciben lípidos marinos, cuanto mayor sea el contenido inicial de grasa, mayor sería la intensidad de la MFD. Este hallazgo se vio reforzado por los resultados de un segundo análisis bivariante (en el que se categorizó a las ovejas según su contenido y producción de grasa inicial) y los análisis multivariantes. También puede existir una relación, aunque más débil, entre la intensidad del síndrome y tanto la producción de leche como la concentración de proteína previas al consumo de la dieta que causa MFD. Además, la mayor MFD en las ovejas más sensibles podría estar relacionada con alteraciones de la función ruminal que aumenten la concentración láctea de AG potencialmente antilipogénicos, como el trans-10 18:1. Aunque el papel de los AG de la leche como factores predeterminantes de la MFD sigue sin estar claro, los resultados de este metanálisis apuntaron a que el mecanismo de captación mamaria de los AG preformados (>C16) jugaría un papel relevante, por lo que convendría profundizar en su estudio. También sería aconsejable seguir investigando las bases fisiológicas de la relación entre la magnitud de la depresión y la concentración de grasa láctea previa al consumo de la dieta inductora de MFD., [EN] Supplementation of dairy ewe diet with marine lipids can modulate the fatty acid (FA) profile of milk and increase the content of certain bioactive lipids that are potentially healthy for consumers. However, it causes the milk fat depression syndrome (MFD), which is characterized by an inhibition of fat synthesis in the mammary gland. For a long time, it was thought that cows were susceptible to MFD, whereas goats and sheep were tolerant, but it was later shown that caprine and ovine species, as well as bovine, are also susceptible to suffer this syndrome when their diet is supplemented with marine lipids. In addition, it has been observed that animals can display very different individual degrees of milk fat depression, which may explain some apparent contradictions in the literature. Because the antilipogenic effect of certain fatty acids (FA) is the most likely origin of MFD, characterising the milk FA profile of animals showing different degrees of MFD seems a helpful step to understand the physiological basis of the tolerance or susceptibility to the syndrome. Analysing whether certain phenotypic traits can predetermine a particular responsiveness would also be of relevance to meet this aim. However, information about these aspects is scant, not only in goats and sheep but in ruminants in general., Therefore, in Chapter I of this thesis, divergences in individual response in terms of severity of MFD syndrome in sheep and goats were compared in terms of production performance and milk lipid profile. This would allow, first, to detect interspecific variations, and second, based mainly on the common responses, to strengthen our knowledge of MFD. A second objective was to examine whether some phenotypic traits of goats and sheep (specifically their productive performance and milk FA profile) may predetermine individual tolerance or susceptibility to MFD. In order to meet both objectives, an experimental trial was conducted with 25 Murciano-Granadina goats and 23 Assaf sheep that were fed a complete mixed ration without lipid supplementation for 3 weeks (Control period). Then, all animals received the same basal diet supplemented with 2% of fish oil (FO) for 5 additional weeks (MFD period). At the end of this second period, and on the basis of the extent of FO-induced decreases in milk fat concentration, the 5 most responsive (RESPON+) and the 5 least responsive (RESPON) animals were selected within each species (20 in total). At the end of each period, milk yield and composition, including a comprehensive FA profile, was examined. By design, between-group variation in milk fat concentration and yield was substantial, but no significant interaction with the effect of species was detected. Reductions in these two performance traits averaged 6% in RESPON and 26% in RESPON+. Results do not allow suggesting that responsiveness to MFD would be clearly predetermined neither by the studied performance traits nor by milk FA profile, although a certain relationship with energy balance might exist. Furthermore, variations in ewes and does displaying different individual degrees of MFD may be associated with changes in certain candidate milk fat inhibitors, such as trans-10 18:1 and cis-9 16:1, whereas trans-10,cis-12 CLA would only have a minor role in determining MFD severity. Alterations in the molar yield of de novo and preformed FA suggest relevant differences in the mechanisms underlying MFD in RESPON+ and RESPON, with inter-species effects being only observed in more tolerant animals., Based on these findings, we considered that a deeper understanding of the mechanisms that might predetermine a particular individual tolerance or susceptibility to MFD was required. Therefore, considering that the milk FA profile is only examined in fat that has been successfully secreted, which may not be an accurate representation of FA leaving the rumen and reaching the mammary gland, we proposed that individual differences may be better detected in rumen fluid than in milk. This hypothesis, common to both sheep and goats, represented the basis for the second study, which is shown in Chapter II and was conducted using the same animals as in Chapter I. Our specific aims were to elucidate whether variations in ruminal fermentation and biohydrogenation could predetermine a higher tolerance or susceptibility to MFD, and whether the severity of MFD depends exclusively on the response to the diet. On the last day of each period (Control and MFD), ruminal fluid samples were collected to examine fermentation parameters and fatty acid profiles. In general, the individual degree of MFD in sheep and goats did not seem to be predetermined by traits related to ruminal fermentation and biohydrogenation, including fatty acids that may serve as biomarkers of microorganisms. Regarding differences in the response to FO, the results suggest no link between MFD susceptibility and concentration of biohydrogenation intermediates such as trans-10-containing C18, C20, and C22 metabolites. The explanation for individual responses based on a shortage of ruminal acetate and 18:0 for mammary uptake also seems to be dismissed, based on the lack of variation in these compounds between RESPON+ and RESPON−. However, the concentration of unsaturated fatty acids provided by FO (e.g., cis-9 16:1, cis-11 18:1 and 20:5n-3) was higher in the rumen of RESPON+ than RESPON− ewes and does. Thus, although further research is needed, it seems that the extent of biohydrogenation of these fatty acids might be associated with tolerance or susceptibility to MFD., Finally, and focusing on the ovine (as this was the species for which most data was available), a meta-analytical approach was used to identify phenotypic traits, both in productive parameters and milk lipid composition, that may predetermine individual MFD extension when marine lipids are used to improve milk FA profile. Thus, in the third study (presented in Chapter III) initial data of animal performance and milk FA profile was collected from 10 trials in which 160 Assaf ewes were fed 16 diets including FO or marine algae for 3 to 5 weeks. The decrease in milk fat concentration and yield was calculated using 3 approaches: absolute change (final – initial), relative change as a percent of pretrial value, and potential change relative to the maximal expected MFD (assuming a maximal decrease to 3% milk fat). Bivariate and multivariate analyses were used to explore whether individual performance and milk FA profile are related with subsequent MFD extent. According to bivariate analyses, there was a linear relationship between initial milk fat concentration and the absolute (R2 = 0,46; partial R2 of 0,08), relative (R2 = 0,39; partial R2 of 0,06), and potential changes in milk fat concentration during MFD (R2 = 0,17; partial R2 = 0,03). Thus, when ewes were fed marine lipids, the higher the initial milk fat content, the greater the extent of MFD. This finding was supported by a second bivariate analysis (categorizing ewes by initial milk fat concentration and yield) and multivariate analyses. A weaker relationship may also exist between MFD intensity and milk yield and protein concentration before consuming the MFD inducing diet. In addition, MFD in more responsive ewes may be related to rumen function alterations that increase milk concentrations of candidate antilipogenic metabolites, such as trans-10 18:1, as suggested by bivariate and multivariate analyses. Although the role of milk FA as predisposing factors for MFD remained unclear, results from this meta-analysis suggest the involvement of preformed FA (>C16) uptake in the syndrome and warrant further investigation. Further research would also be advisable to elucidate the physiological basis underlying the greater susceptibility to MFD of ewes with higher milk fat concentration., [IT] L’ inclusione di lipidi marini della dieta del bestiame da latte permette di migliorare il profilo acidico del latte e di aumentare il contenuto di alcuni lipidi bioattivi, potenzialmente salutari per i consumatori. Allo stesso tempo, questa loro inclusione può indurre la sindrome da basso grasso del latte (dall’inglese milk fat depression, MFD), che consiste nell’inibizione della sintesi del grasso nella ghiandola mammaria. Precedentemente, si riteneva che solo le vacche fossero soggette a MFD, mentre pecore e capre fossero tolleranti, ma in seguito è stato dimostrato che anche ovini e caprini possono sviluppare la MFD quando i lipidi marini vengono aggiunti alla loro razione. Inoltre, è stato dimostrato che gli animali possono presentare diversi gradi della sindrome da basso grasso del latte, il che potrebbe spiegare alcune contraddizioni presenti in letteratura. Poiché l’effetto antilipogenico di alcuni acidi grassi (in inglese fatty acid, FA) rappresenta la causa più plausibile della MFD, la caratterizzazione del profilo acidico del latte degli animali che presentano diversi gradi di MFD potrebbe essere utile per comprendere le basi fisiologiche delle differenze nell’intensità della sindrome. A tale scopo, sarebbe importante anche analizzare se alcuni tratti fenotipici possano predeterminare la risposta individuale alla sindrome., Pertanto, nel Capitolo I di questa tesi, sono state comparate le differenze di risposta individuale in termini di intensità della sindrome della MFD in pecore e capre, in relazione ai parametri produttivi ed al profilo lipidico del latte. Tale comparazione consentirebbe, da un lato, di individuare le variazioni interspecifiche e, dall’altro, basandosi soprattutto sulle risposte comuni, di progredire nella conoscenza della MFD. Un secondo obiettivo è stato quello di analizzare se alcuni tratti fenotipici di capre e pecore (in particolare, i loro parametri produttivi e la composizione degli acidi grassi del latte) possano predeterminare una maggiore tolleranza o suscettibilità individuale alla MFD. Per raggiungere entrambi gli obiettivi, è stata realizzata una prova sperimentale con 25 capre Murciano-Granadina e 23 pecore Assaf alimentate con una razione mista completa senza ulteriori inclusioni di lipidi per 3 settimane (periodo Controllo). Successivamente, tutti gli animali hanno ricevuto la stessa dieta basale, alla quale è stato aggiunto il 2% di olio di pesce (FO, per la sua sigla in inglese fish oil) per altre 5 settimane (periodo MFD). Una volta terminato questo secondo periodo, in funzione della diminuzione della concentrazione del grasso del latte indotto dal FO, sono stati selezionati 5 animali la cui risposta al trattamento era stata più intensa (RESPON+), e 5 con una risposta meno intensa (RESPON−) per ogni specie (20 in totale). Alla fine di ogni periodo, sono state esaminate la produzione e composizione del latte, compreso un profilo acidico dettagliato. Come previsto dal disegno sperimentale, sono state riscontrate differenze sostanziali nella concentrazione e produzione di grasso del latte tra RESPON+ e RESPON−, ma non è stata riscontrata nessuna interazione significativa tra questi parametri e l’effetto della specie. La riduzione media della concentrazione e della produzione di grasso è stata del 26% in RESPON+ e del 6% in RESPON−. I risultati dello studio non hanno permesso di suggerire se la risposta alla MFD sia chiaramente predeterminata dai parametri produttivi presi in considerazione o dal profilo FA del latte, tuttavia potrebbe esserci una relazione con il bilancio energetico. Inoltre, la variazione individuale della suscettibilità alla MFD negli ovini e nei caprini potrebbe anche essere relazionata a cambiamenti nella concentrazione nel latte di alcuni FA con un potenziale effetto antilipogenico, come il trans-10 18:1 e il cis-9 16:1, mentre il trans-10,cis-12 CLA giocherebbe solo un ruolo minore nell'intensità della sindrome. Le variazioni nella produzione molare di FA de novo e preformati suggeriscono differenze rilevanti nei meccanismi, responsabili dello sviluppo della MFD in RESPON+ e RESPON−, con variazioni tra pecore e capre solo negli individui più tolleranti. Sulla base di questi risultati, erano necessarie ulteriori ricerche per approfondire la comprensione dei meccanismi che determinano una maggiore o minore sensibilità alla MFD. Pertanto, partendo dal presupposto che il profilo di FA del latte viene esaminato solo nel grasso che è stato secreto con successo, il che potrebbe non essere una rappresentazione accurata dei FA che si formano nel rumine e che raggiungono la ghiandola mammaria, abbiamo proposto che le differenze individuali possano essere rilevate più facilmente nel liquido del rumine che nel latte. Questa ipotesi, applicabile sia agli ovini che ai caprini, è stata la base dello studio presentato nel Capitolo II. Esso è basato sugli stessi animali selezionati nella prova descritta nel Capitolo I e ha permesso di esaminare se i processi di fermentazione e bioidrogenazione ruminale possano predeterminare maggiore tolleranza o suscettibilità alla MFD in capre e pecore, e se la gravità della sindrome dipenda esclusivamente dalla risposta alla dieta. I parametri di fermentazione ruminale e il profilo acidico sono stati esaminati in campioni di liquido ruminale raccolti alla fine di ciascun periodo sperimentale (Controllo e MFD). In generale, la variazione individuale del grado di MFD negli ovini e nei caprini non sembra essere predeterminata dai parametri legati alla fermentazione e alla bioidrogenazione ruminale, compresi gli acidi grassi che agiscono da biomarcatori del microbiota ruminale. Per quanto riguarda le differenze nella risposta al FO, i risultati suggeriscono che non vi è alcuna relazione tra la suscettibilità alla MFD e la concentrazione di isomeri C18, C20 e C22 con un doppio legame trans-10. I risultati escludono inoltre che la variazione individuale del grado di MFD si spieghi con una minore disponibilità mammaria di acetato e 18:0 di origine ruminale, data l'assenza di differenze tra RESPON+ e RESPON−. Ciò nonostante, il contenuto di FA insaturi contenuti nell’olio di pesce (ad esempio cis-9 16:1, cis-11 18:1 e 20:5n-3) era più alto nel rumine di pecore e capre RESPON+ rispetto a RESPON−. Pertanto, sebbene siano necessarie ulteriori ricerche, si può ipotizzare che l'entità della bioidrogenazione di questi FA possa essere associata alla tolleranza o alla suscettibilità alla MFD., Infine, concentrandosi sugli ovini (in quanto specie per la quale era disponibile la maggior parte dei dati), l'obiettivo è stato quello di effettuare una meta-analisi per identificare i tratti fenotipici delle pecore, sia in termini di parametri produttivi che di composizione lipidica del latte, che potrebbero predisporre a cambiamenti più o meno intensi nella sintesi del grasso del latte quando i lipidi marini vengono utilizzati per migliorarne il profilo. A tal proposito, nel terzo studio (presentato nel Capitolo III) sono stati raccolti dati iniziali del rendimento produttivo e del profilo acidico del latte in 10 esperimenti, in cui 160 pecore Assaf sono state alimentate con 16 diete che includevano olio di pesce o microalghe marine per 3-5 settimane. La diminuzione della concentrazione e della produzione di grasso del latte è stata calcolata in tre modalità: variazione assoluta (valore finale - valore iniziale), variazione relativa (espressa come percentuale del valore iniziale) e variazione potenziale (relativa alla massima MFD prevista, supponendo che il grasso del latte non possa diminuire oltre il 3%). Sono state utilizzate analisi bi- e multivariate per analizzare la relazione tra i parametri produttivi e il profilo acidico del latte e la predisposizione alla MFD. Secondo il primo tipo di analisi, è stata riscontrata una relazione lineare tra la concentrazione iniziale di grasso del latte e le variazioni assolute (R2 = 0,46; R2 parziale di 0,08), relativo (R2 = 0,39; R2 parziale di 0,06) e potenziale del contenuto di grasso del latte durante la MFD (R2 = 0,17; R2 parziale = 0,03). Quindi, nelle pecore alimentate con lipidi marini, maggiore è il contenuto iniziale di grasso, maggiore è l'intensità della MFD. Questo risultato è stato rafforzato dai risultati di una seconda analisi bivariata (in cui le pecore sono state classificate in base alla concentrazione e produzione iniziale di grasso del latte) e dalle analisi multivariate. Potrebbe anche esistere una relazione, sebbene più debole, tra l'intensità della sindrome, la produzione di latte e la concentrazione di proteine prima del consumo della dieta che causa la MFD. Inoltre, l'intensità della MFD nelle pecore più sensibili potrebbe essere correlata ad alterazioni della funzione ruminale che aumentano la concentrazione nel latte di FA potenzialmente antilipogenici, come il trans-10 18:1. Sebbene il ruolo dei FA del latte come fattori predeterminanti della MFD rimanga poco chiaro, i risultati di questa meta-analisi suggeriscono che il meccanismo di assorbimento mammario degli acidi grassi preformati (>C16) abbia un ruolo rilevante e dovrebbe essere ulteriormente studiato. Sarebbe inoltre opportuno approfondire le basi fisiologiche della relazione tra l'entità della depressione e la concentrazione di grasso del latte prima del consumo della dieta che induce la MFD., La autora de esta memoria ha disfrutado de un contrato predoctoral para la formación de doctores (PRE2018-086174) financiado por el Ministerio de Ciencia, Innovación y Universidades, la Agencia Estatal de Investigación y el Fondo Social Europeo (FSE).
Los trabajos que componen esta memoria forman parte de los proyectos AGL2017-87812-R (financiado por el Ministerio de Economía y Competitividad, la Agencia Estatal de Investigación y el Fondo Europeo de Desarrollo Regional; MINECO/AEI/FEDER, UE) y PID-2020-113441RB-I00 (financiado por el Ministerio de Ciencia e Innovación y la Agencia Estatal de Investigación; MCIN/AEI/10.13039/501100011033/)., A. Della Badia, G. Hervás, P.G. Toral, P. Frutos. (2021). Individual differences in responsiveness to diet-induced milk fat depression in dairy sheep and goats. Journal of Dairy Science 104: 11509-11521. American Dairy Science Association. http://dx.doi.org/10.3168/jds.2021-20414, A. Della Badia, P. Frutos, P.G.Toral, G. Hervas. (2023). Susceptibility to milk fat depression in dairy sheep and goats: Individual variation in ruminal fermentation and biohydrogenation. Journal of Dairy Science 106: 245-256. American Dairy Science Association. http://dx.doi.org/10.3168/jds.2022-22248, Peer reviewed

5 páginas, 4 figuras.
Este trabajo se ha publicado en la revista Journal of Dairy Science en abierto y todos los detalles, incluidos los resultados, referencias bibliográficas utilizadas, etc., están disponibles en el enlace https://doi.org/10.3168/jds.2022-23174., Proyectos PID2020-113441RB-100 y Smarter, financiados por MCIN/AEI/10.13039/501100011033 y la Unión Europea (Horizon 2020; Grant Agreement No. 772787), respectivamente. Contrato predoctoral PRE2021-098235 financiado por MCIN/AEI/10.13039/50110001103 y el Fondo Social Europeo (FSE), Peer reviewed

This supplemental material accompanied the Invited review: Research on ruminal biohydrogenation. Achievements, gaps in knowledge and future approaches from the perspective of dairy science, This work forms part of the PID2020-113441RB-I00 project, funded by the Spanish Research State Agency (MCIN/AEI/10.13039/501100011033)., Peer reviewed

26 páginas, 8 figuras., Scientific knowledge about ruminal biohydrogenation (BH) has improved greatly since this metabolic process was empirically confirmed in 1951. For years, BH had mostly been perceived as a process to be avoided to increase the post-ruminal flow of UFA from the diet. Two milestones changed this perception and stimulated great interest in BH intermediates themselves: In 1987, the in vitro anticarcinogenic properties of CLA were described, and in 2000, the inhibition of milk fat synthesis by trans-10 cis-12 CLA was confirmed. Since then, numerous BH metabolites have been described in small and large ruminants, and the major deviation from the common BH pathway (i.e., the trans-10 shift) has been reasonably well established. However, there are some less well-characterized alterations, and the comprehensive description of new BH intermediates (e.g., using isotopic tracers) has not been coupled with research on their biological effects. In this regard, the low quality of some published fatty acid profiles may also be limiting the advance of knowledge in BH. Furthermore, although BH seems to no longer be considered a metabolic niche inhabited by a few bacterial species with a highly specific metabolic capability, researchers have failed to elucidate which specific microbial groups are involved in the process and the basis for alterations in BH pathways (i.e., changes in microbial populations or their activity). Unraveling both issues may be beneficial for the description of new microbial enzymes involved in ruminal lipid metabolism that have industrial interest. From the perspective of diary science, other knowledge gaps that require additional research in the coming years are evaluation of the relationship between BH and feed efficiency and enteric methane emissions, as well as improving our understanding of how alterations in BH are involved in milk fat depression. Addressing these issues will have relevant practical implications in dairy science., This work forms part of the PID2020-113441RB-I00
project, funded by the Spanish Research State Agency
(Madrid, Spain; MCIN/AEI/10.13039/501100011033).
Supplemental material for this article is available at
https: / / doi .org/ 10 .20350/ digitalCSIC/ 16228. No human
or animal subjects were used, so this analysis did not
require approval by an Institutional Animal Care and Use
Committee or Institutional Review Board. The authors
have not stated any conflicts of interest., Peer reviewed

This work forms part of the PID2020-113441RB-I00 project, funded by the Spanish Research State Agency (MCIN/AEI/10.13039/501100011033). E. Barrio benefited from a FPI predoctoral contract (PRE2021-098235) funded by the Spanish Research State Agency (MCIN/AEI/10.13039/501100011033) and by the European Social Fund (“ESF Investing in your future”).
The authors have not stated any conflicts of interest., Peer reviewed

266 p., [ES] La suplementación de la dieta del ganado lechero con lípidos de origen marino permite modular el perfil de ácidos grasos (AG) de la leche y aumentar el contenido de ciertos lípidos bioactivos, potencialmente para los consumidores. Desafortunadamente, produce el síndrome de baja grasa en la leche (MFD, por las siglas en inglés de milk fat despression), que se caracteriza por una inhibición de la síntesis de grasa en la glándula mamaria. Durante mucho tiempo se pensó que las vacas sufrían MFD, mientras que las ovejas y las cabras eran tolerantes, pero posteriormente se demostró que el ovino y el caprino, al igual que el vacuno, desarrollan este síndrome cuando su dieta se suplementa con lípidos marinos., [EN] Supplementation of dairy ewe diet with marine lipids can modulate the fatty acid (FA) profile of milk and increase the content of certain biactive lipids that are potencially healthy for consumers. However, it causes the milk fat depression syndrome (MFD), which is characterized by an inhibition of fat synthesis in the mammary gland. For a long time, it was thought that cows were susceptible to MFD, whereas goats and sheep were tolerant, but it was later shown that caprine and ovine species, as well as bovine, are also susceptible to suffer this syndrome when their diet is supplemented with marine lipids., [ITA] L'inclusione di lipidi marini della dieta del bestiame da lette permette di migloriare il profilo acidico del latte e di aumentare il contenuto di alcuni lipidi bioattivi, potenzialmente salutari per i consumatori. Allo stesso tempo, questa loro inclusione può indurre la sindrome da basso grasso del latte (dall'inglese milk fat depression, MFD), che consiste nell'ininizione della sintesi del grasso nella ghiandola mammaria. Precedentemente, si riteneva che solo le vacche fossero soggette a MFD, mentre pecore e capre fossero tolleranti, ma in seguito è stato dimostrato che anche ovini e caprini possono sviluppare la MFD quando i lipidi marini vengono aggiunti alla loro razione., Ministerio de Economía y Competitividad, Agencia Estatal de Investigación, Fondo Europeo de Desarrollo Regional, Ministerio de Ciencia e Investigación

[EN] Introduction: As higher feed efficiency in dairy ruminants means a higher capability to transform feed nutrients into milk and milk components, differences in feed efficiency are expected to be partly linked to changes in the physiology of the mammary glands. Therefore, this study aimed to determine the biological functions and key regulatory genes associated with feed efficiency in dairy sheep using the milk somatic cell transcriptome. Material and methods: RNA-Seq data from high (H-FE, n = 8) and low (L-FE, n = 8) feed efficiency ewes were compared through differential expression analysis (DEA) and sparse Partial Least Square-Discriminant analysis (sPLS-DA). Results: In the DEA, 79 genes were identified as differentially expressed between both conditions, while the sPLS-DA identified 261 predictive genes [variable importance in projection (VIP) > 2] that discriminated H-FE and L-FE sheep. Discussion: The DEA between sheep with divergent feed efficiency allowed the identification of genes associated with the immune system and stress in L-FE animals. In addition, the sPLS-DA approach revealed the importance of genes involved in cell division (e.g., KIF4A and PRC1) and cellular lipid metabolic process (e.g., LPL, SCD, GPAM, and ACOX3) for the H-FE sheep in the lactating mammary gland transcriptome. A set of discriminant genes, commonly identified by the two statistical approaches, was also detected, including some involved in cell proliferation (e.g., SESN2, KIF20A, or TOP2A) or encoding heat-shock proteins (HSPB1). These results provide novel insights into the biological basis of feed efficiency in dairy sheep, highlighting the informative potential of the mammary gland transcriptome as a target tissue and revealing the usefulness of combining univariate and multivariate analysis approaches to elucidate the molecular mechanisms controlling complex traits, SI, This research was funded by the Junta de Castilla y León (JCyL, Spain; project CSI276P18) and the Spanish Research State Agency (Agencia Estatal de Investigación, Spain; project PID2020-113441RB-I00 and MCIN/AEI/10.13039/501100011033). Cofunding by the European Regional Development Fund (ERDF/FEDER) is also acknowledged. Research activities for the University of Leon were funded by the SMARTER project through the H2020 research and innovation program of the European Commission (Grant Agreement No. 772787)