Responses of selected plasma metabolites to a 2-day nutritional challenge of goats divergently selected for functional longevity.

Understanding the extent to which genetics × environment plays a role in shaping individual strategies to environmental challenges is of considerable interest for future selection of more resilient animals. The objective of this study was to evaluate the metabolic responses of goats, selected for functional longevity, to a nutritional challenge. This evaluation was based on plasma metabolites and was repeated across 2 experimental farms over 2 years. We carried out 6 different experimental trials from 2018 to 2022 (4 trials on site Bourges, 2018-2021 and 2 trials on site Grignon, 2021-2022) in which 267 first kidding goats, daughters of Alpine bucks divergently selected for functional longevity, longevity plus (n = 137), and longevity minus (n = 130), were exposed to a 2-d nutritional challenge in early lactation. The experiments consisted of a 5 or 7-d control period (prechallenge) on a standard lactation diet followed by a 2-d nutritional challenge with straw-only feeding, and then a 7- or 10-d recovery period on a standard lactation diet, for site Bourges and Grignon, respectively. During the challenge plasma metabolite composition was measured. Linear mixed models were used to analyze all traits, considering the individual as a random effect and the 2 × 2 treatments (i.e., genetic line and year nested in site) and litter size as fixed effects. The linear mixed-effects model using a piecewise arrangement was used to analyze the response/recovery profiles to the nutritional challenge. The estimates of the random effect for each individual, using the mixed models without the fixed effects of genetic line, were used in a sparse partial least square discriminant analysis (sPLS-DA) to compare the goat metabolism response to the challenge on a multivariate scale. The plasma glucose, BHB, nonesterified fatty acids (NEFA), and urea concentrations significantly responded to the 2-d nutritional challenge. Selection for functional longevity did not affect plasma glucose, NEFA, BHB, and urea response/recoveries to a 2-d nutritional challenge. However, site, trial, and litter size significantly affected these responses. Moreover, the plasma metabolites seem not to fully recover to prechallenge levels after the recovery phase. The sPLS-DA analysis did not discriminate between the 2 longevity lines. We observed meaningful between-individuals variability in plasma BHB, especially on the prechallenge and rate of response and rate of recovery from the 2-d nutritional challenge (CV = 26.2%, 36.1%, and 41.2%, repeatability = 0.749, 0.322, and 0.741, respectively). Plasma NEFA recovery from challenge also demonstrated high between-individuals variability (CV = 16.4%, repeatability = 0.323). Selection for functional longevity did not affect plasma metabolites responses to a 2-d nutritional challenge in dairy goats. Plasma NEFA and BHB response and recovery presented high between-individuals variability, indicating that individual adaptative characteristics to nutritional challenges are not related to the environmental conditions but to inherent individual characteristics.