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.

It is currently uncertain how selection of more efficient animals might impact other traits such as resilience (which, in this context, is defined as the ability of an animal to sustain or revert quickly to its previous production level and health status after a disturbance), especially in small ruminants. However, improving, or at least maintaining, resilience is of utmost importance to ensure livestock production in the face of external perturbances, which are expected to become more prevalent in the near future due to climate change and global instability. This study was conducted to investigate whether a nutritional challenge consisting of animals receiving only 70% of their voluntary feed intake (DMI) for 26 d, might differentially affect the response of high- and low-feed efficiency (FE) sheep. To meet this aim, residual feed intake (RFI), as a proxy of FE, was calculated in 40 lactating ewes fed a total mixed ration ad libitum. Using the RFI values, the ewes with the highest (H-FE; n = 8) and the lowest (L-FE; n = 8) FE were selected and subjected to the nutritional challenge. After the feed restriction, all sheep were again fed ad libitum for a further 25 d. Temporal patterns of variation in animal performance, ruminal fermentation and blood and milk metabolites in response to, and recovery from, the underfeeding were examined in H-FE versus L-FE. More efficient ewes (H-FE) tended to eat less than less efficient ewes (L-FE) for the same level of production. Linear regressions for DMI and milk yield data showed that time-series response to the challenge was comparable in L-FE and H-FE. Despite temporal changes due to underfeeding, both FE divergent groups displayed a similar response to, and recovery from, the challenge with no significant differences in the temporal patterns of variation of the parameters analyzed, except for a tendency to higher plasma glucose in the L-FE ewes. These results challenge the general hypothesis that more efficient animals would be less resilient, but further research is still needed on the relationship and possible trade-offs between high efficiency and resilience.

The current global scenario of animal feeding is characterized by limited land resources, increasing feed-food-fuel competition, and growing concern about contribution to environmental pollution. Feeding dairy animals with locally produced alternative feeds, such as insect-derived fats, could partially alleviate this competition and contribute to a more sustainable production system. Nevertheless, to date, no in vivo studies have evaluated the use of insect fats as feed in dairy sheep. Therefore, this study was designed to assess the effects of replacing palm fatty acid distillate, a conventional energy source, with black soldier fly (Hermetia illucens) oil in the diet of dairy ewes, with a focus on animal performance, ruminal fermentation, blood parameters, and oxidative status. To this aim, 14 lactating Assaf ewes were included in a 2 × 2 changeover trial with 2 periods of 25 d each and 2 diets obtained by supplementing a TMR with either 2% DM of palm fatty acid distillate (PFAD diet) or 2% DM of black soldier fly oil (BSFO diet). Individual feed intake and milk yield were recorded 6 and 5 times per week, respectively, and individual milk samples were collected 3 times per week to analyze milk composition. At the end of each experimental period, blood samples were taken to assess blood metabolites, enzymes, and oxidative status, and ruminal fluid was collected to measure pH, ammonia, and VFA. Additionally, on d 25 of each period, ruminal fluid samples were also used as inoculum for 20 h in vitro batch cultures of ruminal microorganisms to examine gas and methane production and DM disappearance. Results indicated similar animal performance (i.e., BW, milk yield, and milk composition, and feed efficiency metrics) and ruminal fermentation parameters between PFAD- and BSFO-fed ewes. The only exception was observed for in vitro methane production, which was higher in BSFO than in PFAD diet. Regarding blood metabolites and enzymes, replacing PFAD with BSFO only caused a tendency toward higher blood glucose and cholesterol levels, whereas oxidative status results showed reduced serum antioxidant capacity in BSFO ewes. Overall, replacing 2% DM PFAD with BSFO in the diet of lactating sheep resulted in similar animal performance and most ruminal fermentation parameters. However, its effects on in vitro methane production, certain blood metabolites (i.e., glucose and cholesterol), and oxidative status require further research.

Inflammatory processes, such as mastitis, are well known to impair not only health but also productivity, underscoring the key role of the immune response in supporting sustainable livestock systems. Among dietary compounds with immunomodulatory properties, PUFA are of particular interest as n-6 PUFA are generally associated with pro-inflammatory effects, and n-3 PUFA with anti-inflammatory effects. This study evaluated whether the dietary incorporation of a source of n-3 PUFA (i.e., linseed oil), as a substitute for an n-6 PUFA source (i.e., soybean oil), could modulate the response of lactating sheep to an inflammatory challenge of the mammary gland. To meet this aim, 22 lactating Assaf ewes were allocated to 2 dietary treatments consisting of a TMR supplemented with either 2% DM of soybean oil or 2% DM of linseed oil. After an adaptation period to the diets (pre-challenge), the sheep were challenged with an intramammary infusion of Escherichia coli LPS (10 µg per half-udder), used as an experimental model of mastitis, and the response, subsequent recovery, and stabilization were characterized over the following 3-wk period (post-challenge). Feed intake, milk yield and composition, SCC, and blood hematological and biochemical variables were monitored before and after the LPS challenge to study their temporal dynamics. Substituting soybean oil with linseed oil had very limited effects, with only minor differences detected in DMI and lactate dehydrogenase. In both diets, milk yield and composition, SCC, and most blood variables showed similar patterns of variation, which were primarily driven by the LPS infusion. The temporal changes induced by the inflammatory challenge included significant decreases in DMI and immune cell counts, and increases in SCC. However, during the post-challenge, most variables returned to pre-challenge values rapidly, consistent with the mild nature of the inflammation. Overall, these results failed to support the hypothesis that replacing soybean oil, rich in n-6 PUFA, with linseed oil, rich in n-3 PUFA, in the diet of dairy ewes would modulate the response to and the recovery from an acute but mild intramammary inflammatory challenge.

Milk fatty acid (FA) composition derives from de novo synthesis in the mammary gland and from the uptake of preformed FA derived from diet, ruminal biohydrogenation, and body tissue mobilization. Consequently, milk FA profiles have been related to nutritional stress responses and feed efficiency (FE). This study tested whether dairy sheep with divergent FE would show different milk FA responses to a nutritional challenge. After calculating two FE indices in 40 ewes, the 9 most efficient (H-FE) and 9 least efficient (L-FE) animals were selected and subjected to a 3-day challenge replacing their total mixed ration (TMR) with wheat straw, followed by TMR refeeding. Temporal patterns of milk FA variation showed only minor differences between H-FE and L-FE ewes. The L-FE group exhibited higher concentrations of iso- and anteiso-17:0 and 18:0, suggesting differences in rumen fermentation and biohydrogenation. In contrast, underfeeding induced marked changes in milk FA composition, including a strong reduction in short- and medium-chain FAs (≤C16), consistent with a shift from de novo synthesis toward increased uptake of preformed FA. Overall, limited differences suggest that milk FA composition may not be a suitable marker for FE. Nonetheless, underfeeding-induced changes highlight its value for exploring nutritional stress responses.