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Simple Summary: In the Americas, the Comarca Lagunera (CL), located in North-arid Mexico, concentrates one of the main dairy cattle hubs (>500,000 Holstein cows) managed under highly technified-industrial schemes. Dairy cows' nutrition is based on the use of total mixed rations; whereas feed rejection (i.e., 3–5%) has been observed, such feed-leftovers retain a high-pitched nutritional value. The CL also holds an emergent sheep industry, which exhibited the largest production value growth (i.e., >580%; 2010–2023). With that in mind and considering a circular economy perspective, we envisioned a research opportunity. Our working hypothesis states that a basal diet founded on such dairy cow feed-leftovers and aligned with short-term supplementation (i.e., 40 d) with Withania somnifera L. (Ashwagandha) will enhance some reproductive and behavioral outcomes in Black Belly rams. Such approach should bridge these two interesting animal production systems in the CL. Considering a circular economy perspective, this study evaluates the possible effect of targeted short-term supplementation with Withania somnifera L. (WS; Ashwagandha) on ram's seminal quality, socio-sexual behaviors, and blood constituents. Black Belly rams (n = 20) received a basal diet comprising feed-leftovers from dairy cows in the north-arid Mexico (i.e., Comarca Lagunera CL). The experimental units, with proven libido and fertility, were homogeneous in terms of age (3.41 ± 0.21 yr.), live weight (LW; 53.8 ± 3.3 kg), body condition (BC; 2.96 ± 0.01 units), initial sperm concentration (2387 ± 804 × 106), and viability (23.9 ± 15.6%). Rams were randomly assigned during the transition reproductive period (i.e., May to Jun; 25° NL) to three treatment groups: non-supplemented control group (CONT; n = 6), low WS-supplemented (LWS; i.e., 100 mg kg LW−1 d−1 × 40 d; n = 7), and high-WS-supplemented (HWS; i.e., 200 mg kg LW−1 d−1 × 40 d; n = 7). The basal leftover diet was offered twice daily (0700 and 1600 h); the experimental period (EP) lasted 47 d. No differences (p > 0.05) among treatments occurred regarding LW and BCS at the onset of the EP. Whereas the greater scrotal circumference (SCRC, cm) arose in the LWS and CONT rams, an increased ejaculated volume (VOLEJA, mL) occurred in the WS-rams. A total of 5/9 (i.e., 55%) appetitive and 3/3 (i.e., 100%) consummatory sexual behaviors favored (p < 0.05) the WS-rams, particularly the HWS rams, towards the final EP. The same was true (p < 0.05) regarding the hemogram variables white blood cell count (×109 cells L−1), hemoglobin concentration (g dL−1), and medium corpuscular volume (fL). This study, based on a rethink–reuse–reduce enquiry approach, enabled connectedness between two noteworthy animal systems in the CL: dairy cows and meat sheep schemes. Certainly, the use of dairy cow feed-leftovers aligned with the short-term supplementation with WS promoted enhanced testicular function, augmented seminal volume, and an increased sexual behavior in Black Belly rams in northern Mexico. Finally, while our research outcomes should enhance not only the resilience and sustainability of sheep production and the well-being of sheep-producers and their families, it may also embrace clinical translational applications. [ABSTRACT FROM AUTHOR]

Simple Summary: In the arid lands of Northern Mexico, there are several dairy cattle clusters managed under intensive production systems and fed completely with mixed rations, yet 3–5% feed rejection of the total ration offered has been reported. This surplus feed retains a high nutritional value which could be used to improve the reproductive efficiency of goats managed under marginal–extensive schemes. Therefore, we visualized an interesting research opportunity based on the circular economy approach. We hypothesized that a short-term supplementation with feed leftovers from dairy farms (i.e., intensive system) will increase the reproductive outcomes of rangeland managed goats (i.e., extensive system), trying to promote the circularity/connectedness between two highly discordant production systems. Our study intended to elucidate this working hypothesis. Based on a circular economy approach, we evaluated the possible effect of targeted supplementation with leftover feed from dairy cows (i.e., intensive system) on the reproductive performance of crossbred/rangeland goats (i.e., extensive system) in arid Northern Mexico. During the deep-anestrous season (i.e., March–April, 25° North), multiparous goats (n = 38) with a similar body weight (BW) and body condition score (BCS) were randomly assigned to two groups: (1) supplemented group (SG; n = 19; BCS: 1.76 ± 0.07; BW: 43.7 ± 1.8 kg), receiving 400 g goat d−1 of dairy-cow-feed leftovers prior to grazing; and (2) non-supplemented group (NS; n = 19; BCS: 1.76 ± 0.06; BW: 44.3 ± 2.5 kg). Both groups were directed to the rangeland for a period of ≈8 h. While the experimental period lasted 36 d, the experimental breeding considered 11 d (d0–d10). The anovulatory status of goats was ultrasonographically confirmed on days −20, −10, and −1 prior to male–female interaction. Previously, bucks were separated for 3 weeks from the experimental females and received exogenous testosterone every third day (i.e., 50 mg i.m.) prior to mating. With respect to the response variables, namely BW, BCS, blood glucose levels (BGLs), estrus induction (GIE, %), latency to estrus (LTE, h), estrus duration (ED, h), and luteal tissue volume (LTV, mm), no differences (p > 0.05) occurred between experimental groups. However, the response variables, namely goats ovulating (GO, %; 78.9 vs. 47.3), total number of corpuses luteum (TNCL, n; 27 vs. 13), ovulation rate (OR, n; 1.42 vs. 0.73), multiple ovulation (MO, %; 73.3 vs. 55.5), and pregnancy rate on d 36 (PRd36, %, 68.4 vs. 36.8), favored (p < 0.05) the SG over the NS goats. Our results demonstrate that connecting the circularity of two divergent ruminant production systems (i.e., cow-intensive and goat-extensive) by using dairy cows' feed leftovers as a targeted supplementation strategy in anestrous goats under a marginal-rangeland production system enhanced out-of-season reproductive outcomes (i.e., ovulation rate and pregnancy rate), thus benefiting marginal goat producers and their families. [ABSTRACT FROM AUTHOR]