Connectedness between Intensive and Extensive Ruminant Production Systems: Using Dairy Cow Feed Leftovers to Generate Out-of-Season Bio-Economic Indices in Goats

Founded on a circular economy perspective, the possible effect of targeted supplementation with leftover feed from dairy cows (i.e., intensive system) upon the productive economic performance of crossbred–rangeland goats (i.e., extensive system) in northern arid Mexico was assessed. Multiparous goats ( n = 38) with similar body condition score (BCS) and body weight (BW) were randomly assigned during the deep anestrus season (i.e., March–April, 25° N) into two groups: (1) the control-non-supplemented group (CONT; n = 19; BCS: 1.76 ± 0.06; BW: 44.3 ± 2.5 kg) and (2) the supplemented group (SUPL; n = 19; BCS: 1.76 ± 0.07; BW: 43.7 ± 1.8 kg). While the SUPL group received 400 g goat d −1 of dairy cow feed leftovers prior to grazing, both groups went daily to the rangeland (i.e., ≈8 h). The study considered an experimental period of 36 d with an experimental breeding of 11 d (d0–d10). Previously, on days −20, −10, −1 preceding the male-to-female interaction, the anovulatory status of goats was confirmed through ultrasonographic scanning. Prior to mating, the males were separated from goats and treated for a period of 3 weeks (i.e., every 3rd d) with testosterone (i.e., 50 mg i.m.). The response variables evaluated considered goats induced to estrus (GIE, %), goats ovulating (GO, %), ovulation rate (OR, units), pregnancy rate-1 (PRd36, %), pregnancy rate-2 (PRd50, %), embryo mortality-d50 (EMO, %), potential kidding index-d50 (PKId50,%), kid weight at birth simples (KWBS, kg), potential litter efficiency at birth (PLEB, kg), and potential litter efficiency at weaning (i.e., d21 post kidding), either expressed as kg head −1 (PLEW1) or USD head −1 (PLEW2). Although no differences ( p > 0.05) occurred for GIE and PRd50, increases in the phenotypic expression of OR (1.42 vs. 0.73), PRd36 (68.4 vs. 36.8), EMO (23.0 vs. 0), PKId50 (74.7 vs. 26.8), and KWBS (4.1 vs. 3.3) occurred ( p < 0.05) in the SUPL goats. To have a more integrative evaluation regarding the out-of-season reproductive outcomes, three bio-economic efficiency indices per goat exposed to males were generated: PLEB (4.3 vs. 0.6 kg), PLEW1-kg (7.7 vs. 3.1 kg), and PLEW2-USD (63.9 vs. 26.1 USD), which also favored ( p < 0.05) to the SUPL goats. The last result occurred despite no differences ( p > 0.05) regarding BW, BCS, and serum glucose concentrations between experimental groups. Furthermore, applying the main research outcomes from this specific study toward the large-scale goat production system in the Comarca Lagunera—one of the largest dairy goat production hubs in The Americas—denoted promising expectations, either from an economic or productive–reproductive standpoint. Certainly, goat producers from the region would increase their potential annual income just from the sale of kids by close to 250%; that is from MUSD 1.1 to 3.9. This result should reduce food insecurity and economic stress, as well as enhance the livelihoods of the goat keepers and their families.