Goat production is an important agricultural activity in Mexico due to its productive and social relevance, supporting thousands of smallholder systems across rural regions (Chávez-Espinoza et al., 2021). The country maintains an estimated 8.7 million goats, according to the Servicio de Información Agroalimentaria y Pesquera (SIAP, 2022), positioning Mexico among the top global producers and as a major milk-goat contributor in the Americas (Aréchiga et al., 2008). Within the national context, the Comarca Lagunera stands out as the most important dairy-goat region, concentrating over 404,369 animals and contributing approximately 40% of the goat milk produced in Mexico (SIAP, 2023). This area has become a major production hub and represents the most important goat-milk-producing region nationwide, involving approximately 9,000 production units, mostly belonging to small-scale farmers. According to reports from SIAP, by the end of 2023, the Comarca Lagunera reached a total output of 70.95 million liters of goat milk. Of this amount, Coahuila contributed 46.1 million liters, while Durango produced 24.85 million liters (SIAP, 2023).
       
Goat production systems in Mexico, particularly those managed by smallholders, encompass a wide range of feeding and management strategies. Owing to their strong adaptability and hardiness, goats are capable of thriving across diverse ecological conditions (Chávez-Espinoza et al., 2021). Within this heterogeneity of production environments, nutritional management becomes a central determinant of productivity and metabolic stability. Previous studies have demonstrated that feeding management and nutritional strategies directly influence goat milk composition, productive performance and the nutritional characteristics of dairy products derived from goats (Hammam et al., 2022; Muñoz-Salinas et al., 2023).
       
In these systems, particularly intensive and mixed production units, nutritional management plays a key role, as maintaining an adequate glucose supply represents a major metabolic challenge for ruminants. Because extensive foregut fermentation limits intestinal absorption of dietary carbohydrates, goats rely almost entirely on hepatic gluconeogenesis to sustain their energy metabolism (Radziuk, 2001; Yang et al., 2024; Wang et al., 2024).
       
During lactation, especially under intensive systems with high production demands, glucose requirements increase substantially and may exceed the availability of propionate, the primary gluconeogenic precursor derived from ruminal fermentation (Noro and Wittwer, 2012). Such limitations can compromise energy balance, milk production and milk composition, prompting interest in nutritional strategies aimed at improving glucose availability, including addition of gluconeogenic precursors (Wang et al., 2024).
       
However, scientific evidence regarding the effects of the dietary addition of gluconeogenic precursors in lactating goats, particularly across different production systems, remains limited. Therefore, the aim of this study was to evaluate the effect of dietary supplementation with a commercial gluconeogenic precursor on milk yield and milk quality in lactating goats managed under intensive and mixed production systems.

Study area
 
The study was conducted in two goat-producing communities in the municipality of Lerdo, Durango, Mexico, from February to March 2024. The intensive production system was located in Álvaro Obregón (25.49667° North,
-103.55750° West) and the mixed system in Las Isabeles (25.51423° North, -103.50522° West). The region has a mean annual temperature of 21.3°C (CONAGUA, 2023).
 
Ethical approval
 
All animal handling and experimental procedures were conducted in accordance with internationally accepted ethical principles for the care and use of animals in research. The study complied with the International Code of Ethics under registration number 38111-4255022002-2955.
 
Animals and experimental design
 
Intensive system
 
The trial was conducted from February 14 to March 27, 2024, lasted 42 days and included 30 multiparous crossbred goats (Body Condition Score 2.5±0.5; 38±2 days in milk; milk yield 1.8±0.5 L/day). Animals were homogeneously allocated into three groups (n=10 per group) according to body weight, BCS (Villaquiran et al., 2007) and individual milk yield.
       
Goats managed under the intensive system remained in confinement throughout the experimental period and were fed a diet consisting of alfalfa hay, oat hay, peanut crop residue and a commercial concentrate containing 14% crude protein. Water was available ad libitum.
       
A commercial gluconeogenic precursor (powder; 1-2 propanediol 3.30%, Na/Ca propionate 6.90%, vehicle c.b.p. 100%) was individually added to the animal’s ration during milking from days 1 to 35 of the trial: Low dose group (G1): 3 g/day; high dose group (G2): 6 g/day; control group (G3): 0 g/day.
 
Mixed system
 
The trial was conducted from February 19 to April 01, 2024, lasted 42 days and included a total of 39 multiparous crossbred goats (Average BCS was 2.5±0.5; 35±2 days in milk; milk yield 1.6±0.5 L/day) distributed into three homogeneous groups (n=13 per group) following the same criteria.
       
Goats managed under the mixed production system grazed natural vegetation and shrub forage resources during the day and received supplementary feeding during confinement periods, consisting of alfalfa, ground corn stover and a commercial concentrate containing 14% crude protein. Water was available ad libitum.
       
Goats received a commercial gluconeogenic precursor (1-2 propanediol 3.30%, Na/Ca propionate 6.90%, vehicle c.b.p. 100%) from days 1 to 35. Low dose group (G1): 3 g/day; high dose group (G2): 5 g/day; control group (G3): 0 g/day.
 
Milk production, sampling and quality analysis
 
Individual milk yield (kg/day) was recorded weekly from day 1 to day 35, along with a final post-addition sampling on day 42, using a portable scale (Truper® model 15161). Milk samples were collected following standard manual milking procedures for small ruminants (FAO 2011; Pugh and Baird, 2011) into sterile tubes (45 mL) and transported in insulated containers to the Animal Production Research Center (CIPA), Universidad Autónoma Agraria Antonio Narro, Unidad Laguna (25.55437° N, 103.37582° W).
       
Upon arrival, samples were stored under refrigeration (4°C) until analysis. Prior to analysis, milk samples were gently homogenized and tempered in a water bath until reaching a temperature of approximately 39-40°C, following the manufacturer’s recommendations to ensure proper fat solubilization and analytical accuracy. Subsequently, milk fat, protein, lactose and total solids were determined using a MilkoScan Mars FOSS® analyzer.
 
Statistical analysis
 
Data were analyzed using repeated-measures GLM (PROCGLM, SAS 9.0). Statistical significance was set at P<0.05.

Milk yield (Table 1) was significantly higher (P<0.05) in goats managed under the intensive production system compared to those under the mixed system (1.94±0.03 vs. 1.65±0.02, respectively). However, no significant differences were observed among treatments (P>0.05).
       
This difference can be attributed to greater dietary energy and protein availability, which supports lactose synthesis and milk volume. This agrees with Aschenbach et al. (2010), who identified hepatic gluconeogenesis (mainly driven by ruminal propionate) as a key determinant of milk production, although its impact may be limited when dietary energy requirements are already met.
       
The lack of differences in milk yield among treatments is consistent with studies in goats and cows supplemented with propylene glycol, glycerol, or protected glucose, where productive responses are more evident during the transition period or under metabolic stress (Lien et al., 2010; Behery et al., 2020; Akhtar et al., 2023). In the present study, goats were beyond the immediate postpartum period and averaged 35-38 days in milk at the beginning of the trial, which may have reduced the magnitude of the productive response to the dietary addition.
       
Milk fat percentage was affected by production system, sampling time and their interaction (P<0.05). Fat percentage was higher in the mixed system than in the intensive system (3.71±0.07 and 2.42±0.08, respectively). A reduction in fat percentage was observed from the third week of sampling onwards, with higher values in the mixed system than in the intensive system (P<0.05).
       
The higher milk fat percentage observed in the mixed system may be associated with differences in feeding management and forage resources available between production systems. Goats in the mixed system grazed natural vegetation and shrub forage resources in addition to receiving supplementary feed, which may have contributed to differences in milk composition. The progressive decrease in milk fat percentage over time agrees with previous reports describing changes in goat milk composition throughout lactation (Zeng et al., 1997; Boumediene et al., 2025).
       
Similarly, milk protein percentage was higher in the mixed system than in the intensive system (P<0.05). Regarding the system × treatment interaction, statistically significant differences were observed (P<0.05). In the intensive system, goats that received the gluconeogenic precursor exhibited a higher milk protein percentage than those in the control group (P<0.05). This suggests that the response to gluconeogenic precursors is modulated by the type of production system. In the intensive system, dietary addition increased milk protein content compared with the control group, which agrees with reports by Yu et al. (2024) and Zhang et al. (2020), who described improvements in milk protein synthesis associated with greater glucose supply and enhanced mammary gland energy efficiency.
       
Lactose percentage showed significant differences among production systems, treatments and sampling time (P<0.05). In the intensive system, lactose percentage was lower than in the mixed system (4.17±0.01 and 4.28±0.01, respectively). Likewise, goats receiving a low dose of the precursor had a higher milk lactose percentage than those in the control group (P<0.05), whereas goats receiving a high dose exhibited lactose values similar to those of the low-dose and control groups (P>0.05).
       
The higher lactose concentration observed in the mixed system and in goats with the low dose of the gluconeogenic precursor supports the hypothesis that moderate glucogenic precursor addition enhances hepatic gluconeogenesis and, consequently, glucose availability for lactose synthesis, the main osmotic regulator of milk volume (Aschenbach et al., 2010; Tetrick and Odle, 2020). The absence of differences between the high-dose and control groups may indicate a metabolic saturation effect, as previously suggested in dairy cows supplemented with high levels of propionate or glycerol (Rathert-Williams et al., 2023; Wang et al., 2024).
       
Regarding total solids percentage, a significant effect of production system, treatment and sampling time was observed (P<0.05). In the intensive system (9.93±0.08), total solids were lower than in the mixed system (11.47±0.08). Likewise, goats with the high dose of the gluconeogenic precursor showed a higher total solids percentage (10.85±0.10%) compared with the control group (10.48±0.10%). In contrast, the low-dose treatment (10.78±0.10%) did not differ statistically from the other treatments (P>0.05). Significant differences were also detected across the experimental period (P<0.05). The initial value was the highest and progressively decreased over the first five weeks of the experiment, reaching the lowest point on day 35. Subsequently, an increase was observed on day 42. Multiple comparison analysis indicated significant differences between the initial value and days 14 to 42 (P≤0.0025), whereas no differences were detected at days 14, 21, 28 and 42 (P>0.57; Fig 1).


       
The higher total solids content observed in the mixed system is closely associated with the higher fat and protein percentages in milk. Furthermore, the positive response to the high dose of the gluconeogenic precursor agrees with findings reported by Kupczyński et al. (2020) and Delgado and Galindo (2024), who indicated that increased glucose availability can improve metabolic efficiency and nutrient partitioning toward milk component synthesis, even when milk yield does not increase significantly.
       
Finally, the decrease in total solids during the first weeks of the experiment, followed by a subsequent increase, may reflect a metabolic adaptation process of goats to the dietary addition of the gluconeogenic precursor, as well as physiological changes associated with the progression of lactation. This phenomenon has been previously described in dairy ruminants, particularly in Alpine goats, in which temporal variations in milk composition associated with lactation stage have been documented (Danf et al., 1995; Zeng et al., 1997).
       
In the intensive system, dietary addition of a gluconeogenic precursor improved milk protein content, whereas goats managed under the mixed production system showed higher milk fat, protein and total solids percentages. These differences may be associated with variations in feeding management and forage resources available between production systems. Moderate doses of the precursor appeared most effective for enhancing lactose synthesis, suggesting that excessive supplementation may reach a metabolic saturation point. These findings highlight that gluconeogenic precursors can be used strategically to improve milk quality in dairy goats, even when overall milk production is not significantly affected.
       
These findings partially agree with previous studies in ruminants, in which the effects of gluconeogenic precursors are more consistently observed on milk composition than on milk yield, especially when animals are not under severe negative energy balance (Kupczyński et al., 2020; Yu et al., 2024).

Dietary addition of a gluconeogenic precursor in lactating goats did not significantly increase milk yield under either intensive or mixed production systems. However, it positively influenced milk composition, particularly protein, lactose and total solids content, with effects modulated by the production system and the dose administered. The 3 g/day dose produced the most consistent overall response, whereas the higher dose was associated with improvements in total solids content. Such nutritional interventions may contribute to optimizing metabolic efficiency and milk composition in different production systems, supporting more targeted management practices for smallholder and intensive goat farming in Mexico.

The authors would like to thank to all those who contributed to the successful completion of this research. Special thanks are extended to the Secretaría de Ciencia, Humanidades, Tecnología e Innovación (SECIHTI) for the financial support and budget allocated to the research project, which made it possible to conduct this study and to prepare and submit this article as part of the requirements for the author’s master’s degree.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily reflect the views of their affiliated institutions. The authors are responsible for the accuracy and integrity of the information presented.

All authors declare that they have no conflict of interest regarding the publication of this article.