Edwin Sandoval-Lozano

Small ruminant production is increasingly affected by heat stress, with recent heat waves highlighting growing economic and welfare-related challenges. Chronic exposure to elevated temperatures disrupts thermoregulation, reduces feed intake, slows growth, compromises meat quality, and increases mortality. This study evaluated the effects of chromium-yeast supplementation at different doses and timepoints on physiological and molecular stress biomarkers in heat-stressed lambs. Forty-eight clinically healthy 6-month-old Katahdin lambs (average weight 20 ± 2.9 kg) were assigned to a 2 × 4 factorial design, with two ambient temperature conditions (heat stress [HS] and thermoneutral [TN]) and four levels of dietary Cr-yeast (0, 0.2, 0.4, and 0.8 mg/kg of dry matter intake). Lambs were housed individually in pens (1.2 × 2.5 m), with ad libitum access to water, and fed a 50:50 corn silage and concentrate diet (excluding mineral premix) twice daily. Blood samples were collected at days 0, 30, and 60 to evaluate plasma cortisol and the expression of hsp60 and hsp70. Chromium bioavailability was assessed by blood levels using absorption chromatography, and glucose clearance was measured at the end of the experiment. Significant reductions in cortisol and hsp70 expression were observed after 30 days of Cr-yeast supplementation under HS conditions (p < 0.05), particularly at the highest dose. For hsp60, a significant reduction was observed at the highest dose on day 30 under HS (p < 0.05). These effects were not sustained on day 60 (p > 0.05). No significant differences were detected under TN conditions (p > 0.05). These findings suggest that Cr-yeast may offer short-term physiological and cellular protection against chronic heat stress in lambs.

Extensive livestock management is a common practice in the dry tropics. However, summer conditions can cause high fiber and low protein concentrations, even in grasses adapted to tropical soils, such as Angleton (Dichanthium spp.), widely used in producing small ruminants. On the other hand, Guacimo (Guazuma ulmifolia) is a tree that overcomes high temperatures and hydric stress. This research evaluated the effect of replacing Angleton with four foliage levels of Guacimo on hair lambs’ intake, digestibility, and blood metabolites. Twelve male hair lambs with an average of 22.0 ± 1.3 kg of body weight were used in an experimental 4 × 4 square design. Treatments were as follows: 100 % Angleton hay; 85 % Angleton hay + 15 % Guacimo foliage; 70 % Angleton hay + 30 % Guacimo foliage, and 55 % Angleton hay + 45 % Guacimo foliage. Dry matter (DM), organic matter (OM), crude protein (CP), and neutral detergent fiber (NDF) intake, as well as CP digestibility and glucose concentrations, increased linearly as the level of Guacimo rose (P > 0.05). Guacimo foliage improves intake, blood metabolites, and in vivo digestibility of DM and can be used to replace part of the hay in lamb rations.

The Colombian Creole sheep breed has a high economic and social importance for Colombia. Both males and females of this breed are multipurpose animals, and evaluating the production and meat quality of both sexes is important for small farmers in Colombia. This requires the use of tools that help to evaluate critical production points, such as Real-time quantitative polymerase chain reaction (RT-qPCR), which is a widely used molecular tool for the relative quantification of candidate genes in various tissues. For its correct use, the use of housekeeping genes with stable expression, so-called "reference genes", is required. However, recent studies have shown that the expression of these reference genes can vary among tissues and can be modulated by breed, sex, or external stimuli. Likewise, there is little information regarding the expression of these genes in the Longissimus thoracis et lumborum muscle of male and female Colombian Creole sheep. In this study, the stability in the expression of seven reference genes (ACTB, YWHAZ, SDHA, GAPDH, TUBB2A, B2M, and PGK1) in the Longissimus thoracis et lumborum muscle of male and female Colombian Creole sheep was compared since they are used in RT-qPCR studies to determine the most stable ones for this breed. Twelve animals, six males and six females, with a body weight of 26 ± 4 kg and 12 ± 3 months of age, were used under grazing conditions. Biopsies of the Longissimus thoracis et lumborum muscle were taken, from which RNA was extracted and cDNA was synthesized. Expression was determined using RT-qPCR, and its stability was analyzed by computational algorithms using the geNorm, Normfinder, and BestKeeper software packages, which were integrated using the RefFinder software package. The results indicate that GAPDH, ACTB, and SDHA have the highest stability, whereas the most variable expression was found for B2M. These data provide the basis for more precise results in RT-qPCR studies of gene expression in the muscle of Colombian Creole sheep.