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The aims of this study were to evaluate the effect of genetic and non-genetic factors on the growth of Socorro Island Merino lambs and to model their growth curve using nonlinear mathematical models. The weight of 41 Socorro Island Merino lambs was recorded at birth and at 45, 90, 135, 180, 225, 270, 315 and 365 days of life from May 2019 to September 2021. The effects on growth of sex, genotype, year of birth, and parity of the dam were analyzed. Four non-linear models (Brody, Logistic, Gompertz and von Bertalanffy) were fitted for determining the best model to describe growth curve. Birth weight and pre-weaning growth rate were not affected (P 0.05) by any of the factors studied, while weaning weight was only significantly affected (P 0.05) by sex. Year of birth significantly affected (P 0.05) post-weaning growth rate and weight of the lamb from 270 days, while sex significantly affected (P 0.05) weight at 315 days. The Gompertz and Brody models were the best fitted to describe growth curves of lambs. Purebred males showed a larger response to increasing levels of energy-protein supplementation, while they had greater mature weight and lower maturation rate compared to females and crossbred males. In conclusion, knowledge of growth and factors influencing growth pattern can help implement appropriate management strategies and make decisions aimed at the conservation of Socorro Island Merino lambs.

<p class="Default"><strong>Background. </strong>Propylene glycol has been used successfully since the 1950’s for him acute and prophylactic treatment of ketosis in dairy cows however; its use has been poorly evaluated in beef cattle and meat sheep.<strong> Objective</strong>. Evaluate the effects of different doses of propylene glycol on the productive parameters, blood metabolites and ruminal parameters in fattening lambs. <strong>Methodology</strong>. Twenty lambs 14.70 ±0.57 kg of weigh, 2 months old, males and Katahdin-Black Belly breed, were randomly assigned to one of four treatments, a control mixed ration and an experimental diet with three different levels of propylene glycol: 1.0, 1.5 and 2.0 g/20 kg live weight/day. The effects of propylene glycol on blood metabolites, ruminal and productive parameters were assessed. <strong>Results</strong>. Propylene glycol supplementation did not affect (P&gt;0.05) glucose, total lipids, triglycerides and cholesterol concentration as well as increased (P&lt;0.05) the concentration of beta hydroxybutyrate. In addition, its inclusion resulted in an increase in pH and protozoa population and in a decrease of reductive activity (P&lt;0.05). No effect was observed (P&gt;0.05) on feed intake, weight gain and feed conversion ratio of lambs but carcass yield was improved without increasing the feeding cost of production. <strong>Implications</strong>. Propylene glycol is a viable option as an energy source in fattening lambs. <strong>Conclusion</strong>. Inclusion of PPG increased the pH and the population of ruminal protozoa, reduced the formation of ketone bodies and improved the carcass yield of lambs without increasing the meat production cost.</p>

En Calvillo, Aguascalientes, México, durante 2012 y 2013, se evaluó el efecto del fuego (tratamientos de quema Q y sin quema SQ) sobre la producción y calidad nutritiva del zacate rosado en tres etapas fenológicas: crecimiento C, madurez M, y latencia L. El fuego se aplicó en abril de 2012 a parcelas de 16 m2. Durante 2012 y 2013 la producción de forraje (base seca) fue diferente (p≤ 0.05) con 168.7, 393.7 g m2 y 53.9, 192.7 g m2 para los tratamientos Q y SQ respectivamente. La proteína cruda fue similar entre tratamientos (p≥ 0.05), pero diferente (p≤ 0.05) entre etapas C, M, L, con un total de 13.3, 5.2, 5.6% y 12.6, 4.6, 3.2% respectivamente. La digestibilidad de la materia seca (DISMS) resultó diferente (p≤ 0.05) entre tratamientos Q y SQ y entre las etapas de C, M, y L, con un total de 61.6, 46.0, 48.3% y 50.3, 42.5, 44% respectivamente. La fibra detergente neutro (FDN) resultó diferente (p≤ 0.05) entre las etapas C, M, y L, no así entre tratamientos Q y SQ con valores 67.1, 76.5, 78% y 66.4, 76.3, 79.6% respectivamente. La fibra detergente ácido (FDA) mostró diferencias (p≤ 0.05) entre etapas C, M, y L, más no entre tratamientos Q y SQ con un total de 35.8, 50.6, 57.4%, y 33.2, 54.6, 56.3% respectivamente. El fuego incrementó tanto la producción y calidad del forraje del zacate rosado y podría utilizarse como estrategia de manejo ecológica en áreas de pastoreo extensivo invadidas con zacate rosado.