Two experiments were conducted to evaluate the effects of the level of corn dry distillers grains with solubles (CDDGS) supplementation on growing performance, blood metabolites, digestion characteristics and ruminal fermentation patterns in steers grazing dormant forage. In Exp. 1, of growth performance, 120 steers (204±5 kg initial body weight [BW]) were distributed randomly into 3 groups (each of 40 steers), which were provided with the following levels of CDDGS supplement: 0%, 0.25%, or 0.50% BW. All groups of steers were grazed for 30 days in each of 3 grazing periods (March, April, and May). Approximately 1,000 ha of the land was divided with electric fencing into 3 equally sized pastures (333 ha in size). Blood samples were collected monthly from 20 steers in each grazing group for analysis of glucose (G), urea-nitrogen (UN) and non-esterified fatty acids. Final BW, average daily gain (ADG) and supplement conversion (CDDGS-C) increased with increasing levels of CDDGS supplementation (p<0.05).The CDDGS supplementation also increased the plasma G and UN concentrations (p<0.05). In Exp. 2, of digestive metabolism, 9 ruminally cannulated steers (BW = 350±3 kg) were distributed, following a completely randomized design, into groups of three in each pasture. The ruminally cannulated steers were provided the same levels of CDDGS supplementation as in the growing performance study (0%, 0.25%, and 0.50% BW), and they grazed along with the other 40 steers throughout the grazing periods. The dry matter intake, crude protein intake, neutral detergent fiber intake (NDFI), apparent digestibility of dry matter (ADDM), crude protein (ADCP) and neutral detergent fiber (ADNDF) increased with increasing levels of CDDGS supplementation (p<0.05). The ruminal degradation rates of CP (kdCP), NDF (kdNDF) and passage rate (kp) also increased with increasing levels of CDDGS supplementation (p<0.05). Ruminal ammonia nitrogen (NH3-N) and propionate concentrations also increased with increasing levels of CDDGS supplementation (p<0.05). However, acetate concentrations decreased with increasing levels of CDDGS supplementation (p<0.05). Liquid dilution rate increased with increasing levels of CDDGS supplementation but ruminal liquid volume decreased (p<0.05). On the basis of these findings, we can conclude that CDDGS supplementation enhanced the productive performance of cattle grazing native rangeland without negatively affecting forage intake, glucose and urea-nitrogen blood concentrations, ruminal degradation and ruminal fermentation patterns.

The objective of the study was to quantify annual and seasonal differences in the chemical composition, in vitro gas production, in situ degradability and ruminal fermentation of grazing steers’ diets. Diet samples were collected with four esophageal cannulated steers (350±3 kg BW); and four ruminally cannulated heifers (342±1.5 kg BW) were used to study the dry matter degradation and fermentation in rumen. Data were analyzed with repeated measurements split plot design. The crude protein, in vitro dry matter digestibility and metabolizable energy were higher during the first year of trial and in the summer (p<0.01). The values of calcium, phosphorus, magnesium, zinc and copper were higher in summer (p<0.05). The gas produced by the soluble and insoluble fractions, as well as the constant rate of gas production were greater in summer and fall (p<0.01). The ammonia nitrogen (NH3N) and total volatile fatty acids concentrations in rumen, the soluble and degradable fractions, the constant rate of degradation and the effective degradability of DM and NDF were affected by year (p<0.05) and season (p<0.01). Our study provides new and useful knowledge for the formulation of protein, energetic and mineral supplements that grazing cattle need to improve their productive and reproductive performance.

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Osvaldo Reyes, Manuel Murillo, Esperanza Herrera, and Francisco O. Carrete. 2016. Seasonal and annual changes in the quality of native rangeland selected by grazing steers in northern Mexico. Cien. Inv. Agr. 43(2):203-212. The objective of this study was to determine and compare seasonally the chemical composition, in vitro gas production, in situ degradability and ruminal fermentation of the diet selected by cattle grazing on native rangeland over two years. Diet samples were collected from four esophageal fistulated steers (350 ± 3 kg BW), and four ruminally fistulated steers (342 ± 1.5 kg BW) were used to evaluate degradation and ruminal fermentation. Data were analyzed using a repeated measurements design. The crude protein (CP), in vitro dry matter digestibility (IVDMD) and metabolizable energy (ME) were higher in 2008 (P≤0.01) and in the summer (P≤0.05). The volatile fatty acids (VFA) and propionate concentrations were affected by season and year (P≤0.05). The gas produced by the soluble (a) and insoluble (b) fractions and the constant rate of gas production (c) were greater in the summer and fall (P≤0.05). The values of effective degradability of dry matter (EDDM) were greater in 2008 (P≤0.01) and during the summer (P≤0.05). Likewise, ruminal NH 3 N concentrations were greater in 2008 and during the summer (P≤0.05). The total concentrations of volatile fatty acids (VFA) and propionate were affected by year (P≤0.05) and season (P≤0.05). This study showed a reduction in the nutritive value of the diet selected by grazing cattle due to annual and seasonal changes.

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