Pregnant gilts (n = 126) were assigned randomly to 12 0.4-ha old world-spar bluestem (Bothriochloa ischaemum) pastures in an outdoor swine (Sus scrofa) production system to examine effects of stocking rates (17.5 or 35 gilts/ha; 7 or 14 gilts per pasture) and dietary N on percentage of ground cover, soil nitrate (NO3-) concentration, and reproductive performance. Treatments were arranged factorially with two stocking rates and two diets equivalent in dietary lysine but different in CP (control = 14.7% CP vs experimental = 12.6% CP) with three pastures per treatment. The experiment was repeated during a second parity with the same animals on the same treatments. Each triangular gestation pasture was subdivided into three regions: 1) near the point or radial center; 2) the middle region that contained a hut and a wallow area; and 3) the outer section where gilts were fed each day. Soil samples (15 cm deep) were taken at the beginning and end of the 306-d study, and soil nitrate-N concentrations were determined. Percentage of ground cover was visually estimated initially and every 30 d thereafter through d 306. Before farrowing, gilts were moved to identical pastures for farrowing and were fed a common 16% CP sorghum (Sorghum bicolor)-based lactation diet beginning at the time of movement to the farrowing pasture. Pregnant gilts were weighed at the time of assignment to treatments in the gestation pastures, when they were moved to farrowing pastures, and at weaning. Production data included total number of pigs born per sow, number of pigs born alive or dead, average birth weight, number of pigs weaned, average weaning weight, and mortality. No differences (P > 0.05) were observed between treatments in soil NO3- concentrations. Percentage of ground cover was decreased (P < 0.01) by the higher stocking rate when grazing was initiated in March/April but recovered rapidly after removal of pigs. More (P < 0.01) pigs were weaned per sow (8.4 vs 7.1+/-0.34) from higher gestation-stocking rate groups. Pig mortality in farrowing was greater (P < 0.05) for lower gestation-stocking rates (25.7% vs. 18.1+/-1.9%). A stocking rate of 35 sows/ha might have increased production potential but was associated with a rapid loss of ground cover during spring.

Sustainable outdoor pig production requires vegetation that can maintain ground cover, assimilate manure nutrients, and prevent soil erosion. Two experiments were conducted to evaluate the suitability of four forages: alfalfa (Medicago sativa), tall fescue (Festuca arundinacea), white clover (Trifolium repens), and buffalograss (Buchloe dactyloides) for grazing or ground cover in pastures for pigs. Each forage plot covered 7.5 m2, with nine replicates in a randomized block design. In Exp. 1, eight pregnant gilts had free access to all forages during a 2-d adjustment period. Immediately thereafter, pairs of gilts were assigned randomly to one of each of four blocks of the four forages during a 2-d measurement period. The percentage of ground cover for each forage was visually estimated at 0, 24, and 48 h of study. Behavioral data, including walking, eating, grazing, rooting, drinking, standing, lying, and time spent in hut were video-monitored continuously for 48 h. Initial percentage of ground cover was 100% for all species. By 48 h, percentage of ground cover decreased (P < 0.001) for white clover (11.3 +/- 0.88%) and alfalfa (36.3 +/- 0.88%), but not for tall fescue (98.0 +/- 0.88%) or buffalograss (98.0 +/- 0.88%). Gilts spent more (P < 0.01) time grazing white clover (16.3 +/- 1.97 min/d) and alfalfa (11.2 +/- 1.97) than tall fescue (0.8 +/- 1.97) or buffalograss (0.3 +/- 1.97), and rooted more (P < 0.04) white clover than other forages. In Exp. 2, six gilts from the initial group were put on six blocks of the four forages. Each gilt was assigned randomly to three replicates of each forage, including alfalfa, tall fescue, or buffalograss (white clover was excluded because of damage by gilts during Exp. 1), and gilts grazed single forages for 2 d. After this grazing period, the percentage of ground cover was less (P < 0.01) for alfalfa than for buffalograss or tall fescue (37.5 +/- 0.38, 96.7 +/- 0.39, 96.3 +/- 0.39%, respectively). With access to a single forage, pregnant gilts spent more (P < 0.01) time grazing alfalfa (15.8 +/- 2.36 min/d) than buffalograss (1.5 +/- 2.36) or tall fescue (0.7 +/- 2.37). These gilts clearly preferred grazing white clover and alfalfa, and rooting and eating white clover compared with buffalograss or tall fescue. Rates of ground cover loss were less (P < 0.01) for tall fescue and buffalograss than for the more preferred forages. Less preferred forages could have potential as pasture for swine when the primary objective is ground cover maintenance rather than nutrient supply.

Humic substances include several biological active and inactive compounds that are commonly used for improving soil fertility. Use of humic substances in swine diets is a novel concept. Humic substances contain 8,700 mg/kg of iron but its bioavailability is unknown. This study was conducted to test the bioavailability of iron in humic substances for nursery pigs. One hundred twenty five pigs (Newsham, Colorado Springs, CO) were not given supplemental iron while nursing for 21 d. Pigs were weaned on d 21 and allotted to one of five treatments (four control treatments with different levels of supplemented iron; 0, 30, 70 and 88 mg/kg from FeSO 4 and one treatment with 70 mg/kg iron from humic substances). Pigs were fed diets for 5 wk ad libitum and water was accessible freely. Body weight and feed intake were measured weekly. Blood samples were taken from pigs on d 28 to measure the number of red blood cells and hemoglobin concentration. Pigs fed a diet with the humic substances grew faster (p<0.05) during the first week postweaning, but performance was not different during the entire 5 wk period. Feed intake and gain/feed were the same among treatments. The slope ratio technique was used to estimate relative iron bioavailability. The concentration of blood hemoglobin did not respond to dietary iron levels using this model. However, the number of red blood cells (106/µl) was modeled by 4.438+0.017× 'iron (mg/kg) from FeSO 4 '+0.012×'iron (mg/kg) from the humic substances'. Based on the comparison between the slopes (0.012 from humic substances and 0.017 from FeSO 4 ), iron in humic substances was 71% as available as the iron in FeSO 4 . The slopes for dietary feed intake of FeSO 4 and the iron in humic substances did not differ (p>0.05). Humic substances can replace FeSO 4 as an alternative iron source for pigs at 71% relative bioavailability.

No abstract

RESUMENEl efecto de reducir el nivel de proteína cruda (PC) en la dieta de cerdos en crecimiento se evaluó en dos estudios, usando dietas formuladas para un nivel normal (19%) o reducido (14%) de PC, manteniendo constante la lisina ileal digestible estandarizada (0.85%) y energía (3.37 Mcal ME/kg). El estudio I midió el balance de N en 24 cerdos con peso inicial de 17.7±1.29 kg, mientras que el estudio II usó 24 cerdos con peso inicial de 17.9±0.76 kg, para medir las emisiones aéreas de NH 3 y los niveles de olor en cámaras con flujo de aire dinámico por 21 días. En el estudio I, el N consumido (26.6 %), urinario (56 %) y su excreción total (41 %) se redujeron (P<0.001) en la dieta de PC reducida, mientras que excreción fecal de N fue similar (P>0.4). En el estudio II, reducir la PC no afectó (P>0.10) el comportamiento productivo, pero tendió a reducir (P<0.10) el pH de los purines (6.71, normal a 6.21±0.186 PC reducida) y las emisiones de NH 3 luego del día 9 (interacción dieta y día de estudio, P<0.001). El olor en muestras tomadas a 14 y 21 días, no difirió (512 y 540±115.6 diluciones al umbral de olor, para PC reducida y normal), pero sí aumentó (P<0.01) con el tiempo de alimentación (440 y 612±111.3 diluciones a 14 y 21 días). Los resultados sugieren que por cada unidad porcentual de reducción en la PC se reduce la excreción de N (8 %) y las emisiones de NH 3 en purines (15 %), sin cambiar la intensidad del olor.PALABRAS CLAVE: Amoniaco, Balance de nitrógeno, Olor, Purín de cerdo. ABSTRACTThe effect of reducing the crude protein (CP) levels in diets fed to growing pigs, was evaluated in two experiments, each using two diets formulated to contain either a normal (19%) or a reduced CP level (14%), with constant levels for standardized ileal digestible lysine (0.85%), and metabolizable energy (3.37 Mcal ME/kg). Exp INTRODUCCIÓNTípicamente, más del 70 % del nitrógeno (N) alimentado a los cerdos se excreta en los purines, principalmente vía orina (>75 % de la excreción total de N) en forma de urea, mientras que en el excremento, el N excretado va ligado a proteínas (1) . Cuando se manejan las excretas, cierta cantidad del N soluble se pierde por escurrimiento a mantos de aguas superficiales, o lixiviado a aguas subterráneas como nitrato, o es convertido a N 2 que se volatiliza (2) ; pero la mayor proporción del N se pierde finalmente a la atmósfera en forma de amoniaco (NH 3 ). Por lo anterior, hay una creciente preocupación por el impacto de las emisiones gaseosas y de partículas derivadas de las explotaciones pecuarias en las personas (3,4) y en el ambiente (5) . Por ejemplo, se ha estimado que en los EEUU cerca del 75 % del NH 3 antropogénico que se volatiliza proviene de las explotaciones pecuarias, con 50 % del total producido por bovinos, 25 % por aves y 10 % por los cerdos (6,7) .En la producción de cerdos, el uso de dietas bajas en proteína reduce la excreción de N. Según los datos de Kerr y Easter (8) , por cada unidad porcentual en que se reduzca la proteína cruda (PC) con el uso apropiado de aminoáci...