Grazing time: the missing link : a study of the plant-animal interface by integration of experimental and modelling approaches

A series of grazing (chapters 2, 3, 5 and 6) in-vitro (chapter 4) and modelling trials (chapters 1 and 7) were combined with the following objectives: a) to gain insight in the main mechanisms controlling dry matter intake (DMI), intake rate (IR) and grazing time (GT), during the first grazing session after a.m. milking, b) to judge the relative importance of rumen fill and the concentration of fermentation products in the rumen liquor as candidates to signal the end of the grazing sessions and c) to develop new and modify and evaluate existing simulation model, to operate under non-steady state conditions with the aim to predict DMI, rumen fermentation and supply of nutrients.Increasing the length of the allowed grazing time significantly increased DMI (PThe interaction between starvation time and rumen fill before grazing on GT, although not significant (PThis research offered valuable information about the relative importance of several factors in the control of GT. Clearly it is necessary to understand the way in which the different signals produced at different places are integrated for the animal to modulate eating and other behaviour. In this sense the combination of analytical and synthetic research was proven to be an effective strategy.PhD Thesis, Animal Nutrition Group, Wageningen Agricultural University, Marijkeweg 40, 6709 PG, Wageningen, The Netherlands.</p

Duration of Regrowth of Ryegrass (\u3ci\u3eLolium perenne\u3c/i\u3e) Swards: Effects on Rumen Fermentation of Lactating Dairy Cows

The relative importance of duration of sward regrowth and rumen fill and fermentation on the control of grazing time and intake rate during the first grazing session of the day were studied. Four lactating dairy cows were allowed to graze ryegrass (Lolium perenne) swards, with five different regrowth periods after mowing (6, 9, 16, 22 and 30 d). The cows were allowed to graze until they stopped voluntarily. Samples of rumen liquid were taken at approximately 0, 30, 60, 120 and 240 min after the grazing session was finished. Concentration of volatile fatty acids (VFA) followed a significant quadratic trend with a maximum concentration observed at approximately 110 min after cessation of grazing. In this study, rumen fill, VFA (either total or major components) and ammonia concentration as individual variables were not correlated with grazing time or dry matter intake

Winter Herbage Mass Accumulation and Animals Grazing Days of Set Stocking or Cell Grazing Dairy x Beef Systems in Southwest England

Cell grazing (CG) has shown to increase the production per hectare by allowing higher stocking rates, greater grass production and higher herbage utilisation throughout the grazing season compared to set stocking (SS). Our objective was to compare the herbage growth rate during winter resting (WHGR, October/November to April) and the animals grazing days per ha (AGD-ha) of CG and SS systems grazed by dairy x beef steers. Three 1.75ha (1.5ha in 2018) plots and three 1.0ha were used for the SS and CG, respectively. Forty-two and 48 autumn born dairy x beef steer calves were split into six equal groups and randomly allocated to treatments in April 2018 and April 2020, respectively. In the second grazing seasons (2019 and 2021), the number of animals was reduced to keep stocking rates comparative to the prior year, and steers remained in the plots until finishing (October/November). Herbage mass (HM) was recorded weekly with a rising plate meter. The WHGR was estimated by subtracting the HM recorded at the end of the previous grazing season to the HM recorded at the beginning of the following season and divided by the number of days between readings. The AGD-ha was calculated by summing the days each animal grazed each area and divided by the size of the study enclosure. In three of the four years, the CG had fewer days of winter resting (157-175) than the SS (157-182), whereas the WHGR was greater in three of the four winters (average across years: 5.77 vs. 4.05 kg DM/ha per d, for CG and SS respectively). Despite the shorter winter rest, overall, the CG accumulated 37% more HM (average across years: 976 vs. 710 kg DM/ha) and had 78% more AGD-ha (1102 vs. 620 animal.d/ha) than SS. These differences do not seem to be driven by the herbage residual at the end of the grazing season but by the change in botanical composition across time

Exploración de alternativas para el desarrollo sostenible de sistemas de producción hortícola-ganaderos familiares en el sur de Uruguay

La sostenibilidad de la mayoría de los predios hortícolas familiares en el sur de Uruguay está amenazada por ingresosinsuficientes y por el deterioro de los recursos naturales. En este estudio se cuantificó el efecto de la inclusión de diferentesactividades de producción ganadera en la estructura y en los resultados económico-productivos y ambientales de diferentestipos de sistemas de producción (predios) hortícolas. Se realizó un estudio exploratorio a escala predial con modelos desimulación utilizando dos predios como estudio de caso. Los resultados sugieren que la inclusión de actividades de producciónganadera en los sistemas de producción hortícolas es un factor determinante para reducir la erosión promedio del áreacultivada. Para reducir la erosión el modelo diseñó predios que reducen el área de hortalizas al tiempo que expanden larotación forrajera. Como consecuencia de esto, también se redujo el ingreso familiar (IF) entre 12 % y 31 % según el casoestudiado. Sin embargo, pudimos diseñar sistemas de producción con erosión menor a la tolerable para el tipo de suelo e IFmayor al objetivo, en los dos predios. De las actividades ganaderas evaluadas las más apropiadas para incluir en predios hortícolasson el engorde de novillos o vaquillonas en ciclos de 14 a 18 meses, debido al menor costo para reposición de animales y al menoruso de concentrados, lo que disminuye las necesidades de capital y la dependencia de insumos externos