Conselho Nacional de Desenvolvimento Científico e Tecnológico / The work was carried out to evaluate characteristics of natural grassland and body development of rearing beef heifers, submitted to different types of grazing management in the spring / summer period. The experiment was conducted in natural pasture belonging to EMBRAPA Pecuária Sul, in the municipality of Bagé, Rio Grande do Sul, from October 2014 to March 2015. The treatments were continuous and rotational grazing methods, both managed on variable stocking rate based on forage mass above 8 cm. The experimental animals were Brangus heifers from EMBRAPA Pecuária Sul cattle herd, with initial weight of 267 kg and 18 months old. The stocking rate was increasing during the trial period. The available forage on offer was similar between treatments and between the two periods. There was no interaction treatment x period for average daily gain (ADG), gain per area (GPA) and body condition score (BCS) and these variables were similar between treatments (P> 0.05). At the end of the experiment average heifers reproductive tract score (RTS) was 3.68. The descriptor variables of sward structure showed no significant difference between grazing methods (P>0.05), except for the percentage of stems (P=0.003) that was higher in the continuous treatment (16.06%). Species of greater participation and relative coverage in the area were evaluated Paspalum notatum, Paspalum pumilum, Axonopus affinis, Mnesithea selloana, and the exotic Eragrostis plana species. The descriptor variables of interest and importance of the species did not differ between grazing methods (P>0.05) or interaction treatment x station. For average canopy height there was no difference between treatments (P= 0.798) nor interaction treatment x station (P=0.621). The importance value index (IVI) showed no difference between treatments (P=0.798), or interaction treatment x station (P=0.901). Management of a natural pasture, both under continuous as rotational grazing, during the spring-summer period, enables proper body development for mating beef heifers at 24 months. The grazing method did not change the structure and dynamics of vegetation in the study period. Continuous grazing reduced the floristic diversity comparing to rotational grazing, with clear dominance of Eragrostis plana species. / O trabalho foi conduzido com o objetivo de avaliar características da pastagem natural e do desenvolvimento corporal de novilhas de corte na fase de recria, submetidas a diferentes métodos de pastejo, no período primavera/verão. O experimento foi conduzido em área de pastagem natural pertencente à EMBRAPA Pecuária Sul, no município de Bagé, Rio Grande do Sul, de outubro de 2014 a março de 2015. Os tratamentos foram os métodos de pastejo contínuo e rotativo, ambos manejados com taxa de lotação variável, com base na massa de forragem acima de 8 cm. Os animais experimentais foram novilhas da raça Brangus do rebanho da Embrapa Pecuária Sul, com peso inicial de 267 kg e 18 meses de idade. A taxa de lotação foi crescente no decorrer do período experimental. A oferta de forragem disponibilizada foi semelhante entre os tratamentos e entre os períodos estudados. Não houve interação tratamento x período para ganho médio diário (GMD), ganho por área (GPA) e escore de condição corporal (ECC) e estas variáveis também foram semelhantes entre os tratamentos (P>0,05). Ao final do experimento as novilhas apresentaram escore de trato reprodutivo (ETR) médio de 3,68. As variáveis descritoras da estrutura do pasto não apresentaram diferença significativa entre os métodos de pastejo (P>0,05), à exceção da porcentagem de colmos (P=0,003) que foi superior no tratamento contínuo (16,06%). As espécies de maior participação e cobertura relativa na área avaliada foram Paspalum notatum, Paspalum pumilum, Axonopus affinis, Mnesithea selloana, e a espécie exótica Eragrostis plana. As variáveis descritoras da participação e importância das espécies não apresentaram diferença entre os métodos de pastejo (P>0,05) nem interação tratamento x estação. Para altura média de dossel não houve diferença entre tratamentos (P=0,798), tampouco interação tratamento x estação (P=0,621). O índice de valor de importância (IVI), não apresentou diferença entre tratamentos (P=0,798), nem interação tratamento x estação (P=0,901). O manejo de uma pastagem natural, tanto sob pastejo contínuo quanto rotativo, durante o período de primavera-verão, possibilita o desenvolvimento corporal adequado para acasalamento de novilhas de corte aos 24 meses. O método de pastejo não alterou a estrutura e a dinâmica da vegetação no período avaliado. O pastejo contínuo reduziu a diversidade florística frente ao pastejo rotativo, com evidente dominância da espécie Eragrostis plana.

In den vorliegenden Studien wurde der Fragestellung nachgegangen, wie sich unterschiedliche Fütterungsprotokolle während der Aufzuchtperiode auf den peripartalen Energie- und Fettstoffwechsel und die Insulinsensitivität von Färsen auswirken. Besonderes Augenmerk lag dabei auf der Frage, ob der „Revised Quantitative Insulin Sensitivity Check Index“ (RQUICKI) bei Färsen sinnvoll angewendet werden kann, um eine Aussage hinsichtlich der Insulinsensitivität zu treffen. Auch mögliche Auswirkungen auf das Konzeptionsalter, den Kalbeverlauf, die Milchleistung und die postpartale Morbidität wurden untersucht. Aus 46 Kälbern der Rasse Deutsche Holstein wurden drei Fütterungsgruppen gebildet. Gruppe 1 (n = 18) wurde gemäß den Richtlinien der GfE energetisch optimal gefüttert (Kontrollgruppe), Gruppe 2 (n = 14) wurde intensiv und Gruppe 3 (n = 14) restriktiv gefüttert. Im Abstand von zwei Wochen wurden die Tiere jeweils gewogen. Aus den vorliegenden Daten wurde die durchschnittliche tägliche Körpermassezunahme berechnet. Außerdem wurde zehn, sechs, drei und eine Woche vor der Kalbung sowie zwei Wochen nach der Kalbung die Rückenfettdicke (RFD) sonografisch bestimmt. Weiterhin wurden das Alter bei erfolgreicher Konzeption, Kalbeverlauf sowie Daten der Kälber, Milchleistungsprüfungsdaten und Rastzeit erfasst. Vor und nach der Kalbung wurde aus der Vena caudalis mediana Blut entnommen. Aus dem Serum wurden die Konzentrationen der folgenden Parameter bestimmt: Insulin, Insulin-like growth factor 1 (IGF-1), Glukose, freie Fettsäuren (FFS), Bilirubin, Cholesterol, Harnstoff, Betahydroxybutyrat (BHB) sowie Gesamteiweiß. Erkrankungen im postpartalen Zeitraum, wie Endometritis, Mastitis, Stoffwechselstörungen, Erkrankungen des Bewegungsapparates sowie Zyklusstörungen wurden ebenfalls in die Studien miteinbezogen. Zur Bestimmung der Insulinsensitivität wurde das Rechenmodell „Revised Quantitative Insulin Sensitivity Check Index“ (RQUICKI) verwendet. Unter Einbeziehung der Serumkonzentrationen von Glukose, Insulin und FFS lautete die Formel RQUICKI = 1/[log (Glukose) + log (Insulin) + log (FFS)]. Ein niedriger Index-Wert bedeutet eine verminderte Insulinsensitivität. Die intensiv aufgezogenen Tiere der Gruppe 2 zeigten mit 13,3 ± 1,0 Monaten ein signifikant (p = 0,003) früheres Konzeptionsalter im Gegensatz zu den Tieren der beiden anderen Gruppen (Gruppe 1: 16,0 ± 1,5 Monate; Gruppe 3: 17,7 ± 1,4 Monate). Eine Woche ante partum wiesen die Tiere der Gruppe 2 eine signifikant (p = 0,022) höhere RFD auf als die Tiere der beiden anderen Gruppen. Der RQUICKI korrelierte eine Woche ante partum signifikant negativ mit der RFD (r = -0,573; p = 0,003). RQUICKI war bei den Tieren der Gruppe 2 eine Woche ante partum signifikant (p < 0,05) niedriger als bei den Tieren der anderen Gruppen. In allen drei Gruppen konnten am dritten Tag post partum die niedrigsten Index-Werte nachgewiesen werden. Aus den errechneten Index-Werten lässt sich für Färsen für die Zeitpunkte eine Woche ante partum sowie vier Wochen post partum ein Referenzbereich von RQUICKI = 0,40 ± 0,04 ableiten. Um den dritten Laktationstag liegt bei Färsen der Referenzbereich von RQUICKI = 0,34 ± 0,02. Die intensiv aufgezogenen Färsen zeigten insgesamt mit 85,7 % die höchste Anzahl an Komplikationen bei der Kalbung, der Unterschied war statistisch allerdings nicht zu sichern. Die unterschiedliche Fütterung wirkte sich weder auf das Geschlecht der Kälber noch auf deren Geburtsgewicht aus. Signifikante Unterschiede (p < 0,05) ergaben sich bei den Serumkonzentrationen von Insulin, IGF-1, FFS und Cholesterol ante partum sowie den Bilirubin- und FFS-Konzentrationen 28 Tage post partum. Es konnten keine statistisch signifikanten Unterschiede bei den Konzentrationen von Glukose, Harnstoff, BHB und Totalprotein ermittelt werden (p > 0,05). Beim Vergleich der 305-Tage-Milchleistung wiesen die Tiere der Gruppe 2 die niedrigste Milchleistung auf. Eine signifikant (p = 0,039) höhere Inzidenz von postpartalen Zyklusstörungen war bei den Tieren der Gruppe 2 erkennbar. Eine Woche ante partum korrelierte RQUICKI signifikant negativ (r = -0,509, p = 0,008) mit dem Auftreten von Zyklusstörungen post partum. Die Untersuchungen haben gezeigt, dass durch die Fütterungsintensität während der Aufzuchtperiode die Zuchtreife, der peripartale Energie- und Fettstoffwechsel einschließlich der Insulinsensitivität, die Milchleistung sowie die postpartale Fertilität beeinflusst werden. Aus der intensiven Aufzucht resultieren eine frühere Zuchtreife, höhere Rückenfettdicken, eine gesteigerte peripartale Lipolyse einschließlich reduzierter Insulinsensitivität, eine verminderte Milchleistung und eine schlechtere Fertilität. / The aim of these studies was to investigate how different diets during the rearing period influence peripartal energy and fat metabolism as well as insulin sensitivity of heifers. Special attention was paid to the question if the „Revised Quantitative Insulin Sensitivity Check Index“ (RQUICKI) could be used to estimate insulin sensitivity in heifers. Possible influences on age at first breeding, calving, milk yield and postpartal morbidity were analysed as well. Furthermore, the aim of this investigation was to prove, if different diets at rearing influence the peripartal insulin sensitivity of heifers. 46 German Holstein calves were randomly divided in three groups. Group 1 (n = 18) was fed with an optimal diet (control group) based on recommendations of the German Society of Nutrition Physiology, group 2 (n = 14) was fed with a highly-concentrated diet and group 3 (n = 14) got a low-concentrated diet. In intervals of two weeks the heifers were weighed. With the obtained data the averaged daily weight gain was computed. In addition, ten, six, three and one week ante partum as well as two weeks post partum the backfat thickness (BFT) was measured ultrasonographically. Age at first breeding, calving, data of the calves, milk yield and interval to first service post partum were recorded, too. Before and after calving blood samples were taken from the Vena caudalis mediana. The concentrations of the following parameters were measured in blood serum: Insulin, insulin-like growth factor 1 (IGF-1), glucose, free fatty acids (FFA), bilirubin, cholesterol, urea, betahydroxybutyrat (BHB) as well as total protein. Furthermore, postpartal diseases like endometritis, mastitis, metabolic disorders, limb diseases and fertility disorders were included. To determine insulin sensitivity a mathematic model called “Revised Quantitative Insulin Sensitivity Check Index” (RQUICKI) was used. Serum concentrations of glucose, insulin and FFA were included in the formula RQUICKI = 1/[log (glucose) + log (insulin) + log (FFA)]. A low index value represents a decreased insulin sensitivity. Intensive reared heifers of group 2 reached age at first breeding (13.3 ± 1.0 months) significant (p = 0.003) earlier than heifers of the other both groups (group 1: 16.6 ± 1.5 months; group 3: 17.7 ± 1.4 months). One week ante partum heifers of group 2 showed significant (p = 0.022) higher BFT than heifers of the other groups. At the same timepoint, RQUICKI correlated significant negative with the BFT (r = -0.573; p = 0.003). In heifers of group 2, RQUICKI was significant lower (p < 0.05) one week ante partum than in heifers of the other groups. In all groups, the index values were lowest three days post partum. Based on the received index values reference ranges for RQUICKI in heifers can be proposed. One week ante partum as well as four weeks post partum the reference range for RQUICKI can be defined as RQUICKI = 0.40 ± 0.04. Three days after calving the reference range can be defined as RQUICKI = 0.34 ± 0.02. The intensive reared heifers show with an overall of 85.7 % the most difficulties at calving, but this was statistically not different. The different diets didn’t influence neither the sex of the calves nor their birth weight. Ante partum, serum concentrations of Insulin, IGF-1, FFA and cholesterol differed significantly (p < 0.05) as well as serum concentrations of bilirubin and FFA differed on day 28 post partum. No significant differences could be determined in serum concentrations of glucose, urea, BHB and total protein (p > 0.05). Heifers of group 2 showed the lowest 305-day milk yield. The incidence of postpartal ovarian diseases was significantly (p = 0.039) higher in heifers of group 2. A significant negative correlation (r = -0.509, p = 0.008) existed between RQUICKI ante partum and the incidence of postpartal ovarian diseases. In conclusion, different diets during the rearing period influence age at first breeding, peripartal energy and fat metabolism including insulin sensitivity, milk yield as well as postpartal fertility. An intensive rearing results in an earlier age at first breeding, increased BFT, enhanced peripartal lipolysis as well as reduced insulin sensitivity, decreased milk yield and poorer fertility.