The introduction of legumes in grass-based swards provides some economic and agronomic advantages, often allowing an increase in the performance of grazing ruminants. The aim of this study was to obtain a better quantification of the nutritional benefits to dairy cows after introducing white clover into swards of perennial ryegrass (PRG), using two ages of regrowth. Four treatments were studied in a 2 ✕ 2 factorial design with two sward types and two ages of regrowth. The swards were either a pure perennial ryegrass sward with nitrogen (N) fertilization, or a perennial ryegrass/white clover mixture (GC) with no N fertilization. The regrowth ages were 19 and 35 days (treatments: PRG19, PRG35, GC19 and GC35). The proportion of clover in the GC swards was on average 420 g/kg dry matter (DM). Twelve late-lactation Holstein cows, fistulated at the rumen and duodenum, were used according to a 4 ✕ 4 Latin-square design with four 11-day periods. The pasture was strip-grazed with 12 kg DM per cow of herbage above 5 cm offered daily in all the treatments.The effects of sward type and regrowth age were often additive, in particular for herbage intake and milk yield. Herbage organic matter (OM) intake, duodenal non-ammonia N (NAN) flow and milk yields were higher on the GC swards and lower on the older regrowths. Finally, the performance of the cows was similar on the PRG19 and GC35 treatments. The OM digestibility of the selected herbage as well as the duodenal nitrogen flux per kg digestible OM intake was not affected by the sward type. Ruminal fermentations were more intense with mixed swards and the youngest regrowths. The daily grazing time and the daily pattern of grazing activities were modified by the type of sward and by regrowth age. The average OM intake rate was higher on the GC swards than on the PRG swards. In this study, the nutritional advantage of introducing white clover into swards of perennial ryegrass was related to an increase in herbage intake and not to any improvement in the nutritive value of the sward.

RESUMO -Avanços metodológicos são, usualmente, conseqüência direta de avanços conceituais e tecnológicos.No caso da estimativa do consumo em pastejo, os recentes avanços conceituais relativos ao processo de busca e apreensão da forragem pelo ruminante evidenciaram a importância da unidade básica do consumo -o bocado -, e dos fatores limitantes ao consumo que ocorrem antes da ingestão da forragem pelo animal em pastejo. A abordagem reducionista do processo de pastejo, aliada à sua hierarquização espaço-temporal, trouxeram uma nova concepção de como o animal obtém o seu alimento do pasto. Destes modelos conceituais emergiram novas variáveis que requerem novos procedimentos experimentais e analíticos. Neste contexto, importantes avanços têm ocorrido. Este artigo apresenta e discute os novos procedimentos que permitem estimar o consumo no curto prazo, assim como aqueles mais utilizados pela comunidade científica nacional para estimar o consumo no longo prazo. Adicionalmente, são feitas também considerações sobre o uso de animais ou de piquetes como unidades experimentais em experimentos de pastejo. Conclui-se que, apesar de ainda existir importantes barreiras metodológicas, os recentes avanços conceituais sobre o processo de pastejo, assim como dos procedimentos analíticos, geram fortes expectativas de avanço em curto e médio prazo na obtenção de estimativas qualificadas de consumo por animais em pastejo.Palavras chave: alcanos, bocado, estrutura do pasto, ingestão, óxido de cromo Advances in methods for determining animal intake on pasture ABSTRACT -Methodological advances are usually a direct consequence of conceptual and technical advances.In the case of animal intake on pasture, recent conceptual advances regarding the process of searching and apprehension of the forage by the ruminant provide insight regarding the importance of the basic unit of intake, the bite, and the importance of processes limiting intake that occur before the forage reaches the rumen. Applying a reductionist approach to the grazing process, along with its spatial-temporal hierarchy, brought a new conceptualization of how an animal obtains feed from pasture. From the conceptual models emerged new variables that required new experimental and analytical procedures. Within this context, important advances have occurred. This article describes the new procedures that allow to estimate the consumption on the short-term, as well as that most utilized by the national scientific community for estimating the consumption on the long-term. Procedure for estimating fecal production and digestibility are discussed, as well as the use of n-alkanes and other emerging techniques. Consideration is given to the use of animals or paddocks as experimental units in grazing experiments. The conclusions presented in this article do not differ from those of preceding articles regarding this subject. In a grazing condition, continuous intake is the "black box" to be revealed, complex by nature with regard to the animal as well as the pasture, and there are importa...

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A pesquisa foi realizada durante as estações de crescimento de 1994/95 e 1995/96 (out./abr.), na Estação Experimental de Ituporanga/EPAGRI - SC, objetivando determinar o potencial de produção animal e as respostas em termos de taxa de acúmulo de matéria seca (MS) e qualidade de forragem e estrutura do perfil de uma pastagem de capim-elefante anão `Mott' (CEAM) submetida a quatro níveis de oferta de forragem (OF). Os níveis reais de FO foram 3,8; 7,5; 10,2 e 14,0 kg de MS de lâminas verdes (MSLV)/100 kg de PV/dia, num delineamento em blocos casualizados completos com duas repetições e três novilhos (8 a 10 meses) por potreiro, sob pastejo contínuo e uso da técnica "put-and-take". As OF determinaram resíduos médios de MSLV (RMSLV) de 722; 1537; 2332; e 2542 kg/ha, respectivamente. Ofertas de forragem crescentes condicionaram acréscimos na taxa de acúmulo de MSLV/ha/dia e na densidade da forragem. A OF de 11,3 kg de MSLV/100 kg de PV/dia (RMSLV de 2200 kg/ha) maximiza o desempenho animal com 1,06 kg/dia de ganho médio diário e assegura ganho/ha de 5,6 kg/dia, em condição de sustentabilidade da pastagem de CEAM, em pastejo contínuo.

Esta pesquisa foi conduzida durante as estações de crescimento de 1994/95 e 1995/96 (out./abr.), na Estação Experimental de Ituporanga/EPAGRI - SC, objetivando avaliar a dinâmica de uma pastagem de capim-elefante anão `Mott' (CEAM) submetida a níveis de oferta de forragem (OF). Os níveis reais de OF foram 3,8; 7,5; 10,2 e 14,0 kg de MS de lâminas verdes/100 kg de PV/dia, em pastejo contínuo, por meio da técnica "put-and-take", usando terneiros de 8 a 10 meses, em um delineamento em blocos completos casualizados com duas repetições. As OF determinaram resíduos médios de MS de lâminas verdes (RMSLV) de 722, 1537, 2332 e 2542 kg/ha, respectivamente. A taxa de acúmulo de matéria seca de lâminas verdes, a cobertura do solo, o diâmetro de touceiras, o peso de afilhos, a altura de plantas e o comprimento de entrenós aumentaram com as maiores OF. Já as menores provocaram aumento da densidade aparente, bem como redução da porosidade total do solo e do sistema radicular, com incremento pronunciado de espécies anuais na pastagem de CEAM. OF de 10 a 11 kg de MS de lâminas verdes/100 kg de PV/dia (equivalentes a RMSLV de 2000 a 2300 kg/ha) asseguram condição de sustentabilidade à pastagem de CEAM, em pastejo contínuo.

Oat and ryegrass intercropping in pastures is widely used in regions with subtropical climates. The aim of this study was to evaluate the tiller size/density compensation mechanisms in monoculture and intercropping swards of black oats (Avena strigosa Schreb cv. IAPAR 61) and annual ryegrass (Lolium multiflorum Lam. cv common) under intermittent grazing. Treatments (black oat, annual ryegrass and their mixture) were assigned according to a complete randomized block design with four replicates. Ryegrass, oat and intercropped pastures were grazed when the swards reached a height of 17, 25 and 23 cm, respectively, and with a level of defoliation of 40%. The aerial biomass was determined with a rising plate meter, and the tiller population density (TPD) was estimated by counting tillers in three 10 cm diameter PVC rings per paddock. The mass per tiller was estimated based on the aerial biomass and the TPD of each paddock. Total herbage production did not differ among treatments, with values around 7400 kg DM ha−1. TPD decreased and mass per tiller increased linearly in the monoculture treatments. Tiller size/density compensation was observed in the three plant communities (treatments) according to the self‐thinning rule. In addition, no relationships were found when each species was analysed individually in the intercrop treatment. The results suggest that species in grass mixed swards adjust their population to keep a relatively constant leaf area index (LAI) over the grazing seasons, and that would help pastures to stabilize herbage production.

Involuntary soil intake by cows on pasture can be a potential route of entry for pollutants into the food chain. Therefore, it appears necessary to know and quantify factors affecting soil intake in order to ensure the food safety in outside rearing systems. Thus, soil intake was determined in two Latin square trials with 24 and 12 lactating dairy cows. In Trial 1, the effect of pasture allowance (20 v. 35 kg dry matter (DM) above ground level/cow daily) was studied for two sward types (pure perennial ryegrass v. mixed perennial ryegrass-white clover) in spring. In Trial 2, the effect of pasture allowance (40 v. 65 kg DM above ground level/cow daily) was studied at two supplementation levels (0 or 8 kg DM of a maize silage-based supplement) in autumn. Soil intake was determined by the method based on acid-insoluble ash used as an internal marker. The daily dry soil intake ranged, between treatments, from 0.17 to 0.83 kg per cow in Trial 1 and from 0.15 to 0.85 kg per cow in Trial 2, reaching up to 1.3 kg during some periods. In both trials, soil intake increased with decreasing pasture allowance, by 0.46 and 0.15 kg in Trials 1 and 2, respectively. In Trial 1, this pasture allowance effect was greater on mixed swards than on pure ryegrass swards (0.66 v. 0.26 kg reduction of daily soil intake between medium and low pasture allowance, respectively). In Trial 2, the pasture allowance effect was similar at both supplementation levels. In Trial 2, supplemented cows ate much less soil than unsupplemented cows (0.20 v. 0.75 kg/day, respectively). Differences in soil intake between trials and treatments can be related to grazing conditions, particularly pre-grazing and post-grazing sward height, determining at least in part the time spent grazing close to the ground. A post-grazing sward height lower than 50 mm can be considered as a critical threshold. Finally, a dietary supplement and a low grazing pressure, that is, high pasture allowance increasing post-grazing sward height, would efficiently limit the risk for high level of soil intake, especially when grazing conditions are difficult. Pre-grazing and post-grazing sward heights, as well as faecal crude ash concentration appear to be simple and practical tools for evaluating the risk for critical soil intake in grazing dairy cows.

The use of corn silage to supplement grazing dairy cows can improve milk production and nutrient intake when the substitution rate is low. This enhancement occurs by increasing the total DM intake. The hypothesis tested in this study was that increasing corn silage supplementation level of dairy cows grazing annual ryegrass at medium pasture allowance could increase substitution rate and decrease milk production response. Three supplementation levels (0, 4 and 8 kg DM/day) were compared for dairy cows strip-grazing annual ryegrass (Lolium multiflorum cv. Common). The study was arranged as a 3 × 3 Latin square design, repeated three times using nine Holstein lactating cows. The supplement was a 7 : 1 mixture based on the DM of corn silage and soybean meal and was offered individually twice daily after the morning and afternoon milkings. Each treatment group of cows grazed separately at a common daily pasture allowance of 35 kg DM/cow to ground level. Each experimental period was 12 days, with an 8-day adaptation and a 4-day measurement period. The individual pasture intake was measured from Day 9 to Day 12 using the n-alkane technique. The daily pattern of grazing and ruminating times were measured by visual observations. The supplement DM intake was lower than expected, averaging 3.0 and 4.3 kg DM/day for cows receiving 4 and 8 kg DM/day, respectively. Pasture and supplement energy value were 7.0 and 6.3 MJ of NEL/kg DM, respectively. The substitution rate averaged 0.2 and was unaffected by the supplementation level. The pasture intake was similar for all treatments (14.0 kg of DM/day), and total DM intake and milk production (+0.5 kg of milk/kg DM of supplement) increased linearly with increasing supplementation level. The daily grazing time was shorter by 111 min/day for the supplemented cows than for the unsupplemented cows. Cows grazing the annual ryegrass at medium pasture allowance improved their total DM intake and individual performance when supplemented with corn silage.