Effect of daily herbage allowance restriction on pasture characteristics and milk production by grazing dairy cows in spring

Cien. Inv. Agr. 45(1):21-34. 2018 www.rcia.uc.cl animal production DOI 10.7764/rcia.v45i1.1841 research paper Effect of daily herbage allowance restriction on pasture characteristics and milk production by grazing dairy cows in spring Verónica Merino1,2, Oscar Balocchi3, and Rubén Pulido4 Universidad Austral de Chile, Faculty of Agricultural Sciences, Graduate School. Valdivia, Chile, PO Box 567, Valdivia, Chile. 2 Universidad de Concepción, Faculty of Agronomy, Department of Animal Production. Concepción, Chile. 3 Universidad Austral de Chile, Faculty of Agricultural Sciences, Institute of Animal Production. PO Box 567, Valdivia, Chile 4 Universidad Austral de Chile, Faculty of Veterinary Sciences, Institute of Animal Science. PO Box 567, Valdivia, Chile 1 Abstract V. Merino, O. Balocchi, and R. Pulido. 2018. Effect of daily herbage allowance restriction on pasture characteristics and milk production by grazing dairy cows. Cien. Inv. Agr. 45(1): 21-34. The cumulative effects of daily herbage allowance (DHA) restriction on pasture characteristics and the sustainability of pasture-based dairy systems were evaluated. Sixty-four dairy cows were randomly assigned to one of two grazing treatments (20 and 30 kg DM cow-1 day-1). Milk yield and pre- and post-grazing herbage mass were recorded for every grazing event. Botanical and chemical compositions of the pasture were evaluated. Low DHA increased the stocking rate by 0.7 cows ha-1 and consequently increased grazing efficiency from 41 to 47%. Daily herbage allowance restriction did not affect pasture characteristics or milk production per cow, but DHA restriction increased milk production per hectare (+27%). The results suggest that restriction on daily herbage allowance ensures a higher level of herbage utilization and milk output per ha than high DHA, without affecting pasture characteristics. Therefore, DHA might be a useful grazing management tool for improving the profitability and sustainability of grazing-based dairy systems. Keywords: Dairy systems, grazing management, milk yield, pasture utilization, sustainability. Abbreviations used: ADF (acid detergent fiber); BCS (body condition score); BW (body weight); CP (crude protein); DM (dry matter); DMI (dry matter intake); DHA (daily herbage allowance); K (potassium); ME (metabolizable energy); N (nitrogen); NDF (neutral detergent fiber); P (phosphorous); SR (stocking rate); WSC (water-soluble carbohydrates). Introduction The abundance of pasture-based dairy systems is primarily due to their low cost of production Received Aug 22, 2017. Accepted Mar 21, 2018. Corresponding author: (Peyraud and Delaby, 2001), and they are more cost effective than indoor concentrate-based systems (Peyraud et al., 1996). The success of grazing-based dairy systems, in the medium to long term, depends on the efficient use of pasture and the production of high milk output per hectare. However, the low efficiency of pasture 22 CIENCIA E INVESTIGACIÓN AGRARIA harvest through grazing limits the profitability and sustainability of milk production systems (Dillon et al., 2008). Consequently, one of the greatest challenges for an efficient grazing-system is understanding the underlying effect of DHA on the physiology and quality of the pasture and on the productivity of dairy production systems. This knowledge could contribute to maximizing the grazing efficiency and milk production per hectare, without penalizing the sustainability of dairy production systems. Daily herbage allowance is a grazing practice defined as the quantity of daily herbage offered per cow above a specified height (Roca-Fernandez et al., 2012). It depends on pre-grazing herbage mass (Pérez-Prieto and Delagarde, 2013), and it is proportionate to the stocking rate (SR) because as DHA increases, the stocking rate decreases (Tozer et al., 2004). Studies have focused on identifying the effect of DHA on herbage intake and animal performance (Peyraud et al., 1996; Dalley et al., 1999; Bargo et al., 2002; Kennedy et al., 2007; McEvoy et al., 2008; McCarthy et al., 2011). However, how the restriction of daily herbage allowance influences the pasture characteristics and sustainability of pasture-based dairy systems in the long-term has not yet been fully evaluated. High DHA might have negative impacts on the herbage quality of the following grazing rotations due to increases in the amount of refused pasture (Stakelum et al., 2007). Selecting adequate levels of daily herbage allowance to enhance herbage utilization and milk output per hectare could improve the sustainability and profitability of dairy systems in the long term. The aim of the study was to examine the influence of the cumulative effects of DHA restrictions on grazing management parameters, pasture nutritive quality levels, dynamics of pasture depletion and milk performance of dairy cows in spring. Materials and methods This study was conducted as part of a larger study, which was undertaken at the Vista Alegre Experimental Research Station of the Universidad Austral de Chile, Valdivia, Chile (39°47´ S and 73°14´ W). The study began in spring 2008 and was carried through to spring 2011, and the objective was to evaluate the cumulative effect of DHA restriction on pasture-based dairy production systems. The dietary treatments used in this study, including the two herbage allowances (low and high), are shown in Table 1. Productive results from this study can be obtained from Balocchi et al. (2013). During the third spring of this study, from October 16th to December 21st, 2010, a 63-day period, the present experiment was conducted. The climate of the location has been classified as temperate with Mediterranean influences. The soil is a moderately deep Andisol (Duric Hapludand) Valdivia Series soil, with plane topography (3%) and without drainage problems. The study utilized 27.9 ha of 12-year-old ryegrassdominated pasture (Lolium perenne L.), which had been subjected to rotational grazing management. Twenty-two paddocks, classified in autumn 2008 as high (n=13) or low (n=9) DHA paddocks, each approximately 1.2 ha, were used. Fertilizer was applied twice before the experiment started. Fertilizer levels per hectare were 52 kg P, 50 kg K and 46 kg N in autumn, and 46 kg N were applied in spring, based on a potential production level of 12 t DM ha-1 year-1. Animals Sixty-four Holstein–Friesian dairy cows, 32 in early lactation (milk yield, 29 ± 5.7 kg cow-1 day-1; days in milk, 59 ± 33 days; body weight (BW), 530 ± 63 kg; body condition score (BCS), 2.7 ± 0.4 points on a scale of 1–5) and 32 in late lactation (milk yield, 23 VOLUME 45 Nº1 JANUARY – APRIL 2018 Table 1. Daily herbage allowance, concentrate and grass silage supplementation during the study (kg DM cow-1 day-1) Season of the year Spring Summer Autumn Winter Year 1 (2008-2009) Grass silage 0 6 4 7 Concentrate 3 3 3 3 High Allowance 38 26 30 25 Low allowance 26 14 20 16 Gras (...truncated)