Abstract
Efficient exploitation of grass for cattle requires the application of appropriated grassland management strategies to maximize pasture dry matter intake (PDMI) while maintaining high sward quality by allocating cows to an adequate pasture allowance (PA). The aim of this study was to investigate the effect of two PA, low (L) vs. high (H), on sward quality, PDMI and milk performance of Holstein-Friesian cows (n=72) at two lactation stages (LS), early (E) vs. middle (M). Cows were randomly assigned to four groups (LE, LM, HE and HM) in a 2×2 factorial design. The low PA treatments completed 5 rotations, with more grazing days (+13), lower pre- (14.3) and post-grazing (5.3) sward heights (cm) and higher herbage utilization (81.7%). The low PA had higher stocking rate than the high PA treatments (4.8 vs. 3.9 cows ha-1)and lower PDMI (13.4 kg vs. 14.4 DM cow-1 day-1) with higher (p<0.05) (g kg-1 DM) protein (149.1), carbohydrates (166.7) and digestibility (746.8) while lower (p<0.05) DM (18.4%), acid (283.5) and neutral detergent (508.6) fibers (g kg-1 DM). Sward quality is deteriorated (p<0.05) from rotation 1 to 5, lower decrease was found on low PA treatments. Milk yield (MY) was higher (p<0.05) in cows at early LS (24.8 kg cow-1 day-1), with the lowest (p<0.05) protein (28.9) and fat (36.9) content (g kg-1). No differences were found on MY between PA treatments, but higher protein and fat content were observed on low PA. Decreasing PA resulted in higher sward and milk quality without penalizing MY.
Highlights
Galician agrarian economy is highly oriented to husbandry with dairy sector as the most important social driver, accounting for more than 35% of the total Spanish milk quota (2.2 × 106 kg over 6.0 × 106 kg)
Large increases in milk output per hectare are expected (McMeekan, 1956; Gordon, 1973) but lower milk output per cow may be observed (Bargo et al, 2002) in response to concentrate supplementation when cows are allocated to high levels of pasture allowance (PA)
The base of appropriate grassland management strategies should be to study the interaction between pasture and animal as an integral part of any grassland based dairy system
Summary
Galician agrarian economy is highly oriented to husbandry with dairy sector as the most important social driver, accounting for more than 35% of the total Spanish milk quota (2.2 × 106 kg over 6.0 × 106 kg). The Dairy Section in the Animal Production Department at the Centro de Investigaciones Agrarias de Mabegondo (CIAM) highlights that an increased effort has to be made in Atlantic regions as Galicia on studying effective pasture-based milk production systems by supplying high quality fresh forage, ensuring good herbage use, whilst maintaining acceptable milk performance of the grazing animal. The studies on grassland management strategies to improve profitability of milk production systems under grazing conditions are low in Spanish humid areas (Mosquera-Losada & GonzálezRodríguez, 1998; González-Rodríguez, 2003) and need to be increased for implementing appropriate grazing practices at farm level. Despite the high site differences and seasonality of grass production in Galicia (González-Rodríguez et al, 1996), high proportion of herbage in the ration of dairy cows should be the basis of low inputs milk production systems operating in Galician agricultural land. Enhancing the competitiveness of pasture-based dairy systems has important benefits: 1) feeding costs would be reduced; 2) rural landscape would be preserved; 3) a clean, animalwelfare-friendly image for dairy cattle production would be promoted (Dillon, 2006)
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