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.

Grazing ruminant systems can be sustainably intensified by improving efficiency while reducing their environmental impact. The objective of the present study was to examine the potential of pastures differing in water-soluble carbohydrates (WSC) and crude protein (CP) contents to affect milk production and composition as well as the behaviour of cows grazing perennial ryegrass (PRG) swards. By modifying the nitrogen (N) fertilisation rate (83 and 250 kg/ha per year) and the defoliation frequency (two or three leaves per tiller) in combination with cultivar selection (high-sugar vs. standard cultivars), we obtained two swards differing in WSC and CP contents. The two contrasting swards were each grazed by six dairy cows in nine daily strips in autumn. Pasture samples were collected to determine herbage mass and quality. Cow behaviour was recorded by direct observation. Herbage offered and apparently consumed were similar between swards (averaging 37.3 and 18.2 kg/cow, respectively), although the residual was lower in the high-sugar sward (1735 vs. 2143 kg/ha). Cows spent less time grazing in the high-sugar sward (66.9% v. 71.6%), but the rumination times was similar (14.6%). Milk production and composition were similar between groups, suggesting that high-quality pastures would require a greater difference in nutritional composition to affect animal performance.

Simple Summary: Daily herbage allowance (defined as herbage mass × daily offered area) is recognized as the main grazing management factor to improve pasture utilization and milk output per hectare. Daily herbage allowances should balance the dual objectives of high milk output per hectare while maintaining the quality of the pasture to optimize the profitability of grazing-based dairy production systems. We tested two contrasting herbage allowances (17 and 25 kg dry matter (DM)/cow.day) and two levels of maize silage supplementation (4.5 and 9 kg DM/cow.day) in grazing dairy cows and measured a set of variables related to pasture management, sward characteristics, dynamic of herbage depletion throughout the grazing sessions, and cows grazing behavior, among others. Our results suggest that a more intensive grazing regime of 17 kg DM/cow per day of daily herbage allowance rather than a high level of supplementation with maize silage is appropriate to improve milk production and solids yield per hectare without affecting pasture quality or sward characteristics over the short-term.Abstract: The aim of this study was to evaluate the short-term effects of daily herbage allowance (DHA, defined as the product of pre-grazing herbage mass and offered area per animal) on pasture conditions and milk production of Holstein-Friesian dairy cows. Forty-four early lactation dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design that tested two levels of DHA (17 and 25 kg DM/cow.day) and two levels of maize silage supplementation (MSS, 4.5 and 9 kg DM/cow.day) over a 77-day period. Low DHA decreased the post-grazing herbage mass from 1546 to 1430 kg DM/ha and the compressed sward height from 5 to 4.4 cm, while the grazing efficiency remained unaffected. Low DHA induced a faster herbage mass reduction, while the sward-height and pasture characteristics did not differ from the high DHA regime. Low DHA decreased the tiller production rates and daily lamina growth, while the leaf-production rate was not affected by the DHA. Daily increases of herbage mass were greater in the high DHA than in the low DHA treatments. Individual milk production and milk protein concentration decreased at a low DHA compared to high DHA, while the milk fat concentration was greater and the milk output per hectare increased by 1510 kg. Neither the MSS level nor the interaction DHA by the MSS level had any effect on the sward characteristics or the productivity of the cows. From these results, it is suggested that, Animals 2020, 10, 62 2 of 17 in a high-quality pasture, using 17 kg DM/cow.day was appropriate for improving both herbage utilization and milk production per hectare while maintaining the short-term conditions of a pasture grazed by dairy cows in the autumn.

Daily herbage allowance is recognised as the main tool to control pasture utilisation and milk production per cow. The aim of the present study was to evaluate the long-term effects of daily herbage allowance (DHA) on pasture characteristics and milk production of dairy cows. Forty-four dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design by considering two levels of DHA (20 and 30 kg DM/cow.day) and two types of supplements (high-moisture maize and maize silage) over a 77-day period. Pre- and post-grazing herbage masses, vertical distribution of herbage mass, species density, botanical and chemical composition, sward depletion and changes in morphological components of the pasture were measured. The effect of DHA on soil compaction was evaluated on the basis of the penetration resistance. Milk production and composition levels, bodyweights and body condition scores were recorded. Post-grazing residual declined as the level of DHA decreased, while grazing efficiency increased from 39.8% to 44.8%. We found no effects of DHA on any pasture characteristics, pasture regrowth or soil compaction. Low-DHA conditions induced a faster sward-height reduction, while the herbage mass remained unaffected. Individual milk production decreased with DHA. However, milk outputs per hectare increased by 2772 L/ha. Milk composition, bodyweight and body condition score were not affected by DHA. The results showed that DHA restriction decreases milk production per cow while increasing both herbage utilisation and milk production per hectare, without affecting long-term pasture condition.