Effects of grazing management and concentrate supplementation on intake and milk production of dairy cows grazing orchardgrass

Abstract

In pasture-based dairy systems, grazing management strategies have focused mainly on achieving a high herbage harvest per hectare, whereas strategies oriented to maximizing the intake rate of herbage have been recently explored. The objectives of the study were (i) to evaluate the herbage nutritional value, intake and milk production per animal and per hectare of mid-lactation Holstein dairy cows grazing orchardgrass (Dactylis glomerata) in response to grazing management strategies that prioritize either herbage harvest per hectare or herbage intake rate, and (ii) to assess whether concentrate supplementation affects this response. The experiment was conducted in Uruguay using twenty-four mid-lactation Holstein dairy cows grazing orchardgrass under rotational stocking over an 81-day period. The experimental design was a randomized complete block with a 2 × 2 factorial arrangement consisting of two grazing management strategies [i.e. “high intake rate” (HIR) with pre- and post-grazing sward target heights of 21 and 13 cm, respectively, vs. “high herbage harvest per hectare” (HHH) with a pre-grazing target of 3.5–4 leaves per tiller and a post-grazing target of minimum leaf area corresponding to sward heights between 7 and 11 cm] in combination with concentrate supplementation levels of 0 (CS0) or 4 (CS4) kg of dry matter/cow per day. Sward height, number of leaves, herbage morphological and chemical composition, body weight (BW), body condition score (BCS), feed intake, and milk production per cow and per hectare were measured. Statistical analyses were performed using linear mixed models. Compared to cows under HHH, cows under HIR grazed herbage with greater nutritional value and achieved a greater feed intake and greater milk production per cow (P < 0.05), regardless of concentrate supplementation level. Conversely, under HHH milk production per hectare was marginally greater (P < 0.10) and milk solids production per hectare was greater (P < 0.05). Yet, cows under HHH lost BCS when were managed without supplementation (P < 0.05). In conclusion, HIR grazing management is an effective option for grazing dairy production systems that seek to maximize individual productivity of high-producing cows. On the other hand, HHH grazing strategies remain relevant to dairy farm businesses in which profit is driven by production per hectare. Yet, high producing dairy cows under this strategy are likely to lose BCS if not supplemented.