In Chile, high moisture corn (Zea mays L. [HMC]) has been included mainly in diets for grazing dairy cows on pastures with high crude protein, and is an alternative that improves nutrients supply and rumen synchrony between energy and protein provided by the diet. In addition, supplementation with HMC results in an increase of fatty acids (FA) in milk, desirable for human health. The aim of this study was to evaluate the effect of herbage allowance (HA) and type of supplement on milk FA composition in grazing dairy cows during spring. Thirty-two multiparous Holstein-Friesian dairy cows (533 ± 71 kg BW; 53 ± 4 d in milk [DIM] and milk yield 23.8 ± 4.2 kg d-1) were randomly assigned to four dietary treatments resulting from the combination of two HA levels (low 20 vs. moderate 30 kg DM cow-1 d-1) and two types of supplements HMC and cracked wheat [Triticum aestivum L., CW]) offered at 3.5 kg DM cow-1 d-1. Total FA intake was greater for moderate HA (547.8 g d-1) than low HA (527.2 g d-1) (P < 0.05); but did not affect milk yield, milk constituents and milk FA composition (P > 0.05). Supplementation with HMC increased milk production by 2.3 kg d-1 compared with CW. Cows supplemented with HMC showed a greater intake of total FA (564 g d-1) and had greater concentrations of long-chain monounsaturated FA in milk (27.13 g 100 g-1) compared to cows supplemented with CW (511.0 g d-1 total FA intake and 25.39 g 100 g-1 in milk, respectively) (P < 0.05). It is concluded that grazing dairy cows supplemented with HMC during spring produced milk with higher concentrations of desirable FA, independently of the HA level.

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