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Forage lucerne for grazing dairy cows: effects on milk yield, milk urea and fatty acids composition

Mancoba Mangwe , Racheal Bryant , Paige Beckett, Lucas Tey, Jeffery Curtis, Riki Burgess, Omar Al-Marashdeh

Abstract

Context. The value of milk components is increasingly recognised for human health benefits (e.g., Omega-3 fatty acids; FA), or indicators of nutrient use efficiency for both animal and environmental benefits (e.g. milk urea; MU). Aims. The study explored whether inclusion of lucerne (Medicago sativa L.) in a perennial ryegrass and white clover (Lolium perenne L. and Trifolium repens L; PRW) - based diet impacted milk production, MU concentration, and milk FA composition of dairy cows during mid-lactation. Methods. Thirty-two cows, balanced for milk production (26.1±3.03 kg/cow), MU (16.6±2.84 mg/dL), and days in milk (94±7 days) were evenly allocated into eight groups of four. Groups were then randomly assigned one of two dietary treatments: PRW only (control); and PRW plus lucerne (lucerne). During an eight-day adaptation, control cows were fed a fresh allocation after each milking at 0830 and 1600 hours to provide 25 kg/cow/day DM of fresh PRW herbage above a target post grazing height of 4.5 cm height. Cows on lucerne were allocated 10 kg DM of fresh lucerne at 0830 hours, and 15 kg DM of fresh PRW at 1600 hours. Apparent nutrient intakes and milk composition were determined on days 9 and 10 of the study. Key results. Diet treatment did not significantly alter DM or metabolisable energy intake, milk production, or milk fat and protein percentage. However, compared to control cows, nitrogen and linoleic acid (LA) intake increased, and soluble carbohydrate, neutral detergent fibre, and alpha linoleic acid (ALA) intake decreased for cows fed lucerne. Milk urea increased by 43% for lucerne compared with control cows (22.4 versus 15.7±1.43 mg/dL, P < 0.001). Cows grazing lucerne produced milk with high concentration of LA and ALA than the control. Increases in milk LA from grazing lucerne were congruent with improvement in intake of the FA from the diet, whereas increases in ALA occurred despite the corresponding lower dietary intake. Conclusion and Implications. Lucerne has the potential to enhance concentration of dietary protein during periods of deficiency and increase the supply of functional FA in the milk of grazing dairy cattle.

AN24321  Accepted 11 November 2024

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