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Effect of increasing levels of roasted high oleic soybean on milk fat yield in lactating dairy cows.

K. J. Harvatine



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Effect of increasing levels of roasted high oleic soybean on milk fat yield in lactating dairy cows.
B. Khonkhaeng1,2, R. Bomberger1, K. J. Harvatine*1. 1Penn State University University Park, PA, 2Khon Kaen University Khon Kaen, Thailand.

Oilseeds are an economical source of dietary fat, but the rumen available unsaturated fat they contain is a risk factor for diet-induced milk fat depression (MFD). However, high oleic soybeans have been shown to decrease risk for MFD compared with conventional soybeans. Additionally, it has been demonstrated that milk fat can be increased by increasing dietary fat in some situations. The hypothesis of this experiment was that feeding roasted high-oleic soybeans at an increasing rate would increase milk fat yield in high producing dairy cows. The objective was to demonstrate that high oleic soybeans have a low risk for milk fat depression and are an inexpensive source of dietary fat. Eight primiparous and 8 multiparous lactating Holsteins were arranged in a replicated 4x4 Latin square design with 21 d periods. Treatments were 0, 5, 10, and 15% of roasted high oleic soybeans (Plenish, Pioneer Inc. Johnston, IA). Roasted soybeans were substituted for soybean hulls and heat treated and solvent extracted soybean meal. Data were analyzed using the random effect of cow and period and fixed effect of treatment, parity, and their interaction. Preplanned contrasts tested the linear and quadratic effect of increasing roasted soybeans levels. There were no interactions of treatment and parity. Milk yield was not changed by treatments (mean 36.6 and 46.7 kg/d in primiparous and multiparous, respectively). Milk fat percent (4.07 to 4.17%) and yield (mean 1700 g) were also not modified by treatment. Milk protein percent was decreased from 3.07 to 2.92% (P < 0.001) and MUN was decreased from 15.2 to 11.9 mg/dL (P < 0.001) with increasing level of roasted high oleic soybeans, but milk protein yield was not changed. This may be due to differences in bypass protein or protein digestibility. In conclusion, roasted high oleic soybeans maintained milk and milk component yield when fed at up to 15% of the diet without induction of MFD.

Keywords: high oleic soybeans, milk fat depression, milk fat.