Influence of Prepartum Dietary Crude Protein on Growth Hormone, Insulin, Reproduction, and Lactation of Dairy Cows

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Abstract
Effects of prepartum dietary crude protein on growth hormone, insulin in blood plasma, and subsequent reproduction and lactation were investigated in 30 Holsteins. Cows were fed either 80 or 100% of the crude protein recommended by National Research Council starting about 60 days precalving. After calving, all animals were fed according to recommendations. Blood was sampled on days 220 (start of experiment), 250, 270 and 280 of gestation and on days 10 and 30 postpartum. Cows fed 80% crude protein prepartum showed decreased intake of dry matter and urea N in blood plasma prepartum, and yields of milk and total solids decreased by about 15%. Body weight changes through 30 days postpartum were not significantly different between treatments. There were no significant differences for growth hormone and insulin except growth hormone tended to be higher on day 270 of gestation for cows fed 80% crude protein. Insulin was negatively correlated with lactation number -.51 to -.56. Reproductive efficiency was similar between treatment groups. Lower crude protein intake during the dry period decreased dry matter intake and yields of milk and total solids.