Two experiments measured the quantity and quality of amino acids available for absorption by four dairy cows fed pasture. Experiment 1 compared a diet of ryegrass/white clover pasture offered ad libitum or at 75% of ad libitum intake during October. Experiment 2, conducted in December, compared an all-ryegrass diet with a diet comprising 100% ryegrass, or 50% ryegrass and 50% white clover. Treatments were assigned according to a 2x2 crossover design. Restricted feeding (Experiment 1) significantly reduced the total supply of amino acids to the small intestine by 23% (246 vs. 190g amino acid nitrogen/d). Compared to an all-ryegrass diet, a ryegrass diet which contained 50% white clover (Experiment 2) significantly increased the total supply of amino acids by 10% (284 vs. 259g amino acid nitrogen/d). For all four pasture diets, arginine, methionine, and histidine were identified, in that order, as being most limiting, supplying 67, 71, and 77%, respectively, of the absorbable amino acid requirement. The supply of absorbable lysine from all four pasture diets was found to meet requirements of dairy cows in early to mid lactation.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 180-183, 1999
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