Determination of digestion parameters to develop and evaluate forage mixtures for pasture-fed ruminants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
Animal production can be improved by lessening the dependence on ryegrass-based pastures as the sole source of nutrients for production. Ryegrass varies in quality and availability and supplementation with appropriate forages will maintain or improve production. This thesis defines the nutritive characteristics of a range of forages, including temperate and tropical grasses, legumes with and without condensed tannins, herbs and silages, in terms of chemical composition, products of degradation and rates of digestion using in sacco and in vitro methods. The forages assessed varied in crude protein concentration (CP; 7.6 - 29.9 % of dry matter; DM) and neutral detergent fibre (NDF; 22.4 - 57.8% DM), with commensurate net appearance of plant N as ammonia (0 to 49%) and in sacco DM, CP and NDF degradation rates (%/h) from 3 - 26, 3 - 19 and 4 - 28, respectively. The Cornell Net Carbohydrate Protein System (CNCPS) was used to evaluate the ability of forages to meet the energy and protein requirements of dairy cows. Data suggested sulla (Hedysarum coronarium), lucerne (Medicago sativa), red clover (Trifolium pratense) and white clover (Trifolium repens) as potential forages for feeding with medium to low quality pasture. Lambs were fed pasture, white clover, lucerne and sulla alone or in mixtures and production, rumen digestion parameters and estimates of protein synthesis were measured. Lambs fed white clover, sulla, lucerne:sulla and white clover:sulla had the highest daily intakes (1.47 - 1.54 kg DM) and liveweight gains (281 - 308 g) compared to lambs fed pasture (1.10 kg DM; 116 g). Sulla had potential for feeding with pasture and lucerne, but energy limited production. Protein synthesis between lambs fed lucerne, sulla and lucerne:sulla were similar (162 - 180 g/day) and greater than pasture (93 g/day). In a trial with dairy cows fed pasture (P), supplementation with maize silage (M) or sulla (S) did affect in sacco degradation and the maize silage lowered in sacco DM degradation rates (P, 7; M, 4; S, 16; P:M; 5; P:S, 11 and P:M:S, 6 %/h). The work presented provides a foundation for formulating mixed forage rations to meet cow nutrient requirements and improve productivity in ryegrass-based pasture systems. Animal trials demonstrated synergistic effects of dietary components on both animal production and rumen microbial function.