The effects of incorporating small quantities of straw in grass/grass silage-based diets for dairy cows

Two studies were conducted to examine the effects of incorporating small qu antities of straw in the diets of dairy cows. In Experiment 1, forty Holste in Friesian dairy cows were used in a 2 x 4 factorial design experiment, wi th factors examined consisting of two parities (primiparous and multiparous animals) and four levels of straw inclusion in the diet (0, 0.08, 0.16 and 0.24 of forage dry matter). The basal forage offered in this study was gra ss silage, and the primiparous and multiparous animals were supplemented wi th 9.0 and 11.0 kg concentrate d(-1) respectively. In Experiment 2, forty-e ight Holstein Friesian dairy cows were used in a 2 x 3 factorial design exp eriment, with factors examined consisting of two basal forage types (grass silage and zero-grazed grass) and three levels of straw inclusion (0, 1.0 a nd 2.0 kg d(-1)). All animals were offered 7.0 kg d(-1) of a concentrate su pplement. Both experiments were partially balanced changeover designs, cons isting of two, 4-week periods. In Experiment 1, the total dry-matter intake followed a significant quadrat ic relationship (P < 0.05), increasing with low levels of straw inclusion a nd decreasing at higher levels of inclusion. With increasing levels of stra w inclusion, there was a linear decline in milk yield (P < 0.001) and milk protein concentration (P < 0.05), but milk fat concentration was unaffected (P > 0.05). In Experiment 2, the effect of straw inclusion on total dry-matter intake w as quadratic (P < 0.001), with intakes being maximum at the 1.0-kg level of straw inclusion. Milk yield exhibited a linear decrease (P < 0.001) with i ncreasing level of straw inclusion. Milk fat concentration was lowest at th e 1.0 kg rate of straw inclusion (P < 0.05), but milk protein concentration was unaffected by straw inclusion. There were no significant interactions between basal forage type and level of straw inclusion for any of the varia bles examined (P > 0.05). Despite small increases in total dry-matter intake at a low level of straw inclusion, there was no evidence that straw inclusion improved either nutri ent utilization or animal performance. The reduction in milk yield observed with straw inclusion reflects, to a large extent, a reduction in metaboliz able energy intake.