Quantifying the influence of sward height, concentrate level and initial milk yield on the milk production and grazing behaviour of continuously stocked dairy cows

Two factorial design experiments were carried out in the spring of 1094 and 1995, each of 6 weeks, to quantify the effects of sward height ISH), conce ntrate level (CL) and initial, milk yield (IMY) on milli production and gra zing behaviour of continuously stocked dairy cows. In Experiment 1, forty-f ive Holstein Friesian cows were in five groups with initial milk yields of 16.9, 21.1, 28.0, 31.5 and 35.5 kg d(-1), grazed sward heights were 3-5, 5- 7 and 7-9 cm (LSH, MSH and HSH respectively), and concentrates were fed at rates of 0, 3 and 6 kg d(-1). In Experiment 2, 48 cows were in two groups w ith IMY of 21.3 and 35.5 kg d(-1), grazed sward heights were 3-5 and 7-9 cm (LSI-I and I-ISH), and concentrates were fed at 0 and 6 kg d(-1) and ad li bitum. Multiple regression models were used to quantify the effects of the three variables on milli yield persistency (MYP), estimated herbage dry-mat ter (DM) intake (HDMI), grazing time (GT) and rate of DM intake (RI). The p artial regression coefficients showed that increased SH led to increased MY P (Experiment 1 P< 0.001, Experiment 2 P < 0.05),increased HDMI (P < 0.01, P<0.01), increased GT (P < 0.001, P < 0.05) and increased RI (P < 0.001, P < 0.05). Increasing CL led to increased MYP [NS, P < 0.001), decreased HDMI (P < 0.001, P < 0.001), decreased GT (NS, P < 0.001) and decreased RI (P<0 .001, P<0.001). Higher IMY level of cows decreased MYP (P< 0.001, P<0.001), increased HDMI (P < 0.001, P < 0.001), increased GT (P<0.001, P<0.05) and increased RI (P<0.05. P<0.01). The models were highly significant (P< 0.001 ), and accounted for 0.48-0.87 of the total variance. The partial regressio n coefficients quantified the extent to which CT and RI by cows respond pos itively to higher IMY, and negatively to increased CL, but respond differen tly (GT declines in response to a higher RI) with increasing SH.