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

Abstract

Two factorial design experiments were carried out in the spring of 1994 and 1995, each of 6 weeks, to quantify the effects of sward height (SH), concentrate level (CL) and initial milk yield (IMY) on milk production and grazing behaviour of continuously stocked dairy cows. In Experiment 1, forty‐five 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 with IMY of 21·3 and 35·5 kg d–1, grazed sward heights were 3–5 and 7–9 cm (LSH and HSH), and concentrates were fed at 0 and 6 kg d–1 and ad libitum. Multiple regression models were used to quantify the effects of the three variables on milk yield persistency (MYP), estimated herbage dry‐matter (DM) intake (HDMI), grazing time (GT) and rate of DM intake (RI). The partial regression coefficients showed that increased SH led to increased MYP (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 regression coefficients quantified the extent to which GT and RI by cows respond positively to higher IMY, and negatively to increased CL, but respond differently (GT declines in response to a higher RI) with increasing SH.

Effect of increasing pasture allowance and concentrate supplementation on animal performance and microbial protein synthesis in dairy cows

“…The lack of effect of supplementation with concentrate on grazing time could be explained by a social effect, where Phillips (1993) suggests that supplementation also affects non-supplemented cows in cases where they were grazing together, such as decreasing their grazing time or, the intake speed in supplemented cows. Although Delaby et al (2003) agree with this study, a considerable number of authors (Pulido and Leaver 2001, Bargo et al 2003 show decreasing grazing times under conditions of generous pasture availability in spring. The bite rate was not affected by supplementation with concentrate, just like in the reports of Bargo et al (2002) but opposed to that of Pulido and Leaver (2001).…”

“…Although Delaby et al (2003) agree with this study, a considerable number of authors (Pulido and Leaver 2001, Bargo et al 2003 show decreasing grazing times under conditions of generous pasture availability in spring. The bite rate was not affected by supplementation with concentrate, just like in the reports of Bargo et al (2002) but opposed to that of Pulido and Leaver (2001). In this regard, Pulido and Leaver (2003) point out that it is possible to expect a decrease in bite rate of cows with supplementation levels that are higher than 6 kg cow -1 accompanied of high pasture allowances, as a result of these animals having a lack of interest on grazing.…”

“…Herbage DM intake was estimated indirectly from animal performance results (Pulido and Leaver 2001) in one opportunity during the experiment as follows:…”

“…During the experiment, cows grazing the low PA had lower pasture (P < 0.05, -0.8 kg) and total DM intake. On the low mass pasture, dairy cows tried to maintain pasture intake by increasing grazing time, but in the presence of a very short sward cows are unable to fully compensate the reduction of intake rate and the total daily intake is reduced Leaver 2001 andPerez-Prieto et al 2011). In this experiment, the increase of pasture allowance resulted in a total increase of grazing time of 112 min day -1 , a decrease of the bite rate of 8 bites min -1 and an increase of the total food intake (Table 3).…”

Effect of time at pasture combined with restricted indoor feeding on production and behaviour in dairy cows

“…The energy requirements for maintenance, grazing activity, lactation and live-weight change in net energy of lactation (NEL) as described by Macoon et al (2003) were estimated from animal performance data at group level, as the intake of the indoor feed was registered at group level and converted to ME, assuming a utilisation of ME by 0.65 (Agricultural Research Council, 1980). Herbage DM intake was estimated as the difference between the Time at pasture effects on dairy cows requirement and ME in supplemental feed at group level divided by the ME concentration of the handplucked herbage samples (Pulido and Leaver, 2001).…”