Effect of herbage mass and allowance on sward characteristics, milk production, intake and rumen volatile fatty acid concentration

Abstract

The objective of this study was to examine the effect of herbage mass and daily herbage allowance (DHA) on sward characteristics and animal performance, drymatter intake, rumen pH and volatile fatty acid production of unsupplemented spring-calving dairy cows throughout the main grazing season. Sixty-eight Holstein-Friesian dairy cows were randomly assigned across four treatments (n = 17) in a 2 · 2 factorial design. Two swards were created with different levels of pre-grazing herbage mass [allocated above 4 cm (>4 cm); 1700 kg DM ha )1 (medium; M) or 2200 kg DM ha )1 (high; H)] and two levels of DHA (>4 cm; 16 or 20 kg DM per cow d )1 ). An additional eight lactating ruminally cannulated Holstein-Friesian dairy cows were randomly assigned to each treatment in a replicated 4 · 4 Latin square design. Sward and animal measurements were collected across four periods each of 1 week duration in April and May (PI) and July and August (PII). Maintaining the medium-mass sward across the season improved the nutritive value of the sward in the latter part of the grazing season compared with high-mass swards, thus resulting in increased animal intakes and milk production throughout PII. The higher organic matter digestibility of the medium-compared with high-masses during PII indicates that grazing severity and herbage mass in the spring to mid-summer period will determine sward quality parameters in the late summer period.

Effect of rotationally grazing perennial ryegrass white clover or perennial ryegrass only swards on dairy cow feeding behaviour, rumen characteristics and sward depletion patterns

“…The lower pre-grazing herbage mass offered by both the GO and GWc swards during this phase compared to the other measurement phases resulted in lower sward fibre content, resulting in a smaller difference in ruminating time between sward types over 24 h. Similar to the trends reported here, less ruminating time has been reported for cows grazing mixed swards compared to ryegrass only swards when the clover content was high (22%; Phillips et al, 2000), but not when clover content was low (10%; Phillips and James, 1998). Total rumen VFA concentrations were within the range previously reported for cows grazing ryegrass (McEvoy et al, 2010;O'Connor et al, 2013) and mixed swards (Ribeiro Filho et al, 2003). The lack of differences between the swards was somewhat unexpected as previous studies showed higher VFA concentration for cattle when clover was included as part of the diet (Ulyatt, 1970;Dewhurst et al, 2003;Ribeiro Filho et al, 2003).…”

“…No negative effects of the low rumen pH on animal health (metabolic acidosis, laminitis, and milk fat depression; Kleen et al, 2003) were observed. This supports previous suggestions that on grass diets the rumen can tolerate lower pH values for a longer time without the negative impact observed on grain-based diets (McEvoy et al, 2010).…”

Effect of grazing severity on perennial ryegrass herbage production and sward structural characteristics throughout an entire grazing season

“…() and McEvoy et al . (). The herbage harvested from each cut strip was collected, weighed and sampled, and a subsample (100 g) was dried overnight at 90°C in a forced‐draught oven to determine DM content.…”

Managing variations in dairy cow nutrient supply under grazing

“…Therefore, high-producing dairy cows exhibits intensive ruminal fermentation with grasses. However, none of the risk associated to low rumen pH is reported (McEvoy et al, 2010). This suggests that the cow and the rumen can tolerate low pH and high VFA production without the negative impacts that are generally associated with grain-based diets.…”

“…High ruminal VFA concentration have also been reported by Stakelum and Dillon (2003). At grazing, Delagarde and Peyraud (2000), Stakelum and Dillon (2003) and McEvoy et al (2010) showed that the average pH of the rumen became ,6 approximately 3 to 4 h following allocation of a new paddock and remained ,6 during at least 12 h. Ruminal pH around 5.5 is frequent at the end of the day on leafy swards. Therefore, high-producing dairy cows exhibits intensive ruminal fermentation with grasses.…”