Performance of lambs and the incidence of staggers and heat stress on two perennial ryegrass (Lolium perenne) cultivars using a leader-follower rotational grazing management system

Abstract

A summer lamb finishing experiment at Palmerston North, New Zealand compared the performance and health of weaned lambs grazing Aries HD or Yatsyn 1 perennial ryegrass (Lolium perenne). Aries HD ryegrass was originally selected for increased digestibility over summer and early autumn. Two groups of RomneyiSuffolk lambs (15 per group) were rotationally grazed on each cultivar in a leader-follower sequence to assess both the nutritive value of the pastures and the alkaloid challenge imposed by the respective cultivar\endophyte (Neotyphodium lolii) associations. Herbage from leader pastures contained a higher content of ryegrass (600 v. 474p27n3 g\kg, P 0n001) and a lower content of dead material (355 v. 479p34n2 g\kg, P 0n001) than follower pastures. The in vitro organic matter digestibility coefficient of leader pastures was greater (0n62 v. 0n55p0n024, P 0n05) and the neutral detergent fibre content lower (592 v. 631p11n4 g\kg, P 0n005) than follower pastures. Consequently, the leader lambs had faster liveweight gains (92 v. 53p10n6 g\day, P 0n0005) than the follower lambs. Aries HD and Yatsyn 1 cultivars were similar in sward composition, in vitro organic matter digestibility, neutral detergent fibre content and nitrogen content. Lambs grazing Aries HD had a higher herbage intake in late January than lambs grazing Yatsyn 1 pasture (0n95 v. 0n85p0n023 kg OM\day, P 0n005). Overall, the liveweight gains of lambs grazing Aries HD and Yatsyn 1 were similar (71 v. 73p10n6 g\day, P 0n7).Grazing sequence and cultivar did not affect the concentrations of lolitrem B and peramine from herbage cut to ground level. However, serum prolactin concentration, which can indicate ergovaline intoxication, was lower in lambs grazing follower swards (181 v. 120p18n0 ng\ml, P 0n005). Ergovaline concentration in Aries HD herbage was about half the concentration detected in Yatsyn 1 herbage (0n25 v. 0n49p0n050 mg\kg, P 0n001). In addition, respiration rate, which can be an indicator of heat stress, was higher in lambs grazing Yatsyn 1 than Aries HD (77 v. 74p1n1 breaths per minute, P 0n005). All lambs on all treatments had clinical ryegrass staggers from 10 February to 9 March. Lambs were removed from the experiment on 9 March. Both grazing sequence and cultivar affected the severity of ryegrass staggers. Staggers score was highest in Yatsyn 1 followers (4n4) and lowest in Aries HD leaders (3n1). Both grazing sequence and cultivar affected the alkaloid challenge imposed on lambs, resulting in differences in staggers severity, heat stress and performance of the lambs over the summer and autumn period.

The use of legume and herb forage species to create high performance pastures for sheep and cattle grazing systems

“…Average lamb growth rates on pure perennial ryegrass or on browntop pastures are typically 80-150 g live weight/day (Kerr, 2000;Bluett et al, 2001). Lambs grown to their slaughter weight more quickly eat less feed in total than lambs grown slowly and so use the feed more efficiently.…”

Ergovaline, an endophytic alkaloid. 2. Intake and impact on animal production, with reference to New Zealand

“…Symptoms of heat stress (e.g. panting, excess salivation) can be induced during exposure to high ambient temperature (32À36 C) and relative humidity (69% RH) in sheep that have had a moderate intake of ergovaline (Fletcher et al 1994;Bluett et al 2001). When evaluating the effects of ergovaline in endophyte-infected tall fescue, the effects of fescue toxicosis are exacerbated at higher ambient temperatures.…”

“…This makes it unrealistic to apportion separately the effects of the two alkaloids or to determine the primary suspect of the pair, particularly if there is possible synergy between them (Bluett et al 2001). Of the New Zealand data, only the work of Layton et al (2004) and Cosgrove et al (1996), using 187BB-containing (a high ergovaline-low lolitrem-producing endophyte) pasture removed the potential for a major lolitrem B effect and minimised confounding.…”

“…Whether this results in a higher ergovaline intakedependsnotonlyontheincreaseinendophyteconcentration in lower plant parts but also on the counterbalancing effect of reduced grazing intake associated with the lower postgrazing pasture height. This interaction was explored by Bluett et al (2001) who incorporated 'leader' and 'follower' groups of lambs grazing standard endophyte-containing pastures. However, in this work the decrease in grazing intake of the Table 1, showing significant or non-significant effects of ergovaline intake on milk production or liveweight gain.…”

“…A synergistic relationship between ergovaline and lolitrem B intake has been suggested (Bluett et al 2001) and exposure to other compounds such as isoflavones or phyto-oestrogens may influence the effects of ergovaline.…”