The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles

Figures & data

Table 1. Mean (±SEM) concentrations of endophyte alkaloids (mg/kg) in ryegrass herbage measured in 2012 in paddocks sown with different cultivar-endophyte combinations (n=3 per cultivar), in which lambs were grazed from 14 February to 2 April 2012.

Alkaloid	Cultivar-endophyte	26 Jan (Day −19)	16 Feb (Day 2)	6 Mar (Day 21)	29 Mar (Day 44)
Ergovaline
	T-NEA2	0.4±0.2	0.5±0.3	0.7±0.2	0.9±0.2
	S-AR37	NA	NA	NA	0.0±0.0
	T-Nil	NA	NA	NA	0.0±0.0
	S-Nil	NA	NA	0.0^a	0.0±0.0
Lolitrem B
	T-NEA2	0.4±0.1	0.7±0.1	0.5±0.1	1.1±0.1
	S-AR37	NA	NA	NA	0.0±0.0
	T-Nil	NA	NA	NA	0.0±0.0
	S-Nil	NA	NA	0.0^a	0.0±0.0
Peramine
	T-NEA2	11.0±0.8	2.1±1.0	10.6±0.8	5.2±0.8
	S-AR37	NA	NA	NA	0.0±0.0
	T-Nil	NA	NA	NA	0.0±0.0
	S-Nil	NA	NA	0.0^a	0.0±0.0
Epoxy-janthitrems
	S-AR37	19.8±4.7	18.5±8.1	23.2±4.7	26.0±4.7
	S-Nil	NA	NA	0.0±0.0	NA

^a One sample only was analysed.

NA=not analysed; S-AR37=Samson ryegrass infected with AR37 endophyte; S-NIL=endophyte-free Samson ryegrass; T-NIL=endophyte-free Trojan ryegrass; T-NEA2=Trojan ryegrass infected with NEA endophytes

Table 2. Mean (±SEM) concentrations of endophyte alkaloids (mg/kg) in ryegrass herbage measured in 2013 in paddocks sown with different cultivar-endophyte combinations (n=3 per cultivar), in which lambs were grazed from 1 February to 21 March 2013.

Alkaloid	Cultivar-endophyte	20 Feb (Day 19)	15 Mar (Day 42)
Ergovaline
	T-NEA2	1.0±0.2	1.7±0.2
	S-STD	0.5±0.2	1.2±0.3
Lolitrem B
	T-NEA2	0.9±0.1	1.0±0.1
	S-STD	2.8±0.1	4.1±0.1
Peramine
	T-NEA2	4.7±0.8	4.4±0.8
	S-STD	23.5±0.8	19.3±1.0
Epoxy-janthitrems
	S-AR37	27.0±4.7	50.5±5.7

S-AR37=Samson ryegrass infected with AR37 endophyte; S-STD=Samson ryegrass infected with standard endophyte; T-NEA2=Trojan ryegrass infected with NEA endophytes

Figure 1. Mean (±SEM) liveweight gain (g/day) of lambs grazing pastures sown with different cultivar-endophyte combinations (n=30 per cultivar) for 48 days in February and March in (a) 2012 (Year 1) and (b) 2013 (Year 2). The cultivars were endophyte-free Trojan ryegrass (grey bars), Trojan ryegrass infected with NEA endophytes (black bars), endophyte-free Samson ryegrass (coarsely striped bars), Samson ryegrass infected with standard endophyte (S-STD, white bars) and Samson ryegrass infected with AR37 endophyte (finely striped bars). Note that in 2013 liveweight gain was not determined for the S-STD group because all animals were removed before Day 48 due to severe staggers.

Table 3. Number of lambs categorised by ryegrass staggers score (Keogh 1973) on two occasions in 2012, that were grazing different cultivar-endophyte combinations between 14 February and 2 April 2012.

		Cultivar-endophyte			P-value^b
	Score	T-NEA2	S-STD^a	S-AR37	T-NEA2 vs. S-STD	T-NEA2 vs. S-AR37	S-STD vs. S-AR37
12 Mar 2012 (Day 27)					<0.001	0.392	0.001
	0	23	7	20
	1	7	10	10
	2	0	4	0
	3	0	4	0
	4	0	5	0
2 Apr 2012 (Day 48)					0.002	0.096	0.079
	0	24	9	18
	1	6	3	10
	2	0	9	2
	3	0	2	0
	4	0	2	0

^a Due to severe staggers, five sheep were removed from S-STD cultivar after assessment on Day 27.

^b Significance of difference in distribution between cultivar groups, based on ordinal logistic regression analysis

S-AR37=Samson ryegrass infected with AR37 endophyte; S-STD=Samson ryegrass infected with standard endophyte;T-NEA2=Trojan ryegrass infected with NEA endophytes

Table 4. Number of lambs categorised by ryegrass staggers score (Keogh 1973) on four occasions in 2013, that were grazing different cultivar-endophyte combinations between 1 February and 21 March 2013.

		Cultivar-endophyte			P-value^b
	Score	T-NEA2	S-STD^a	S-AR37	T-NEA2 vs. S-STD	T-NEA2 vs. S-AR37	S-STD vs. S-AR37
21 Feb 2013 (Day 20)					<0.001	0.520	<0.001
	0	25	4	23
	1	5	12	7
	2	0	3	0
	3	0	2	0
	4	0	4	0
	5	0	5	0
5 Mar 2013 (Day 32)					<0.001	0.003	<0.001
	0	26	3	14
	1	3	1	10
	2	1	1	5
	3	0	3	1
	4	0	12	0
	5	0	10	0
11 Mar 2013 (Day 38)						0.814
	0	11		17
	1	5		9
	2	2		1
	3	1		1
	4	1		2
20 Mar 2013 (Day 47)						<0.001
	0	8		2
	1	6		3
	2	8		3
	3	4		4
	4	3		15
	5	1		3

^a Due to severe staggers, all sheep were removed from S-STD cultivar after assessment on Day 32

^b Significance of difference in distribution between cultivar groups, based on ordinal logistic regression analysis

S-AR37=Samson ryegrass infected with AR37 endophyte; S-STD=Samson ryegrass infected with standard endophyte;T-NEA2=Trojan ryegrass infected with NEA endophytes

Figure 2. Mean (±SEM) (a) rectal temperature (°C) and (b) respiration rate (breaths/minute) of lambs when subject to heat stress after grazing pastures sown with different cultivar-endophyte combinations (n=30 per cultivar) for 24 days in 2012 (Year 1) and 26 days in 2013 (Year 2). The cultivars were endophyte-free Trojan ryegrass (grey bars), Trojan ryegrass infected with NEA endophytes (black bars) and Samson ryegrass infected with standard endophyte (white bars).

Keogh RG. Induction and prevention of ryegrass staggers in grazing sheep. New Zealand Journal of Experimental Agriculture 1, 55–7, 1973 doi: 10.1080/03015521.1973.10427616

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