Ovine Observer

Using lupins and the ram effect to improve reproductive performance in Merino ewes in southern Australia

Introduction

The ability of lupins to increase ovulation rate by increasing the number of multiple ovulations in Merino ewes in as little as four days (Stewart and Oldham, 1986) continues to interest researchers and producers alike (Vinoles et al., 2010; Errandonea et al., 2018; Banchero et al., 2021).

Australia is the world’s largest producer of lupin grain, much of which is used by the sheep industry (White et al., 2007).

Numerous studies have shown that as well as increasing ovulation rate in sheep, lupins can also improve lamb survival (Earle and Male 1988; Lindsay et al., 1990), colostrum and milk production (Bencini and Purvis 1990; Murphy et al., 1996) and weaner and wool growth (Petterson, 2000; White, 2007).

This review summarises work undertaken by the authors (Nottle et al., 1997a, b; 1988) over several years aimed at improving reproductive performance of Merinos in southern Australia by combining lupin feeding with the ram effect to minimise the number of days required for supplementation.

Key findings

• Feeding lupins to Merino flocks mated using the ram effect for 14 days can enhance ovulation rate and improve lamb survival.
• The effectiveness of lupin supplementation may vary based on the nutritional status of ewes during different stages of folliculogenesis.
• Lupin feeding at expected lambing date for 14 days did not impact birthweight, however, it significantly boosted lamb survival rates, particularly for twins.

Using lupins and the ram effect to increase ovulation rate

In southern Australia, Merino ewes are normally mated in late spring/early summer to ensure that lambs can be sold prior to end of the pasture growing season. This is possible because Merino ewes are less seasonal and can be mated prior to their spontaneous breeding season using the ram effect (Martin et al., 1986). This results in more than 90% of ewes having a silent ovulation prior to their first oestrous around 18 or 24 days later (Pearce and Oldham, 1984).

To best adapt the lupin response on farm, we reasoned that the synchrony afforded by the ram effect could be used to shorten the time needed for supplementation to 14 days. This would cover the last half of the oestrous cycle in most ewes given that more than 70–80% of ewes conceive at their first oestrus (Edey, 1972), and feeding for a longer period to cover ewes that fail to conceive at their first mating would be uneconomic.

The results from 2 on-farm trials for ewes fed a maintenance energy diet, showed that feeding 500 g/hd lupins daily for 14 days, 12 days after the introduction of vasectomised rams (or testosterone treated wethers) increased ovulation rate and subsequent lambing and weaning percentages across farms by 15.9, 12.4 and 12.% respectively (Table 1; Nottle et al., 1997a).

Table 1: Reproductive performance of Merino ewes synchronised using the ram effect and supplemented with lupin grain for 14 days, commencing 12 days after introduction of vasectomised rams on two commercial properties. Source: Nottle et al. (1997a).

Attribute	Treatment		Farm
	Control	Lupins	Farm A	Farm B
Incidence of oestrus (%) 0–14 c days	16.1a (40/248)	14.0a (35/250)	15.1 (75/ 498)	nad
15-29 days	94.0a (453/482)	93.6a (452/ 483)	97.0a (483/ 498)	90.4b (422/ 467)
Incidence of non-returns to service (%)	83.9a (380/453)	87.2a (394/452)	90.3a (436/483)	80.1b (338/422)
Liveweight day 29 (kg) e	51.9 ± 0.5a	52.4 ± 0.5a	52.7 ± 0.5a	51.6 ± 0.4a
Ovulation rate	1.26a (189/150)	1.46b (247/169)	1.41a (221/157)	1.33a (215/162)
Ewes lambing per ewe exposed to rams (%)	94.6a (456/482)	94.8a (458/483)	96.0a (478/498)	93.4a (436/467)
Lambs born per ewe lambing	1.21a (552/456)	1.36b (624/458)	1.33a (634/478)	1.24b (542/436)
Lambs weaned per lamb born (%) Single	79.7a (287/360)	78.1a (228/292)	89.8a (289/322)	68.5b (226/330
Twin	68.8a (132/192)	73.5a (244/332)	89.1a (278/312)	46.2b (98/212)
Overall	75.9a (419/552)	75.6a (472/624)	89.4a (567/634)	59.8b (324/542)
Lambs weaned per ewe exposed to rams (%)	86.9 (419/482)	97.7 (472/483)	113.9 (567/498)	69.4 (324/467)

c Vasectomised rams joined with ewes on day 0

d na: not available.

e Least squares mean ± SE.

Within main effects and rows, means not followed by a common letter differ significantly (P < 0.05).

*In all studies ewes were fed 100g/ewe/d for 2 days immediately prior to the start of full supplementation to adapt ewes to lupins. As it is the author’s experience that feeding 500 g immediately results in a proportion of ewes going off lupins.

The effect of previous nutrition on the ovulatory response to lupins

The response to lupins is not consistent. In large scale on-farm trials in the 1980s the effect was negligible in terms of lambs born, ranging from - 14 to + 21 % when 250 g of lupins were fed from 14 days before joining until day 17 of mating. Increasing supplementation to 500 g did not overcome this variability (Croker et al., 1985). However, we reasoned that much of this variation might be explained by the fact that it takes 6 months for a follicle to grow and ovulate (most don’t and are lost though atresia) and that changes in nutrition, particularly undernutrition, during this time may influence this response (Fletcher, 1974; Driancourt et al., 1993). To examine this suggestion, we undertook a series of studies where nutritional handicaps were imposed at different stages of folliculogenesis and their effect on the response to lupins examined (Nottle et al., 1997b).

Experiment 1

In the first experiment, nutritional restrictions were imposed for 8 weeks, 6 months prior to mating when follicles exit the primordial pool and commence growing. These restrictions resulted in ewes losing around 10% of their liveweight.

After this period both groups were recombined and run as one flock and stocked at rates designed to maintain their pre-treatment liveweight until 3 weeks prior to ovulation when they were divided into control and lupin fed groups.

The results from this study (Table 2) showed that ovulation rate was reduced by 17% in ewes that had lost liveweight 6 months previously (1.06 vs 1.28; P < 0.05) and that feeding lupins for 10 days prior to ovulation could overcome this handicap and increase ovulation rate to a similar level to that achieved with lupins in the control group which had not lost weight (1.63 vs 1.57; P > 0.05).

Table 2: Ovulation rate (mean ± SEM) of ewes placed on a low or high plane of nutrition for 8 weeks, 6 months prior to ovulation and supplemented with lupins for 10 days prior to ovulation (Experiment 1). Source: Nottle et al. (1997b).

Attribute	Low plane of nutrition		High plane of nutrition
	- Lupins	+ Lupins	- Lupins	+ Lupins
No. of ewes	50	49	50	49
Ewes with:
0 CL a	4	3	4	1
1 CL	39	12	28	19
2 CL	7	34	18	29
Ovulation rate	1.06 ± 0.07	1.63 ± 0.09	1.28 ± 0.09	1.57 ± 0.08

a Corpora lutea.

Experiment 2

In the second experiment we showed that ewes which lost around 3 kg of their liveweight over 8 weeks prior to ovulation responded only slightly to lupins (13%; 1.22 v 1.38; P = 0.06;Table 3).

In contrast, control ewes which gained a similar amount of liveweight had a higher ovulation compared with the control group which lost weight (1.67 vs 1.22; P < 0.001). This group also failed to show a response to lupins (1.64 vs 1.67; P > 0.05; Table 3), presumably because they were already expressing their maximum ovulation rate.

Table 3: Ovulation rate (mean ± SEM) of ewes placed on a low or high plane of nutrition for 8 weeks prior to ovulation and supplemented with lupins for 10 days prior to ovulation (Experiment 2). Source: Nottle et al. (1997b).

Attribute	Low plane of nutrition		High plane of nutrition
	- Lupins	+ Lupins	- Lupins	+ Lupins
No. of ewes	70	64	72	69
Ewes with:
0 CL a	2	5	5	6
1 CL	50	34	18	18
2 CL	18	21	45	41
3 CL	0	4	4	3
4 CL	0	0	0	1
Ovulation rate	1.22 ± 0.06	1.38 ± 0.09	1.67 ± 0.08	1.64 ± 0.09

a Corpora lutea.

Summary

How undernutrition influences ovulation rate at the time of follicle development and immediately prior to the time of ovulation remains to be determined.

Restricting nutrition 6 months prior to ovulation may increase the number of follicles that commence growing but are lost to atresia. Restricting nutrition 8 weeks prior to ovulation may have influenced ovulation rate by reducing the number of preantral follicles that enter the antral phase and their continual development.

Whatever the effect, short term lupin feeding does not appear to involve an increase in the number of follicles present on the surface of the ovary or recruitment (Driancourt and Cahill, 1984), but rather an increase in the number of these selected to ovulate (Nottle et al., 1985) suggesting that the effect of lupins in both instances is to restore the ovulatory capacity of a follicle(s) which had been compromised previously. Alternatively, lupins may promote a follicle which was not destined to ovulate in both instances.

In summary, this study demonstrated that nutrition, in particular undernutrition, at different stages of folliculogenesis, could influence the ovulatory response to lupins. Variability in response among commercial flocks may stem from this factor.

Our results suggest that for ewes losing weight during mating in late spring/early summer, might see minor increases in ovulation rate with lupin supplementation, but this may not translate into more lambs born. Ewes with a body condition score of 4 or more (Russel et al., 1969) are unlikely to respond because they are already expressing their maximum ovulatory potential.

In short, a ewe’s net nutritional status (Lindsay, 1976) across the 6 months it takes a follicle to grow can influence the response to lupins, with implications for previously identified static (months), dynamic (weeks) and acute (days) effects (Coop, 1966; Fletcher, 1971; Scaramuzzi et al., 2006).

Lupins could help mitigate nutritional deficiencies, particularly those from 6 months prior, a period coinciding with ewes' lactation and significant nutritional demands (Cahill et al., 1984).

Using lupins and the ram effect to increase lamb survival

Around the same time these trials were being undertaken, Kleemann and Walker (2005) completed an extensive survey of reproductive performance of maiden and mature Merinos on 43 properties over 4 years in southern Australia.

The results from this study showed that ovulation rate in Merino flocks was already relatively high (average 1.41) which meant that many producers were already achieving 100% lambing and the real problem was lamb survival with an average of 44% of twin lambs lost before weaning.

This led us to refocus our strategy on lamb survival. Given that synchrony from the ram effect results in a concentrated lambing, we reasoned that feeding lupins for 14 days starting 12 days after the onset of lambing (Day 0 = introduction of teasers or rams) may be a more effective use of supplementation, as many producers practice some form of supplementation around lambing in March/April when pasture is in poor supply and quality. Work around this time had also shown that feeding lupins immediately prior to parturition could increase lamb birth weight (Earl and Male, 1988) and colostrum production (Murphy et al., 1996). Both had been identified previously as major factors in determining lamb survival (Lindsay et al., 1990).

To examine this strategy, an initial study was done on-farm using one of the same farms as the previously discussed studies. In this trial ewes were fed wheaten hay and oats that met the energy requirements of late pregnant/lactating ewes (ARC, 1980). This was fed 6 weeks prior to the predicted start of lambing. One group was supplemented with 500g of lupins for 14 days (fed 3 times per week) commencing 12 days after the expected start of lambing (Nottle et al., 1998). The results from year 1 of the trial showed that the number of lambs weaned increased by 8.3 % (Table 4). Surprisingly birth weight was unchanged, whereas weaning weight was on average 1.4 kg higher.

A more detailed study was undertaken the following year. The results from this study confirmed that birth weight was not increased, but lamb survival was similarly increased by 8.8%, particularly in twin lambs where the increase was 10.8% (Table 4). Again, lambs were on average 1.3 kg heavier at tail docking around 8 weeks after birth.

Based on these findings we suggested that these increases were the result of increased colostrum and milk production. Something which others had shown previously (Murphy et al., 1996; Bencini and Purvis, 1990) and confirming a need for bypass protein for ewes late in pregnancy even when their energy requirements were being met (ARC, 1980).

Table 4: Effect of feeding lupins to ewes mated using the ram effect for 14 days commencing 12 days after the expected start of lambing on lamb weight at birth and tail docking/weaning, and on lamb survival in Years 1 and 2. Source: Nottle et al. (1998).

Attribute	Treatment		Probability value
	Control	Lupins
Year 1
No. of ewes allocated	340	340
No. of ewes at weaning	332	326
Lambs weaned / 100 ewes allocated	77.9 (265/ 340)	84.4 (287/ 340)
Birth weight (kg)	4.88 ± 0.10a	4.87 ± 0.09	0.71
Weaning weight (kg)	23.0 ± 0.50	24.4 ± 0.50	0.06
Year 2
No. of ewes allocated	163	162
No. of ewes at tail docking	157	153
Lambs tail docked / 100 ewes allocated	89.6 (146/163)	96.9 (157/162)
Birth weight (kg) Single	5.12 ± 0.12	5.26 ± 0.12
Twin	3.61 ± 0.18	3.58 ± 0.19
Overall	4.37 ± 0.11	4.42 ± 0.11	0.70
Ewe live weight at tail docking (kg)	67.9 ± 0.80	67.0 ± 0.80	0.43
Lambs tail docked per lamb born (%) Single	82.5 (94/114)	88.6 (101/114)
Twin	74.3 (52/70)	82.3 (56/68)
Overall	79.3 (146/184)	86.3 (157/182)	0.000

a Least squares mean ± SE.

*For the lambing strategy oats and lupins were fed out 3 times per week i.e. Mon (1000 g/ewe),  Wed (1000 g) and Fri (1500 g) for ease of management.

Economic considerations

The economic viability of feeding any supplement is based on several factors with duration being a major determinant. The aim of the present review was to highlight that the ram effect can be used to limit the period of lupin feeding to improve reproductive performance to 14 days.

In a recent analysis of the economic viability of a range of strategies to increase/rebuild Merino flocks in southern Australia, Brien et al. (2023) concluded that our strategy to improve ovulation rate was amongst the top 6 strategies of the 17 examined.

In relation to improving lamb survival, pregnancy scanning for twins now allows producers to treat this group differently during lambing. A more economic strategy, than that originally developed by us, may be to supplement only these ewes. In this regard, Brien (pers comm) concluded that using our lambing strategy, but feeding only twin-bearing ewes lupins in late pregnancy ranked second out of the same 17 strategies examined in their study (Brien et al., 2023).

Conclusion

Together our results show that on-farm lupin feeding for 14 days in Merino flocks mated using the ram effect can be used to increase ovulation rate as well as improve lamb survival.

The unanswered question is whether combining both strategies can have an additive effect on reproductive performance with the potential to increase weaning percentages by upwards of 20% or possibly more, given that this work was conducted under controlled conditions where ewes with an average body condition score of 3, were fed at maintenance energy levels during mating and lambing. This is not normally the case for most farms in southern Australia as pastures are, or have already, senesced at mating and are often in poor supply around lambing in autumn. This results in ewes losing weight, reducing lamb birth weights, particularly for twins.

Importantly we have also showed that feeding lupins at mating may also overcome nutritional handicaps on ovulation rate imposed up to 6 months earlier, which coincides with the nutritional drain that is lactation.

Whether feeding lupins at mating and/or at lambing can also improve lifetime production including growth rate, wool production, and reproductive performance (so called fetal programming; Martin, 2022) also remains to be determined. However, such an effect may justify the cost of feeding lupins alone.

Full paper (including full reference list)

Acknowledgements

We thank Messrs. R. Norton, B. Cowan, T. Grosser and staff from the University of Adelaide and the South Australian Research and Development, and H. O’Connor and N. Moyle of ‘Buckland Park’ for the use of their ewe flock and willing assistance in the study. The financial assistance of Australian Wool Innovation Ltd (formerly the Wool Research and Development Corporation) is gratefully acknowledged.