9 1985 by The HumanaPress Inc. All rights of any nature whatsoeverreserved. 0163-4984/85/0300-0089 $02.00
Zinc Supplements and Reproduction in Grazing Ewes DAVID Go MASTERS* School of Agriculture (Animal Science), University of Western Australia, Nedlands, Western Australia 6009 AND H. E. FELS
Western Australian Department of Agriculture, Jarrah Road, South Perth, Western Australia 6151 Received April 16, 1984; Accepted October 24, 1984
ABSTRACT Six experiments were carried out in Western Australia to further investigate the effect of zinc supplementation on the reproductive performance of grazing Merino ewes. There was a small increase (7%, P = 0.1) in the number of lambs produced by zinc-supplemented ewes in only one of the six experiments. Plasma zinc levels just prior to lambing were increased by zinc supplementation in two experiments. These results are discussed and compared to the previously published reproductive responses to zinc supplementation by grazing Merino ewes. Index Entries: Zinc, and reproductive performance; reproduction, and zinc in sheep; supplementation, of zinc in reproduction; ewes, and zinc in reproduction.
INTRODUCTION In pre,~dous experiments in Western Australia, the reproductive performance of grazing Merino ewes was improved by zinc supplementa*Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
89
Vot. 7, 1985
90
Masters and Fels
tion d u r i n g pregnancy. Furthermore it was suggested that at least 25 txg Zn/g may be required by the ewe during gestation (1). M a n y of the pastures t h r o u g h o u t the southwest of Western Australia contain less than 25 ~g Zn/g for part of the year (2); therefore a further series of experiments was carried out to determine w h e t h e r responses to zinc are w i d e s p r e a d in that state.
METHODS Locations
Experiments were carried out at Badgingarra (30 ~ 25'S, 115 ~ 32'E), Woodanilling (33 ~ 34'S, 117~ 24'E), Salmon Gums (32 ~ 59'S, 121 ~ 39'E)~ Esperance (33 ~ 52'S, 121 ~ 50'E), Mt. Barker (34~ 37'S, 117 ~ 40'E) and N e w d e g a t e (33 ~ 6'S, 119 ~ I'E) (Experiments I to 6t respectively). The sites are distributed in the sheep-growing areas of s o u t h e r n Western Australia. At all sites most of the rain falls b e t w e e n April and October. After October the annual species of pasture mature and dry off; no n e w g r o w t h then occurs until the rain begins 5-6 mo later.
Sheep and Experimental Design In each experiment two treatment groups were compared. The first received two zinc pellets prior to mating and an additional pellet every 6-7 wk; the other was given no additional zinc. The zinc pellets used contain 5 g of metallic iron and 5 g of metallic zinc and act as a shorted voltaic celt actively releasing zinc (3). The initial release rate is approximately 20 m g Zn/d declining to 3 mg Zrt/d after 7 wk. The ewes in all experiments were joined with vasectomized rams (except in Experiment 2) and t h e n m a t e d for 5 w k with entire rams in December or January. The e w e s w e r e kept in one group except for 6-8 w k during lambing, w h e n they were separated into treatment groups in separate paddocks. The flocks were inspected daily or at some sites less frequently and lamb carcasses were counted and removed. The total n u m b e r of lambs born was estimated from the n u m b e r of lambs alive at the end of lambing and the n u m b e r of carcasses recovered. In addition the n u m b e r of ewes producing at least one lamb was determ i n e d by a combination of pregnancy diagnosis, using an e c h o - s o u n d i n g device (Scanopreg, Model 738, Ithaca, N e w York; Experiments, 1, 4, 6), inspection of the ewe's u d d e r before and/or after lambing (4) (Experiments, 1, 2, 3, 6), and by comparing live weights before and after lambing. Only those ewes whose data could be clearly interpreted using these three methods were included in the analysis. Reproductive performance was then evaluated as both the total n u m b e r of lambs born and the n u m b e r of e w e s producing a lamb. These two methods will not give identical results since the n u m b e r of ewes producing a lamb does not difBiological Trace E]ernent Research
VoL 7. 1985
Zinc and Reproduction in Grazing Ewes
91
ferentiate b e t w e e n the e w e s p r o d u c i n g singles or twins. H o w e v e r , u n d e r the extensive conditions utilized in these e x p e r i m e n t s u n d e t e c t e d losses of lambs or carcasses are possible a n d it is essential to c o n s i d e r b o t h sets of results. In all e x p e r i m e n t s pasture s a m p l e s w e r e collected e v e r y 6-8 w e e k s a n d p l a s m a s a m p l e s w e r e collected i m m e d i a t e l y prior to the start of l a m b i n g f r o m s u b s a m p l e s of 12 or 13 e w e s in each t r e a t m e n t g r o u p . L a m b i n g data w e r e c o m p a r e d by X2 analysis. Plasma zinc c o n c e n t r a tions w e r e c o m p a r e d using S t u d e n t s ' t-test.
RESULTS AND DISCUSSION In E x p e r i m e n t 2, 11% m o r e zinc-treated e w e s p r o d u c e d lambs t h a n control e w e s (P < 0.05). ']7his resulted in 7% m o r e lambs b o r n to the zincs u p p l e m e n t e d e w e s than to the control e w e s (P = 0.1) (Table 1). In Exp e r i m e n t 1, t h e r e was a small (8%) increase in the n u m b e r of zincs u p p l e m e n t e d e w e s p r o d u c i n g one or m o r e lambs (P < 0.1) in c o m p a r i s o n to the control ewes. This did n o t result in a n y difference bet w e e n g r o u p s in the n u m b e r of r e c o r d e d lamb births. In three o t h e r exp e r i m e n t s there w e r e no r e p r o d u c t i v e r e s p o n s e s . In E x p e r i m e n t 6, f e w e r TABLE 1 Reproductive Responses to Zinc Supplementation
Experiment No.
Lambs born
(No. lambs/ No. ewes)
Plus zinc
No zinc
Ewes producing lambs/ Ewes giving record Plus zinc
No zinc
1
102 (70%) 146
103 (70%) 147
112 (77%) 145
99 (69%) t43
2
139 (90%) 155
123 (83%y" 149
133 (93%) 143
__115 (82%) ~, 140
3
147 (103%) 143
144 (99%) 145
130 (92%) 142
13__44 (93%y 144
4
134 (91%) 148
138 (93%) 149
14__11 (95%) 148
138 (94%) 147
5
109 (93%) 117
112 (94%) 119
--
6
t27 (85%) 150
146 (97%y 150
137 (91%) 150
143 (95%) 150
Comparisons were made between plus zinc and no zinc groups: ~ P = 0.1; ~indicates P < 0.05; qndicates P < O.OOl. Biological Trace Element Research
VoL 7, t985
92
34asters and Fels
lambs w e r e recorded born to zinc-supplemented ewes than to controls. However, 91% of the plus-zinc ewes p r o d u c e d a lamb, but only 85 lambs per 100 ewes were recorded. Thus the apparent negative response was caused by undetected and u n r e c o r d e d losses of lambs born to the zinctreated ewes. Plasma zinc levels immediately prior to lambing in the zincs u p p l e m e n t e d ewes were significantly higher than in the controls in two experiments (Table 2). These increases were recorded only w h e n plasma zinc concentrations of control ewes fell below 0.7 p~g/mL. In all the other experiments, plasma zinc levels were consistently, t h o u g h not significantly, higher in the ewes given zinc than in the control ewes. Most pastures contained between 10 and 30 ~g Zn/g, however, at four sites (Experiments 1, 2, 3, and 6) pastures contained less than 10 p,g Zn/g during mid- or late pregnancy. In comparing these results with the positive responses previously reported (1), a n u m b e r of factors are apparent. With the exception of Experiment 1, the n u m b e r of lambs born per 100 control ewes exceeded 80%. tn Experiment 2, where the zinc-supplemented ewes had 7% m o r e lambs than controls, the controls had an 83% lambing rate; at the other four sites, lambing rates were b e t w e e n 90 and 97%. A s s u m i n g that some ewes did not become pregnant, these lambing percentages are exceptionally high for Merino ewes in Western Australia, and indicate almost no loss of embryos and fetuses. These high lambing rates are not typical of lamb production in Western Australia. A survey of agricultural regions in the south of Western Australia revealed that the n u m b e r of lambs born per 100 ewes is generally b e t w e e n 70 and 80, and that ewes m a t i n g but failing to lamb are responsible for approximately 20% of the reproductive wastage (5). The authors of this survey suggested that embryo mortality is a major problem. U n d e r the conditions of the current experiments, few embryos were lost and since the beneficial effect of zinc is probably in maintaining pregnancy in grazing ewes (1), no response to s u p p l e m e n t a tion could be expected. TABLE 2 Effect of Zinc Supplement on Plasma Zinc Concentrations Just Prior to Lambing (~g/mL) Experiment No. 1 2 3 4 5 6
Plus zinc 0.76 0.79 0.64 0.83 0.76 0.85
(0.04)~ (0.03) (0.03) (0.06) (0.03) (0.04)
No zinc 0.71 0.74 0.56 0.79 0.65 0.81
(0.03) (0.03) (0.02) (0.04) (0.03) (0.03)
Significance, t-test ns a ns P < 0.05 ns P < 0.05 ns
"Standard error of the mean in parentheses. ~Not significant. Biological Trace Elernent Research
VoL 7, 1985
Zinc and Reproduction in Grazing Ewes
93
In addition, plasma zinc levels just prior to lambing were influenced bv zinc at only two sites in the current experiments a n d only w h e n control levels were below 0.7 p~g/mL. O n the basis of these results, the zinc intake towards the e n d of p r e g n a n c y in four of the e x p e r i m e n t s was sufficient to m a i n t a i n zinc levels in the ewes, a n d only in two experim e n t s were these levels not maintained. In conclusion, it appears that, although at s o m e times p a s t u r e zinc levels were below the suggested m i n i m u m r e q u i r e m e n t (6), the ewes were probably not zinc-deficient. It is possible that because m a n y other n u t r i e n t s are also in short supply d u r i n g p r e g n a n c y that zinc m a y have been released from maternal tissues d u r i n g tissue catabolism (7) a n d redistributed to the d e v e l o p i n g fetus. The different responses to zinc suggest that, like other trace element deficiencies, such as those of selenium a n d copper, zinc deficiency m a y be sporadic and d e p e n d e n t on other nutritional or seasonal factors.
ACKNOWLEDGMENTS The W e s t e r n Australian D e p a r t m e n t of Agriculture a n d Mr. J. Carter for the use of their sheep and facilities; a n d Mr. B. Rose, Mr. P. Moore a n d the staff of the research stations for their technical assistance. This w o r k was .supported by a grant from the Wool Research Trust F u n d on the r e c o m m e n d a t i o n of the Australian Wool Corporation.
REFERENCES D. G. Masters and H. E. Fels, Biol. Trace Elem. Res. 2, 281 (1980). D. G. Masters and M. Somers, Aust. J. Exp. Agric. Anita. Hush. 20, 20 (1980). D. G. Masters and R. J. Moir, Aust. J. Exp. Agric. Anita. Husb. 20, 574 (1980). R. B. Dun, Aust. J. Exp. Agric. Anita. Husb. 3, 228 (1963) T. W. Knight, C. M. Oldham, J. F. Smith, and D. R. Lindsay, Aust. y. Exp. Agric. Anita. Husb. 15, (1975). 6. Agricultural Research Council, The Nutrient Requirements of Ruminant Livestock, CAB, Slough, 1980, p. 256. 7. D. G. Masters, C. L. Keen, B. L6nnerdal, and L. S. Hurley. J. Nutr. 113, 905 (1983). 1. 2. 3. 4. 5.
Biological Trace Element Research
VoL 7. 1985
Zinc Supplements and Reproduction in Grazing Ewes DAVID Go MASTERS* School of Agriculture (Animal Science), University of Western Australia, Nedlands, Western Australia 6009 AND H. E. FELS
Western Australian Department of Agriculture, Jarrah Road, South Perth, Western Australia 6151 Received April 16, 1984; Accepted October 24, 1984
ABSTRACT Six experiments were carried out in Western Australia to further investigate the effect of zinc supplementation on the reproductive performance of grazing Merino ewes. There was a small increase (7%, P = 0.1) in the number of lambs produced by zinc-supplemented ewes in only one of the six experiments. Plasma zinc levels just prior to lambing were increased by zinc supplementation in two experiments. These results are discussed and compared to the previously published reproductive responses to zinc supplementation by grazing Merino ewes. Index Entries: Zinc, and reproductive performance; reproduction, and zinc in sheep; supplementation, of zinc in reproduction; ewes, and zinc in reproduction.
INTRODUCTION In pre,~dous experiments in Western Australia, the reproductive performance of grazing Merino ewes was improved by zinc supplementa*Author to whom all correspondence and reprint requests should be addressed. Biological Trace Element Research
89
Vot. 7, 1985
90
Masters and Fels
tion d u r i n g pregnancy. Furthermore it was suggested that at least 25 txg Zn/g may be required by the ewe during gestation (1). M a n y of the pastures t h r o u g h o u t the southwest of Western Australia contain less than 25 ~g Zn/g for part of the year (2); therefore a further series of experiments was carried out to determine w h e t h e r responses to zinc are w i d e s p r e a d in that state.
METHODS Locations
Experiments were carried out at Badgingarra (30 ~ 25'S, 115 ~ 32'E), Woodanilling (33 ~ 34'S, 117~ 24'E), Salmon Gums (32 ~ 59'S, 121 ~ 39'E)~ Esperance (33 ~ 52'S, 121 ~ 50'E), Mt. Barker (34~ 37'S, 117 ~ 40'E) and N e w d e g a t e (33 ~ 6'S, 119 ~ I'E) (Experiments I to 6t respectively). The sites are distributed in the sheep-growing areas of s o u t h e r n Western Australia. At all sites most of the rain falls b e t w e e n April and October. After October the annual species of pasture mature and dry off; no n e w g r o w t h then occurs until the rain begins 5-6 mo later.
Sheep and Experimental Design In each experiment two treatment groups were compared. The first received two zinc pellets prior to mating and an additional pellet every 6-7 wk; the other was given no additional zinc. The zinc pellets used contain 5 g of metallic iron and 5 g of metallic zinc and act as a shorted voltaic celt actively releasing zinc (3). The initial release rate is approximately 20 m g Zn/d declining to 3 mg Zrt/d after 7 wk. The ewes in all experiments were joined with vasectomized rams (except in Experiment 2) and t h e n m a t e d for 5 w k with entire rams in December or January. The e w e s w e r e kept in one group except for 6-8 w k during lambing, w h e n they were separated into treatment groups in separate paddocks. The flocks were inspected daily or at some sites less frequently and lamb carcasses were counted and removed. The total n u m b e r of lambs born was estimated from the n u m b e r of lambs alive at the end of lambing and the n u m b e r of carcasses recovered. In addition the n u m b e r of ewes producing at least one lamb was determ i n e d by a combination of pregnancy diagnosis, using an e c h o - s o u n d i n g device (Scanopreg, Model 738, Ithaca, N e w York; Experiments, 1, 4, 6), inspection of the ewe's u d d e r before and/or after lambing (4) (Experiments, 1, 2, 3, 6), and by comparing live weights before and after lambing. Only those ewes whose data could be clearly interpreted using these three methods were included in the analysis. Reproductive performance was then evaluated as both the total n u m b e r of lambs born and the n u m b e r of e w e s producing a lamb. These two methods will not give identical results since the n u m b e r of ewes producing a lamb does not difBiological Trace E]ernent Research
VoL 7. 1985
Zinc and Reproduction in Grazing Ewes
91
ferentiate b e t w e e n the e w e s p r o d u c i n g singles or twins. H o w e v e r , u n d e r the extensive conditions utilized in these e x p e r i m e n t s u n d e t e c t e d losses of lambs or carcasses are possible a n d it is essential to c o n s i d e r b o t h sets of results. In all e x p e r i m e n t s pasture s a m p l e s w e r e collected e v e r y 6-8 w e e k s a n d p l a s m a s a m p l e s w e r e collected i m m e d i a t e l y prior to the start of l a m b i n g f r o m s u b s a m p l e s of 12 or 13 e w e s in each t r e a t m e n t g r o u p . L a m b i n g data w e r e c o m p a r e d by X2 analysis. Plasma zinc c o n c e n t r a tions w e r e c o m p a r e d using S t u d e n t s ' t-test.
RESULTS AND DISCUSSION In E x p e r i m e n t 2, 11% m o r e zinc-treated e w e s p r o d u c e d lambs t h a n control e w e s (P < 0.05). ']7his resulted in 7% m o r e lambs b o r n to the zincs u p p l e m e n t e d e w e s than to the control e w e s (P = 0.1) (Table 1). In Exp e r i m e n t 1, t h e r e was a small (8%) increase in the n u m b e r of zincs u p p l e m e n t e d e w e s p r o d u c i n g one or m o r e lambs (P < 0.1) in c o m p a r i s o n to the control ewes. This did n o t result in a n y difference bet w e e n g r o u p s in the n u m b e r of r e c o r d e d lamb births. In three o t h e r exp e r i m e n t s there w e r e no r e p r o d u c t i v e r e s p o n s e s . In E x p e r i m e n t 6, f e w e r TABLE 1 Reproductive Responses to Zinc Supplementation
Experiment No.
Lambs born
(No. lambs/ No. ewes)
Plus zinc
No zinc
Ewes producing lambs/ Ewes giving record Plus zinc
No zinc
1
102 (70%) 146
103 (70%) 147
112 (77%) 145
99 (69%) t43
2
139 (90%) 155
123 (83%y" 149
133 (93%) 143
__115 (82%) ~, 140
3
147 (103%) 143
144 (99%) 145
130 (92%) 142
13__44 (93%y 144
4
134 (91%) 148
138 (93%) 149
14__11 (95%) 148
138 (94%) 147
5
109 (93%) 117
112 (94%) 119
--
6
t27 (85%) 150
146 (97%y 150
137 (91%) 150
143 (95%) 150
Comparisons were made between plus zinc and no zinc groups: ~ P = 0.1; ~indicates P < 0.05; qndicates P < O.OOl. Biological Trace Element Research
VoL 7, t985
92
34asters and Fels
lambs w e r e recorded born to zinc-supplemented ewes than to controls. However, 91% of the plus-zinc ewes p r o d u c e d a lamb, but only 85 lambs per 100 ewes were recorded. Thus the apparent negative response was caused by undetected and u n r e c o r d e d losses of lambs born to the zinctreated ewes. Plasma zinc levels immediately prior to lambing in the zincs u p p l e m e n t e d ewes were significantly higher than in the controls in two experiments (Table 2). These increases were recorded only w h e n plasma zinc concentrations of control ewes fell below 0.7 p~g/mL. In all the other experiments, plasma zinc levels were consistently, t h o u g h not significantly, higher in the ewes given zinc than in the control ewes. Most pastures contained between 10 and 30 ~g Zn/g, however, at four sites (Experiments 1, 2, 3, and 6) pastures contained less than 10 p,g Zn/g during mid- or late pregnancy. In comparing these results with the positive responses previously reported (1), a n u m b e r of factors are apparent. With the exception of Experiment 1, the n u m b e r of lambs born per 100 control ewes exceeded 80%. tn Experiment 2, where the zinc-supplemented ewes had 7% m o r e lambs than controls, the controls had an 83% lambing rate; at the other four sites, lambing rates were b e t w e e n 90 and 97%. A s s u m i n g that some ewes did not become pregnant, these lambing percentages are exceptionally high for Merino ewes in Western Australia, and indicate almost no loss of embryos and fetuses. These high lambing rates are not typical of lamb production in Western Australia. A survey of agricultural regions in the south of Western Australia revealed that the n u m b e r of lambs born per 100 ewes is generally b e t w e e n 70 and 80, and that ewes m a t i n g but failing to lamb are responsible for approximately 20% of the reproductive wastage (5). The authors of this survey suggested that embryo mortality is a major problem. U n d e r the conditions of the current experiments, few embryos were lost and since the beneficial effect of zinc is probably in maintaining pregnancy in grazing ewes (1), no response to s u p p l e m e n t a tion could be expected. TABLE 2 Effect of Zinc Supplement on Plasma Zinc Concentrations Just Prior to Lambing (~g/mL) Experiment No. 1 2 3 4 5 6
Plus zinc 0.76 0.79 0.64 0.83 0.76 0.85
(0.04)~ (0.03) (0.03) (0.06) (0.03) (0.04)
No zinc 0.71 0.74 0.56 0.79 0.65 0.81
(0.03) (0.03) (0.02) (0.04) (0.03) (0.03)
Significance, t-test ns a ns P < 0.05 ns P < 0.05 ns
"Standard error of the mean in parentheses. ~Not significant. Biological Trace Elernent Research
VoL 7, 1985
Zinc and Reproduction in Grazing Ewes
93
In addition, plasma zinc levels just prior to lambing were influenced bv zinc at only two sites in the current experiments a n d only w h e n control levels were below 0.7 p~g/mL. O n the basis of these results, the zinc intake towards the e n d of p r e g n a n c y in four of the e x p e r i m e n t s was sufficient to m a i n t a i n zinc levels in the ewes, a n d only in two experim e n t s were these levels not maintained. In conclusion, it appears that, although at s o m e times p a s t u r e zinc levels were below the suggested m i n i m u m r e q u i r e m e n t (6), the ewes were probably not zinc-deficient. It is possible that because m a n y other n u t r i e n t s are also in short supply d u r i n g p r e g n a n c y that zinc m a y have been released from maternal tissues d u r i n g tissue catabolism (7) a n d redistributed to the d e v e l o p i n g fetus. The different responses to zinc suggest that, like other trace element deficiencies, such as those of selenium a n d copper, zinc deficiency m a y be sporadic and d e p e n d e n t on other nutritional or seasonal factors.
ACKNOWLEDGMENTS The W e s t e r n Australian D e p a r t m e n t of Agriculture a n d Mr. J. Carter for the use of their sheep and facilities; a n d Mr. B. Rose, Mr. P. Moore a n d the staff of the research stations for their technical assistance. This w o r k was .supported by a grant from the Wool Research Trust F u n d on the r e c o m m e n d a t i o n of the Australian Wool Corporation.
REFERENCES D. G. Masters and H. E. Fels, Biol. Trace Elem. Res. 2, 281 (1980). D. G. Masters and M. Somers, Aust. J. Exp. Agric. Anita. Hush. 20, 20 (1980). D. G. Masters and R. J. Moir, Aust. J. Exp. Agric. Anita. Husb. 20, 574 (1980). R. B. Dun, Aust. J. Exp. Agric. Anita. Husb. 3, 228 (1963) T. W. Knight, C. M. Oldham, J. F. Smith, and D. R. Lindsay, Aust. y. Exp. Agric. Anita. Husb. 15, (1975). 6. Agricultural Research Council, The Nutrient Requirements of Ruminant Livestock, CAB, Slough, 1980, p. 256. 7. D. G. Masters, C. L. Keen, B. L6nnerdal, and L. S. Hurley. J. Nutr. 113, 905 (1983). 1. 2. 3. 4. 5.
Biological Trace Element Research
VoL 7. 1985
