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ASRC, Harper Adams University College, Edgmond, Newport, Shropshire, TF10 8NB, UK
2 To whom correspondence should be addressed. E-mail: lsinclair{at}harper-adams.ac.uk.
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ABSTRACT |
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 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • arachidonic acid • colostrum • docosahexaenoic acid • neonatal behavior • polyunsaturated fatty acids
A major factor contributing to high lamb mortality rates in sheep systems is hypothermia due to delayed suckling and exhaustion of brown fat reserves (1). Standing and suckling as soon as possible after birth are therefore vital to facilitate the ingestion of colostrum and ensure maximal lamb survival, particularly in extensive production systems (2). Neonatal behavior may be influenced by maternal long-chain PUFA supplementation, particularly docosahexaenoic acid [DHA3; 20:6(n-3)] and arachidonic acid [20:4(n-6)] (3,4). These PUFA influence neuronal division, synaptic transmission, and retinal development (5). Improved 22:6(n-3) status of the human fetus is thought to increase brain 22:6(n-3) concentrations and was shown to improve indices of motor and mental development in infants (6,7), whereas studies in pigs reported that increasing the maternal supply of long-chain PUFA during late pregnancy reduced the latency of suckling (8). Long-chain PUFA supplementation was also shown to increase gestation length in rats (9), humans (10), and pigs (11), resulting in a more physiologically mature fetus at birth, which may influence neonatal behavior.
Sheep are a sensitive model with which to study the effects of long-chain PUFA on neonatal behavior because their natural diet is low in preformed 22:6(n-3) and 20:4(n-6) (12). Additionally, duodenal supply is further reduced by extensive ruminal hydrogenation of PUFA (13,14), whereas tissue elongation and desaturation of linoleic [18:2(n-6)] and linolenic acid [18:3(n-3)], the precursors for 20:4(n-6) and 22:6(n-3), respectively, were shown to be limited in sheep (15,16). Increased tissue incorporation of n-3 PUFA reduces oxidative stability in sheep (16), and strategies to increase tissue n-3 PUFA levels may benefit from a concomitant increase in the supply of antioxidants such as vitamin E.
The objectives of this study were to investigate the effects of dietary long-chain PUFA and vitamin E supplementation of pregnant ewes on ewe and lamb fatty acid status, behavior, and colostrum production. Results relating to the effects of dietary vitamin E on the antioxidant status of the ewe and neonate were reported previously (17).
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MATERIALS AND METHODS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experimental animals, housing and diets. Twin-bearing (n = 36) and triplet-bearing (n = 12) ewes, (mean ± SD) 3.2 ± 1.86 y old, with a live weight of 77 ± 6.1 kg and a condition score (18) of 3.3 ± 0.51 were used in a 2 x 2 factorial design. Ewe breeds were Suffolk x North Country Mule (n = 24), Charollais x Friesland (n = 20), and Friesland x Lleyn (n = 4). All ewes were served by Charollais rams. Ewes were scanned at 84 d of gestation and housed and individually penned on sawdust from d 103 of gestation until the end of the experiment. At the time of housing, the ewes were weighed and condition scored before being allocated to treatment according to litter size, breed, age, live weight, and condition score. The building was continually lit and ewes had free access to fresh water. To provide foster lambs for ewes that did not bear 2 or 3 live lambs, an additional 6 ewes that were due to lamb at the same time as the treatment ewes were group-housed on straw and fed the control diet.
Four concentrates based on barley, sugar beet feed, and soybean meal were formulated to be isoenergetic [13.2 MJ metabolizable energy/kg dry matter (DM)], isonitrogenous (33.9 g N/kg DM), and to have a similar fatty acid concentration (
95 g/kg DM; Table 1). The control diet (M) contained Megalac®, a calcium soap of palm oil [high in 16:0 and 18:1(n-9); Volac]. The PUFA source (F) comprised a mixture of crude unrefined Scandinavian fish oil mixed at a ratio of 0.75:0.25 with Incromega® (Trouw UK), a by-product of (n-3) fatty acid production for the human market that is high in 22:6(n-3). Both the fish oil and Incromega were combined with a vermiculite carrier (Trouw UK) and BHT added as an antioxidant at 500 mg/kg added oil. The concentrates were supplemented with either a basal concentration of vitamin E (50 mg/kg; B) or a supranutritional concentration (500 mg/kg: S; Roche UK). The treatment diets were therefore as follows: control fat + basal vitamin E (MB); control fat + supranutritional vitamin E (MS); fish oil/Incromega + basal vitamin E (FB); or fish oil/Incromega + supranutritional vitamin E (FS). Ewes were offered winter barley straw at 125% of ad libitum intake, with refusals weighed back 3 times weekly. The concentrates were offered in 2 equal meals prepartum at 0800 and 1600, with feeding levels rising from 0.7 kg/d at 110 d of gestation for twin-bearing ewes (0.8 kg/d for triplet-bearing ewes), to 1.2 kg/d (1.3 kg/d for triplet-bearing) at 145 d of gestation. All ewes received 1.7 kg/d of concentrates postpartum in 3 equal meals at 0800, 1200 and 1600.
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Colostrum samples were taken from ewes using a method adapted from Pattinson and Thomas (20). At 12 h postpartum, lambs were confined behind a wire mesh barrier within the pen and a 1-mL i.m. injection of oxytocin (10 kIU/L; Oxytocin, Leo Animal Health) was administered to the ewe. The udder was then hand milked until empty. At 16 h postpartum, a 1-mL i.m. injection of oxytocin was administered, and the udder was again hand milked until empty. The total volume of colostrum produced was recorded and the secretion rate calculated from the interval between the end of the first and second milking. Subsamples were taken and stored at –20°C before analysis.
Behavioral measurements. The duration of lambing was recorded as the time from the appearance of the first lamb at the vulva to the expulsion of the final (second or third) lamb. To avoid confounding maternal and behavioral observations, assistance was provided to ewes during parturition only if the lamb was not seen 1 h after fluids appeared at the vulva, if a lamb was present at the vulva for 2 h without further progress, or if contractions occurred for 2 h without the appearance of parturient fluids or a lamb. Assistance given was minimal, consisting of correcting lamb presentation unless the ewe was considered unable to continue without further intervention, and recorded. Definitions of maternal behaviors were adapted from Dwyer and Lawrence (21), and scored using the system presented in Table 2. Ewes were focal-sampled after birth until both lambs had successfully suckled and the performance of specific behaviors recorded. Two maternal behavior scores were calculated for each ewe (one for each lamb) and combined to give a total maternal score according to the weightings for each behavior. Neonatal lambs were focal-sampled from expulsion until successful suckling and the latencies of specific behaviors recorded (21).
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Statistical analyses. All data were analyzed as a 2 x 2 factorial randomized block design with fat source and dietary vitamin E concentration and their interaction as the main effects using a general ANOVA in the statistical package Genstat® 6.2 (VSN International). Assistance of the ewe at lambing beyond the correction of presentation was used as a covariate when analyzing behavioral measurements because this was reported to influence neonatal behavior (24). Results are presented as treatment means and SEM. When the interaction was significant, means were compared by the Least Significant Difference test. Differences were considered significant at P < 0.05.
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RESULTS |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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3.1 and 3.3 g/kg DM, respectively, to the fish oil–based diets.
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5-fold and 10% (P = 0.055), respectively, in lambs borne to ewes fed fish oil compared with Megalac. The 22:6(n-3):20:4(n-6) ratio in the neonatal brain was also increased by maternal fish oil supplementation.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Fatty acid status.
Ewes supplemented with fish oil during pregnancy and lactation had an intake of 20:5(n-3) and 22:6(n-3) of 3.4 g/d. Assuming ruminal hydrogenation of 20:5(n-3) and 22:6(n-3) to be 90% in sheep (13,14), supplementation with fish oil was estimated to have increased daily duodenal supply by 0.3 g/ewe compared with ewes fed Megalac, for which dietary supply was negligible. As a consequence, prepartum plasma levels of 20:5(n-3) and 22:6(n-3) were 3.8- and 2.4-fold higher, respectively, in ewes supplemented with fish oil. These increases are in accordance with other work in which sheep were supplemented with fish oil (14). Even though dietary levels of 18:3(n-3) did not differ among treatments, the proportion in ewe plasma was higher in sheep supplemented with fish oil, a finding that concurs with our previous observation that tissue elongation and desaturation of 18:3(n-3) to 20:5(n-3) and 22:6(n-3) in sheep are inhibited by the long-chain PUFA in fish oil (15,16). Ewe plasma proportions of 18:2(n-6) reflected dietary supply, and were higher in sheep supplemented with Megalac than fish oil. Despite the higher dietary supply of 20:4(n-6) in ewes fed fish oil, the higher plasma 18:2(n-6):18:3(n-3) ratio in ewes fed Megalac resulted in a similar plasma 20:4(n-6) proportion.
In contrast to ewe plasma fatty acid profiles, neonatal plasma in lambs borne to ewes supplemented with fish oil had similar proportions of all fatty acids measured, except for 20:5(n-3) and particularly 22:6(n-3), which were enhanced, confirming that specific fatty acids can preferentially cross the placenta in late pregnancy (8). The majority of 22:6(n-3) accumulation in the brain occurs during the brain growth spurt (26,27), which takes place in utero in lambs (28). This increase in brain concentration of 22:6(n-3) concurs with synaptogenesis (27); 22:6(n-3) deficiency reduces neuron size, which may be linked to loss of optimal nerve function (29). Within the current study, higher concentrations of 22:6(n-3), and to a greater extent 20:5(n-3), were observed within brain tissue of lambs borne by ewes fed fish oil compared with Megalac. Other studies also reported an increase in 20:5(n-3) and 22:6(n-3) proportions in the brain of piglets borne by sows supplemented with tuna oil (30).
Gestation length.
Both 20:4(n-6) and 20:5(n-3) act as major prostaglandin (PG) precursors within the ruminant; the bioactive dienoic PGE2 and PGF2
are synthesized from 20:4(n-6), whereas PGE3 is produced from 20:5(n-3) (31). An increase in the ratio of 20:5(n-3) to 20:4(n-6) available to the ewe results in a shift in PG production from bioactive dienoic PG, which have an established role in the induction of parturition, toward less active trienoic PG (32). Additionally, there may be a reduction in uterine muscle contractility by an increased supply of 22:6(n-3) (9). Baguma-Nibasheka et al. (33) and Hong-Ma et al. (34) demonstrated a delay in the initiation of glucocorticoid-induced parturition in ewes infused with fish oil, with concurrent reductions in maternal estradiol and prostaglandin-H-synthetase-2. Similarly, the infusion of 20:5(n-3) was shown to reverse labor in sheep (33), whereas in sows, the inclusion in the diet of salmon oil high in 20:5(n-3) was associated with an increased gestation length of 0.5 d (11). In the current study, plasma ratios of 20:5(n-3) to 20:4(n-6) in pregnant ewes increased from 0.6 to 2.7 when Megalac was replaced with fish oil and were associated with a 2-d increase in gestation length. This increase may have resulted in a physiologically more mature lamb at parturition, thus altering neonatal behavior.
The observed increase in gestation length was not associated with an increase in lamb birth weight. Increasing lamb birth weight is negatively correlated with mortality rates (35), but only increased dietary concentrations of vitamin E had a significant effect on this variable within the current study. Gentry et al. (36) also reported that lambs from vitamin E–supplemented ewes tended to have higher birth weights and increased preweaning live weight gain.
Neonatal behavior. The latencies of neonatal behaviors observed in the current study agree with those reported previously (37). The addition of fish oil to the maternal diet significantly reduced the latencies of successful suckling in neonatal lambs. This result concurs with that reported by Rooke et al. (8) in which neonatal piglets from sows supplemented with tuna oil during late pregnancy tended to make contact with the udder and teats more quickly than control piglets. It was postulated (2) that delays in suckling may be due in part to myopia, which reduces the ability of the lamb to successfully locate the udder. Studies in humans related improved visual acuity, cognitive development, and motor skills during infancy to the intake of (n-3) PUFA, specifically 22:6(n-3), before weaning, suggesting that supplementation with these fatty acids improves neural development (6,38). Similarly, learning behavior was improved in rats (3) and pigs (39) by (n-3) fatty acid supplementation, results that support the findings reported here. By contrast, others (40) reported no significant effect of 22:6(n-3) supplementation upon visual acuity in breast-fed infants.
It was reported that lambs borne by ewes supplemented with vitamin E during pregnancy tended to stand and suckle sooner than those borne by control ewes (25) and have an increased vigor score (41). The supranutritional vitamin E concentration used in the current study was higher than those employed in the aforementioned experiments but no significant main effect of supplementation upon lamb vigor was observed. There was, however, a significant interaction between dietary vitamin E and fatty acid source observed for the latency of lamb standing, with supranutritional vitamin E supplementation reducing this latency when fed in combination with fish oil but not Megalac. Benefits of supranutritional concentrations of vitamin E on neonatal behavior would therefore appear to be most likely when oxidative challenge is greatest.
Ewe performance and colostrum production. Fish oils were shown to have a large, negative effect on milk fat concentration and yield in dairy cows (42), and sheep (43), an effect that has been attributed to hydrogenation intermediaries including trans-10 18:1 and trans-10, cis-12 CLA (44). In the current study, supplementation with fish oil reduced the estimated milk fat yield by 48% as a consequence of a reduced milk yield and fat concentration. The effect of marine oils on milk and milk protein yield are equivocal; some studies reported an increase in milk yield (45), or little effect on milk or protein yield (46), whereas others reported a decrease in protein yield in dairy cattle (47) and sheep (43). The initial colostrum protein concentration reported here was lower than that reported in other studies with ewes (20), although measurements in the current study were not conducted until 12 h postpartum when concentrations were shown to be reduced (48). The combined effects of a large reduction in colostrum fat and protein, whose major component is IgG (48), may predispose lambs to an increased risk of hypothermia and reduction in the ability to combat infection (20).
In conclusion, supplementing pregnant ewes with fish oil enhanced the (n-3) fatty acid status of the ewe and lamb and resulted in a decreased latency to suckle, which may have beneficial effects on lamb survival. It is unclear whether this effect was due to an increased gestation length or an increased 22:6(n-3):20:4(n-6) ratio in the neonatal brain. The inclusion of fish oil in the prepartum diet also severely reduced colostrum fat and protein yield, and dietary strategies investigating the effects of timing of fish oil supplementation in the periparturient period warrant further investigation.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: CLA, conjugated linoleic acid; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; FB, fish oil + 50 mg/kg vitamin E; FS, fish oil + 500 mg/kg vitamin E; MB, Megalac® + 50 mg/kg vitamin E; MS, Megalac + 500 mg/kg vitamin E; PG, prostaglandin.
Manuscript received 7 September 2005. Initial review completed 11 October 2005. Revision accepted 18 November 2005.
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